Low volume on Mofeta build.

[shake__appral]

Hey y’all. First time posting here, hope I’m doing this right. Just built the Mofeta (Sunn Model T preamp) pedal yesterday, and having serious issues with volume output. It’s significantly quieter when the pedal is engaged, when not engaged the volume from my amp sounds about doubled. I’ve heard this was a fairly common issue with “other” Sunn T pcb builds, but am not seeing anything posted about it on this forum with this particular pcb. Any ideas for troubleshooting? There aren’t any instructions for biasing the trim pots, so I suppose this could be an issue. I just did this by ear, but I fiddled around with them quite a bit and the loudest, fuzziest setting still doesn’t produce volume anywhere near equivalent to my amps clean tone when the pedal is not engaged.

Posted a photo, I also am looking to run two leds (a standard 5mm above the Footswitch and then a 3mm to fill a hole where a switch was supposed to go) any ideas for wiring/getting power to the 3mm off to the side with this particular 3dpt pcb? Also curious if anyone has experimented with other JFet transistors. I’m a huge Sunn/doom in general fan and am not all that impressed with the tone of this pedal, wondering if there’s any way to make this maybe a little more fuzzy and gnarly and a little less “farty” and underwhelming. I’ve yet to stack this with other pedals, I’m sure it sounds rad with a Rat or something but at this point I’m sure glad I didn’t pay $250 for one of these suckers.

 

[GizzWizzKing]

I don't see anything immediately off, but I can't read all your component values.

Are your 5457s legit? Are all the transistors set in their sockets well? Are your pots all the correct values?
Maybe try reflowing your joints if you haven't.
And then check your component values to be sure you didn't accidentally drop a 4.7k in a spot for a 47k or something like that if you haven't.

Pics of the other side of the board may help people to assist as well.

 

[shake__appral]

Yeah pots are all correct, transistors are legit (presumably, “2N5457 Central Brand” ordered from Tayda). Only thing possibly out of the ordinary are those ceramic 470p’s are labeled “monolithic” (which I don’t know what means, but I believe I’ve used them before in other builds), and I used a 560k resistor instead of the 562k it calls for. Pretty positive all my other parts are correct.

There’s another post regarding this pcb, supposedly there’s talk of a Reddit thread where the dude from EAE said that some of these components were different from the actual build, but I doubt that’s the cause of a volume issue like this or else there would be more posts about it. Some folks on Reddit suggested some resistor changes. Anyway I screwed up my last two builds so I’m hoping to get this one sounding right, otherwise I might have to give up my short-lived career as a pedalbuilder LOL.

 

[Robert]

There’s another post regarding this pcb, supposedly there’s talk of a Reddit thread where the dude from EAE said that some of these components were different from the actual build,

There was a time a couple years ago where John mentioned that a couple component values were incorrect, but in reality there was just some variation in the particular unit that was traced. This is no longer the case, but even then, there was no volume issue.

If you hang around long enough you'll find that it's common for some builders to falsely claim "the trace is wrong" as a last resort...

(presumably, “2N5457 Central Brand” ordered from Tayda). Only thing possibly out of the ordinary are those ceramic 470p’s are labeled “monolithic” (which I don’t know what means, but I believe I’ve used them before in other builds), and I used a 560k resistor instead of the 562k it calls for. Pretty positive all my other parts are correct.

We won't jump to conclusions just yet because I've never gotten a fake JFET from Tayda, but we also shouldn't rule it out as a possibility.

The MLCC caps and 560K resistor won't be a problem.

Have you adjusted the bias trim pots?

Here are the voltages as measured on the original:

Q1 - 8.89V
Q2 - 8.88V
Q3 - 9.18V
Q4 - 18V (source follower, not adjustable)

Just to confirm, there is plenty of volume on tap in my prototype and original.

 

[chris.knudson]

And then check your component values to be sure you didn't accidentally drop a 4.7k in a spot for a 47k or something like that if you haven't.

It's been my experience that this should always be the first place to start with a volume issue. A wrong resistor value can cut your signal by a factor of 10 by just misreading one color band.

If you hang around long enough you'll find that it's common for some builders to falsely claim "the trace is wrong" as a last resort...

@GizzWizzKing said is way more likely to be the problem than anything you'll find on Reddit. You're far more likely to get good advice here than you are on Reddit.

