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Old 06-17-2020, 11:33 PM   #1
eq1
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Default help w/ audio interface (E-MU 1616m) uneven headphone volume response?

I had good response when I asked about upgrading studio monitors. So not really knowing where else to turn, I'm back with another question. I'm thinking it could be an easy one, for someone in-the-know...

In short, the headphone volume control on my audio interface is 'lopsided': At next to no volume I can hear the right channel but not the left, and as I turn the volume up, the stereo image shifts slightly from right to left - the right is initially louder up to moderate volumes, and as I turn up more, the left starts to get louder. In only one knob position does the stereo image seem centered and balanced.

I haven't been able to tell if the problem exists anywhere else. The 1 and 2 outputs on this audio interface (an old E-MU 1616 'doc') feed monitor outs and the headphone jack, but it seems like only the headphone portion has a problem.

Is there maybe a simple answer to why this might be the case - maybe a bad pot? Or a faulty capacitor? Something I might be able to fix/replace?

It's not super critical, as I just bought a replacement (the same thing, used). But it'd be nice to fix this generally minor problem if I can... Any insights greatly appreciated.


edit: I found this one simple statement - in a sea of stuff - that might point to one potential problem:

"Pots also have issues with signal crossover between left and right channels and also matching the resistance curves of each channel within a two channel stereo pot."

If my E-Mu has a "two-channel stereo pot" on the headphone amp, then one or both of these issues seem likely to be able to cause the problem I'm having...

Last edited by eq1; 06-18-2020 at 07:15 PM.
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Old 06-18-2020, 12:38 AM   #2
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My Mackie Blackjack has a region on a headphone knob, where near the minimum volume it's very noticeably lopsided to the left. I think I've see someone complaining about the similar phenomenon in a new Onyx series too. So I guess it's a thing.
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Old 06-18-2020, 04:03 AM   #3
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My Mackie Blackjack has a region on a headphone knob, where near the minimum volume it's very noticeably lopsided to the left. I think I've see someone complaining about the similar phenomenon in a new Onyx series too. So I guess it's a thing.
My Presonus Monitor Station v1 does the exact same thing.
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Old 06-18-2020, 11:39 AM   #4
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^ Does the stereo image shift as you turn it up? Might be hard to tell.

Mine starts out nothing at left/louder at right, but as I turn it up the left gradually gets louder - not readily noticeable as loud per se, but as the center of the stereo image shifting from right to left...
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Old 06-18-2020, 12:16 PM   #5
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It shifts in the sense of I'm only hearing the right side at extremely low volumes, then as I turn it up slowly the left side gradually becomes audible.

I always assumed that it had something to do with the design of the volume knob, but since it occurs at such absurdly low volumes I never cared enough to research it further.
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Old 06-18-2020, 12:48 PM   #6
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Some thoughts but I am not really convinced!!

There are a number of ways to alter the gain of an amp. Without knowing the specific circuits in use it is difficult to comment!

However a common simple way is by feeding from one stage of the amp into the next stage just via a potentiometer.
In this case there are a couple of likely reasons. Here we have two pots (one for left and one for right) on a common spindle.

The accuracy of the two pots so that they do not track together might be an issue. One would hope that manufacturers use quality components to make that fine!

Another problem can arise with the load placed on the pot. Usually a log pot is used but the same applies with a linear pot (considered here just as an example!)

For a pot the load is usually an impedence much higher than the total resistance of the pot eg a 1kohm pot loaded with 10kohms. High enough to have no significant loading effect. The output voltage then is the input x the rotational percentage i.e. slider position.

If the load is sufficiently low to have an effect on the pot then that linear relationship is modified and becomes non-linear. In the case of a log pot it deviates from that nearly true logarithmic change.

Probably not very noticeable on a single channel. With stereo it is more important as slight changes alter the stereo image balance.....but only if one channel is different to the other.

I do not know if any of the above might be the cause except for poor quality (tracking pots) and load component differences between channels or faults causing those errors.

Now, I would hope not in quality equipment but, the pot might be on the output with the load being the headphones, or some other output coming directly off the pot slider (a second output?). Any differences then between the channel loads could cause what you experience.

