Gitaar Effect pedaal: Shin Ei 1968 univibe - voltage advice

Hi guys, I'm doing this in english so I can explain it a bit better with what I have found.
I am making an original 1960's shin ei univibe but I have the following problem.
As you can see in the schematic, it requires a step down transformer (110 - 16-20 ac in the picture because it's japanese). Now I have several dilemmas:

1 - I want to not use a transformer since it's a bit outdated, but finding a 16-20volt ac power supply proved to be difficult, and I dont know if they exist.
2 - if I do use the transformer, I had trouble finding one that did 230 - 16-20 v ac. (for european mains)
3 - considering these two problems I was thinking the following: to bypass the half rectifier circuit in the PCB and go straight in with the operating voltage of the pedal at that point (this I haven't calculated yet) but this obviously brings another problem up: Since it's only a half rectifier circuit, I can't feed in a dc supply, right?

to summerise I wanted somoenes advice on how I could power this, the needed voltage supply is in the picture, along with the pcb. If I need to bypass the rectifier circuit could somebody point out where I then need to connect my "new" power source to?

kind regards,

Connect a DC voltage of about 24 volts DC here.
The single rectifier diode can stay in place, it lowers the voltage slightly (by about 0.6v) but that's not a problem. (But you can also replace it with a wire.)
Look for a suitable external adapter, for example, at a recycle store.
There are often bins full of adapters.

As you can see, the indicator light no longer works. If that's a LED, you can also connect it to that 24 volts via a ballast resistor.

Awesome! I'll do this. Thank you so much. And like this the circuit should behave as if I were to supply as in the schematic right?
Like you say the indicator bulb isn't too much of an issue, I think I will replace it with an LED anyways (I think the were filament bulbs originally)

For guitar / audio I would suggest to look for an old fashioned heavy "copper and iron" double insulated adapter, not a SMPS. This to avoid common mode issues.

I have increased the DC voltage to 24 volts. Because that is the voltage you get on the 1000μF capacitor if you rectify 18v AC by a single diode.

Op zaterdag 20 juni 2026 17:32:08 schreef vergeten:
I have increased the DC voltage to 24 volts. Because that is the voltage you get on the 1000μF capacitor if you rectify 18v AC by a single diode.

And then, feeding 24 volts into the circuit where you would normally do 16-20 ac would be fine? or do I have to do it after the rectifier? Also one last thing, the two 220 uF capacitors above the 1000uF are currently rater 16 volts in the actual PCB I made so far, but I assume I'll have to change these to something like 63 Volts?

[Bericht gewijzigd door DCMB op (20%)]

You can simply connect that 24V DC to the AC input of the circuit board. Do pay attention to the polarity, otherwise it won't work.
Then the diode acts as polarity protection that slightly reduces the voltage.

The two 220µF electrolytic capacitors do not operate on the supply voltage; only the 1000µF capacitor does. However, you could measure the voltage across those capacitors and then possibly choose a slightly higher value.

[Bericht gewijzigd door vergeten op (10%)]

Op dinsdag 23 juni 2026 10:06:20 schreef vergeten:
You can simply connect that 24V DC to the AC input of the circuit board. Do pay attention to the polarity, otherwise it won't work.
Then the diode acts as polarity protection that slightly reduces the voltage.

The two 220µF electrolytic capacitors do not operate on the supply voltage; only the 1000µF capacitor does. However, you could measure the voltage across those capacitors and then possibly choose a slightly higher value.

Awesome, I'll do that. thank you!

Denk dat het dit pedaal is.

https://www.next.gr/circuits/audio/univibe-pedal-circuit-diagram-c2334…

https://www.prowessamplifiers.com/schematics/effects/univibe.pdf

So keep B+ under 25V.