Your solder joints look good, so I doubt that's the issue, but sometimes it never hurts to reflow them if any look suspect.

The ceramic capacitors wouldn't be your problem with a volume issue.

Have you adjusted the bias trim pots?

Another good place to start...

Also with respect to fake parts and Tayda -- I've never personally experienced it, but I've heard a story or two where people have claimed to get a bogus part from Tayda. It's very unlikely, but it could happen. Tayda sources parts just like the rest of us, and no matter how hard you try, sometimes a supplier will ship you a bad part. The only way to be 99% certain is to use a supplier like Mouser or DigiKey -- if they ship bogus parts, they go out of business. Having said that, if came from Tayda, it's likely a good part.

If you got it from Amazon or Ebay -- start there -- that's likely your problem.

 

[Giorfida]

It's been my experience that this should always be the first place to start with a volume issue. A wrong resistor value can cut your signal by a factor of 10 by just misreading one color band.

I can say I’ve been guilty of that a few times. Especially when using 1% metal films with the “extra” band (after using 4 band carbon film/comp resistors for decades— where I know many common values codes from memory ). Not hard to be off by factor of 10

 

[music6000]

By your description in the Original post satying it's farty, it sounds like a Biasing issue so Check the 4 transistors voltage as listed by Robert above!

 

[chris.knudson]

I can say I’ve been guilty of that a few times. Especially when using 1% metal films with the “extra” band (after using 4 band carbon film/comp resistors for decades— where I know many common values codes from memory ). Not hard to be off by factor of 10

I always check the with the DMM, but my meter does weird things with the decimal point. For example, it's show me the value of a 100K as 0.1M etc. If it's late ad there's thinking involved, I've been known to get it wrong a time or two.

 

[comradehoser]

I would second everything that everyone has said here. I'd say start with the bias first, because it's the easiest. I'd say try biasing by ear first as opposed to DMM readings.

I tried the cap subs mandated by EAE John, and the difference is .... negligeable. Maybe a smidge less mud, but it's still kinda muddy. The theorized noise issue with the layout has remained theoretical.

It is not on its own a brutally wonderful doom pedal, although you should have some okay tubeish distortion with either/both the "bright" and "normal" gain channels cranked. You should have plenty of volume on tap, though. I find the pedal by itself a bit tame and muffly-sounding. Earlier Sunn amps in general, I think, were ultra-linear clean boxes, basically. I have a Sonaro bass head, and that's definitely true.

However, if you feed it something, that is when you really hear that Model T/Sunn (O))) (band) sound and it responds like a pushed tube preamp. (Treble boosting will get you that Sabbath/pushed muddy Laney sound pretty well).

However, pushing other preamp pedals might also get you there (Orange/Matamp 120 clones, for example). I think Sunn (the band) just defaulted to Model Ts because that's what was cheap and loud in Seattle secondhand music markets at the time. Marshall ish pedals with EQs adjusted work fine--if it works for Windhand, it works for me.

 

[GizzWizzKing]

My initial mofeta I had fake/way out o spec FETS that I could not get to bias properly (low enough/high enough I don't remember at the moment) but they did still work to some extent without any lack of volume.

To start bias by ear I believe you will want to 1 at a time bias the normal channel for MAXIMUM headroom. Repeat for the Treble channel. Then the same for the master. Repeat the process as necessary but you for sure want to find yourself the most possible headroom out of this.

 

[shake__appral]

Wow thanks for all the replies on here, this is all really helpful information. I’ve been super busy with school exams, but I’ll mess around with this pedal again this weekend and see if I can get it going. I’ll be sure to check all my parts and bias these to the correct voltage, but I really don’t think it’s bad transistors from Tayda (unless all 10 or so they sent me were bad). Also just fucked up a King of Tone build so I’m super frustrated! Had to repurchase the pcb… not giving up that easy but I swear, anything with a trim pot is my enemy.

I wasn’t expecting a crazy doom pedal from this, but even aside from the volume issue I’m not all that impressed. I’m sure “Matamp in a box” would be more my speed.

 

[shake__appral]

There was a time a couple years ago where John mentioned that a couple component values were incorrect, but in reality there was just some variation in the particular unit that was traced. This is no longer the case, but even then, there was no volume issue.

If you hang around long enough you'll find that it's common for some builders to falsely claim "the trace is wrong" as a last resort...




