I recently tried building an ABY box with isolating transformers on the outputs, and I just could not get it to work (well, everything worked, apart from the constant buzzing that I could not get rid of, which was incredibly frustrating).
I then pulled out most of the components, just leaving the switching and LED indicators, which worked without any buzzing; however, I did want a phase switch, which brings me to this.
It's a simple opamp buffer running on a dual rail supply for ample headroom, and it also has an inverter to flip the phase of channel B if required, or maybe you just like the sound of out-of-phase amps.
Any dual opamp can be used, and if you only have 7660 instead of 1054 for power inversion, just remove the cut between pins 1 & 8. If you feel uncomfortable about the lack of a capacitor on the buffer's input, there's room to add one - I'm sure you can see where and how.
If you have two amps and no switcher, you're really missing out - buy or build one.
A/B/Y AMP SWITCH BOX - VERO LAYOUT
Hi There,
ReplyDeleteso i built this, and the A B and Y switches work really well, no popping noises or anything! So thanks!
But i ran into trouble with the phase inverter on channel 2, when i change the phase, the output 2 completely disappears, no signal at all on channel 2. This also happens on channel 2 by itself, as well as when in the Y configuration. Channel 1 remains unaffected throughout.
I have checked my wiring all ok, all the jumpers, cuts, and components on my vero board - all ok.
there is voltage to the TL072, and there is output voltage from the LT154. What could i be overlooking?
Have you run into this with this circuit?
Thanks in advance,
Lee
Hi Lee
DeleteHave you tested the inverter on its own? So just run signal into the op amp and straight out. If that works, then it’s the switch.
Good luck
HI Andy, I did do that, and it was good. So i checked the switch as well, and that was good as well.
ReplyDeleteI did get everything to work though. What i found was that the inverter out line should be on column 18, row 11 instead of row 10 as that is the output of the TL0172. Thanks!
Lee
So you bypassed the 10u cap on the output?
Deletei guess so...lol
ReplyDeletenot sure why the inverted signal doesn't come through the cap. i checked the connections and it should but it doesn't. i'm going to use an audio probe to see if that help to diagnose.
Yeah that is weird. Really uncommon, almost unheard of, but could it be a dead cap?
Deleteso Eureka!
ReplyDeletei took the cap out, checked it - it was ok, but replaced it anyway. same result (not bypassing the cap of course) :(
however, the strip on the board was the culprit!
there was no continuity between the cap and the inverter out! really strange because it looked okay...so i put a jumper across from the cap to the wire and voilà :) works like a charm!!
thank you for your help and patience!!
Satisfying to sort out unusual problems like this. Glad you have it running as it should.
DeleteHi There, How much Vpp input signal can this circuit pass through TL072 without clipping?
ReplyDeleteHi Artem - it should have incredibly high headroom. The opamp is running +/- 9 volts which allows for a max pp output of about 15volts. Given this is a buffer, Vin should match Vout.
DeleteHi, I assembled it and it works great. Thank you!
DeleteHello, would it be possible to have the schematic of this circuit please? Thanks in advance
ReplyDeleteI never drew one up - sorry. Not a lot of components to work ouk.
Deletecomo es un inversor que es un circuito o un ic podrias ayudarme al respecto
ReplyDeleteBuilt it yesterday and worked fine, just there's a slight high pitch oscillation in the background, quite low volume, but still a bit annoying, any idea what could it be or where to look after? Cheers
ReplyDeleteIt's most likely to be the inverter IC. Did you buy it from a reputable source? eBay ICs can be sketchy.
DeleteTry adding a 100n ceramic cap across the same pins as the 220uf filter caps.
thanks a lot, i think i bought them on Banzai Music, should be reputable source.... anyhow. today i check inside the box, and the output B jack tip inside was quite close to the board, maybe that was cousing it, sort of crosstalk maybe... i will test it soon with full volume and see if its still there , and then maybe try the cap trick you just suggest me, thanks a lot... super nice addition to the pedal board! cheers
DeleteI have some questions
ReplyDeleteWhere exactly to add the 100nf cap, since there are some pins touching the positive and negative side of the 220uf caps
About the off board wiring, I connected all my groundints to dc jack Gnd and from there I soldered a wire to board gnd track, and the Gnd from vero board i connected to A/B switch ground point, not sure if thats causing the issue
Hello
DeleteThe 100nf ceramic caps are placed across the 220uf electrolytic caps. They go in the same position.
Grounding everything to a single point that also connects to the enclosure is a good way to go - that being said, there are a lot of pedals that work just fine that don't do it this way. I'd say run with whatever you think is the neatest and shortest wiring soloution.
I guess the other question is - what are you powering this with? Is it a good isolated power supply, or are there a few pedals chained together? I'd remove your pedals from the signal power supply / signal chain to see if this makes any difference.