But to sum up unless a fault situation, poor design, or a headphone load with differences between channels........look for a better explanation!��

It passed some lockdown time for me but I might just delete it!!! ��

Last edited by Allybye; 06-19-2020 at 01:47 AM. Reason: typo only
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Old 06-18-2020, 02:03 PM   #7
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I notice channel-balance issues on all of my mixers' headphone outputs when I drop the gain below a certain level. I think it's a pretty common problem with headphone pots. I guess I've just learned to live with it.
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Old 06-18-2020, 03:38 PM   #8
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^ OK, all, thanks for the feedback...

In general I wouldn't have a problem with this if it were only an imbalance at very low volume - something I have noticed in other setups as well, like you guys. But the way the image shifts as I turn up is a problem. I'm going to take it apart and look at the volume pot, see if there's anything I might be able do with that, probably just clean it first and if that doesn't help, replace it.

I should note that the replacement interface I bought, same model, doesn't have this issue. The pots also feel a lot tighter, like they haven't been used much...

I'll report back if I find anything. Meanwhile, if anyone else has ideas please feel free to share them. It's really hard to find this kind of info searching online. If anyone has any good references, links for such stuff, maybe a website dedicated to fixing audio electronics? - please share!
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Old 06-18-2020, 07:08 PM   #9
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I got it opened up and figured out a few things.

The headphone volume pot / on-off switch is sealed and there's nothing that can be "cleaned."

I don't see any specific part number, but in general the pot is:

-a dual-gang with switch
-"A10K" meaning 10K ohms with a logarithmic/audio taper ("A" means log, "B" means linear, I've gathered).
-It has 8 pins, panel or PCB mount, or through-hole.

I looked everywhere and could only find one close match but it's not available until August. Bummer. If anyone has a lead on such a pot I'm all ears...

I've attached an image of the PCBs. The on/off switch/headphone volume control is in the lower right corner... The file size limitations on this forum make this pretty useless, the image quality is bad.
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Old 06-18-2020, 08:45 PM   #10
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That problem has existed in audio gear as long as I remember. It's likely using a dual "ganged" potentiometer for L/R and the resistance doesn't hit zero for both at the exact same time, sometimes that's just a piece of dust, or just a variance in the construction since the tolerance can only go so tight without getting expensive. It's really only ever bother me when turning it all the way down and one side is barely there.

In my experience it's in sync right above zero though, if lower on one side vs the other further up at levels you actually need to use it, and that difference between the two is slowly changing, I'd think the pot is bad but I would not consider that very common.
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Old 06-18-2020, 08:51 PM   #11
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Originally Posted by eq1 View Post
If anyone has a lead on such a pot I'm all ears...
You mean those 9mm green pots on the right? The one on the far right looks like the dual gang I was talking about. If you mean that one, this is probably it:

http://smallbear-electronics.mybigco...-9mm-pc-mount/

Does the same job not sure it will fit though without some hacking, it might fit though.

Meh... it has a push/pull switch too? It can likely be found but not sure small bear has any.
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Old 06-18-2020, 09:02 PM   #12
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This is close...

https://www.ebay.ca/itm/2-x-9mm-ALPS...kAAOSwv9hW54XH

Are you sure it's a 10k? I assume it can but would have expected 100k but could be wrong. Either way the basic description of what you want to find is:

9mm dual gang pot push/pull audio taper 10k (or whatever the correct resistance value is)

With matching pins for the PCB (can't see those in the pic). It's remotely possible you could clean the one you have, if so, you have to use contact cleaner and go in from the shaft end but I can't remember if those are sealed.
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Old 06-19-2020, 01:35 AM   #13
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Are you sure it's a 10k?
It says "A10K" on the pot. Also, it's a rotary switch rather than a push-pull type... The actuator is knurled and slotted. The brand is "Alpha"...

I took some resistance measurements, but mostly for only one side of the center tap, and now I'm thinking I need both sides. The max difference between channels, on the pos side of the center tap, was 'only'(?)about 30Ω.

I'll take new measurements, make a graph and post later.

The maximum resistance I measured was only about 2.6k.

With the switch OFF, as well as ON but just above minimum, I measured about 1400Ω on the positive side of the center tap, both channels about the same.

