Maestro MPF-1. Only clean sound

[nonost]

Hi. I'm building a Maestro MPF-1. It's a big one:

https://tagboardeffects.blogspot.com/2015/10/maestro-mpf-1.html

The thing sounds, but I don't get any kind of grit/gain of it. There's almost no difference between the clean and dirty modes.

The pots and the bandwidth switch are working good. But this thing is totally clean.

Where should I focus? I've checked every damn corner...I'm using a couple tl022 and a cd4007ube by Texas Instruments.

BTW, the freq. pot at Mark's is backwards

[iainpunk]

1) voltages on IC pins?
2) have you checked all solder connections?
3) do you have pictures? both the solder and the component side
4) there is a thread: check it:
https://www.diystompboxes.com/smfforum/index.php?topic=29816.0

cheers, Iain

[nonost]

Voltages from the couple TL022 are ok. I'm not sure about the 4007 one, since I'm not familiar with it. But taking a quick a look at the data sheet it seems not bad. I will take more time with it though.

4007UBE

1: 0v
2: 6.3v
3: 3.2v
4: 0v
5: 0v
6: 6.8v
7: 0v

14: 9.2v
13: 2.6v
12: 5v
11: 7.6v
10: 5v
9: 1.6v
8: 0v

TL022

1: 4.6v
2: 4.6v
3: 4.1v
4: 0v

8: 9.2v
7: 4.6v
6: 4.6v
5: 4.6v

TL022 bottom

1: 4.6v
2: 4.6v
3: 4.6v
4: 0v

8: 9.2v
7: 4.6v
6: 4.6v
5. 4.6v

Yeah...All the tedious stuff done: reflow, checked every component value&placement, links, holes...

[nonost]

I think the problem is it's not getting any boost. It's supposed to have a 20db boost but I  can't hear any even with the height pot cranked.

Which part is in charge of the boost?

[antonis]

Both TL072 voltages are fine.. 

CD4007 pin13 voltage is awkward..
(according to 6.8V on pin 6, it should be about 50mV.. - or I'm missing something..)

P.S.1
1N4148 diode pair appears directly connected to GND on some schematics..

P.S.2
op-amp biased by 2 X 2M2 voltage divider (the one with 10k feedback & 1k gain reisitors) is in charge of the boost..

[nonost]

Thank you Antonis

I've checked again those pins 6&8 voltages. No luck

Yeah, I've read something about it. These go through a 2.2uf capacitor.

It's driving me mad this thing.

[antonis]

Could you double-check 4M7, 22k & 5k6 values..??
(from 4007 pin 6 to GND..)

edit: 4M7 must be OK unless both 2M2 & 4M7 are of wrong value..

[iainpunk]

has the 4007 been subject to ESD? (electro static discharge)
it can kill them, fully, or more commonly, partially.
i used a partially fried 4007 as clipping diodes once.

cheers, Iain

[nonost]

I've already checked them. But I'm going to desolder one lug to be sure they are ok.

I've never fried one by ESD...But I guess I will try a new one if there is no exit.

[duck_arse]

let us see the colour bands on your resistors, in situ, that we might double check what you say is corrct. please.

[nonost]

Socketed the 4007ube without luck. No grit.

here a pic a took before wiring things up:



This thing is torturing me.

[nonost]

Ok. I've been messing around with an audio probe test.

The output at pin number 13 is louder.. A lot. It's boosted, but after the 22k resistor it goes down and all the boost is lost.

After that 22k resistor the output is more or less as the bypass signal.

Any help? Any other test I can make?

I really appreciate help. This is by far the more PITA I've ever come across in pedal building. 

[iainpunk]

the signal out of pin 13 should be distorted, what does the signal sound like on the other side of the 2.2k, where the diodes meet? what guitar/pickups are you using?
is the signal affected by the filter at that point in the signal?

cheers, Iain

[nonost]

I play with a HSS Strat. Neck&Middle alnico V around 6k and the HB is a classic P.A.F. with alnico II bar and around 7.2k. I play through an Orange Ad30 twin channel. I usually set the amp with little headroom, if not any, so singles are clean or about to break up and the HB clearly overdriving.

The sound at the other side of the 2.2k is the same as before. I can't hear a difference. Very boosted.

The signal at the input of the tl022 in charge of boosting is kind of weak. The 022 boost it to unity level more or less

The signal at the first half of the other 022 is really really weak (pin 2&3). At pin 1 it oscillates. I mean the opamp with the freq. pot.

I've also set the amp very clean with lots of headroom just in case my settings were fooling with me. But no surprises.

Thanks Iain, really.

[iainpunk]

what is the signal like on the other side to the clipping diodes? it should be near quiet.
also, i can't seem to see them on your board, where are they?

cheers, Iain

[nonost]

Where they meet the 2.2uF the signal is dead silent.

They are under the 4th 2.2uf electrolytic yellow cap. The one close to the greenie and red wima cap.

[antonis]

Where they meet the 2.2uF the signal is dead silent.

Well done, then..
(2.2μF shorts diode pair lower junction to GND..)

Does signal vary within 550 - 650 mV at diode pair / 2k2 resistor junction..??

[nonost]

Do you mean the audio signal? AC  voltage?

I've measured dc voltages...It's basically the same before and after 2k2 resistor and it drops around 200mV across the diodes.

[antonis]

I'm confused a bit now..

You refered on "dead silent signal" above, didn't you??

[nonost]

Oh god, right. Yeah I'm stupid. If there's no audio = no AC voltage. Sorry 

So yes, where diodes meet the 2.2uf cap there's no audio. DC at that point is around 2v and at the other side of the diodes is 200mV higher.