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View Full Version : Amp mod FNG - In over my head? Help

fishin' musician
06-19-2008, 02:27 PM
Hi people. I recently recieved an output transformer and choke upgrade for a Laney LC15R. Installed the choke - great! Installed the multi-tap OT. Instead of adding an impedence selector switch I decided to install 3 output jacks, one each for 4, 8, and 16 ohms. Soldered it up, looked good to me, plugged in an 8 ohm speaker and turned it on. Tubes glow beautifully but ouput is thin, buzzy, and almost imperceptible. Where should I start the troubleshoot?
Help me Obi-Wan, you're my only hope...
Gunny
06-19-2008, 02:34 PM
Are those output jacks "open circuit" types or do they have a shorting connection when nothing is plugged in.
That's kind of a long shot guess at your problem. In many guitar amps you can get that symptom when you plug the speaker into the EXT jack instead of the SPKR jack (which is fitted with a shorting jack).
If that's not the problem, do you have a chassis ground connected to one of the output leads?
Let's start with those ideas and go from there. I know others will chime in too.
fishin' musician
06-19-2008, 02:41 PM
Thanks Gunny,
The jacks are a closed type. Wired the sleeve connector from each jack to the common lead of the OT then to a star ground on the chassis
greco
06-19-2008, 03:18 PM
Deleted post
fishin' musician
06-19-2008, 03:26 PM
They are a shorting type jack.
greco
06-19-2008, 03:45 PM
They are a shorting type jack.
Sorry for questioning.....
fishin' musician
06-19-2008, 04:18 PM
Sorry for questioning.....
so, should I use a shorting type jack in all 3 outputs?
Scottone
06-19-2008, 07:17 PM
They are a shorting type jack.

That's your problem then. Disconnect the un-used ones and it should be ok
fishin' musician
06-19-2008, 11:00 PM
Okay, wired in open jacks. Some improvement but output is still weak and buzzy. Anyone have any more ideas before I take the walk of shame down to the amp tech?
fishin' musician
06-20-2008, 02:15 PM
Any chance that it may be the speaker cable?
bagpipe
06-20-2008, 02:28 PM
Anyone have any more ideas before I take the walk of shame down to the amp tech?

Sorry, I dont have any suggestions. But, I have taken that walk of shame before ... I feel your pain! :frown:
greco
06-20-2008, 03:42 PM
Did you try it with only one open jack wired to the OT and all the others diconnected* (*i.e., unsoldered from the OT end)?

Are you sure that you have the OT (secondaries to the jack) connections wired properly?

What gauge and length of speaker wire are you using? You might want to try a minimum of 16 gauge wire and use twisted pairs (or similar)

Did you check the comnections on each end of the speaker wire?

Just some ideas to consider.

Good Luck with it.

Dave
fishin' musician
06-20-2008, 05:10 PM
Dave, these are all good ideas, I haven't tried disconnecting the other two leads but it sounds like a good idea, it may help to isolate the problem.
Speaker wire is a 14 gauge cable that I fabricated myself. If the cable is faulty could it lead to the symptoms I have described?
I've checked and double checked my OT connections. My fear is that I have unknowingly broken some Golden Rule of electronics.
greco
06-20-2008, 06:35 PM
Dave, these are all good ideas, I haven't tried disconnecting the other two leads but it sounds like a good idea, it may help to isolate the problem.
Speaker wire is a 14 gauge cable that I fabricated myself. If the cable is faulty could it lead to the symptoms I have described?
I've checked and double checked my OT connections. My fear is that I have unknowingly broken some Golden Rule of electronics.

I can only hope that these are "reasonable" ideas...electronics is my hobby, not my profession, and worse yet (for you) is the fact that I am only a beginner.

If the cable is faulty, I would think that it could give you a weak signal for sure (maybe "buzzy" also). This has happened to me in the past with guitar cables.

Any chance of a pic of your OT connections?...I'd just hate to see you damage your OT, and a pic would help the pros to look at your connections and see if they are correct.

Cheers

Dave
fishin' musician
06-20-2008, 11:08 PM
Hooray, everything is working. Open jacks and resoldered grounds were the answer. Now this little amp peels paint and I'm going to install a new pair of NOS Philips Miniwatt el84's...the cat hates me already. Thanks to everyone that helped, I couldn't have done it without you

Dwayne
greco
06-21-2008, 11:28 AM
Hooray, everything is working. Open jacks and resoldered grounds were the answer. Now this little amp peels paint and I'm going to install a new pair of NOS Philips Miniwatt el84's...the cat hates me already. Thanks to everyone that helped, I couldn't have done it without you

Dwayne

COOL:food-smiley-004:

I just have to ask...what does "FNG" in your thread title stand for?

Dave
fishin' musician
06-21-2008, 09:28 PM
FNG was a term used in Vietnam, it meant "F*ckin' New Guy".

Cheers, Dwayne

PS. The Choke and OT are from Mercury Magnetics and I cannot believe the improvement in sound quality. Clean "cleans" and rich flute-like tones at higher gain settings. The vintage el84's have helped as well but the new transformers make this little practice amp breathe fire. I'm gonna mike it up and gig with it tonight (don't worry, there is a back-up in case I didn't do everything right and the amp craps out half way through the night).
Scottone
06-22-2008, 04:03 PM
Hooray, everything is working. Open jacks and resoldered grounds were the answer. Now this little amp peels paint and I'm going to install a new pair of NOS Philips Miniwatt el84's...the cat hates me already. Thanks to everyone that helped, I couldn't have done it without you

Dwayne

happy to hear that you resolved it yoursel Dwayne. Amp modding is a great hobby....still wish I had the time to do it myself.