With volume knob about 1/2 way up, I measured 2200Ω on the pos side of center tap, 1200Ω GND side of center tap.

FULL volume I measured under 1Ω pos side, about 1280Ω GND side...

Where/when exactly is 10,000Ω supposed to be measurable -- being a 10K pot?

Heck, I guess I'll post the graph I already made. It might mean something to someone. Note that I labeled left and right but I'm not sure that's correct.

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Old 06-19-2020, 03:06 AM   #14
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@eq1 you cannot be sure of the measurements you took with the pot in circuit. They will be affected by any resistance connected to the pot by the rest of the circuits. Measure out of circuit as your figures do not stack up with the markings!

On reflection and a nights sleep the probability is the tracks are a bit worn rather than that which I made in my ramble.....

It does seem that it is a 10kohms pot from the markings. I have found similar but not identical in the uk (you are in the states?) . Without a bodge you need to get some things identical!

Pcb mount, pcb hole pitch/layout, shaft orientation, 10klog/audio track taper, physical size, single shaft (not dual concentric).

There are several manufacturers worldwide with similar perhaps not identical products generally readily available but not always in stock. ALPS, TT Bourns, Vishay all major manufacturers. Plastic track pots rather than carbon to be preferred.

2-x-9mm-Alps-A10K-10K-Audio-Taper-Potentiometer18mm-D-Shaft-RtAngle-pcb-Mount is very similar (you need to check!) but it does not have a switch. Available on ebay and Mouser Electronics plus other suppliers no doubt.

Easiest option to get things right, especially the physical bit is to source another ALPS (Taiwan) pot otherwise fit could well be a problem!

See examples https://www.newark.com/w/c/passive-c...o-|logarithmic.

Quick check - I have not found an identical one, so may take a bit of searching!!
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Old 06-19-2020, 03:16 AM   #15
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I have the exact same interface, thought I was the only one & never had a moments problem except when I moved to W10 then things started going wrong & just continued until I went back to W7 so I shall watch this thread with interest?.
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Old 06-19-2020, 06:40 AM   #16
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Quote:
Where/when exactly is 10,000Ω supposed to be measurable -- being a 10K pot?
Measure the resistance of the two outside pins (1 and 3), assuming you can get to them and being in circuit doesn't matter (possibly not since pin 1 goes to ground most likely). I suppose there would be two sets of those pins being a ganged pot FYI.

If it says 10k it probably is though and OK to be that. I'm not 100% sure this will fix it though.
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Old 06-19-2020, 10:41 AM   #17
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Sorry Karbo, cannot agree that being in circuit does not matter!

Two reasons:
firstly without knowing the circuit we do not know what is in parallel across the pot or connected on the slider and that can affect readings
Secondly some meters measuring resistance can use a relatively high voltage and that can damage some active components.

Often not a problem but without knowing the circuit and the meter characteristics is it worth the risk of confusing readings or causing damage?
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Old 06-19-2020, 12:42 PM   #18
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Originally Posted by Allybye View Post
Sorry Karbo, cannot agree that being in circuit does not matter!

Two reasons:
firstly without knowing the circuit we do not know what is in parallel across the pot or connected on the slider and that can affect readings
Secondly some meters measuring resistance can use a relatively high voltage and that can damage some active components.

Often not a problem but without knowing the circuit and the meter characteristics is it worth the risk of confusing readings or causing damage?
Most anywhere else in a circuit you are exactly right as far as a misread but...

I know the basics of that part of the circuit, I build them all the time... it's an opamp and we are measuring the output side of it. Measuring it in circuit and unplugged will cause zero damage with a slight chance of a misreading.

Most all volume pots have pin 1 = ground, 2 = output, 3 = coming from the output of the opamp. So while it is possible there will be some stray ability to misread, one should be able to confirm whether it is 10k or 100k.

Here is a similar circuit that I just measured, it reads only 14 ohms different between connected disconnected, it's a 500k pot and it's allowed tolerance means the value below is definitely a 500k pot. So what I'm trying to say is you should easily be able to tell if 100k or 10k by the measurement but it is also already listed on the pot itself so you can trust that anyway unless it is broken.



