Maestro MPF-1. Only clean sound

[iainpunk]

first question, can we please see the solder side of your board? that would be nice.

DC at that point is around 2v and at the other side of the diodes is 200mV higher.

that's not weird, capacitor leakage can account for that, especially with electrolytics.

what DOES strike me as odd tho is that the signal isn't boosted enough to cause the diodes to clip, have you tried another 4007 chip, maybe there is a too low gain in one of the mosfets in your chip.

are you using those 4016's? or do you have the switching circuit omitted and one of the settings hardwired? (that's what i expect since i don't see a rotary switch on your pics, and only 3 of the 5 chips.)

you mentioned that the filter section does work as its supposed to, right? because you also mention oscillations... that feels like conflicting statements, or i am misunderstanding something....

i don't plan on quitting this thread until its solved, we will prevail!!!!!!!!!
cheers, Iain

[nonost]

ahaha thanks! I really appreciate the help you and antonis are giving.

The signal at pin 13 is way above unity. A big boost. Then after the 22k it goes down. I don't know how this circuit works but that's strange to me. I think the 4007 is boosting properly, I can hear a big boost. Yes, I tried another 4007 with same results.

No 4016 at all. I'm using a DPDT (on/off/on) for the three modes: broad, sharp and med. And a SPDT for the normal/overdrive modes. Well, actually I'm using a 3PDT for the latter.

The freq. pot behaves correctly. I mention the oscillations because when I was testing with the audio probe on pin 1 of the bottom 022, the signal oscillated. But only on this pin. Maybe I wasn't making enough contact with the audio probe or something. But the pot works right. I can clearly hear how the sound changes around all the sweep. Love the %^&*ed wah sounds around the 60%.

Tomorrow I will take a picture of the solder side.

[nonost]

Here a pic:

[nonost]

This circuit is complex enough for me to understand but it looks like the problem is between de 4007 and the freq. tl022.

Is it ok that drop voltage across the 22k resistor? It goes from 2.2v or so to 0.4v. At that point the signal is way below  unity.

Both tl022 are doing their thing, but the signal is not loud enough. As I said, the audio signal that the tl022 receives is quite weak (the bottom tl022).

[antonis]

Some points of checking interest ...

[nonost]

Ey antonis, I will check them...But I have spent soo much time looking for something with no luck. The picture can't tell much, every shadow looks like a bridge.

This build is really annoying me.

[iainpunk]

both the signal and the DC voltage are supposed to drop over that 22k, since it makes a voltage divider with that 5k6 to ground.
the signal is supposed to be big enough to get clipped by the diodes, causing distortion, so the problem is BEFORE that point, not after, this excludes the filter section.

how loud is the signal at pins 2,3 and 6? they should be at the same volume as your input signal. if that's not it, it might be the diodes being bust, or something it that leg being damaged.

cheers, Iain

[kaycee]

I know this is marked as a verified build, but I couldn't get it to go either, even after checking and re-checking my attempt. In the end, I pulled the IC's and binned it. I've periodically looked for someone making a PCB for it, but haven't turned one up yet.

[nonost]

You're right iainpunk. I didn't think about the diodes, it should distort after de 2k2 resistor. I would say that the signal is loud enough there to make the diodes clip...But for some reason it isn't happening. I'm going to make the test you suggest.

Ey kaycee, what was your problem with this build? My only problem is the signal not being boosted. It's at unity or so levels. The rest works ok.

[nonost]

Ok I did the tests.

Pin 2,3 and 6 sound as louder as bypass to me. Unity more or less.

But I've used a DAW this time.

Pin 13 --------->   -2.0 db
Pin 3&6 -------->  -5db
Pin 2 -----------> -15db
Bypass ---------> -14db

The difference between bypass/2 and 3/6 looks big it isn't. Without the DAW they sound almost the same. The big one is pin 13.

BTW, the db before and after the diodes are the same. They aren't clipping at all.


pd: I've adjust the usb preamp so the louder signal(pin 13) were close to 0db but without distortion.

[iainpunk]

what level are you getting without the pedal at all, just guitar in to interface?

i still think its something around the diodes, can you post the layout?
i guess that there's something wrong in the layout...
(i can't believe i asked for a layout, i strongly dislike vero/strip board, the main reason i didn't ignore this is because i loved the original i borrowed from a friend, i loved the fixed wah sounds it delivered)

cheers

[nonost]

I adjusted the signal so the louder one (pin 13) were close to 0. With the pin 13 at -2.2 db the bypass sound (straight to the interface) it was around -15 db.

I've also measured the ac voltage and at pin 13 is 300mV at max. I'm using a loop that I record with a pedal. The 1n4148 clip around 0.6v so...Yep, it looks something's wrong.

The wah sounds are the best of this devil thing.

Thanks man, I really appreciate it.

[nonost]

I've playing with the guitar. In the "sharp" position is hard to hear a difference between natural/overdrive modes but with the other two (wide and broad) you can feel it. These are a bit boosted in overdrive mode, I can hear more grit. But the difference between natural/overdrive is subtle.

[iainpunk]

this pedal usually has quite a lot of grit in the sound, it feels really raw and natural, but quite distorted.

With the pin 13 at -2.2 db the bypass sound (straight to the interface) it was around -15 db.

in that case, it seems your guitar is peaking at 75mV (-12dB over 300mV), that's not much at all...
i have a bass with lipsticks (low output pickups) and with only one pickup on, with a single string puts out about 1V peaks and the sustain is at 370mV... have you checked the guitar you are using is fully up to snuff???

the layout seems to be correct, but quite hard to follow.

cheers, Iain

[nonost]

I don't think that's very low for a vintage spec Strat single coil. Also is set up quite low (around 4mm fretting last fret).

I've just measured them, never done before. Strumming hard:

Neck: 75mv
Middle: 100mv
PAF: 240mv

That's with a cheap multimeter with the AC function and the button MAX.

I can hear a bit of overdrive in the "overdrive" mode with broad/med. With sharp, very little.

Are the diodes suppose to clip? I could swap them for some BATs around 350mv of Vf.

[iainpunk]

that's quite low output for a PAF tho, but the height matters a lot as well.
you could try some Germanium or Schottkey diodes

so i took a fresh (sober) look at the schematic and the info you provide;
the gain the circuit seems a bit low and so does the bias, maybe replace the 22k and 5,6k with higher values, maybe 56k and 10k, maybe put them in sockets, so you can change the values to have correct bias, aim for around 4volt, higher resistance means higher bias voltage and lower resistance means lower voltage, higher resistance also means higher gain!.

cheers, Iain

[antonis]

Try to make 2k2 resistor of much lower value..
(e.g. place in parallel a 470R - 560R..)

[iainpunk]

Try to make 2k2 resistor of much lower value..
(e.g. place in parallel a 470R - 560R..)

won't work, the sound on the other side of the resistor, where it meets the diodes, is also not clipped... its just a lack of gain.

cheers, Iain

[nonost]

I've socketed both resistors.

Stock values get 2.7v
With 10k and 56k I get 3v
With 22k and 100k  I get 3.2v

I can't turn the amp on, is quite late. But it looks that I would have to increase those resistor a lot in order to reach the 4 volts.

[iainpunk]

try it with sound, and adjust the values to what sounds best. 3v is already a big improvement, the gain is probably higher too then, im exited for the results.

the ratio between the 2 values change the volume, the total value change the gain/bias

cheers, Iain