MarkIIC+ FX loop trouble - HELP

Hi,

The FX Loop of MarkIIC+ sounds strange. As it is a serie loop, normally, 100% of the signal goes in the FX Loop when it is engaged.

However, this is not the case.

I did a test:
I plug my guitar in Amp IN

then, if I plug a jack in the FX SEND and nothing in the FX Return, the sound stays exactly the same. That means that connecting a jack in the FX SEND doesn't engage the FX Loop...

the problem is that when i plug a jack in the FX Return and nothing in the FX Send, normally, the signal should be totally muted. But I still have something like 10% of the signal...

The problem is that I can't use a volume pedal in my fx loop to make volume swells for instance.

HELP !!!

KR

Gerald

Hi Gerald,

You've stumbled upon a design flaw concerning tube powered serial loops, where about 5% of the dry signal can be heard and you can't get rid of it.

Cause: there are in fact two tubes inside the case of a 12ax7 tube. Each side's called a triode, and each can be used as a separate amplifier stage. However because the triodes are close together some signal bleeds through between the two halves. With the IIC+, the tube responsible for the effects loop is V2 - with the two halves being V2a & V2b respectively. V2a amplifies the signal before the effect send, and the V2b buffers the returned signal. So there is actually a small amount of unwanted parallel signal bleeding through between the V2a (send) and v2b (return).

I suppose the ideal solution would be to add another totally dedicated tube instead of either V2a or V2b, or re-wire the preamp to change the order of connectivity of the tubes in the signal path, which's easier said than done!

jvk said:

Hi Gerald,

You've stumbled upon a design flaw concerning tube powered serial loops, where about 5% of the dry signal can be heard and you can't get rid of it.

Cause: there are in fact two tubes inside the case of a 12ax7 tube. Each side's called a triode, and each can be used as a separate amplifier stage. However some signal bleeds between the two halves. With the IIC+, the tube responsible for the effects loop is V2 - with the two halves being V2a & V2b respectively. V2a amplifies the signal before the effect send, and the V2b buffers the returned signal. So there is actually a small amount of unwanted parallel signal bleeding through between the V2a (send) and v2b (return).

I suppose the ideal solution would be to add another totally dedicated tube instead of either V2a or V2b, or re-wire the preamp to change the order of connectivity of the tubes in the signal path, which's easier said than done!

Click to expand...

Thanks my friend for your support as usual !!

Take care

G