The Week on the Breadboard: The Emperor of Tone

[cooder]

I want to ask everyone about their preferences w.r.t. the charge pump.
1. No charge pump. Run it on 9V or 18V. That's the schematic in post #13.
2. Optional charge pump. The charge pump can be installed or not. Or you can put a voltage switch on the board. If the charge pump is not installed, then you have option #1.
3. Split rails. That's the schematic in post #1. Charge pump is mandatory. Must run on 9V only.

I don't have a strong preference one way or the other. They all have advantages & disadvantages and none of them are show-stoppers. #1 is the minimalist solution. #2 is the most flexible, but also has the highest parts count. #3 removes one electrolytic cap from the audio path in each channel (C6 & C16).

If there's no real sound advantage to the split rail design I would vote for option 1, no charge pump.

 

[jimilee]

I would like to have the option of both, because options. I have no other good reason.

 

[joelorigo]

It’s interesting to finally find out what mike did to the bluesbreaker to get to the KOT.

 

[Chuck D. Bones]

The advantage of split rails is there's no Vref. Everything that connects to Vref in #1 or #2 connects to GND in #3. We don't need C6 or C16 to block DC, so they are removed. Theoretically, every component that the signal passes thru colors the tone whether we want it to or not. So it should sound better with those two caps removed. I doubt any of us would hear the difference.

 

[Chuck D. Bones]

Just FYA, this is what the power section looks like with a charge pump and a voltage switch. Ignore the ref des,

 

[kristopher]

Help me understand: what is the benefit of running the channels in parallel? Both channels do basically the same thing. Have you tried it?

I have not tried it. My friend wanted to know, I believe he wanted to be able to blend the two together.
I didn’t mean to distract from the Charge Pump talk.

 

[MattG]

I personally like the bipolar power option. More complex power supply, but allows simplification of the audio path. Feels more hifi. 9 and 18v KOT has already been done, bipolar is unique (at least from what I’ve seen).

You could go the bipolar route, but then add space for a couple LDOs to drop it down to say +/- 5v, so you’re closer to the original single 9v rail (for more drive/less headroom), but still have the benefit of split rail power.

 

[Chuck D. Bones]

At some point it gets too complex. Are we there yet?

Maybe we should add a VOLTS trimpot for power supply sag?

But seriously, I don't think we need opamp clipping for this pedal. We have The Gator Drive for that!

 

[szukalski]

Less complexity with the audio path seems a pretty good to me. This thread even got me playing a KoT clone. Looking forward to getting this onto the BB. Thanks Dave.

 

[temol]

I have Rhythm channel on a breadboard now with +/- 9V supply.
I only managed to play for a moment, so I can't say much. Just a quick one - with +-9V power supply there is quite a large output signal (although it depends on the Hard pot setting). Also - for me - a lot of lows with the 470n connected (Bottom sw). Hard pot - effect of the pot is subtle.

 

[MattG]

At some point it gets too complex. Are we there yet?

Can’t call it done until the parts count of the power supply exceeds the parts count of the effect!

I was thinking, for outdoor gigs, an integrated battery and solar charging circuit.

And a super capacitor for bass slam…

 

[Brett]

How's this control layout look @Chuck D. Bones?

 

[Brett]

I'm opting for 16mm pots and sub-miniature toggles on this one. The non-threaded sub-miniature toggles look cleaner and are very low-profile, allowing for more space and a cleaner layout.

 

[temol]

Hard pot - effect of the pot is subtle.

Mystery solved.. before I wrote the above I checked output signal on the oscilloscope. And the Hard potentiometer made quite visible impact on the singnal amplitude but the I could not hear much of a difference in the headphones. Now I know why.. even with the Hard maxed the output signal level is quite large and it easily drives the amp into clipping. Turn down Vol to 9 o'clock or so and voila.. now I can hear the difference.

 

[Chuck D. Bones]

Brett,
Looks good, except I wouldn't put the LEDs between the knobs. Looks crowded. How about above the stomp switches?

 

[Chuck D. Bones]

Tomasz,
The 470nF cap is supposed to let pretty much all of the bass thru. Not subtle, it's for those who want sludge & doom. With both halves engaged, try light bass on the right (input) side and heavy bass on the left (output) side.

 

[Brett]

How about above the stomp switches?

How's this?

First layout attempt (based on revision 0.4). 1590BB2 with on-board relay bypass:




I'll wait to put finishing touches on my traces in case there are any updates to the circuit.

 

[Sturdag Lagernathy]

I put a 9/18 volts switch in mine, and I much prefer 9 volts. Guess I just like it a little dirty.. So I'd say pull the charge pump out completely. If you must have a charge pump, I say go with dual +9v/-9v rails!

 

[Flying]

I didn't have room for the charge pump

 

[temol]

I think there's plenty of room for the charge pump