2 Amp switching!

[pushonhigher]

Hi!

I have some stomp-boxes and some rack-gear chained after each other in 2 gcx switcher (all mono).
From the output of loop 6 (of gcx-2) I connect via a y-cables (brand: cordial, see http://www.thomann.de/at/cordial_cfy_09_vpp.htm) left-side to the input of loop 7, from send of loop 7 i connect to the input of my vox ac-30 nr1. From the y-cables right-side I connect to the input of loop 8, and from send of loop 8 to my vox ac-30 nr.2.

Now I have the problem, that on amp nr. 2 i have a massive signal loss, about half of the volume is reduced (no matter if I only activate amp nr.1 and/or amp nr.2). When I switch the left and right output cables of the y-cable to the inputs of loop 7 & 8, the signal loss occurs with the other amp.

So i presume it must be a connection and/or cable problem.
From the gcx-manual I read theat combining multiple amps should work like this. I want to have the same output-levels on both amps.

Any advice?
Wrong y-cable, or wrong connection?

Thanks a lot for your help,
Gernot

[mikeromancer]

It seems to me to be the wrong y cable. The link shows an insert cable (trs to send and return). I think you need a mono y cable, where the same signal is sent to both y plugs.

[JohnClark]

That is an Insert Cable and will not work for this. You need to use a mono Y Split cable to send the signal to both amps. Let us know how it goes once you change to the other cable.

[pushonhigher]

Hi John!

Thanks for your quick reply, I'll change the cable then.

I posted my question also in an other forum, and there I got the following reply:

The GCX loops are MONO, not STEREO. The y-cable you referenced splits a STEREO (TRS plug) signal into two MONO signals (TS plugs).

The signal that is reaching one of the amps is a true connection, while the other is really just some sort of leakage from using the wrong plug type.

What you might want to use is a MONO split cable, where it takes a MONO plug and splits off to two MONO signals. However, I don't agree with this approach. What you ought to use is a buffer with isolated outputs so the amplifiers are not connected to each other and creating all sorts of noise. The Axxess Electronics BS2 is an example of such a buffer.

This is where the electronics get a little confusing.

In actuality, you just need the two amplifiers to be isolated. In a perfect world, this can be achieved using a signal transformer. However, the signal transformer is imperfect and incurs electrical loss. Also, the transformer will typically have a low-impedance primary and therefore load the signal too much causing low-output and a muddy sound (loss of high-end fidelity). These losses require the use of a buffer, which will counter-act the bad effects of using the signal transformer by providing a low-impedance signal.

What you need is a buffer with two isolated outputs.

Do I really need an extra buffer for this setup?

Bye,
Gernot

[JohnClark]

It is true that ground isolation between the amps may be needed. If you are using the Guitar In on the front panel of the GCX then the signal is already buffered (i.e. low impedance) and can be split without loss. You can insert an Isolation Transformer before the input of one or both of the amps. If your amplifiers have ground switches on them then you may be able to get away with no transformer(s) needed. The best bet is to go ahead and set this up first and listen for any ground buzz before buying anything to correct a problem that may not even exist. Let us know how it goes.