Rare stuff- Epider Sound Heavy Metal

[bmsiddall]

Who doesn't love a nice Brazilian?

I stumbled across a layout at dirtboxlayouts but couldn't find a schematic after a quick google search.  Traced it from the layout yesterday and about half an hour later realised pedal PCB have it on their site 

I haven't started to build yet but I have been very interested in experimenting with crossover distortion, so this has just gone to the top of to-do list.  Thought I'd post it here as someone else might like to take a shot at it as well.

Cheers,
Brett

[aron]

What other heavy metal pedal used crossover distortion? It's a BOSS unit I think.

[Quackzed]

hm-2 'heavy metal pedal used crossover diodes, though the most popular mod is to remove 'em
i sometimes use some low threshold crossover diodes as a heavy handed noise gate, but its not a smooth on .to off gate ,it gets fizzier / nastier as it starts to cut off the signal so i tend to use it in VERY high gain 'nasty' type distortions for abrupt power chord stuff

[antonis]

Are you sure about the value of R5..??

'Cause by biasing a BJT of h_FE200 with a single resistor of 330k  gives about 5mA Collector current and with a 4k7 Collector resistor results into heavy saturation (bottomed)..
Even if we suppose that there is signal negative waveform of amplitude enough to bring it into forward-active region, D5 is useless..
(Q2 output is already positively clipped..)

P.S.
I'm back of a tsipouro meating so maybe all the above are hogwash..

[bmsiddall]

It's correct if these are correct.  But of course it depends if the original was traced without any errors...
https://dirtboxlayouts.blogspot.com/2020/05/epider-sound-heavy-metal.html
https://www.pedalpcb.com/product/heavyspider/

Btw, here's the only youtube demo I've found so far.
https://www.youtube.com/watch?v=tMz6alYslM4&t=465s

[bmsiddall]

Built it just after posting this thread and it didn't work, so i put the project to one side while finishing others.

Having a lazy Sunday so thought i might revisit this. Rechecked dirtbox and pedalpcb and both have updated the schematic- the 330k resistors are now 3.3M.    Antonis knows a thing or 2   

[antonis]

  Antonis knows a thing or 2   

Antonis knows the answer is tsipouro but he tends to forget the questions..

P.S.
Just a BJT bias common sense issue..

[bmsiddall]

I'm more an Assyrtiko and sardines guy myself 

[Marcos - Munky]

Built it just after posting this thread and it didn't work, so i put the project to one side while finishing others.

Having a lazy Sunday so thought i might revisit this. Rechecked dirtbox and pedalpcb and both have updated the schematic- the 330k resistors are now 3.3M.    Antonis knows a thing or 2   

If you read the comments on dirtbox layouts page, it says the pedal worked after using 3M3 resistors, so it's a simple fix.

Btw, thanks for posting this. I'm from Brazil and never heard of this one before.

[bmsiddall]

Hi Marcos.

i changed the resistors earlier today and it fired up. I'm not 100% convinced about it at this stage- winding the texture pot anticlockwise (crossover diodes) gives a splatty superfuzz/fy2 hybrid sound (not as good as it sounds!) and it seems a little thin fully clockwise.  i used <200hfe transistors and the collector voltages are 7.9 and 6.8v respectively.  Might benefit from hotter transistors and/or a little tweaking?

Cheers,
Brett

[Marcos - Munky]

I don't know the original transistors used, but they could be the BC547C, which is the 547 with highest hfe. Probably a hotter transistor pair will sound better.

[analogMensch]

...the BC547C, which is the 547 with highest hfe...

BC547A have a typical hfe of 90, B have 150 and C have 270. So C will habe three times the power of A, will make a nice difference

[antonis]

Do transistors have power..?? 

[analogMensch]

Do transistors have power..?? 

Haha, no, I mean the sound will have more power Sorry, it's just my bad english.