Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on September 24, 2012, 05:35:26 pm
-
Hi, ladies and gentlemen,
A client just brought to me an oooooollllllllllllllllllddddddddddd Traynor guitar amplifier in which he wants me to install an effect loop. I think the best place to install the 2 jacks is between the 2 sections of the phase inverter tube, but since I have nerver done that, I am not totally sure. Active or passive effect loop, what is the best ?
Regards, buddies !
Colas Coppola.
-
Whether to use an active or passive loop probably boils down to where the loop is inserted in the preamp.
If you insert the loop at the phase inverter, you'll probably need an active loop. The effects most likely to be used are stompboxes, expecting guitar-level signals and outputting slightly-bigger-than-guitar-level signals. The phase inverter is expecting a preamp-boosted signal of 1-2v to enable it to drive the power tubes.
So with that loop location, you probably need to knock down the existing signal to keep from overdriving the effects inputs, and the return signal will probably need to be boosted to adequately drive the phase inverter. Of course, if the player will only ever use professional line-level effects (+4dB), then you could probably use a passive setup.
If you inserted the effects earlier in the preamp, you could probably use a passive loop. But then you have to figure out if you (your customer) wants the preamp to shape the effect sound, or have the effects alter the preamp's sound. which happens depends on where in the preamp the effects loop is added.
There's a lot of ways to do a loop: active, passive, where in the circuit, no controls, lots of controls/switches, etc. I can't pretend to be familiar enough with them to make a suggestion on the best circuit to use, only point out the pros/cons of each approach.
-
IF you are using 9specifically) a MXR analog delay OR a Boss digital delay, you "should" be able to use a passive effects loop just prior to the entry of the LTPI and it should work fine. Look at the D'Mars OD Special, TOS or Tweed BluezMeister schematic for an example.
Reverb or any other FX, then I'd use an active loop. You have some options there:
http://www.el34world.com/Forum/index.php?topic=10208.0 (http://www.el34world.com/Forum/index.php?topic=10208.0)
or you can buy a kit to install an active FX on board here:
http://www.ironsounds.com/ (http://www.ironsounds.com/)
With respect, Tubenit
-
suppose I take the signal out from the first preamp tube, what value the send volume would have to be ? 250k, 25 K ?
-
Hi Colas
You have an e-mail
K
-
You have a message too !
Grazie
Colas
-
Hi, over the last week I have read all kinds of threads concerning effect loops installation, gee I was lost. I tried the voltage divider option after the 2nd preamp tube plate coupling cap, and the problem withs this arrangement is that it was acting as a dimmer and with a simple patch cord hooked up between the send and return jacks, I had a big loss of gain, more or less depending on the values of the resistors I was using. I read this morning that a bad thing to do was too hook up a 1 meg pot between the send and return jacks.
Bingo ! I tried that ( always liked to do what was forbidden hey hey ) and it works right, no loss of gain, because I haven't hooked up no resistor b4 the pot, to act as a voltage divider. So when no pedal on the signal path is used, the gain is the same as if nothing was plugged in the send/out. The prob. I can see is that the signal level, full open, might be too strong for certain kinds of pedal, and what about the impedance ? God knows :laugh:
Regards
Coca Colas
-
Your send impedance will probably be higher than a typical pickup, but this shouldn't be a big problem unless the cables are 50-100ft long. Many guitar pedals seem to have a reasonably high input impedance, so they might only reduce the gain of the previous tube stage a little.
-
> an oooooollllllllllllllllllddddddddddd Traynor guitar amplifier
What model?
Schematic?
-
Good morning !
It is a CUSTOM REVERB YSR 1. For the schem, I took it here, in the library. Thanks
Colas