NEED HELP! Big Muff clone has too less gain

[walnutzh]

Hello there, this is my first post on this lovely forum. I'm trying to build my first Ram's Head Big Muff clone, using the schematic below.



besides the schematic, I also use a EHX rams's head big muff reissue for reference. The EHX reissue I have uses BC457 transistor. I use BC547 too.

Now, the problem is my clone has very little gain, when I cranked the sustain all the way up, it sounds like the EHX's sustain at 1 or 2. It clearly has diode clipping going on, but nowhere near what a big muff should be.

I suspect the input stage of my build has something wrong, it's output might be too low for the clipping stages. So I put a boost pedal in front of my build, cranked the boost and I get what a normal big muff sounds. But I still can't figure out what's going wrong with my build. I'll post my input stage transistor voltage below:

Vb: 0.631V
Ve: 0.035V
Vc: 4.74V

and for comparison, I measured the EHX reissue's input transistor:
Vb: 0.621V,
Ve: 0.035V,
Vc: 4.62V

from the reading I can't find anything useful.
I also swapped the BC547 for 2N5088, 2N5089, 2N2222, all have ultra low gain. in fact those transistor sounds nearly the same to me.

Anyone can help? thanks a lot!

[antonis]

Hi & Welcome..

>I also swapped the BC547 for 2N5088, 2N5089, 2N2222, all have ultra low gain<

You probably refer on Q4 stage gain..
(and not on actual devices one..)

First of all, check for R2/R9 values..
(especially for R2..)

P.S.
What is your guitar pickup(s) impedance..??

[walnutzh]

Hi & Welcome..

>I also swapped the BC547 for 2N5088, 2N5089, 2N2222, all have ultra low gain<

You probably refer on Q4 stage gain..
(and not on actual devices one..)

First of all, check for R2/R9 values..
(especially for R2..)

P.S.
What is your guitar pickup(s) impedance..??

thanks for reply!
yes, I mean the Q4 gain, aka the input stage transistor. the R2 is 33K, R9 is 470K but I also swapped for 560K to test. with 470K, the Vc of Q4 reads 4.17V, and with 560K the Vc is about 4.7V. A little more gain, by little I mean a tiny tiny little 

My guitar has three single coils, impedance about 7K-8K for the neck and middle, the bridge is about 13K.

[Marcos - Munky]

Welcome.

What's the voltages on the other transistors? And do you know how to do an audio probe test?

[walnutzh]

Welcome.

What's the voltages on the other transistors? And do you know how to do an audio probe test?

Hello!

Q3: Vc 4.79V    Vb 0.635V.    Ve 0.037V
Q2: Vc 4.75V    Vb 0.63V.      Ve 0.034V
Q1: Vc 4.93V.   Vb 1.792V.    Ve 1.205V

about audio probe, I have not made one yet, but I use a stupid method to test different stage output. for example If I wanna test the input stage output, I just disconnect the other three stages and route the output to my guitar amp. I'm using breadboard so it's pretty easy to do.

here's what I noticed, the input stage's ouput sounds little bit louder than my clean guitar signal. But I suppose this is desired?

[antonis]

All voltages are perfect..!! 

Do you get any signal with SUSTAIN pot all the way down (Fully CCW)..??

[walnutzh]

All voltages are perfect..!! 

Do you get any signal with SUSTAIN pot all the way down (Fully CCW)..??

yes, with Sustain all the way down, if I turn the Volume up I can still hear the guitar signal, just dull and no distortion at all.

[duck_arse]

on the breadboard? pull C10, C12 and C11, and see if the levels shoot up. maybe post a photo of your breadboard.

and also welcome.

[walnutzh]

on the breadboard? pull C10, C12 and C11, and see if the levels shoot up. maybe post a photo of your breadboard.

and also welcome.

I'll try that tomorrow! Could you please give me your insight on the reason to pull out thoes three capacitors? Does those capacitors block some frequencies and affect the gain?

