TR75 Reverb Question

[Barris]

Last week I got a TR75GT combo amp for a song because one of the channels was not working and the reverb was not working either, but it sounded so nice anyway that I got it. It was made in 1984 according to the serial number decoder. Anyway, I got it home and took it apart and immediately noticed that there was a loose wire. I connected it according to the schematic I downloaded, and both channels work wonderfully now. Very clean, very quiet, but powerful. Wonderful solid state amp, reminding me a lot of the Roland Twin JC, especially since this amp has two 12s. It sounds particularly nice when I use Ric-O-Sound and run the neck pickup to the TR75 with a little bit of tremelo and the bridge pickup to my Vox amp with some nice transparent-sopunding compression.

Anyway, here is something I was curious about that someone maybe can tell me (perhaps Tracy Sands?). Since I have not been able to find a manual anywhere, the operation of this amp has been trial and error. I figured out that the reverb DOES work if I place a 1/4" plug into the rear effect in/out jack, but only if the tip of the plug is inserted. If it goes in all the way, the reverb stops working again. Was this jack designed to accept a very short 1/4" plug perhaps? And get this.....the plug is not sending or receiving anything. Its just plugged into that jack. Can anyone explain to me why this is occurring? Not complaing, because everything seems to be working great now, and I go this amp for very little money!!! Forgive my ignorance if the reason for this is common knowledge, but evidently I am not the only person who does not understand this. Thanks...

[chuck_king]

I don't know for sure, but the way you describe it, it sounds like the reverb may be the "ring" connector on a tip-ring-sleeve jack (i.e., a stereo jack). Is there some other feature that would be selected by footswitch on that amp? That might be the tip connection.

[Barris]

Good clarifying question. The other built-in effect of the amp is distortion. On the rear panel there is also a footswitch jack for turning effects on and off. It is located right under the effects in/out jack. The footswitch jack clearly IS a TRS (Tip/Ring/Sleeve) type. I have an old Kustom footswitch I am using with it, and it is a 2 button controller. One button on the footswitch switch turns the distortion on or off, and the other turns the reverb on or off. However, when the plug for the effects in/out switch is not plugged in as I described in the original post, the reverb will not engage at all, with or without the footswitch in use.

The effects in/out switch seems to have no effect on the distortion like it does the reverb. The distortion works no matter what.

Thanks for the input....Does this help clarify to the point that it makes sense to someone who can explain it to me?

[Barris]

Anybody else with input about Tr-75?

Thanks in advance!

[chuck_king]

Again, I have no familiarity with this particular amp, but based on what you've described, I would guess that the effects jack is a switching jack that is supposed to disconnect the internal reverb when using the effects loop. Something is probably misaligned in the jack that prevents that switch from closing like it's supposed to when the plug is not inserted, but inserting a plug moves things around in there enough that at one point it closes, although it is not closed when the plug is all the way in.

You should be able to get a schematic from Rickenbacker. They don't have schematics for all the TR amps posted on their web site, but they have them and will provide them if you ask them. At least, IIRC that's what John Hall said in a post about it at some point.

[Barris]

Thanks Chuck,

That makes a lot of sense. I already have downloaded the schematic, allthough I have a little trouble interpreting parts of it. I do appreciate the help.