Vref on tube booster (pedal i designed) is ~3.5v instead of 4.5v

[duck_arse]

yes, See2, at switch RELAYB, contact A. coffee for me?

[antonis]

Avec plaisir..

[duck_arse]

no, I don't speak Greek. sorry.

[snow123]

i just breadboarded the circuit, and it sounds normal. and VREF and VA are around where they should be.

[antonis]

So, where are we now..??

[duck_arse]

i just breadboarded the circuit, and it sounds normal. and VREF and VA are around where they should be.

the original post mentions nothing about the sound, only sez "....but for some reason the Vref is around 3.5v instead of 4.5v ....". was the sound a problem as well?

[snow123]

i just breadboarded the circuit, and it sounds normal. and VREF and VA are around where they should be.

the original post mentions nothing about the sound, only sez "....but for some reason the Vref is around 3.5v instead of 4.5v ....". was the sound a problem as well?

yep, the VREF being 3.5v instead of 4.5v was causing it to sound voltage-starved/misbiased

[snow123]

So, where are we now..??

i guess we're wondering why its working correctly when breadboarded, but not when built on a pcb?

[snow123]

and if anyone is wondering, i breadboarded the circuit to try the changes that Vivek and antonis initially suggested, before desoldering everything.

[antonis]

So, do you intend to use the breadboarded circuit as a pedal or to fix/modify the PCB..??

[snow123]

So, do you intend to use the breadboarded circuit as a pedal or to fix/modify the PCB..??

i initially breadboarded the circuit to see what was wrong with it, but now that i know that it works as intended when breadboarded, ill focus on the pcb and we can see if i messed anything up.

[snow123]

also, ive only breadboarded the main circuit, without the relay bypass thing, so yea.

[diffeq]

So, where are we now..??

i guess we're wondering why its working correctly when breadboarded, but not when built on a pcb?

It is hard to tell by photo, but R101-2 look like they have 4th band as orange, meaning they could be 100K instead of 10K, which would skew bias. Can you confirm the real value? e.g. by desoldering one of them.

[snow123]

So, where are we now..??

i guess we're wondering why its working correctly when breadboarded, but not when built on a pcb?

It is hard to tell by photo, but R101-2 look like they have 4th band as orange, meaning they could be 100K instead of 10K, which would skew bias. Can you confirm the real value? e.g. by desoldering one of them.

you mean R102? im 99.9% sure that its 10k.
heres a better picture:

[snow123]

ive just made C2 100nf, made R4 100k, removed R11, and added R100 back into the circuit, and nothings changed, and its still sounding a bit buzzy.

[snow123]

and somehow VREF didnt change, despite adding R100 back into the circuit.

[duck_arse]

and somehow VREF didnt change, despite adding R100 back into the circuit.

VREF didn't change from 4V5?

but no relay bypass business? it's the relay that draws the current through the supply filter R that causes the voltage drop to the entire circuit that is then divided by the bias string to apear as "~3.5v instead of 4.5v". as someone pointed out page ago.

[GibsonGM]

What are you powering this with? A battery or wall wart?  Sorry if you already said, these bifocals are driving me nuts   

[snow123]

What are you powering this with? A battery or wall wart?  Sorry if you already said, these bifocals are driving me nuts   

im using a 1spot CS12.

[snow123]

and somehow VREF didnt change, despite adding R100 back into the circuit.

VREF didn't change from 4V5?

but no relay bypass business? it's the relay that draws the current through the supply filter R that causes the voltage drop to the entire circuit that is then divided by the bias string to apear as "~3.5v instead of 4.5v". as someone pointed out page ago.

wait is that why the voltages are different on the breadboarded version and the pcb? 'cause i didnt add the relay bypass stuff to the circuit when i breadboarded it, since i didnt have a enough space. but i do have the relay stuff on the pcb.