Quote from: g1 on November 16, 2025, 10:46:16 AMI would see if you can verify switch contacts for bad ranges/functions.

Agree with G1.  I had a similar issue to a meter.  The dial is connected to a circular metallic gizmo that turns and makes connections to points on a circuit board.  That metallic gizmo was dirty and had slightly deformed.  So I bent it here, bent it there, reassembled and voila, the meter and functions came back to life.  Make sure you also use some spray cleaner on all contacts and pots. 

I would see if you can verify switch contacts for bad ranges/functions.

Picked up this multimeter known to be not working

Had no display whatsoever

Hoped it was a dead battery 

Opened it up.  No battery 

Installed new battery....only display on certain modes.   

Checked internal $30 fuse.  Open 

Installed new fuse.  Fingers crossed.  No change 

Connected mini-grabbers and 150 ohm resistor

Continuity mode.  Nothing

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200 ohm range
Working

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2000 ohm range
Working

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20,000 ohm range
Working

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200 kohm range

Back to nothing 

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Not really equipped to diagnose or repair tiny surface mount stuff.

 

Vox has just released the new baby to the 25w MSB25 Mini Superbeetle stack - the Micro Superbeetle Guitar (there is an audio version for those that just want to use it as a bluetooth speaker).

You can use just the head as a portable bluetooth speaker/guitar amp and get 5w of power, or plug into the cab and have an additional 15w, bringing the total to 20w of practice power!  Three modes give you clean, drive, and high gain.  Honestly, it sounds pretty impressive - and it should, given it is retailing currently for $399 USD.

https://www.gearnews.com/vox-micro-superbeetle-guitar/

I want to crank it back up and measure the collector emitter voltage Vce man that's crazy it can get really high.

I told the owner of the junk store where I got it we need to try it out with a mic and maybe he can use it to talk to his shoppers 

EDIT:
I attached the mini grabbers to the collector and emitter and cranked it up all to max
I didn't really see any crazy high voltage
Strange I had about 50-55 volts DC and AC at "idle" and when I increased volume(s) it bounced around sometimes hitting 80-90 but settling back down

Ok nm yes it does get pretty loud I had the knobs facing away from me I thought the two on the end were aux/phono volume and master volume.

Turns out the tone knob is on the end so when I turned aux/phono it started to get loud. 

Well I got my capaci-TATERS in

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Got home from work and installed

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Clipped the leads

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Reattached the board which was a major pita getting that little spade fork under the ground screw

Powered it up and its about the same it doesn't get loud with both volumes maxed.

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Im declaring a marginal "success" because I've had it on for a while and it's not shutting off like it was before.

Also I noticed that the bottom chassis is not getting warm 🥵 anymore.

I just felt the little "heatsink" and it's pretty warm but not hot.

So kinda inconclusive since I wouldn't even know how to operate this amp if it was brand new.  Might be time to get a 🎤 microphone 🎙�

When I first powered it up to test it I got no sound but forgot about this already molested wire wrap so I attached it and had the same low sound.

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There are two posts maybe I should try the other one but I don't want to short something out.   

Or maybe I need to study the schematic kindly provided and try to figure it out. 

Or maybe they both need to be connected to a wire   

 

That 'heatsink' looks to me to be a ceramic pad (for heatsinking purposes).
It should be nonconductive.

Quote from: dmeek on November 12, 2025, 09:42:16 PMHere it is
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Thanks so much!

Quote from: aquataur on November 07, 2025, 05:05:11 AMWhat are you trying to protect your input from? Electrical damage?
I guess you are trying to protect from artifacts that are bad sounding.

Bingo!

QuoteFor a predominantly clean system, op-amp clipping or -latch up might sound unpleasant and distracting. In this case, a fast acting limiter would be the cure. But then, how much headroom does this one have...

This one is supplied by ±10.7 or so volts, due to use of a ±12V power supply from an old computer, which is rather noisy so I add some filtering, and that drops the voltage some.  If I ever build this circuit proper, I'm going to use proper power transformers and regulators to make ±15V, which just may solve my problem, don't know yet.

QuoteFor a distorted system, subsequent distortion stages would mask everything.

I beg to differ; For various reasons that I don't have time to explain, in the past I found myself doing tests attempting to find out if rail-clipping (in particular) leaves a "fingerprint" on the tone that you can hear even through a subsequent clipping engine.  I don't know how or why, but it does.

QuoteFor benign "bounding", a string of zener diodes (anode to anode) with a 100R dropper resistor in series with the input would do the job, as Merlin has used it here.

Even on a clean system, a such limited transit would likely go unnoticed.

You know, I had thought of doing soft-clipping with Zeners (because they are made for different voltages, so you don't have to "stack" diodes to get your desired headroom), but wasn't sure how to implement it.  Here you've provided the solution; I'll search around for more info on this arrangement, thank you!