Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on September 26, 2010, 09:55:22 am
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I have a question:
I used mini sheilded cable on the EQ of my 2204/plexi build. I was having a squeel near full volume that i could not track down
I removed the sheilded cable from the EQ and the squeel is gone
Could i have created a ground loop by having all that sheilded cable running along the board?
There were a total of 5 sheilded cables that i used / I thought this would assure me of no squeeling
I know in the past there has been a few threads on the impedance possibly being effected in the EQ by using all sheilded cables
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Ground only one end of the cable shields.
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I only ground one end of sheilded cables
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Hi Plexi,
When I have more than a couple shielded cables to run (13 in my TOS build), I run a separate bus JUST for the shielding.
I make it out of the ground wire from a length of romex. I crimp a ring terminal at each end and shape the whole thing into a nice structure that won't touch anything else. It grounds sufficiently when you screw it in place through the ring terminals.
My reasoning is this: pretty much all the grounds we run, including the buss on the back of the pots are part of the signal chain. we usually don't ground out HT CT, Earth ground or any other NON signal grounds anywhere near a signal path, shields on cables are the same thing to me. if they are actually shielding and deflecting stray EMF to ground, I don't want it anywhere near my signal path.
I have no Idea why yours is howling. I have found the even shielded wires are influenced by lead dress in this last build. (hi gain amps are a PITA). You just can't run them willy nilly and expect them to just work. At least that is my limited experience with this build.
Without seeing a pic of your controls, I can only guess what may be wrong. I've found myself to blame more often than not. mis-landed wires, poor soldering technique, bad lead dress are my usual culprits.
Break out the chopstick and solder braid, a nice cup of strong coffee and a sandwich helps too.
Just my .02 for what it's worth
Ray
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Thanks Stingray. Yeah high gain amps are PITA at times. But i just found the problem.
The twisted OT primary wires were just a hair too close to one of the power tubes so i rerouted them after moving wires in the amp around and found this to be the problem
Full volume and no squeeling at all. Nice and quiet but deadly volume. I have had this problem before in HG builds but never found the primary OT wires placement to interfere like this was
Back in it's cage after 4 months for good. This is my best HG amp to date. There were 3 others that were in the same class
This one turned out very good / I dont need to build anymore HG 100 watt amplifiers
(http://i356.photobucket.com/albums/oo5/plexijtm45/BuildFinished.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/PowerDampingControl.jpg)
(http://i356.photobucket.com/albums/oo5/plexijtm45/OnCabs.jpg)
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NIIIICE!
Curios? did you use an audio pot for your MV?
and is that why there is a Log spacing on your dial?
Ray
OH! and how did you determine the output power to mark your MV dial
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I used 1Meg Audio pot's for the volume,bright,gain,master & bass
I have not used it long enough to be familiar yet with the pot's
But it is roughly 40 watts with the PI pot CCW and 100 watts CW
Man im especially happy with it's tone / The BD-2 was really not needed as it breaks up really well smooth or dark
I only added it for an extra tweaking kinda thing. It's a killer
(http://i356.photobucket.com/albums/oo5/plexijtm45/PotFunctions.jpg)