And, I don't think measuring this pot in or out of the circuit has a huge value for the problem at hand unless we think it is broken - and as I said before that little L/R discrepancy right before it hits zero is pretty common (but not hearing it myself, I can't comment that much). I don't want the OP ordering another pot and going through all this trouble and it not fix the issue.
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Old 06-19-2020, 12:53 PM   #19
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@eq1 you cannot be sure of the measurements you took with the pot in circuit...
OK, maybe I'll remove it and measure. But it's starting to look like this might be more trouble than it's worth. On the other hand, I have real hard time letting otherwise good 'kit' going to waste.

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Originally Posted by Allybye View Post
It does seem that it is a 10kohms pot from the markings. I have found similar but not identical in the uk (you are in the states?). Without a bodge you need to get some things identical!
Indeed, I realize that I do need something identical. I don't want to hack something. I have thought about adding a separate ON/OFF switch though and then getting just a dual-gang 10K pot without switch, as I recall those were available now. I did find one with a switch, a Bourn, but it's not available until August - at ALL the electronics places, Digikey, Newark, Mouser, Jameco, ebay, Amazon...


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Originally Posted by jiff 41 View Post
I have the exact same interface, thought I was the only one & never had a moments problem except when I moved to W10 then things started going wrong & just continued until I went back to W7 so I shall watch this thread with interest?.
Jiff, I bumped into an article about using the 1616 on Windows 10. If you ever wanted to go back to 10 it might be worth checking it out, here's a link:

https://www.kvraudio.com/forum/viewtopic.php?t=529349

Also, fyi, I've seen a youtube video of a guy dismantling a 1616 to fix a bad noise, he replaced a handful of capacitors. I've seen reference to 'bad capacitors' in a couple places, so I gather that might be one fairly common problem that can crop up in time...

In general, if anyone reading this is confused about why I'm even bothering with this, I've read that the E-MU 1616 and related (1010, 1212) are really good. I was looking into new audio interfaces and comparable ones were WAY expensive, like in the $500-$1,000 range, it seemed. You can get inexpensive USB interfaces, like around $150, but I have an older computer with like USB 1 or 2, or "A" - the 1616 connects to a PCIe card (or PCI if older), which is supposed to be a lot faster.

Basically, it seems like lot a ton of 'audio interface' for the buck. Not to mention I've been using it forever... I just bought a replacement used 1616 breakout box for $90... My PCIe card cost like ~$120 about 7 years ago, though I don't see any of those available anywhere any more...

Quote:
Originally Posted by karbomusic View Post
Measure the resistance of the two outside pins (1 and 3), assuming you can get to them and being in circuit doesn't matter (possibly not since pin 1 goes to ground most likely).
I did take some measurements of the outside pins, yesterday. With knob a little below 1/2 way turned up it was 1420Ω one channel, 1423 other channel. Full it was 1280Ω one channel, 1276 other...


Quote:
Originally Posted by Allybye View Post
Sorry Karbo, cannot agree that being in circuit does not matter!
I think Karbo was simply saying I can measure the outside pins IF we assume it doesn't matter - but that it might matter.
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Old 06-19-2020, 12:57 PM   #20
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You can remove and measure but I measure them often and I can usually tell the value of the pot. One reason it sometimes works in this kind of output is because pin 1 goes to ground, pin 3 goes to the output of the opamp, which already blocks DC with the output cap assuming the output cap isn't leaking. This is one of the very few places you can "possibly" measure in circuit, with the circuit off and have less chance of being in circuit mattering that much. If the measurement is more critical then you can't trust 100%. The real value was if it was close to the advertised value, you know it's right - if it's way off, just remove it and measure to be safe.

A side note is where the pot turn position is, is not related to the pot value. That's why you use pins 1 and 3 so that the wiper position doesn't affect the reading in any significant way. The knob/wiper only affects pin 2 - measuring between 1 and 3 gives you the actual value of the pot.
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Old 06-19-2020, 01:07 PM   #21
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I think Karbo was simply saying I can measure the outside pins IF we assume it doesn't matter - but that it might matter.
Correct. It could very well matter but it will save time to try it before removing it which I think you just did. As I blabbed above, where it is in the circuit, makes trying first worthwhile.

