Asteroid effects loop

[passfan]

I've put a low voltage Asteroid together and wired up a dumble type effects loop on the input grid to the PI. It appears to be switching properly and works just fine with a straight wire. The problem occurs when I insert an effects unit in the loop. I get more then enough input into the unit but lose it on the return. I am going to set it up and meter the signal later to see where I might be losing it but so far cords check out, jacks check out and bypassed signal feeds through. Anyone run into this?

[Reeltarded]

Yes, in other amps all the time! It's common to use a triode for make-up gain in the loop return, if not another triode for send buffer as well.

[martin manning]

The Dumble loop has a cathode follower send buffer and a common-cathode return recovery stage. Something is wrong on the return end here.

[passfan]

I suspect an impedance mismatch in my hurry to insert a loop rather quickly I was trying to drive the grid of my PI straight from the return. Plenty of signal from the send , nothing on the return.

[Reeltarded]

What are you putting in the loop?

I have success with using something that is buffered first and has makeup gain last, like a racked delay line or reverb or whatever.

[JazzGuitarGimp]

It sounds like you're going to have to add a recovery stage between the return jack and PI input.

[guitardude57]

Which loop did you use? If a tube loop...

How many volts are you getting on the Cathode Follower cathode?

You want 30-34 volts there. If low, raise the tail resistor a notch or two
up. Mine was low, and I had the same issue as you.

It is OK now.

[Firestorm]

I suspect an impedance mismatch in my hurry to insert a loop rather quickly I was trying to drive the grid of my PI straight from the return. Plenty of signal from the send , nothing on the return.

There are more ways to screw this up than to get it right. Typically, you want space for a 12AT7 so can run the send off the cathode of one triode and recover off the plate of the second (with appropriate level control). It also matters what you have inserted into the loop: stomp box; semi-pro; or pro audio. Merlin has a very effective loop (better with stomp boxes and semi-pro gear). KOC has a ridiculously complicated one that mates with anything; and another that is slightly simpler, but seems mostly geared to parallel operation.

[passfan]

Thanks for the responses. I should have no problem with a solution come the weekend. This pretty much happens with whatever I plug in, Stomp , rack , all the same,

[badtweed]

I've put a low voltage Asteroid together and wired up a dumble type effects loop on the input grid to the PI. It appears to be switching properly and works just fine with a straight wire. The problem occurs when I insert an effects unit in the loop. I get more then enough input into the unit but lose it on the return. I am going to set it up and meter the signal later to see where I might be losing it but so far cords check out, jacks check out and bypassed signal feeds through. Anyone run into this?

When you say "dumble type effects loop" are you referring to the simple, passive type of effects loop as used on the Dumble amps or the Dumblator tube based effect loop circuit?

[guitardude57]

If you have room, build the active tube loop. Or build a free standing Tube loop.

If you don't like rack stuff, this is a small enough circuit to build in a smallish tabletop sized box. And there are designs on the forum here, to make a transistorized version that could be even smaller.

Without a D-lator of some kind, the loop may not be real friendly with what you plug in there... hence the Dumbleator. The tube loop could be fitted with any amp with a loop. Might need a tweak or two to balance things, but will work fine.

There was an extra tube in my Bassman convert to a "D" style" that was built into the loop. I'm glad it is there for sure.

[passfan]

This was the passive loop hence my comment about impedance issues. Obviously it cannot drive the grid of the PI.