I'll try to take a photo of my breadboard tomorrow too. Thanks a lot!

[duck_arse]

if your caps are not 470pF but say 4n7 or more, they will eat up all your gain. they are meant to roll-off gain for higher frequencies, but the bigger the cap, the lower that cut-freq goes, maybe into the freqs you actually want to hear. it was only a few days ago someone had 330pF in a circuit when he thought it was 33pF, won't mention any names. also C8 too big will eat signal.

[walnutzh]

if your caps are not 470pF but say 4n7 or more, they will eat up all your gain. they are meant to roll-off gain for higher frequencies, but the bigger the cap, the lower that cut-freq goes, maybe into the freqs you actually want to hear. it was only a few days ago someone had 330pF in a circuit when he thought it was 33pF, won't mention any names. also C8 too big will eat signal.

I didn't even buy 4n7 capacitors, so it might be not my case 
I checked those capacitors to ensure there're 471 on them. But I will try to pull them out to see what would happened:-)

[antonis]

It's time to build and use an audio probe..
(much more easy than you might think..)

Check signal on input and then on Sustain pot Lug 3 - the second should be heard much louder..

[walnutzh]

It's time to build and use an audio probe..
(much more easy than you might think..)

Check signal on input and then on Sustain pot Lug 3 - the second should be heard much louder..

you mean the lug2(the middle lug)?

[walnutzh]

on the breadboard? pull C10, C12 and C11, and see if the levels shoot up. maybe post a photo of your breadboard.

and also welcome.

I tried this today and it worked!!! turns out one of these caps is faulty! Replace the bad one and the gain went normal, now it sings like the real big muff

I think I learned my lesson  stupid me
Thank you sir!

[Jdansti]

Glad you got it going! No stupidity involved. Just exploring the many issues that can cause a problem until you find the solution. It's detective work. It'll get easier as you go, but even the best builders here hit debugging walls and need help now and then.

See my signature below. 

Good catch, Duck!

[walnutzh]

Glad you got it going! No stupidity involved. Just exploring the many issues that can cause a problem until you find the solution. It's detective work. It'll get easier as you go, but even the best builders here hit debugging walls and need help now and then.

See my signature below. 

Good catch, Duck!

Haha Thank you! I definitely will remember your signature!

[walnutzh]

Now as I solved my problem through you guys' help, I wanna share my experience on my build.

Like I said this is my first time trying to build a pedal and in fact my first time using the breadboard. I encountered some noise issues but solved them in the end.

At first my build was extremely noisy, I knew that breadboard tends to be noisy because lacking shielding, but noise level was too high to experiment pedals like big muff. And I thought that must be a solution, otherwise those famous builders won't use breadboard anymore. So I searched a lot of articles and posts and found a thing called GROUND PLANE. I'm sure experienced builders like many people in this forum know this.

Basically gound plane was a big metal plate or foil that connects to circuits ground. So I found an old computer enclosure and took the side panel, soldered a wire to it and connect it to the circuits, it works like a charm! much much quieter than before. Now I can fully utilize the breadboard for my experiments.

Another thing I did was putting a 20uF capacitor between power rail and the ground rail, that filtered out some buzz noise from the power supply.

Here's my breadboard looks like now:



Before I started my build I learned a lot from this forum. Thank you guys I'll continue to learn from here

[duck_arse]

I think I learned my lesson  stupid me

stupid? why? also, how was the cap faulty?

as you had presented us with a good set of DC voltages, it had to be an AC problem. that points to caps, that made far fewer suspects. easy.

[walnutzh]

I think I learned my lesson  stupid me

stupid? why? also, how was the cap faulty?

as you had presented us with a good set of DC voltages, it had to be an AC problem. that points to caps, that made far fewer suspects. easy.

I just checked the "faulty" cap to see what's wrong with it. Before I just thought it maybe damaged. But now it turns out to be a wrong value one. It clearly has 474 on it... it's a 470nF cap...  Your suspects are spot on.