Effects Loop - Implementing it into an Amp

[captntasty]

I know this thread should possibly be in OT or on an amp forum but it sort of straddles the line.  I run two small (Champ) heads after 2 seperate delays.  I love the setup except for the fact that I have to run the delays straight into the front end of the amps - there are numerous problems with this setup mostly having to do with input level and degradationof sound quality.  I have on occasion gotten the bug to implement onboard effects loops (solid state) but usually come up with nothing that is feasible or affordable. 

I started thinking I could place something like the Buff ' n Blend, Paralooper, etc. between the two halves of the preamp (12ax7) tube - I think this is the right place to put it...  I would want to run power from the amp so I assume I would have to tap a 9v (or 12v or 15v) from the 120v supply - or perhaps the 6.3v DC filament heaters?  Would that be enough?  MAX1044?  Does the circuit need to modified in any way to work with the amp?  I have so many questions and probably more that I haven't thought of.

So, I'm putting out an open call for help on this project... your help and ideas would be appreciated so much.  I've looked over sites and searched google so many times I'm going blind...  I get bits and pieces but not the whole picture.

Many thanks,
Patrick   

[gez]

I started thinking I could place something like the Buff ' n Blend, Paralooper, etc. between the two halves of the preamp (12ax7) tube - I think this is the right place to put it... 

I have a loop in my champ.  IIR it's between the first two stages (all one tube), as you were suggesting.  No buffer(s) in my case, I just wanted a warmer sound from a digi reverb I used to have.  Can't say it did much, though.

I love the setup except for the fact that I have to run the delays straight into the front end of the amps - there are numerous problems with this setup mostly having to do with input level and degradationof sound quality. 

Could you elaborate?  Would be a hell of a lot easier to sort out the problems with your pedals rather than trying to cram extra circuitry into your amp.

[d95err]

The problem in using a solid state loop is that you probably won't get enough headroom for the tube amp signal levels. In a champ, you would probably want the loop between the preamp and the power tube, and at that point you will have fairly high signal voltages (enough to push the power tube into distortion).

You need a circuit that can take the signal level down to line level and then back up to "tube" levels again. A tube based loop is probably the easiest solution, although a high-voltage solid state loop would work as well (checkout the loops described in Kevin O'Connor's "The Ultimate Tone 1").

A passive loop (just a pair of jacks between the preamp and power tube) together with an opamp based loop running a bipolar supply of e.g. +-18 migh give enough headroom, at least if you're not playing very loud.

The typical reason to put an fx loop into an amp is to have effects like reverb or delay after preamp distortion. However, in a Champ, almost all distortion is generated in the poweramp, so distortion would be generated after the loop anyway.

[captntasty]

...to sort out the problems with your pedals rather than trying to cram extra circuitry into your amp.

My problem is that I'm running straight in to 2 old school digital delays that have variable input levels - when they peak, bad things happen... so every new distortion or clean sound has me adjusting that level to avoid peaking it out.  If I have a loop I can set it and forget it as I'll have straight signal from my guitar/pedal effects going through as well - any peaks will be masked.  The loops would be only for delay and possibly reverb.  That was my thinking, but....

However, in a Champ, almost all distortion is generated in the poweramp, so distortion would be generated after the loop anyway.

My Champs are sort of mongrels... they have a Master Volume and Volume, one of them runs 2 6V6's in parallel... but still - I dig what you're layin' down.  No reason I can't use two Buff n Blends, Paraloopers or whichever with the delays through them before the amp...  I'm    I'm trying to reinvent the wheel...  Thanks both for clearing my head!

[gez]

...to sort out the problems with your pedals rather than trying to cram extra circuitry into your amp.

My problem is that I'm running straight in to 2 old school digital delays that have variable input levels - when they peak, bad things happen... so every new distortion or clean sound has me adjusting that level to avoid peaking it out.  If I have a loop I can set it and forget it as I'll have straight signal from my guitar/pedal effects going through as well - any peaks will be masked.  The loops would be only for delay and possibly reverb.  That was my thinking, but....

I don't see how a loop is going to change anything.  The pedals are still going to have to deal with whatever input signal is thrown at them.  The first tube stage is going to amplify whatever signal is present at its input: use a booster/distortion and this gets amplified and the delays in the loop see a larger signal.

I modded a delay for someone here last year.  If it has an active mixer at the output it's usually fairly easy to get a little more headroom: divide down the input (or just the wet signal) and boost at the mixer.  There's a limit to what you can get away with, though, as noise levels can increase if you go too far.  Is there a schematic floating around?  Alternatively, could you trace the output and input stages?

Another option is to use a limiter in your setup, just before the delays.