I fully understand the rule about measuring in circuit btw, but once in awhile it doesn't necessarily apply.
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Old 06-19-2020, 01:20 PM   #22
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I measured the outside pins again, both channels, and also worked the knob as I measured. Both channels read about the same and remain about the same as I turn the knob up, but once I get to about 80% full the values drop a bit:

One channel 1426Ω and after about 80% it drops, reaching 1281Ω by Full.
Other channel 1422Ω and after about 80% it drops, to 1278Ω by Full...

Shouldn't this read at least closer to 10,000Ω being a 10k pot?
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Old 06-19-2020, 01:23 PM   #23
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Shouldn't this read at least closer to 10,000Ω being a 10k pot?
Yes, so either measuring in circuit is a problem here, something is wrong with it, or the meter displays in a way where 1000 really = 10000. If you remove it and measure, ignore the knob position, just measure pins 1 and 3 to find the value of the pot itself. Just make sure you know what 1 and 3 are.
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Old 06-19-2020, 01:31 PM   #24
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Here's what I mean, this is a 10k pot just like yours but no switch and no dual (I have loads of these lying around). Notice what the two outside pins show on the meter, 10k - though that exact number is rare, allowed variance is usually just above or below but you get the idea of how to measure as this way of measuring takes makes the knob position irrelevant

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Old 06-19-2020, 02:08 PM   #25
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Yes, so either measuring in circuit is a problem here, something is wrong with it, or the meter displays in a way where 1000 really = 10000. If you remove it and measure, ignore the knob position, just measure pins 1 and 3 to find the value of the pot itself. Just make sure you know what 1 and 3 are.
The meter actually reads "1.426 kΩ", etc., I'm just writing it as 1426...

Here's an image of the pot pins I'm measuring, labeled. I don't know what that tiny trace coming out of one channel's center tap is... Not sure I want to pull it off the board, because then I'd be pretty much locked-in to buying a replacement, which would mean waiting until August, it seems. I don't see any way to open it up to inspect innards without damaging it or not being able to put it back together well enough...

hmm, just thought of another option: I could open up the replacement unit I bought and make the same measurements for comparison. I think I'll try that.

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Old 06-19-2020, 02:19 PM   #26
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The meter actually reads "1.426 kΩ", etc., I'm just writing it as 1426...

Here's an image of the pot pins I'm measuring, labeled. I don't know what that tiny trace coming out of one channel's center tap is... Not sure I want to pull it off the board, because then I'd be pretty much locked-in to buying a replacement, which would mean waiting until August, it seems. I don't see any way to open it up to inspect innards without damaging it or not being able to put it back together well enough...
Being upside down and connected to ground, the pins on the right are pin 1 which appears correct - pin 1 (instead of pin 3) has to be ground or you'd have to turn the knob backwards to turn the volume down.

The two on the left with the two 12mil/skinny traces coming down should be the L/R outputs from the OpAmp going to pin 3, center "should" connect to the headphones.

The two mystery pins could just be for mounting, not sure but they are out of the circuit best I can tell as they don't connect to ground or any traces so probably just mount convenience. I do see that tiny trace but not sure, I don't consider it that important right now though.

To clarify some, here's how pots like that are normally wired - just assume mono for simplicity - In your picture we are looking bottom up instead of top down, below is looking down from the top aka the reverse.



So signal comes in on pin 3, as you turn the volume "down", it raises the resistance between 2 and 3, and anything leftover gets shunted to ground. That's your basic volume control 101. This is also why I'll try measuring before removing - there isn't a huge amount of paths where the reading can be off due to being in circuit.

As far as removing, that's up to your equipment and soldering skills, it's likely able to be removed and put back if needed but I agree on not wanting to deal with breaking/fixing for something we don't even know changing the pot will fix. Especially if you haven't done this type of work before. I may have missed but have you searched the net for this issue with this device?
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Old 06-19-2020, 04:11 PM   #27
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First, let me say thanks everyone for your help and input. Thanks Karbo...

