Drawing that much current it might be possible to feel the guilty component getting warm. Towards the end of this thread there is link to the schematic https://www.freestompboxes.org/viewtopic.php?f=1&t=323&p=224384#p224384 but that is the true bypass version as well but is probably very sim...

Around 1973 I used to read all the UK electronics magazines and vaugley remember some of them and built 1 or 2 but have no idea what happened to them.

Thanks for posting them, they are bringing back lots of memories.

It's like a riddle : what does an opamp do when it's not powered ? It's not a question that has kept me awake at night as it is not how you would use an opamp. My guess is either nothing or if you crank the input sufficiently it might pass a rather distorted much attenuated signal (due to the PN ju...

"I would like to add an "interruptor-button" to make it work as an A+B pedal so I can plug 2 guitars and send them out to 1 amp." The above might make sense to you because you know what you want but to me it doesn't. If I'm reading it correctly what you would like is a mixer so b...

Yes, Happy New Year to all on FSB.

Ice-9 wrote: ↑22 Sep 2019, 11:03 Never even noticed that, but I'm up for a pub run.

Hell yea, do you know of any that are open, they're all shut around here!
The last pub I was in was the last gig I played on 28th February.

It must be worth $4 just for the case.

It looks to me like the lamp is powered with a dropper resistor direct from the incoming mains.

I've done some pretty cavalier things with mains in my time (240 volts here) but don't think that I would want to use it like that.

1. wrong input and output caps orientation 2. mis-biased transistor 3. unneeded dual diode protection (don't need both) 4. 37k output resistor, yeesh 5. top part of the circuit does practically nothing Agree with plush on most points. 1. Electrolytic capacitors start to leak and act as noisy resist...

Put a capacitor to ground from the pin and a pull up resistor to the supply. This is often used as a "Power On Reset" in digital circuits that need the reset line holding low for a short period on power up. At power up the capacitor will be discharged and so have zero volts across it. This...

Thanks for all this design work Manfred, it is really appreciated.

I can generate a -22v bias voltage easily with a separate small transformer, I have lots to choose from and am sure I can find one suitable.

I haven't got back to it yet as other jobs keep getting in the way.

I have a copy but it is 1.3Gb so not sure if I should upload it to FSB.

They are there to block not only internally generated noise, which on an analogue circuit is probably minimal, but also to suppress any noise on the incoming DC supply. (e.g. switched mode power supplies or digital pedals with inadequate filtering.)

C6 and C7 are also strange to me, they are right next to each other on the circuit board, I see no reason for them at all. It's common practice when designing low noise smoothing/decoupling circuits. One will be an electrolytic, good for smoothing out low frequency (ripple) but less so at high freq...

Manfred, I got a bit of time on it with the scope.

It's the PI that is clipping not the output stage, it is biased too high so is clipping to the HT. I'm using the one from the 18Watt Lite IIb. When I get some more free time I need to get that sorted out.

I used EL84s. As they are out of my spares box and untested I tried 4 different ones with no change in output.

Thanks for the correction on parallel/series, it was bothering me that parallel didn't seem right.

Number 5 is alive! PI and output stage, as suggested by Manfred, on the breadboard and after a minor delay because I'd picked a faulty ECC81 out of my spares box (only half of it working) did a few measurements. Quiescent current 45mA @ transformer CT (no input signal). The following measurements ta...

Thanks Manfred. I will try this out.

I have a choice of 16 ohm 12 inch speakers I can use, a Celestion G12 or a Hiwatt out of an old PA cab.

I've been reading up on transformer turns ratio and impedance, something that I hadn't really thought about before, it's all starting to make sense now.

The PCB on this amp looks identical to the Laney LC15. I had one in to fix recently with an intermittent resettable fuse in the heater supply (same position on the PCB as this one). Apparently there was a bad batch of resettable fuses that were made in Mexico. Replacement with a generic 6A 30V Chine...

The 10R resistor needs to go between +9v input and the 220uF capacitor - C11.

Where you have it on your PCB it does not form a low pass filter, to block any high frequencies which might be on the incoming 9V, with C11.

I would also include the reverse polarity protection diode D2 on the PCB.

FeVeR2112 wrote: ↑06 Dec 2020, 07:31 ... and here is my layout so far - please note the polarity resistor is off board on the foot switch PCB. The 10R resistor is not here (yet) as I don't see whether it serves a purpose (yet).

It is part of the power supply smoothing/decoupling along with C11.