Secretefx - Secret-1 STD overdrive

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Secretefx - Secret-1 STD overdrive

Postby YuGi » 09 Feb 2014, 17:45

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/index.php?topic=11684.0
The soul of this hobby is sharing informations, so.. my two cents to the community :mrgreen:
pedale_esterno.jpg

As you can see, lot of degooping work :slap:
pedale_interno.jpg

pedale_interno_front.jpg
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Last edited by YuGi on 09 Feb 2014, 17:56, edited 1 time in total.

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Re: Secret-1 STD overdrive

Postby YuGi » 09 Feb 2014, 17:52

I removed and measured all components. This is the "naked" PCB :D
PCB_top_bottom.jpg

And finally the schematics :applause:
Secret-1_Schematics.jpg


What you think about? On the other forum we are discussing about in and out buffers.. is not strange that biasing? :scratch:
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Re: Secretefx - Secret-1 STD overdrive

Postby IvIark » 09 Feb 2014, 18:24

Thanks for this :applause:
What are the transistors?
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Re: Secretefx - Secret-1 STD overdrive

Postby YuGi » 09 Feb 2014, 18:30

IvIark wrote:Thanks for this :applause:
What are the transistors?

All components values are scraped! Then i can only say BJT NPN, hFE around 200.
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Re: Secretefx - Secret-1 STD overdrive

Postby IvIark » 09 Feb 2014, 18:42

Great, thanks
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP
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Re: Secretefx - Secret-1 STD overdrive

Postby AAntonio » 09 Feb 2014, 19:18

Great!!!!! :applause:
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Re: Secretefx - Secret-1 STD overdrive

Postby okgb » 09 Feb 2014, 19:25

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 .
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Re: Secret-1 STD overdrive

Postby Nocentelli » 09 Feb 2014, 19:28

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


+1
It looks like it's missing a 1M to ground from the base of both BJTs. That would make sense.
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Re: Secretefx - Secret-1 STD overdrive

Postby IvIark » 09 Feb 2014, 19:37

In the Tubescreamer and similar the base resistor goes to VCC/2
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Re: Secret-1 STD overdrive

Postby YuGi » 09 Feb 2014, 19:42

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? :scratch:


+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?! :scratch:
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Re: Secretefx - Secret-1 STD overdrive

Postby Cub » 09 Feb 2014, 20:53

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 ! :thumbsup
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Re: Secretefx - Secret-1 STD overdrive

Postby smanq » 10 Feb 2014, 12:03

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? :D
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Re: Secretefx - Secret-1 STD overdrive

Postby pamaz » 10 Feb 2014, 12:35

hey smanq, its' exactly what I've written yesterday in the italian forum. We share the same thought.
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Re: Secretefx - Secret-1 STD overdrive

Postby Cannibal » 10 Feb 2014, 12:41

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?
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Re: Secretefx - Secret-1 STD overdrive

Postby IvIark » 10 Feb 2014, 12:49

Here's the vero:

Image
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Re: Secretefx - Secret-1 STD overdrive

Postby YuGi » 10 Feb 2014, 14:02

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.

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Re: Secretefx - Secret-1 STD overdrive

Postby Nick123 » 11 Feb 2014, 13:53

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

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Re: Secretefx - Secret-1 STD overdrive

Postby Mbas974 » 11 Feb 2014, 20:34

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
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Re: Secretefx - Secret-1 STD overdrive

Postby Agent86 » 13 Jul 2014, 14:12

is similars to Boss OD-1
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