Second, I guess it's time to put this to bed. I opened up my second unit and measured the resistance between the outside pins - it's virtually identical to the other unit. I also took a few measurements like I did with the other unit, such as between 'pwr' and center tap on each channel. Also the same.

So... whatever I'm experiencing with the lopsidedness, it looks like it's probably not the pot... Or if it is, it might just be 'normal' deviation. In any event, I can't justify spending more time on the issue.

Let me add that these E-MU units really seem well engineered and manufactured. The cases are nice and robust, and everything aligns just perfectly. Easy to take apart, easy to put back together, logical fastener choices, et al. It's a lot different than miscellaneous other new stuff I've tinkered with in the past few years, though I've never actually taken apart any other audio interfaces.
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Old 06-19-2020, 04:28 PM   #28
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I do not want to get into an argument with Karbo (but this post is and includes something that is on topic too!) .... it might be the case for that particular circuit (that Karbo knows) and in general with op amp output drives into a potentiometer that no damage will occurr. I was just pointing out that there can be a risk. Not all circuits are capacitively coupled and sometimes these (as one example only) can be problematic.

Further the potentiometer output might be loaded and depending on the circuit and that load and the position of the slider aka wiper that can give rise to odd readings.
Consider Karbo's example (pretty common in simple circuits) with one side of the pot getting the op amp feed (the input), the other being connected to ground. In eq1's case the pot end to end should read 10kohms (+/- actual and measurement tolerance) -we agree on that. But if the wiper has a load to ground then when 'up full' that load is in parallel with the pot giving an apparently incorrect (lower) reading.
Potential deviders like that pot action rely on a relatively high load resistance (having a negligible affect on the pot) as otherwise the paralleling action of the load on the pot makes the tracking deviate from true be it linear or log by design.

So specifically in eq1's case it appears that the expected 10kohms is only 1280+ ish ohms [ full volume, slider effectively = pos terminal= input pin 3 ] This could be explained by a load too low a value ( Presumably the circuit following, which provides the output for the headset, or something else such as a fault.

With the pot fully turned down the pot should still read the 10k input to ground. [Which would be off to pos in eq1's description] eq1 writes it does not

Clearly the readings made are at odds with what should be measured - in both cases!! Something odd is going on. A faulty pot? No, two similarly fault pots! It might be measuring at the wrong points in the circuit? I suggest this not to criticise but to suggest why the unit works well except for that balance tracking error!

I presume that the headphones are not connected directly to the wiper/slider or if so (which would be an odd design!) they are disconnected during measurements.

Deeper investigation/diagnostics are required but whether feel competent, eq1 to do that or if you think it is worth the effort, only you can decide. I agree with Karbo's sentiment regarding doing work that might be potentially damaging.

(That's my understanding from over 40 years electronics/audio+ design construction and use experience in professional roles) my writing is perhaps not the best though!
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Old 06-19-2020, 04:38 PM   #29
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Quote:
Originally Posted by Allybye View Post
I do not want to get into an argument with Karbo (but this post is and includes something that is on topic too!) .... it might be the case for that particular circuit (that Karbo knows) and in general with op amp output drives into a potentiometer that no damage will occurr. I was just pointing out that there can be a risk. Not all circuits are capacitively coupled and sometimes these (as one example only) can be problematic.
All good!

My figuring was most audio opamp circuits that feed into something where the target device is not controlled by the designer, should have a coupling cap at minimum to block the bias voltage that is also on the output (assuming single ended power) - because no one wants a DC voltage going to the input of another audio device (which also should couple because all should be good citizens). I should have pulled out a more complex circuit to test with.

I tried to always qualified my suggestion with "if" and "might" because if it reads correctly on the first try, it can save a lot of extra work. The meter having a high enough voltage to damage is news to me, that would make it practically useless for measuring many components - I thought maybe you meant the opamp being sensitive to static but that risk goes away when it is in the circuit but I'm open to learning something new. It's not that I don't believe you, I'm sure you've done it more and as soon as the readings are that far off then it fails the "quick and easy" test anyway.

