Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on May 03, 2015, 04:25:38 pm
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This is something that's beenon my mind for a quite a while now. I have a few things going against me in my shop. One is poor grounding. I'm curious how much noise is normal noise for a hand built tube amp. The last 3 I did, has a little bit of a "hum" at idle. My grounding is good. Layout seams fine. Nothing to close to transformers or high current wires. My questions are:
Should my amps be "silent" at idle or is a little noise normal?
What are some things you guys do to ensure a quiet amp?
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A reference point for me for "silent" at idle with all amp knobs dialed at the level that I'd play at home is the following:
My builds need to be quieter at idle then the production amps I've owned like Fender and Carvin. (Comparing production amps at the volume that I normally play in comparison with my build at the same volume that I normally play at)
They need to be quiet enough that if they were on in a room and I didn't see the amp indicator/on light turned on, that I could walk thru the room and not "hear/notice" them. This is on the "clean" not OD channel.
They need to be quiet enough at idle that when I play a chord that it surprises me how quiet the amp is at idle. Sort of like "if the amp is that loud when played why is it so remarkably quiet at idle when I am not playing?"
I have two amps & both meet that criteria for me. IF, I engage the OD ............. then the idle noise is more noticeable. Maybe 50% more idle noise?
with respect, Tubenit
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A reference point for me for "silent" at idle with all amp knobs dialed at the level that I'd play at home is the following:
My builds need to be quieter at idle then the production amps I've owned like Fender and Carvin. (Comparing production amps at the volume that I normally play in comparison with my build at the same volume that I normally play at)
They need to be quiet enough that if they were on in a room and I didn't see the amp indicator/on light turned on, that I could walk thru the room and not "hear/notice" them. This is on the "clean" not OD channel.
I have two amps & both meet that criteria for me.
with respect, Tubenit
Well these are kinda hot amps I should have mentioned. And these noises are at a gain level ready for some rockin leads. Maybe what I'll do is film some video and get your opinion.
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Not enough info. If the el. your shop is not well grounded, this implies poor wiring generally. The shop el. power might be noisy. Other ambient noise may be from el. motors, fans, fluorescent lights, dimmer switches, etc. These extraneous factors may induce noise in an amp that is otherwise quiet. An amp that is noisy in your shop may be quiet somewhere else.
Ground schemes, layout and lead dress are factors. This includes the positioning of trannies (headphone trick). Also, hi-gain preamps are inherently more noisy.
You need to isolate the possible cause(s) of noise & hum.
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"This includes the positioning of trannies (headphone trick)"
Yes I was wondering how uou should position the transformers for least noise. I have heard of this but not really sure what or how you would position ir.
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The headphone trick from our friends over at AX84 site.
This is the best way to find the quietest place to put a reverb, output, driver, or any other signal transformer to get the least hum. CAUTION: THIS INVOLVES WORKING ON THE AMP WITH WALL VOLTAGE PRESENT. WALL VOLTAGE CAN BE FATAL.First set up the power transformer. If it's not installed yet, all the better, but if it is, this will still help. If the PT is not installed, wire up the primaries to a power cord, but do not wire up any secondaries-- tape the ends of the secondaries. If the PT is installed, fine, just make sure there is no circuit on any of the secondary leads (pull all tubes, and disconnect leads and tape them as necessary).
Now set up the signal transformer (output, reverb, whatever). Hook one set of OT secondaries (your choice, but I usually go from ground to the highest impedance tap, don't worry about impedance matching here!) to a set of headphones. Tape the primary leads.
Put the headphones on, plug in the power cord, and start moving the signal transformer around. Try it all over the chassis, and also rotate it. While you might expect the least hum with the transformers as far from each other as possible and at right angles (and that may be the case for you), it might come at an odd angle and/or position. Sometimes the least hum occurs when the transformers are side by side. When you find the quietest spot, use a permanent marker to mark where the mounting holes should be.
If you have more than one signal transformer, repeat this for each one. When you're finished, unplug the PT. That's it!
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Thsnks for the link. Yes I actually read that one but I've decided to try it lol.
reason being it looks to be a bit too complicated at least for me. I'm still learning layman's way. Plus working with high voltage is still a bit scary for me.
Even though I've already built a few amps I'm still a but queasy when it comes to hooking up.transforners directly to a power source. Since I won't know what I'm doing.