We won't jump to conclusions just yet because I've never gotten a fake JFET from Tayda, but we also shouldn't rule it out as a possibility.

The MLCC caps and 560K resistor won't be a problem.

Have you adjusted the bias trim pots?

Here are the voltages as measured on the original:

Q1 - 8.89V
Q2 - 8.88V
Q3 - 9.18V
Q4 - 18V (source follower, not adjustable)

Just to confirm, there is plenty of volume on tap in my prototype and original.

Good to know, I’ll try biasing to these voltages and see if that helps.

 

[comradehoser]

Coda Black Hole is more of a straight doom pedal based on the Model T if you want.

Like I said, run some boosts into the Model FeT and see what you think.

A great (but not necessarily straightforward) build is the GCI N.E.W. Apostle for Matamp/Orange CR 120 tones. I believe there are also Matamp and Orange circuit copies floating around, including here, but I can't speak on them.

 

[comradehoser]

Have been really enjoying El Sol (acapulco gold). On the neck pickup it really nails the ragged, raspy, throaty, loose fuzz of doom bands like Conan and the like.

Easy to build! I even did a P2P of it

 

[shake__appral]

So I reflowed all my solder joints, checked all my caps, swapped out the transistors for a different brand, my multimeter is down right now so I’m still biasing to ear… even still there’s just not a lot of volume on tap without even measuring the voltages, and still a pretty significant drop in volume when playing through a clean amp. It does sound a little better when I have the gain cranked on my Sunn amp, there the volume difference isn’t as noticeable. Tried boosting it with a RAT… not much difference at all which was surprising. Not sure what else to do here, I’m kind of at a loss. it sounds decent but switching from pedal to bypass is quite alarming considering the extreme volume difference. I suppose the pedal is useable if I keep it on and don’t switch to clean (which is no joke with my Sunn solid state). Anyway I’m pretty sure my resistors are correct, I’m super careful about that process but I suppose that’s my last resort to get this thing functioning properly. Kinda disappointing considering this pedal doesn’t even stack well with a RAT (supposedly a match made in hell). Anyway thanks for everyone’s advice. I’ll keep messing around with it and will maybe figure it out eventually, or just use as is. I don’t play clean very much anyway but I’d prefer not to bomb out my apartment building with volume if I accidentally hit the footswitch off. Could’ve used a win on this one, considering I’ve fucked up the last two builds I’ve done. On a losing streak I guess, I’m sure Robert is stoked though with all the orders (and re-orders) I’ve made!

This is off topic, but would there be any way to use a pedal footswitch for other purposes, like say, an on/off device for a power strip (ya know, the surge protectors ones that have multiple plug- ins). Would it be able to handle the voltage and how exactly would I wire this up for it to function properly?

 

[comradehoser]

The wiring would be dead easy, but I would check the max voltage on the switch specs and recommended awg. 9v vs. 110v is different worlds. Maybe conductivity/jumping through the metal bits of the pedal into your foot wouldn't be a good idea.

My wife's space heater ate through three toggle switches-- just melted the switch housing enough that it didn't work anymore.

 

[comradehoser]

Don't give up on the pedal. Buy a new multimeter. They are a good investment. Once you can [measure] voltages, continuities, and resistance and such, you will be in a much better place to diagnose the issue and fix it.

My money is on a bad transistor or potentiometer

 

[comradehoser]

Also, hold on to those 3pdts! Along with the enclosure, they are one of the most expensive pedal ingredients

 

[shake__appral]

Good to know, I’ll try biasing to these voltages and see if that helps.

Sorry had finals hell week for school and I’m finally able to revisit
this pedal. Does it run on 18v then? So if the transistors won’t bias this low, does that mean the issue is with the transistors? I’d be surprised at that considering I’ve used multiple transistors from different batches and different sources… Q1 I can get under 9, Q2 about 11.5, Q3 17 (the one that can’t be biased), and Q4 is about 13.9.

Honestly right now it’s not sounding terrible, still have quite a difference in unity volumes, which I hate… going from louder clean to quieter fuzz, but it doesn’t seem as drastic as before after swapping out some of the transistors. Not sure how else I can troubleshoot this mf… change out the IC chips? Or just finish boxing it up with a volume caveat? Pretty disappointing I had high hopes for this one. At least my artwork turned out cool, I guess.

 

[music6000]

Can you show a picture of the Print/Writing on the 2N5457's in the Pedal?