Big Muff Diode clipping switch issue

[Locrian99]

Hello,

So I ordered some PCB's for a modified muff and I'm having an issue with the diode clipping switch.   I'm not sure if I did it right.


So I am using an on/off/on switch for the diode clipping.   In the off position I'm reading 4.4x v at the collector of q2 and q3 and getting a nice overdrive.   When I switch over to the red led's I get sort of a sputtery fuzz and I'm reading 2.2v on the collector, same when switched to the 4148 but I don't get any signal passing there.  Board continuity appears good in the area.    I wasn't sure if the cap before or after the diodes would matter there.   Anyways just wondering if anyone sees anything in the scheme that might be incorrect.   I've checked values etc.   but since it works with the diodes out of the circuit I tend to think it has something with how I did the switch.   

Thx

[ElectricDruid]

On the face of it, your switching looks fine.

However, I notice one thing looking closer. The caps seem to have a connection shorted across them:

[antonis]

If that short is only on schematic, no problem..

If it's also on board, it makes R10 and R15 practically useless and sets Collector voltage one diode forward voltage drop above Base..
(ala Buzz Fuss style..)

[Locrian99]

Nope looks like  it made it into the pcb too.   Thanks guys I'll have to do a little surgery, and fix schematic redo my routing.   Major drawback to using any auto router I suppose...

[duck_arse]

can we see the offending board layout? the fix should be as simple as pulling the cap from the baord and adding it to the wire to the switch, if it is baord short.

[Locrian99]

can we see the offending board layout? the fix should be as simple as pulling the cap from the baord and adding it to the wire to the switch, if it is baord short.

Yea i can share that when i get back to my pc.   I was messing with the board some more this morning but didnt seem to fix it.     Seems like some other weird routing happened more eyes will help  

[Locrian99]

can we see the offending board layout? the fix should be as simple as pulling the cap from the baord and adding it to the wire to the switch, if it is baord short.

Here you go, I haven't really dug in yet as to why it didn't work when I cut the trace, it looks like part of the switch is not connected though still.  I re did that switching area on the schematic after I drew it the first time.  Didn't pop up any errors,  looks like when I redrew I left part of it still there.  Oops.  Then the auto router just did its thing.  I'm working on redoing the layout and will be likely hand routed it with a copper pour for ground etc.  First try at diptrace...  But no point in tossing 5 boards if I can make them usable easily enough. 

[duck_arse]

board board board. I must not misspell board again.



I found this with GIMP. it seeeeemmmmsssss to show the shorted caps don't go anywhere at one end.

[ElectricDruid]

That auto-router did a horrible job, sorry! The reasons why:

1) Two layers, and yet *loads* of tracks routed between 0.1" spaced pins. Use the other side of the board!
2) Skinny tracks peel easily. They could easily be three times as fat given the amount of space there is.
3) So many vias for such a simple job!

For stuff like this, I think humans still do a much superior job. Sure, there's 6-layer motherboards that I could never *hope* to lay out if I lived to be 150 years old, and the software that does those jobs probably costs thousands but is worth every penny. But all the autorouters I've ever seen on my budget  are terrible! I also use Diptrace, but I avoid the autorouter like the plague since it manages to make even a simple job look awful.

[duck_arse]

ohh, onboard switches? makes it a bit more complicated to fix.

[Locrian99]

That auto-router did a horrible job, sorry! The reasons why:

1) Two layers, and yet *loads* of tracks routed between 0.1" spaced pins. Use the other side of the board!
2) Skinny tracks peel easily. They could easily be three times as fat given the amount of space there is.
3) So many vias for such a simple job!

For stuff like this, I think humans still do a much superior job. Sure, there's 6-layer motherboards that I could never *hope* to lay out if I lived to be 150 years old, and the software that does those jobs probably costs thousands but is worth every penny. But all the autorouters I've ever seen on my budget  are terrible! I also use Diptrace, but I avoid the autorouter like the plague since it manages to make even a simple job look awful.

Yea.  Ive decided to call it a lesson learned and traced it out by hand and order some more boards.   Good thing its only 5$ right!

[Zveeen]

If you added the Diode switch to alter the compression/clipping threshold, I once breadboarded a modified Muff where I used a Potentiometer and resistor combo instead of the collector resistor on the 2nd clipping stage to introduce resistance before the diodes, thus increasing the headroom. I thought it sounded pretty good, especially with higher fV diodes in the first clipping stage, had a very monstrous bass to it.
I can dig out the schematic if you are interested.