Out of geek curiosity, what did/do you design? I do mostly small preamp type circuits, guitar related circuits, pedals and another hobby in IoT/Micro controllers etc. I think the last serious project I built was a tempo-meter for snare drum - I have the details somewhere but basically I designed a comparator to track the input from the piezo then arduino to process the calculations and drive a huge 7-segment LED. Oh well I did design a tiny buffer a couple weeks ago that runs off a watch battery - it goes in my guitar to drive the piezo output and fixes a filtering issue when changing volume.
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Old 06-19-2020, 05:07 PM   #30
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Just to add a footnote that the tracking error is a common problem that often requires expensive selected pots (some constructions are better than others!) or better still fine stepped attenuators are best being, through selection of fixed resistors, much easier to achieve a professional match of 1dB through the whole range.

There is a mod to help the match but I forget the details!
Doh. More brain failure!!
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Old 06-19-2020, 06:17 PM   #31
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Just to add a footnote that the tracking error is a common problem that often requires expensive selected pots (some constructions are better than others!)
True, I think that was what my very first reply was about.
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Old 06-20-2020, 12:38 AM   #32
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Many thanks for the link I'll *Think* about it, I notice a few saying after they did it another update from W10 screwed it up again & they had to re-install?... I might just stick with W7 offline seeing as W10 annoys me on this lappy with things changing all the time?, I did try Linux a while back & was mightily impressed but so many plugins can't be used I thought just go back to good old W7.... I'll keep an eye on that KVR thread though it's VERY interesting?.
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Old 06-20-2020, 02:41 AM   #33
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Hi Karbo.
Good that we try to help even if we sometimes differ eh?

Fyi I can well remember in years gone by the common use of circuit continuity testers (buzzers) some were (at quite low voltage) prone to damaging some ICs which resulted in the intro of a safe lower voltage version. Still have one in the drawer sold in the UK by RS Components! I guess people tend to ignore what voltage a DVM puts out under resistance testing which can be higher at high R value ranges.

Being retired I now limit any electronics to essentials and hobby 'work' not as diverse as yourself but includes audio preamp and the like or control circuits. Not really progressed to Arduino type things and it would be a new study for me. Missing out on some great technology there! Maybe get the single board teaching stuff out of the attick if I ever make time to use it again!.....nay other interests have priority!

In the past career has been in audio and video engineering, analogue and digital instrumentation/controls/comms/recording and high level computing. Can't say more as according to the film's lines "I would have to shoot you"!

Take your point about your early note you made about the pot tracking limitations (I missed that). With that tracking 'difficulty' in mind, coming to a guessed conclusion that eq1's and others' problems could well be down to that and damage of the resistive surfaces (wear and tear) exacerbating it....plus those odd measurement figures that are yet unexplained!

EDIT: p.s. yes having looked back how did I miss that early post response....must be eye as well as brain fade coming to match the ears ��

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Old 06-20-2020, 07:24 AM   #34
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All good and interesting info, thanks for sharing and take care!
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Old 06-20-2020, 04:56 PM   #35
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So, Allybye, Karbo...

With the pot in place on both devices - the one with the lopsidedness problem and the replacement without a problem - I measured nearly identical resistances between the outer pins, as well as at various spots across the volume range.

Even though the pots are in circuit, can we conclude that the pots are in affect the same and that, therefore, the problem isn't likely to be the pot? (or if it is the pot it's due to very minor but typical 'slop').

I guess that's the main conclusion I got some posts up, when I thought I was done. But then reading the rest of what y'all write, I'm not sure any longer...

I wouldn't be totally opposed to opening up the device again and pulling the pot, but only if we can conclude with like 98% certainty that the pots can be different, one bad, one good, yet produce the same resistance values when measured in circuit...
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Old 06-20-2020, 05:41 PM   #36
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I'm 98% sure lots of stereo volume controls like that tend to drop L or R faster or slower than the other during that last little smidge before it's all the way down. So IMHO, it depends on "how" much slop your's has, I would assume there is a point where it's defective instead of expected.

I did check a couple of headphone outs that I have, both had the issue but the level at which it occurs is at a level far lower than I will ever use. Hope that helps.
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Old 06-21-2020, 05:13 AM   #37
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I do like that term 'slop'. Very descriptive!! Must use it in future!

The differences, given especially that a replacement pot is better, then it is almost certainly (as Karbo writes) down to that tracking error.

