noise on DMP3 gain pot - normal?

rhythm

New member
Before I return this, I want to get some input, since this is the first mic preamp I've bought and therefore I'm not very experienced with them.

The new DMP3 that just arrived seems to be in good shape, but the channel 1 gain pot seems a bit noisy. If I plug my headphones into the channel 1 output, plug nothing into the input, and slowly move the gain knob clockwise and counterclockwise, I hear that scratchy sound that sounds like a noisy or "dirty" pot. I realize that in many situations I won't be moving the knob around while in the middle of a recording, but it could happen at times, and in any case this just doesn't seem right to me. I would have thought that it would be nice and quiet when moving the knob. Channel 2 seems OK.

I would have thought this is a defective unit, but the truth is that I've tried three of these units now, and I've experienced this with every one of them. So I'm starting to second guess myself. I've only heard good things about the DMP3, and definitely haven't heard any complaints about noisy pots on them. Is this normal for these units, or have I just been very unlucky so far with them?

Thanks,
Greg
 
The circuit topology of the DMP3 uses an instrumentation amp. Part of that is DC across the gain set resistor, or in this case pot. If you want pots to be quiet, you need to keep DC out of them, otherwise you get noise from little fluctuations in DC offset. It's pretty much unavoidable when using a pot with an instrumentation amp; you get some variation in noise as the amount of DC offset between different units varies.

Higher-end instrumentation amp designs use stepped rotary switches instead, which of course don't scratch but are equally useless if you are trying to do a gain change during recording. For that, you need a fader or trim after the amplifier.
 
Thanks for the reply.

So, I take it that the pot noise something I'm going to get with any of the lower priced mic pres (or recording interfaces with mic pres built in)? I've never heard this complaint about mic pres or interfaces, but perhaps it's just something that's known and accepted?


BTW, for those of you who own a DMP3, I take it you're getting the same noise on yours when you rotate the gain pots?


-Greg
 
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Thanks for the reply.

So, I take it that the pot noise something I'm going to get with any of the lower priced mic pres (or recording interfaces with mic pres built in)? I've never heard this complaint about mic pres or interfaces, but perhaps it's just something that's known and accepted?

No, plenty of other gear will have quiet pots. It has to do with the type of circuit used in the DMP3; most other low-end gear doesn't use it.
 
mshilarious, thanks again. I guess I'll have to think it over a bit. Maybe it's just me, but it bugs me a bit to hear the noise on the pot when using it...I guess I'm just used to quiet pots on everything else electronic that I own. Nobody else has chimed in about their DMP3 units, but from what you've said I guess this is normal and I'll have to decide if I want to get used to it, or return it and get something else.

Thanks again,
Greg
 
Nope, mine is quiet no matter how much i crank it up. It's a very nice piece of equipment. Never gave me any problems.
 
Nope, mine is quiet no matter how much i crank it up. It's a very nice piece of equipment. Never gave me any problems.

saads, mine is quiet too, even if it's cranked way up. But what about while you're actually moving the pot? I get scratchy noise when the pot is in travel, but when it's set at any particular spot the unit is indeed very quiet.

Greg
 
Oh you meant that. I'm not sure...now that you mention it i think it does produce a scratching sound. I'll check and let you know. Does that bother you? I never thought it was too annoying.
 
saads, mine is quiet too, even if it's cranked way up. But what about while you're actually moving the pot? I get scratchy noise when the pot is in travel, but when it's set at any particular spot the unit is indeed very quiet.

Greg

For what it's worth, I can't think of a single time in my entire home recording career where I've adjusted the input gain while in the middle of a take. If it's too high, by the time you've noticed you've already irrepairably damaged the first part of your take, and it's really not very hard to take a quieter-than-you-might-prefer signal and make it louder, in the digital domain. If you're happy with the noise floor when you're not touching a knob and think it's a clean, accurate, good-sounding pre, then don't worry about a little bit of scratchiness when adjusting gain, because I really doubt you'll ever do that mid take (as if nothing else it'll require a lot of finesse with a volume envelope in the mix to "undo" the sudden increase/decrease in volume when you twist the knob).
 
For what it's worth, I can't think of a single time in my entire home recording career where I've adjusted the input gain while in the middle of a take. If it's too high, by the time you've noticed you've already irrepairably damaged the first part of your take, and it's really not very hard to take a quieter-than-you-might-prefer signal and make it louder, in the digital domain. If you're happy with the noise floor when you're not touching a knob and think it's a clean, accurate, good-sounding pre, then don't worry about a little bit of scratchiness when adjusting gain, because I really doubt you'll ever do that mid take (as if nothing else it'll require a lot of finesse with a volume envelope in the mix to "undo" the sudden increase/decrease in volume when you twist the knob).

Exactly, thats why i'm a little confused why thats a problem.
 
I can understand his concern to a point... Originally he was worried that the issue was a defect in an individual unit, but after 3 pres displayed the same symptom, he realized that it may not be a defect, but a design issue. He's just trying to justify in his own head, that a unit designed with the expected result of noisy audio when adjusting input gain is a design he wants to trust... it just doesn't feel right...

But if they'd used a step attenuator then the complaints would be about not having enough granular gain controller on the input, it was a decision made developing the unit, it doesn't effect the performance, and if you like the pre, then there's no reason for concern...
 
Yep...it was just something I wasn't expecting, and initially thought it was a defect, then perhaps a design issue. Now I know it's neither. The fact that I've noticed it on only one channel in each case definitely threw me off too. My "logic" was telling me that if it was by design, I'd hear it on both channels.

I agree with you that I really don't need to worry about adjusting the gain while in the middle of the recording, and I will stick with this unit, knowing what I know now. Thanks for all of your replies and comments. It was a very helpful discussion for me, and I feel good about owning the unit now.

Now it's up to me to learn how to make the most of it....

Greg
 
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