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Here's a trace of a J. Rockett Tim Pierce signature OD that I had on hand. It's a dual pedal with a four-knob OD followed by a MOSFET "power amp" boost. This PCB is stenciled rev 5 and the pedal dates from 2015. This post is mostly for curiosity's sake since I couldn't find an existing trace. It's a decent but not spectacular pedal and there's nothing innovative inside. The most interesting thing about the OD side is that is uses just half of a dual op amp, and leaves the other half unterminated. Maximum OD gain measured on the bench is just over 16 dB, and it symmetrically peaks the waveform as the gain is increased. The Tone (treble) and Bass pots have a pleasant response.

The "power amp" side is advertised as emulating the power amp section of a Naylor Super-Drive 60. It's a stock BS170 MOSFET boost, much like the AMZ MOSFET or the EQD Black Eye but less flexible, with a fixed gain measuring about 12 dB on the bench. You can get either clean or distorted outputs by varying the input level to the boost. As you increase the input level, the boost clips off the top of the waveform and peaks the bottom. I don't have an SD60 so I can't say if it sounds similar.

Both sides seem to be designed for input signals at the level of a guitar pickup (< 500 mV) rather than from another OD or boost pedal in front. Which makes sense if Tim asked Rockett for a pedal to use in the studio with just a guitar in front of it. With higher input levels, the OD side just limits the output with the same waveform, while the boost side increases distortion. Maximum gain with both sides in series is ~25 dB on the bench.

Bypass switching is true bypass for each side, with the OD wired first ("On/Off") and boost wired second ("Power Amp") in an "either or both" configuration. Current draw @ 9V is 3.5 mA max with both sides active.

The most interesting thing about the OD side is that is uses just half of a dual op amp, and leaves the other half unterminated.

I think there is no single op-amp that has the same characteristics as the JRC4558DD type.

What surprised me was not terminating the unused half. What Rockett did is shown in figure A below, quoting from Analog Devices application note # 1957: A. This is the worst thing to do with an uncommitted op amp. Both inputs are floating and will pick up noise and the output may switch from rail to rail unpredictably. This configuration will draw varying amounts of supply current and will couple noise into the other op amps and may add noise to the power and ground traces.

mauman wrote: ↑22 Sep 2022, 03:01 What surprised me was not terminating the unused half.

The best use of that remaining opamp would have been to have a more stable reference voltage, IMHO

BTW, what is the point of making a chain with a 1N4001 and a 1N4148 in series ?

Is it something very different from having put the four diodes of the same type ?

Cheers,
Jose

Its possible the traces on the op amp are terminated underneath the socket as it is a double sided board. Did you check them with a multimeter?

CheapPedalCollector wrote: ↑23 Sep 2022, 00:07 Its possible the traces on the op amp are terminated underneath the socket as it is a double sided board. Did you check them with a multimeter?

Double sided board with traces visible on both sides, although under a black top layer. I was skeptical too, so I removed the IC from the socket and checked each pin on the socket with a meter. Pins 5, 6 & 7 were completely unterminated.

Jose, I don't have an insight into the use of 1N400x vs. 1N4148 in the feedback loop, they're almost identical. I modeled it in LTSpice and the only difference is a small increase (100 mV) in maximum gain with the two 1N400x compared with four 1N4148. The waveform is the same.

I'm not sure about that, but the boost is before or after the OD?
Thanks.

OD first, boost second.

ppluis0 wrote: ↑22 Sep 2022, 12:02
BTW, what is the point of making a chain with a 1N4001 and a 1N4148 in series ?

An attempt to suggest this is a bit different to a timmy and a super hardon crammed into a single box?

Nocentelli wrote: ↑10 Oct 2022, 05:32

ppluis0 wrote: ↑22 Sep 2022, 12:02
BTW, what is the point of making a chain with a 1N4001 and a 1N4148 in series ?

An attempt to suggest this is a bit different to a timmy and a super hardon crammed into a single box?

That was my first thought.
It's Timmy with a Boner...

Hello everyone, I have assembled this pedal and when I press the switch the guitar does not sound, the leds light up, if I press the switch again the guitar sounds but the effect does not work. Has anyone experienced the same thing? all the best

Welcome to the forum!
Could you please post some pictures of your build?
Are you using perfboard, or veroboard, or did you make your own PCB?

Hi enclosed photos of Pcb and Pcb with components Kind regards

Hi sbdtoni, does it work with:
- OD active only?
- Boost active only?
- Both OD and boost active in series?

Hi Bauman both when I press OD not work, when I press Boost not work, separetly or at the same time, when I not press any switch guitar have sound without effect
Kind regards

hi to all
have some system to not put the switches and test ? is to check if the problem is the switch or the PCB.
thanks a lot.
best regards.

Since it works when bypassed, and your LEDs light up, it sounds like something common to both sides of the PCB, and they're independent except for power and ground.
- Measure the voltages on the op amp pins and the transistor pins. You should have +9V on op amp pin 8 and ground on pin 4. On the transistor, you should see about +5V on the drain and ground on the source.
- If those are OK, it may be an error in your wiring or in your PCB layout. An audio probe (linked here) would help you trace the guitar signal from the input jack to the switches, then into the PCB, and then from point to point on the PCB.

Hi Mauman, first of all many thanks for your help in this project I test and I have 9v between pin 4 and 8 that is correct I’ll check the other points that you talk, many thanks but in the transistor I have 9v between drain and ground not 5v like you says.
Kind regards from Barcelona

Hi have a component list with same name like photo of this post? Is to see that I not wrong in the components thanks

Since you have power on both the op amp and the transistor, the next step is to trace the signal with that audio probe.

The component values are all listed on the schematic I posted. But I don't see how a single component could cause both sides to fail. I think the fault must be something common to both sides, which only leaves switching, wiring and PCB layout.

The transistor drain should be biased about 1/2 the supply voltage, so 4.5 to 5.5 volts. 9V sounds high. What are the voltage readings from the transistor source to ground (should be about 700 mV) and gate to ground (should be about 2.6V)?

Op amp pins 1, 2, 3 should all be about 4.5V.