Cheers

[Locrian99]

If you added the Diode switch to alter the compression/clipping threshold, I once breadboarded a modified Muff where I used a Potentiometer and resistor combo instead of the collector resistor on the 2nd clipping stage to introduce resistance before the diodes, thus increasing the headroom. I thought it sounded pretty good, especially with higher fV diodes in the first clipping stage, had a very monstrous bass to it.
I can dig out the schematic if you are interested.

Cheers

Yea if its not too much I'd love to see it.    Muff mods are always fun.

[Zveeen]

Agreed, the Muff is one of my favourite circuits to mod. I found the schematic much quicker than i hoped. Seems like I didn´t use clipping diodes in the first clipping stage at all. No wonder it had so much bass. I also used a different gain stage with probably my favourite mods of all, at least when I intend to use the pedal on bass. It essentially does what the pinch knob on a woolly mammoth does. It gets you in the synth like territory. An absolute must if you are a fan of Muse.

Anyway I hope you can use it.
Cheers

[R.G.]

Autorouters.

I've thought for at least three decades that autorouters would eventually be as good or better than human layout. It's been a lot like fusion power - the cheap, clean power of the future that for ... what, forty years now, is only thirty years in the future. And still is.

I have periodically sampled autorouting programs, including a couple of multi-thousand dollar setup I was let try out. They are now faster than I am, only a few hours versus a day or so by hand for a complex circuit. But they often don't go to completion, leaving hand work they didn't finish, or have silly oddities left in the routing.

E.D. is right - for high density logic needing more than two layers, they're critical. The tasks quickly get too big for a human to do effective optimization. One of today's computer motherboards would never get done by purely human layout. But an effect pedal is usually best done by hand.

What would be a huge step forward is a good, effective auto-PLACER for parts. Routing can be made into an almost-afterthought by good part placement.

[mozz]

No diodes in the first clipping stage= Colorsound Supa tonebender.

[Mark Hammer]

Agreed, the Muff is one of my favourite circuits to mod. I found the schematic much quicker than i hoped. Seems like I didn´t use clipping diodes in the first clipping stage at all. No wonder it had so much bass. I also used a different gain stage with probably my favourite mods of all, at least when I intend to use the pedal on bass. It essentially does what the pinch knob on a woolly mammoth does. It gets you in the synth like territory. An absolute must if you are a fan of Muse.

Anyway I hope you can use it.
Cheers

VERY interesting variation on the classic circuit.  I'll just note in passing that the Sola Supa Tonebender, a sort of precursor (or perhaps contemporary in the early days) to the BMP also skipped use of the Q2 stage as a diode clipper.  On one of my BMP builds, I included a toggle for lifting/engaging the diode-clipping in that stage.  For whatever reasons, I find the dual-clipper arrangement to sound"smoother" than the single-clipper arrangement.  Could just be my build.

(EDIT: Mozz beat me to it)

[mozz]

Another one of those" I have it on my bench right now" moments. 
Permanent Electronics - Silver Cord PCB *2-pack* circuit board DIY Fuzz Distortion pedal project https://reverb.com/item/40478399?utm_source=android-app&utm_medium=android-share&utm_campaign=listing&utm_content=40478399

Built one with 2 choices of diodes, 1n914 and some old Rca silicon, definitely a difference.  Other mod was the 0.1 cap values right by those diodes. 

[Zveeen]

Agreed, the Muff is one of my favourite circuits to mod. I found the schematic much quicker than i hoped. Seems like I didn´t use clipping diodes in the first clipping stage at all. No wonder it had so much bass. I also used a different gain stage with probably my favourite mods of all, at least when I intend to use the pedal on bass. It essentially does what the pinch knob on a woolly mammoth does. It gets you in the synth like territory. An absolute must if you are a fan of Muse.

Anyway I hope you can use it.
Cheers

VERY interesting variation on the classic circuit.  I'll just note in passing that the Sola Supa Tonebender, a sort of precursor (or perhaps contemporary in the early days) to the BMP also skipped use of the Q2 stage as a diode clipper.  On one of my BMP builds, I included a toggle for lifting/engaging the diode-clipping in that stage.  For whatever reasons, I find the dual-clipper arrangement to sound"smoother" than the single-clipper arrangement.  Could just be my build.

(EDIT: Mozz beat me to it)

As of now I also tend to prefer red leds or something else with high fV in the first clipping stage, as I found it to be a bit to loose in the low end, when using no clipping diodes at all.

[Mark Hammer]

Bear n mind that whatever diodes one uses in this stage or the other, the Vf of the diodes is fixed.  HOWEVER, the gain of the transistor stage can be varied, whether increased or decreased.  The sonic perks of using a higher Vf LED can be achieved by using silicon diodes and lower gain.  Not a criticism, just a different strategy to employ to achieve the same sonic goals.