Have you tried replacing the dual opamps, A200 and A400 ? Are they in sockets ? Check the resistors on their outputs, R221 and R421.

Note: a TL072 probably won't work in this circuit, 5532 have higher output current capability.

Do any of the amps have digital circuitry or Switch Mode Power Supplies which would require testing for emissions ?

It is unclear to me what you are trying to accomplish. Do you want to control 8 relays or loops with three foot-switches ?

Please refer to any circuits in RG Keen's or Mr Elliot's articles by the numbers of the illustrations in those articles.

Side note: Figure 8 of Mr Elliot's article shows how a resistor is used to make a good logic low when diodes are used as an OR gate. You don't want CMOS inputs to be floating around causing circuits to intermittently malfunction... and they would seem to magically fix themselves when you tried to measure logic levels with a DVM which would pull the floating input low.

Quote from: Miyagi_83 on August 25, 2024, 02:46:57 AMWell, bless my heart (am I using this phrase correctly, Loudthud?

I'm not the best person to explain this, and sometimes phrases such as this do not translate well into other languages, but I'll give it a try.

Typically, the phrase would be 'Well, bless YOUR heart'. This would be used to express gratitude to another person for an act of kindness towards yourself, possibly unexpected. The degree of your gratitude would be somewhat above a mere 'Thank You' or 'Thank You very much'.

Just when all the input signals are going through diodes.

I think you need a resistor to ground on each of the last inverters on the right so the output can go high. Here's my circuit for 3 circuits.

You cannot view this attachment.

Another subtle problem to solve is switch bouncing where there can be noise across switch contacts that may trigger digital logic. Many circuits just place a capacitor across the switch contacts. Digital logic does not like slow clock transitions. The beauty of S-R flip flops is that you can Set it one hundred times and the output just changes state once. Same with Reset. I dislike circuits where they derive a clock signal by some passive circuit across all the switches. Too much to go wrong. The real digital engineers I've worked with would never use such a circuit.

I didn't see my approach in either of the links you posted. My approach is to build S-R flip-flops from discrete CMOS gates. One of the problems to overcome with S-R flops is that asserting Set and Reset at the same time is really an illegal state. Not all chip manufacturers handle it the same way. My way involves multiple input gates on the Reset side so when you Set one flop, you Reset all the others. If you step on two or more switches, the last one to be released wins and only one output is Set. I think some of Mr Elliot's solutions solve that problem. My solution gets more complicated the more channels you need.

First question, do you just want to select one of several loops of pedals, or do you want random combinations of several pedals ? The random combination thing is much more difficult unless you are using a micro-controller.

Next question, how many loops or combinations do you want or require ?

A typical circuit will include a low pass filter to simulate the response of a guitar speaker. If you search here, you can find several.

Quote from: RookieRecurve on July 26, 2024, 10:08:52 AMIs grounding necessary here?  Is the lack of a metal enclosure going to introduce a bunch of noise?  Will the lack of an earth-ground make this amp noisy?

Yes, the ground side of your Voltage output should be connected to the Mains Safety Ground. Without that ground, a guitar will pickup hum and you may get a mild shock or tingle when you touch something that is grounded (like a microphone) while holding the guitar.

After rectification and a filter cap, the output will be close to 24VDC. To get 16VDC, you will need some kind of Voltage regulator.

Matched components are not really needed and are a waste of money unless you get them from a trusted source.

If you are using ESP's circuit boards, make sure you don't mix up the two R24s and Q12s. The amp won't work and you will likely damage several components.

Generally, to prevent hard saturation of transistors (the kind that takes significant time to undo) you install a Schottky or Germanium diode between Base and Collector. I question whether it makes an audible difference in an audio circuit. The way this guy has installed the diodes, it makes sure any big negative input is able to degrade the Base-Emitter junction. 

Quote from: Randy Lahey on May 19, 2024, 06:35:53 PMTransistor pin resistance measurements:
Original Gate - Source: 550 ohms
Original Gate - Drain: 306 ohms
Original Drain - Source: 300 ohms

New Gate - Source: 11M ohms
New Gate - Drain: 320 ohms
New Drain - Source: 10M ohms

The Gate should measure like a diode to Drain or Source. If you measure from Drain to Source you should see the ON Resistance of the JFET (a couple of hundred Ohms). If you short the Gate to one of your meter leads while you are measuring resistance from Drain to Source, the resistance will go down slightly on one lead and rise slightly on the other lead. Those readings of 10M or 11M are probably just the resistance of you fingers across the leads.

From your schematics with the Volume pot at min and max it looks like the JFET is installed with Gate and Source reversed. It may pass a little signal but will have a gain less than one.

See my comments in this thread: https://music-electronics-forum.com/forum/amplification/guitar-amps/build-your-amp/debugging-your-build/20115-please-help-me-out-debugging-my-ruby-bassman-amp
about how to Ohm-check a JFET out of circuit. Note that with the vast majority of JFETs, the Drain and Source are interchangeable.