FX Loop - need your councils

[Kagliostro]

I'm planning to build a tube stand alone preamp

as from my son request I want to put on it an FX Loop
yes, I know there is no necessity of an FX Loop in a stand alone preamp
because the exit of the preamp is the FX Loop Send
and the input of the power amp is the FX Loop Return

but that is for serial FX Loop, my son want a serial/parallel FX Loop

I have the schematic # 1 for that purpose (that comes from a well known Brand of tube amp manufacturer)

looking into the net I find this interesting circuit (schematic #2) that is a double serial FX Loop circuit (you can connect two external effects at the same time) with the ability to blend the two channels, or it may be (with one channel connected directly) a parallel FX Loop
here the link to the original page (schematic #2) with explanations: http://www.runoffgroove.com/splitter-blend.html

What I need is to know what do you think about this two circuits, also I would like to have from you councils about any mod to be inserted as to obtain the ideal FX Loop circuit

Many Thanks

Kagliostro

[Structo]

Look in the Dumble file section, there is a parallel loop.

[David Root]

I use Normster's buffered FX loop, it is in the Dumble files and can easily be made switchable series-parallel. I use one 12AT7 in it, but you can use a 12AX7 as well if you prefer. NOS 12AT7 cost much less than NOS 12AX7.

[Structo]

Having tried both opamp FX loops and a tube buffered loop, at least for me there is no comparison.
The tube buffered loops simple sounds better.

I have read that the voltage swings necessary for good performance will lead to clipping in the opamps.

Some guys can get JFET transistors to perform well.

But a simple single 12ax7 buffered loop serial or parallel will sound great once you get the voltages and tone dialed in.

[Kagliostro]

Thanks to both friends for answers

The tube FX Loop in the Dumble File section is very nice, interesting and well documented.

But for the preamp I'm going to build the problem is:
a little about space
and most is in order of current and right voltage availability

for B+ I've a 220v SS rectified, so I'm in the range of ~310v and current is low because, principally for space reasons (low profile), I use two 220v-9v 10VA transformers connected back to back (220v-9v/9v-220v)

this will give me not very much current

So I must use OpAmps

What about schematic # 2, the doubled send with the ability to use two external effects ?

Thanks

Kagliostro

[Structo]

So far the best SS loop I have heard about is the Metro Zero Loss loop.

It is JFET powered.

But I believe it is serial only.

http://metroamp.com/store/index.php?mai ... cts_id=499

[Kagliostro]

Hi Structo

the FX Loop in the link you posted is one of the first FX Loop I've find looking for ideas for my project

I belive it is interesting, but I haven't the schematic

in an italian forum I've also find a project developed by one member that uses IRF820 mosfet (to have high voltage management without problems)

http://img692.imageshack.us/img692/1228 ... ivopcb.jpg
http://img87.imageshack.us/img87/3966/l ... layout.jpg
http://img211.imageshack.us/i/fxloop3diy.jpg/

http://new.diyitalia.eu/forum/viewtopic.php?f=22&t=7290


About schematic I think I'll use one of those I have, but would like to know which are the function that you think an FX Loop MUST have

Thanks

Kagliostro

[Structo]

By all means, experiment.
You may be able to come up something unique that will work well for you.

I sure like the sound the tube FX loop imparts though.

Here is one a forum member designed a while back currently being marketed by Ceriatone.

[Structo]

Perfboard layout

[M Fowler]

Here is Ceriatone version.

[Kagliostro]

Thanks again Structo & M Fowler

Kagliostro

[vibratoking]

I disagree with the comments regarding SS loops being inferior. I have a Fuchs series/parallel loop and it is very good. There is a VERY small tonal impact in series mode and is perfect in parallel mode. I have never used a series loop, tube or SS, that did not have a tonal impact.

I have also built SS loops very similar to those in KOC's books and they perform wonderfully. I personally wouldn't waste my time building a tube loop again.