Daisy Chaining the GEO A/B/Y questions.......just found cure...

[KMS]

I have the 1999 version of R.G. Keen's A/B/Y splitter laid out on an experimenter board and it works great. The circuit....http://www.geofex.com/FX_images/splitter.gif

I then laid out three of theses on the experimenter board and daisy chained them together via the direct output.  The direct out becomes the input for each subsequent A/B/Y circuit.  I used three TL072 (s) everything else is exactly the same except I am using R.G. power supply from the improved version found here......http://www.geofex.com/FX_images/humfree2.gif  This gives me 6 transformer isolated outputs and one direct out.

Problem........Each subsequent A/B/Y increases the gain. 

How can I make all three A/B/Y have the same gain?

I tried putting a 10K trim pot in place of each 1K resistor and nothing happened at all not even set on full 10K.


I guess I can just adjust the levles of each FX on each chain to decrease the gain as needed, but it would be nice to have each output at the same level.

Thanks in advance for your help.

[KMS]

I guess I was just too worried about hum.

If your going to make a bunch of chains, look at this.........

Since each stage seemed to have a little gain, I decided to split my guitar signal directly with no circuit to a three way split.. call it T/U/V.  Each of those now wired as an input into each GEO A/B/Y separately.  So I still have 6 transformer isolated outputs and three direct outputs for a total 9 potential outputs.  I only need 6 outputs and the isolated outputs are all equal gain and stay equal no matter which split is on or off, even if I cut any leg of the T/U/V split.

It sounds great........I've never had control on my Kustom 4 channel like this before.  No noise! No Hum! Nice Headroom!

I haven't tested the direct outputs on this last wiring, but I don't need them anyway.  Nice to have the extra room to expand.

I can see no reason not to move forward with this 6-Chain set up (someday 9?), so I guess I will go ahead and make the PCB for this, and post the pics on the BIG Stompbox thread.

[R.G.]

Yeah, there is a gain of about 2 on the unit as show. You can make that a gain of one by removing the resistor/capcitor to ground from the opamp inverting input, though. But I think that daisychaining is not the best way.

The way you've already come up with is better. Use a single buffer to drive as many isolator stages as needed. One buffer opamp section should be able to drive maybe a dozen transformer-driving isolation stages.

[KMS]

I tried it with just one opamp like you suggested. I can't turn it up loud tonight but it sounds the same as the T/U/V method I used on low settings.  6 outputs all the same gain and buffered, isolated just fine.  I'll have a chance to go full volume tommorow.

Thanks.  Now I have saved a lot parts that I can use on my mixer circuit.

The direct approach always seems to be the best place to start, as you have made that clear in your comical pic on GEO with the tube being hammered into a stompbox.  I had thought of doing it this way from the beginning but don't know anything about the output power of the opamp vs the power consumption of the transformers.  I should have just hooked it up and tried it like that to start with.

Next will be AC adapter +9/-9 V power supply.  Need that for the mixer too.