Volume Pedal Boss buffer Project

[blester1]

hey guys, first feel free to move to the correct location of this post.

I'm thinking of making a buffered volume pedal, is it correct to do it this way?

I put the 250k potentiometer between the buffers. which potentiometer ideal for this circuit?

thanks

[stonerbox]

Welcome! Unfortunately we can not see your schematic. Could you post it again?

As for volume pot, anything between 100k-1000k will do. A 100k is pretty standard. If you don't want to loose high end when the pot is turned down you can experiment with a bleed cap (start with a 47pF and work your way up to 330pF) attached between the lug 1 and lug 2.

[Rob Strand]

As for volume pot, anything between 100k-1000k will do. A 100k is pretty standard. If you don't want to loose high end when the pot is turned down you can experiment with a bleed cap (start with a 47pF and work your way up to 330pF) attached between the lug 1 and lug 2.

With the two buffers you don't have to worry about the HF attenuation and caps.

It looks like 22k to 47k would be optimal.  100k is OK but technically it adds more noise.

Note the Vref bias has been tweaked for more swing, approx 4.5V at emitters.

Schematic


Signal loss at full volume


Noise


Signal swing

[stonerbox]

With the two buffers you don't have to worry about the HF attenuation and caps.

You are absolutely right! I was still in bed waking up and a bit groggy. The output buffer will restore the impedance.

[uk_surf]

This is super helpful. I've got a somewhat-related question, apols if this the wrong spot or otherwise protocol-bothering.

After a long, long hiatus I'm dipping my toe back into diy pedal building. Starting gently, I wanted to go the kit route, and build a simple buffer. However, to reduce the footprint (and helpfully procrastinating getting back into drill press work) I want to install that in a Morley Little Alligator - first thing in the signal chain.

I think it's a matter of connecting the buffer's output to volume pedal's input, and connecting the buffer's power supply in parallel to the volume pedal's. It would be 'always on' and non-switchable, assuming it works.

Please tell me where I've gone wrong and why, I really appreciate the extraordinary depth of knowledge on this page, though a lot of it goes right over my head.

Cheers, Eric

[antonis]

Hi & Welcome..

Presuming you're talking about something like below, it should be OK..



P.S.
In case of op-amp buffer, place a 100nF cap (preferably ceramic) between +9V and GND, as close as physically possible to op-amp respective pins..

[Rob Strand]

You are absolutely right! I was still in bed waking up and a bit groggy. The output buffer will restore the impedance.

No worries, I've spent the last two weeks like that.

[antonis]

Note the Vref bias has been tweaked for more swing, approx 4.5V at emitters.

I have to admit that you are one of the very few persons who DO care about buffer output symmetrical swing, Rob..
(the vast majority just throw a big value bias resistor from Vcc/2 to Base and don't give a damn about Emitter voltage and negative swing distortion due to Emitter loading..)

P.S.
I'd make R2 18k for not worry too much neither about Volume pot value nor for next stage input impedance..

[Rob Strand]

I have to admit that you are one of the very few persons who DO care about buffer output symmetrical swing, Rob..
(the vast majority just throw a big value bias resistor from Vcc/2 to Base and don't give a damn about Emitter voltage and negative swing distortion due to Emitter loading..)

I didn't want to compare swing when the bias was way off!

Not sure why people don't do it more often.   For Boss pedals they use Vcc/2 for convenience as they already have a Vcc/2 for the opamps.

P.S.
I'd make R2 18k for not worry too much neither about Volume pot value nor for next stage input impedance..

18k just as good as 15k.  Comes down to what the transistor hFE is.

FYI, the old Ibanez Soundtanks used a higher base bias: 9k1 and 22k and the hFE was 200 to 400.  They only did it on the input buffer, not the output buffer.  The input buffer had two DC coupled buffers - so you lose even more swing, and something had to be done.

[stonerbox]

No worries, I've spent the last two weeks like that.

Rough, what did you suffer through? I hope you are feeling better now.
Got food poison some months back and did not eat or leave the bed for six days. Felt like I was slipping away.

[Rob Strand]

Rough, what did you suffer through? I hope you are feeling better now.

Some sort of flu but I had a weird headache and sinus problems for about two weeks.  Don't think I've had the flu for a few years so it's about time I got one.

Got food poison some months back and did not eat or leave the bed for six days. Felt like I was slipping away.

I'm with you on that one.   That type of thing really takes it out of you.  About 25 years ago I had something like that.  I remember walking from one room to another and just lying on the ground half way, totally overwhelmed from "illness".  You simply can't go on no matter how hard you try.   I was also thinking is this what happens when you die from something.   

[uk_surf]

Hi & Welcome..

Presuming you're talking about something like below, it should be OK..



P.S.
In case of op-amp buffer, place a 100nF cap (preferably ceramic) between +9V and GND, as close as physically possible to op-amp respective pins..

Brilliant, thanks so much for your reply! Yes, that kind of thing - I'm looking at a Fuzz Dog cream buff.

Hope you're both feeling better, and thanks for the knowledge here.