I have a problem with certain compressors all the time, I would like to know if my favourite one could be modified to solve that problem.
Here is a video. I am showing the mentioned compressor: GURUS OPTIVALVE, an LA-2A inspired item. The problem is what you can hear right away: it is distorting. My guitar has humbucker pickups. What happens in the video:
1. The volume pot on the guitar is at max. The compressor is set to average/high compression. You can hear it is distorting. You may think it is because of the amount of compression but no. You can see me turning down the Input, it is distorting. If you turn down the Input to the level that no compression is indicated, it still distorts.
2. After the flash, you can see the Optivalve again. This time, I turned down the volume pot on the guitar. I am demonstrating, that you need to turn down the volume pot to nearly 0, that way the pedal stops distorting. But that volume level is not very favourable from the guitar. Any higher setting starts distortion in the pedal. But even so, at the highest notes, you can still hear some distortion.
3. You can see my Carl Martin pedal. I am demonstrating with that it does not distort. The volume pot is at max again. I am showing 2 situations: one is with slower attack, other is with faster. Both are okay, you cannot hear the distortion.
https://drive.google.com/file/d/1EY11JWevvn5kR2TB2FCp94V13LWg6xie/view?usp=sharing
I experienced the same distortion with many pedals, not only compressors. Now I have only compressors, I found these pedals distort: Keeley Compressor+, Marshall ED1 and this Optivalve. The Carl Martin Compressor you can see in the video does not distort. I also have a Demeter with a trim pot, that one is interesting: with a new 9V battery, or with a 9V PSU it distorts. Even if the trim pot is at 0. I have a home made 12V PSU with filter built in, with that one the Demeter does not distort, even on higher trimpot settings.
Guitars: you may say my guitar has very high output, but it is not only my guitar I experienced this distortion with. These guitars also distorted with the mentioned pedals: PRS Custom, Cort kx508. Just like you hear in the video.
My quesition is: can I tweak this Optivalve to make it not distort, like the Carl Martin? I love the sound of the Optivalve. It is very inconvenient you need to turn the volume knob to nearly zero, you can easily overshoot, very inconvenient in live situations.
If needed I can take a photo of the inside of the pedal.
There are generally two sources of heard distortion in compressors. One is most obviously exceeding the available headroom in the audio path. The other, which is actually NOT distortion but really sounds like it, is in the rectification of the audio signal to provide the controlling voltage (or current) driving the gain cell. Ideally, the rectified signal voltage should be smooth. But rectifier circuits vary in the degree to which they convert an AC audio signal into a smooth positive-going DC voltage. Imperfect rectification and smoothing will result in what is referred to as "envelope ripple". If a gain cell is having its gain turned up and down, up and down, dozens or even hundreds of time a second, that will sound very much like harmonic distortion to our ears. Traditionally, a full-wave rectifier will be better at minimizing this ripple than a half-wave rectifier. And because guitar strings are imperfect in their vibrations, such "distortion" will be most noticeable during the decay phase of a strummed instrument. If you find it most noticeable when you strum a chord, and listen to the sound as it fades out, then chances are pretty good the "distortion" you hear is due to envelope ripple. And if you don't hear distortion in response to pick attack, but only as the string dies out, that pretty much cinches the source as envelope ripple.
The traditional "fix" for this second type of heard distortion is to slow down the decay (and attack time if possible) of the rectification. The more sluggish the response of the rectification, the less responsive it will be to any ripple in the string signal.
I don't know if this addresses your concerns or not.
I am already very glad that I brought up this problem here, because one of my concerns seems to have been solved. I know exactly what you mean by that ripple distortion, but it appears so oddly (on the decay) that so far I thought it is due to an element being faulty in the pedal.
Anyway, the situation distortionwise is this:
-In case of the Optivalve, the Keeley and the Marshall ED-1, it is the "headroom" distortion I guess, based on what you wrote. I could describe it as a crackling, that you hear when a pot is faulty, and when you turn it or touch it, you hear that kind of crackling sound. It is exactly the same kind of sound. And it is heard until the initial part of the note or chord, until the volume of the note is over a certain level, then it disappears on the decay.
- In case of the Demeter Compulator it is the ripple distortion. You strum the chord or pick a note and you hear a kind of vibrato or tremolo being formed on the decay, and depending on the volume of the signal on the decay, it can distort - again, following the pattern of the tremolo. This is when it is used with the 9v battery or PSU as I mentioned. If I turn down the volume on the guitar down at least half way, it mostly disappears, and the same applies to when I use a 12-18V PSU with it, even at full volume. If I plug a single coil guitar into the Demeter, even with the 9V battery, the sound is clean and no tremolo. We tested this with a Burns Brian May series guitar.
Quote from: bencuri on December 12, 2024, 06:36:21 PMGURUS OPTIVALVE, an LA-2A inspired item
I don't have a schematic but it's quite possible the first tube stage has too much gain and is clipping. Simple as that. If that's the case the input would be going to the first tube then the (first) level control would be after the first tube stage.
(The other examples you quote could have different issues.)
Don't worry about the other examples by the way. I just mentioned them, that maybe my experience with them can be useful for solving the issue with the Optivalve. But the focus is on Optivalve now.
So if I understand correctly, you mean the problem is that the level control was not placed before the first tube?
If I disassemble the item, can you determine the situation you suspect from the photos, or we needed some more schematic or information about the pedal from the manufacturer?
Please find the requested photos here:
(https://i.postimg.cc/2L48gGyy/P1050004.jpg) (https://postimg.cc/2L48gGyy) (https://i.postimg.cc/XXFJZjLW/P1050005.jpg) (https://postimg.cc/XXFJZjLW) (https://i.postimg.cc/56VtLhKC/P1050006.jpg) (https://postimg.cc/56VtLhKC) (https://i.postimg.cc/CzsxNc96/P1050007.jpg) (https://postimg.cc/CzsxNc96)
(https://i.postimg.cc/sMfD0prf/P1050008.jpg) (https://postimg.cc/sMfD0prf) (https://i.postimg.cc/PC6rGPXW/P1050009.jpg) (https://postimg.cc/PC6rGPXW) (https://i.postimg.cc/8FjkTNcq/P1050010.jpg) (https://postimg.cc/8FjkTNcq) (https://i.postimg.cc/62Z9Gcdc/P1050011.jpg) (https://postimg.cc/62Z9Gcdc)
(https://i.postimg.cc/t1wqTwV7/P1050012.jpg) (https://postimg.cc/t1wqTwV7) (https://i.postimg.cc/vxdG7nhs/P1050013.jpg) (https://postimg.cc/vxdG7nhs) (https://i.postimg.cc/DmqvvCfy/P1050014.jpg) (https://postimg.cc/DmqvvCfy) (https://i.postimg.cc/XBc4sv1y/P1050015.jpg) (https://postimg.cc/XBc4sv1y)
(https://i.postimg.cc/8jN1jhsd/P1050016.jpg) (https://postimg.cc/8jN1jhsd) (https://i.postimg.cc/qzwpnzCP/P1050017.jpg) (https://postimg.cc/qzwpnzCP) (https://i.postimg.cc/4YFZLqPw/P1050018.jpg) (https://postimg.cc/4YFZLqPw) (https://i.postimg.cc/68Qthtry/P1050019.jpg) (https://postimg.cc/68Qthtry)