Covert - Low Volume

reubenreub

reubenreub

Active member
Just wrapped this thing up using the SMD 4393's and for whatever reason, unity volume is with the knob at max. I believe it sounds like it should, gainy and Marshally, but is just more quiet than I'd like. I'm guessing it might be something around R17, Q5, or the volume pot. Anyone else have any volume issues with this one?
 
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Chuck D. Bones said:
Mine has plenty of volume.
Check the source voltages on all 5 FETs. That will tell us if things are biased correctly.
But first, clean your board with IPA & a toothbrush.
Click to expand...
Yeah I usually don't clean the tops but that 4pdt sure left a mess!

Anyways, source voltages are as follows from a 9.1v onespot:
Q1 - 0.82v
Q2 - 5.39v
Q3 - 0.80v
Q4 - 5.20v
Q5 - 5.37v

And those green caps are non-polarized so they're good! Wanted to try them out for a change.
 
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Q1 - 0.82v ___ 0.82V / 820 Ohms = 1.00mA drain current for Q1 & Q2. I got 1.06V on mine, Id = 1.29mA
Q2 - 5.39v ___ got 5.4 on mine
Q3 - 0.80v ___ 0.80V / 560 Ohms = 1.36mA drain current for Q3 & Q4. I got 0.94V on mine, Id = 1.68mA
Q4 - 5.20v ___ got 5.4 on mine
Q5 - 5.37v ___ 5.37V / 4.7K = 1.14mA drain current for Q5. I got 5.6V on mine, Id = 1.19mA

Your JFETs are a little colder than mine, but that does not explain the low volume.

Have you tried running the PRES trimpot from end-to-end?

Verify that the BASS, MID & TREBLE pots do what they're supposed to do.

With the switch down (SB) you should be able to play clean or nearly so with PREAMP all the way down and get plenty of sweet FET distortion with PREAMP dimed.

With the switch up (SL), this pedal plays dirty at any PREAMP setting.

The parts all look like the right ones, I'm thinking bad connection somewhere or a mismarked part (it happens). Time to break out the audio probe.

If there is any possibility that the switch was overheated during soldering, then check continuity in both positions.

As for cleaning, I install everything except the pots and then submerge the board in IPA in an old pie-tin. Then scrub, inspect, submerge, inspect & repeat until there is no visible flux residue. IPA won't hurt pots, but it could wash flux into the pots and that's not good. After the pots are in, a wet toothbrush finishes the job. I doubt the flux reside is causing the problem here, but part of troubleshooting is eliminating possible causes.
 
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I had exactly the same problem, with the switch toggle down, it was very low volume and less highs/pres (even with trim pot full clockwise) .
I never figured out what the problem was and now I ruined my board and have to order an new one, because of heavy soldering (parts in and out etc.)
One thing confused me, the Pres trim pot worked exactly vice versa as the trim pot in the Tweet Man (wich is more or less the same schematic),
Covert : max pres - full Right / TweetMan : max pres - full left !
 
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stevtron said:
I had exactly the same problem, with the switch toggle down, it was very low volume and less highs/pres (even with trim pot full clockwise) .
I never figured out what the problem was and now I ruined my board and have to order an new one, because of heavy soldering (parts in and out etc.)
One thing confused me, the Pres trim pot worked exactly vice versa as the trim pot in the Tweet Man (wich is more or less the same schematic),
Covert : max pres - full Right / TweetMan : max pres - full left !
Click to expand...
Curious, Did you use Mammoth Pots in your build?
 
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I used Alpha pots from Small Bear, Bourns trimpot from DigiKey. My VOLUME pot is an A50K. I rarely use B taper for volume, although it would have worked OK on this pedal. 50K provides a lower output impedance and Q5 has no problem driving 50K. The 50K has <0.5dB effect on volume vs. 250K and the A taper moves unity toward noon. I just checked my Covert, with the switch down (SB), PREAMP, TREBLE, MID & BASS At noon, unity on the VOLUME control is:

2:00 with a Les Paul (either pickup)
1:30 with a Strat (any pickup)

The Fender has Tex-Mex pickups, Gibson has stock humbuckers.

If my VOLUME pot was B-taper, unity would be lower. Unity is lower with the switch in the up (SL) position.

Is there anything between your Covert and the amp besides cable?
 
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Chuck D. Bones said:
Q1 - 0.82v ___ 0.82V / 820 Ohms = 1.00mA drain current for Q1 & Q2. I got 1.06V on mine, Id = 1.29mA
Q2 - 5.39v ___ got 5.4 on mine
Q3 - 0.80v ___ 0.80V / 560 Ohms = 1.36mA drain current for Q3 & Q4. I got 0.94V on mine, Id = 1.68mA
Q4 - 5.20v ___ got 5.4 on mine
Q5 - 5.37v ___ 5.37V / 4.7K = 1.14mA drain current for Q5. I got 5.6V on mine, Id = 1.19mA

Your JFETs are a little colder than mine, but that does not explain the low volume.

Have you tried running the PRES trimpot from end-to-end?

Verify that the BASS, MID & TREBLE pots do what they're supposed to do.

With the switch down (SB) you should be able to play clean or nearly so with PREAMP all the way down and get plenty of sweet FET distortion with PREAMP dimed.

With the switch up (SL), this pedal plays dirty at any PREAMP setting.

The parts all look like the right ones, I'm thinking bad connection somewhere or a mismarked part (it happens). Time to break out the audio probe.

If there is any possibility that the switch was overheated during soldering, then check continuity in both positions.

As for cleaning, I install everything except the pots and then submerge the board in IPA in an old pie-tin. Then scrub, inspect, submerge, inspect & repeat until there is no visible flux residue. IPA won't hurt pots, but it could wash flux into the pots and that's not good. After the pots are in, a wet toothbrush finishes the job. I doubt the flux reside is causing the problem here, but part of troubleshooting is eliminating possible causes.
Click to expand...

Thanks so very much for the voltages and assurance on those. Everything seems to sound exactly as it should, all eq pots working correctly, getting a great range of gains in both toggle positions, and the presence pot sounds best just shy of max. The only thing seems to be the low overall volume. I think I might just go ahead and swap out the volume pot and see if it makes any difference. Probably reflow my solder joints as well just to be safe.

Yeah, been running guitar into covert into amp. All eq at noon, gain at noon, unity volume is at 3 o'clock with the switch up and at max with the switch down.
 
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Maybe your guitar has hot pickups? I have my Presence trimmer turned to maximum presence. I think this pedal is too dark otherwise.

You'll get ~8dB more output if you run the pedal at 18V. Just make sure C100 is rated for 25V or higher.

A simple mod to increase output is to reduce R14. You can go down to 33K or even 10K. The downside is you'll have to set MID and BASS lower and TREBLE higher for the same tone.

The only other mod I can think of is to increase the gain of the last stage. Basically rewire it to be like the last stage in a Big Muff.
 
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