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Hi all, I dissected the secret-1 pedal. The work is already on the italian forum http://www.fennecelectronics.it, http://www.fennecelectronics.it/smf/ind ... ic=11684.0
The soul of this hobby is sharing informations, so.. my two cents to the community As you can see, lot of degooping work

I removed and measured all components. This is the "naked" PCB And finally the schematics What you think about? On the other forum we are discussing about in and out buffers.. is not strange that biasing?

Thanks for this
What are the transistors?

IvIark wrote:Thanks for this
What are the transistors?

All components values are scraped! Then i can only say BJT NPN, hFE around 200.

Great, thanks

Great!!!!!

Nice work , seems to be nothing special is that considered active tone control ?
and funny that those huge caps are even silk screened on the pcb .

YuGi wrote:What you think about? On the other forum we are discussing about in and out buffers.. is not strange that biasing?

+1
It looks like it's missing a 1M to ground from the base of both BJTs. That would make sense.

In the Tubescreamer and similar the base resistor goes to VCC/2

Nocentelli wrote:

YuGi wrote:What you think about? On the other forum we are discussing about in and out buffers.. is not strange that biasing?

+1
It looks like it's missing a 1M to ground from the base of both BJTs. That would make sense.

The schematics is absolutely correct (I have the PCB on my desktop..).
I simulated the buffers with LTspice and the headroom is better then a classic bjt buffer (bias with 1M to v/2 and 10K emitter resistor). Why?!

I don't remember where, but I saw a demo if it in front of a number of Big Muff pedals and it was a really nice sounding combination.
Thanks for sharing, YuGi !

It's possible to bias a buffer in this way, but it's definitely the worse one, simply because it's higlhy hfe and temperature related.
A classic 2 resistors partition from supply and ground it's more stable and it permits to use a wide range of transistors (wide range of hfe), without any relevant difference in bias point. It will sound the same... or better (more dinamic, because you can adjust the bias point by design, not trying some different BJTs)!

If we connect the 1M resistor to V/2 like in a classic tube screamer, we've less trouble (less voltage difference across the resistor) and it will bias at good point.
If a circuit works fine from some decades, why we need to change it?

hey smanq, its' exactly what I've written yesterday in the italian forum. We share the same thought.

Aside from the buffers, is R5 just a positive feedback resistor? Also the frist opamp max gain is around 500x, so this thing should have a massive amount of distortion going on, instead is just a medium gain overdrive. Am i missing something?

Here's the vero:

Cannibal wrote:Aside from the buffers, is R5 just a positive feedback resistor? Also the frist opamp max gain is around 500x, so this thing should have a massive amount of distortion going on, instead is just a medium gain overdrive. Am i missing something?

The inverting opamp mixes dry and wet so the resulting wave is smootly distorted.

Schematic shows that the Gretsch Controfuzz could have been the source of the inspiration.

Please note that IL072 JRC4558 will works but in the original unit the chip is too silent...
we do not know exactly what it is but an OPA will be better choice

is similars to Boss OD-1

Someone pointed out an error in the layout, the link to pin 2 should be going to pin 3, but I can't edit the post above so here is the updated layout.