Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on January 06, 2013, 06:41:32 pm
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The amp has very low volume. As soon as i plug in a cable to the FX send and return the amp is working fine with balls O fire. The FX jacks appear to be making good contact after the cable is removed. The jacks are what i first suspected. But i dont believe this is the problem. I see what are LDR's or relays in the FX loop on the schematic. The FX mod has been done to this amp removing the (3) transistors and using the jumper wire method removing the send pot from the circuit making the signal direct.
I DONT RECOMMEND DOING THE SERIES MOD, USE ANALOG EFFECTS
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Locate the Jfets used for channel muting and make sure those are good.I just change them to make sure in many boogie amps. Dumb design and not the best Jfets to use either.
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Back on the Mesa DR. phsyconoodler do you recall where those channel muting transistor are located on the FX board by number? The jumper wires on the board have replaced the send pot and 3 transistors that were on the FX board to make this a series FX loop. I would thiink it would be working now period without the patch. I see LDR labled though. LDR11 & LDR12 have to be working as i have full amplifier volume after using patch cord in Return & Send
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Going to just remove the series FX mod which disables the footswitch function for the (Loop ON Switch) and replace with (3) new J175 fets and wire the send pot back to the board. The customer wants the amp to function on all loop switch options as was made by Mesa. The Parallel/Series loop sucks but he going to have to live with it if he does not want keep the mod and use a patch cord to bypass the fx manually. Ive read of a few people trying to use digital effects that wont work well with this amps stock fx design and so they look to do the series mod which again disables some functions of the master fx loop switch and footswitch capabilities
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Removed FX mod jumpers. Replaced J175 Fets. Reconnected send pot to board. Finished. Works as intended. FS as well