Secretefx - Secret-1 STD overdrive  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.
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YuGi
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Post by YuGi »

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 :mrgreen:
pedale_esterno.jpg
pedale_esterno.jpg (57.84 KiB) Viewed 7151 times
As you can see, lot of degooping work :slap:
pedale_interno.jpg
pedale_interno.jpg (70.9 KiB) Viewed 7151 times
pedale_interno_front.jpg
pedale_interno_front.jpg (56.09 KiB) Viewed 7151 times
Last edited by YuGi on 09 Feb 2014, 16:56, edited 1 time in total.

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YuGi
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Post by YuGi »

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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IvIark
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Post by IvIark »

Thanks for this :applause:
What are the transistors?
"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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YuGi
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Post by YuGi »

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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Post by IvIark »

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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AAntonio
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Post by AAntonio »

Great!!!!! :applause:

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okgb
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Post by okgb »

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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Post by Nocentelli »

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.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Post by IvIark »

In the Tubescreamer and similar the base resistor goes to VCC/2
"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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YuGi
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Post by YuGi »

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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Cub
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Post by Cub »

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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Post by smanq »

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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Post by pamaz »

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

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Post by Cannibal »

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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Post by IvIark »

Here's the vero:
"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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YuGi
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Post by YuGi »

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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Post by Nick123 »

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

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Post by Mbas974 »

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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Post by Agent86 »

is similars to Boss OD-1

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Post by IvIark »

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.
Secret efx - Secret-1 Standard - FIXED.png
"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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