Shaka 5

[WhiskeyMadeMeDoIt]

High pass filter to get rid of the hum?

Tried the CCS last night with my daughter it was a fun little project to breadboard. It wasn't fantastic but could be improved with a few tweaks. I will probably remove the diodes and retest.  Had lots of gain but it didn't clean up well on low guitar volume. 

[Cozybuilder]

I replaced the 100n at U1a pin 1 with 56n, followed by 47R to ground, which got rid of most of the hum. And a lot of the volume. Tone was ice picky, very little bass, so I replaced quite a few things to see how much could be brought back. These were replaced:
1) the 33n feeding Q2-G with 100n
2) tone circuit components: replaced the 33K with 22K, 1n5 with 10n, and 22n with 33n. More usable now, but theres room for improvement.
3) the 500K gain pot with 1M.
4) 25K volume pot with 50K.

In total, these brought back a lot of the volume and tone, although theres still room for improvement. The hum is greatly reduced, so yes it was worth it.

[Kipper4]

I'll leave the 100 nf in and see if I can find a 20_30 ohm resistor for the hum filter.
Thanks again for the help. I'll try some more of your mods.

I'll post up some other links for you Mac

[Kipper4]

Heres the rub the hum must be introduced in the mini booster because it tried the high pass filter at output of the op amp, between the 100k trimmer and mini booster, and just before the tone stack. The only one that lessened it was the last and it sucked the life out of the pedal. All the output volume is gone.
Time for me to rethink.

[Cozybuilder]

I also moved the high pass to the beginning of the tone stack, reasoning that the harmonic generation in the SRPP was important. The trouble with the first location is this circuit turned into a great overdrive or treble booster, but killed a lot of what this pedal is about. Moving the high pass to the the tone side got it back, a great sound like the original without the 60 cycle hum, but almost no volume. Even with the 50K volume pot. I'll try a 100K there, but theres a better solution, we just have to find it.

[Kipper4]

So you think that the srpp does add character to the sounds of the pedal. Good.
Is this hum caused by DC getting out from the Srpp?
I would find this a little strange since the Srpp is dc decoupled by the 100nf into the tonestack.

So now im wondering if I should use a tl074 buffer the srpp output , (hum filter) and make two active notch filters ala thunderbird and a buffer or make up stage just before the output pot.

[Kipper4]

Thunderbird notch filters seern here just before the output

http://runoffgroove.com/thunderbird.html

[Kipper4]

Hut hum. Just tested the DC voltages either side of the tonestack decouplng cap.
4.5v going in 0 v dc coming out.
Conclusion The dc from the srpp is not causing the hum. The cap is doing what its supposed to. Where is this hum coming from?

[WhiskeyMadeMeDoIt]

Maybe this is a dumb thought but could you be getting that hum from your diodes?
All diodes exhibit a photoelectric effect but many are covered in black plastic to prevent this. The 1n34a is a glass body diode.  Try blocking all light to the diodes and see if your hum goes away.

[Kipper4]

No dice Whisky Tried it. Thanks for the thought though.

[Cozybuilder]

I thought the hum was 60 cycle, wiring on the breadboard picking it up and the high gain circuit amplifying. The high-pass kills it in the 2 locations I tried. The next step is to try the high-pass after the SRPP, then go into the second op-amp, then (as PRR says) do more pruning with the tone circuit.

[Kipper4]

I tried the filter after the srpp (my case the mini booster) I guess it might work with differant values but putting a 27ohm after the 100nf decoupling cap didnt do it for me.
I think the resistor is so small its letting all my signal go to ground. Maybe scaling it up mght work better.

[samhay]

The SRPP is not going to have great power supply rejection. Try the usual tricks with a small resistor in series with the supply and a big cap to ground on the circuit side of this.

[Kipper4]

I already have power filtering caps and am using a half of an op amp for v bias.
I'll try another cap closer to the srpp and a series resistor. meanwhile ill try it with a battery.

[mac]

Rich,

- try an independent Vref for the SRPP,
- add a cap between the SRPP trimmer and the diodes/mosfets,
- another breadboard, or undo and start over.

mac

[Kipper4]

Here's the schematic I'm using

http://www.muzique.com/schem/shaka5.gif

The mini booster has its own v bias (2x 1M)
I'll try some of those it's still on the breadboard. (and on perfboard too)
I did change some decoupling cap, and some values in the tone stack but the rest is stock.

[samhay]

>I already have power filtering caps and am using a half of an op amp for v bias.
I would share your buffer v bias with the SRPP, it will be quieter than your 2 x 1M option.

>I'll try another cap closer to the srpp and a series resistor. meanwhile ill try it with a battery.
The series resistor can make a big difference. If it helps, but isn't perfect, you can always add 2 resistors with a cap in between. Just watch the voltage drop. You can tap off the supply before these for the op-amp to help with headroom there too.

[Cozybuilder]

Heres what I wound up with. By paying attention to the ground wires on the breadboard, the hum was substantially reduced. I think it will be fine once its in an enclosure.

[Kipper4]

Some SRPP stuff for you guys


http://www.ecircuitcenter.com/Circuits/pushpull/pushpull.htm


http://www.allaboutcircuits.com/textbook/experiments/chpt-6/class-b-audio-amplifier/


http://www.tubecad.com/2014/05/blog0291.htm


http://sound.westhost.com/valves/preamps.html

http://www.muzique.com/news/images2/mosfet2.gif

http://www.muzique.com/news/superhot-mosfet-boost/

http://www.tubecad.com/2005/February/blog0037.htm


http://champ.chips.jp/sonota3/booster2.html

http://www.geofex.com/Article_Folders/jfetdoub/mudoubler.htm

[Kipper4]

This too

http://www.muzique.com/amz/mini.htm

And here's an example of where I got the inverting/non inverting output theory from the like


http://www.diyaudio.com/media/files/articles/ampcamp1/ampcamp1_simple1_350.png