With regards to the measurement apparent anomaly, if the balance problem only occurs at low levels (and given the above replacement) then the pertinent measurement will be the slider/wiper resistance to the ground terminal at positions almost fully down. You need to accurately measure the resistance between left and right on one pot..accurately, without any movement of the slider. You need a good meter and technique ensure consistent results!

As it is very difficult to compare between pots as setting rotational position the same is in practice virtually impossible.

The best way to compare is by using a Wheatstone bridge technique. Not easy in circuit!

I would put it down to both the slope and wear increasing the difference!
If your new one is fine (for now) by ear or by measurement of results in Reaper (there are other case I understand!) With something like a sine wave input (you can use null technique between l and r tracks) and you have found a source of new pots....I would just change any 'defective' one!


EDIT: It just occured to me that, not likely but as well, to check the pot ground l and r terminals each to the main ground point to the point where the ground is used by the next stage (or output if next) or to a point in the circuit where both pots grounds are common. That could also affect balance tracking owing to bad joint, damaged track etc. It is the resistance from wiper to ground that is important and that might not be tha same as wiper to pot ground terminal!
If you have changed the pot you might just have cured a bad joint!!

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Old 06-21-2020, 01:09 PM   #38
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hmm... Let me see if I can re-formulate the question/idea:

Let's assume I measure all possible resistances for each pot (end pins, center tap to gnd, each channel, etc.), one in a device that doesn't have the 'lopsided' problem, the other in the device with the problem. And the values are all identical.

But the measurements are done in circuit, and we don't know exactly what's 'down stream' (or upstream).

Nevertheless, if the measurements are all identical, I can't think of anything in circuit that would allow me to measure identical resistances - unless the pots are indeed identical...

Maybe being in circuit produces the wrong values, such as '1400Ω' instead of ~10k, but the wrongness is the same for each pot.

If the pots are truly different, they should produce different resistance values, regardless of being in circuit. Whatever impact something 'downstream' has on the resistance readings, it should be the same on each pot, so if the resistance measurements at the pots are the same, we have to conclude that the pots are the same.

Isn't this true? Or what am I missing here?
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Old 06-21-2020, 02:57 PM   #39
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I think the better option for that is to measure out of circuit and between pins 2/3 and 1/2 for L and R. It's a dual gang pot so you want to compare Left and Right taper curves...

2/3 Left to 2/3 Right
1/2 Left to 1/2 Right

Those discrepancies at various positions of rotation is where the divergence is assuming I understand the problem. But you could run into precision issues. That said, you still might see the discrepancy between good bad pots by plotting their L/R curves respectively.

This is why AllyBye talked earlier about the big and expensive precision pots that use matched arrays of very low tolerance resistors.
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Old 06-21-2020, 03:36 PM   #40
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As writ by Karbo!
However for me, considering the pot (and ignoring the ground issue mentioned above)

The actual value of the pot end to end (the 10k) between pots and between left and right is not too critical. 5 or 10% even probably makes no difference. That resistance is the load of the previous stage and even with a small variation it still gets full input.

What is critical is the resistance between wiper/slider and ground as it is that in a potentiometer (in this type of circuit) that decides how much output!

At any particular rotational position if that resistance is different left to right there is a tracking discrepancy (balance in stereo).

As Karbo wrote you can take measurements at specific rotational positions. The lower angles of rotation affect the low signal level tracking. By the time you are at 100% rotation there should be no problem as output signal then equals input! Similarly the other way when wiper is right down there should by no output either channel.

Between different pots? Difficult. I would not by eye expect to get even the 1% rotational accuracy between them and with log/audio pots that can be quite a difference in resistance! So your 'centre tap' to ground is very difficult to compare except an individual pot l to r. If you cannot set the wiper rotational position identical then the resistances should not be identical. Max and min are the special cases.

I am sure your name 'centre tap' for the wiper is just your naming convention as it is not in the centre, electrically but variable!

Your final question "if they differ then surely they should measure differently" in circuit you might not be measuring the pot but something else (or a combination of them). That something else can easily mask any difference in the identity of resistance you are trying to check! So answer untrue.
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