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Help!!! Tubes4Hifi SP14 noisy
Help!!! Tubes4Hifi SP14 noisy
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Old 3rd January 2020, 01:54 AM   #11
rayma is offline rayma  United States
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Quote:
Originally Posted by luvrockin View Post
I tried that earlier tonight with no benefit but I didn’t flip the plug over.
The only reason to ever use one is for testing by reversing the plug.
The safety grounds must always remain connected. Never float the chassis,
that can be deadly.

See page 40 here:
https://web.mit.edu/jhawk/tmp/p/EST0...ps_handout.pdf

Last edited by rayma; 3rd January 2020 at 02:02 AM.
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Old 3rd January 2020, 09:26 AM   #12
petertub is offline petertub  Sweden
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Help!!! Tubes4Hifi SP14 noisy
Quote:
Originally Posted by luvrockin View Post
%snip%

If the preamp is connected to the amps by itself, (nothing plugged into it, no other source inputs) there is the noise issue.
Good observation!

Do you have noise with volume turned down ? Does it change by switching
input ? Does it change by changing volume ?


Will the noise change if you disconnect the protective ground ( cheater plug ) ?


And what is the noise anyway? Do you have access to a scope to show the noise ?
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Old 3rd January 2020, 10:42 AM   #13
luvrockin is offline luvrockin
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The volume control has no effect. This thing buzzes the same amount at zero as half way turned up. The input selector has NO effect. The same input 1-4. I tried the cheater plug for a minute. When I saw it made no difference, I removed it and plugged back in without it. I don’t know what kind of noise it is. I don’t have a scope. I suppose I could possibly look for a cheap used one and purchase it. But then I’d have to learn how to use it as well. That may be a stretch.
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Old 3rd January 2020, 02:26 PM   #14
petertub is offline petertub  Sweden
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Help!!! Tubes4Hifi SP14 noisy
Quote:
Originally Posted by luvrockin View Post
The volume control has no effect. This thing buzzes the same amount at zero as half way turned up. The input selector has NO effect. The same input 1-4. I tried the cheater plug for a minute. When I saw it made no difference, I removed it and plugged back in without it. I donít know what kind of noise it is. I donít have a scope. I suppose I could possibly look for a cheap used one and purchase it. But then Iíd have to learn how to use it as well. That may be a stretch.
Thanx.
It seems to be the B+ ( or at least the outermost stage) that generates noise.
At lest grounding issues are eliminated. It would be interesting to measure
internals. Do you got schematics with the unit ?
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Old 3rd January 2020, 05:41 PM   #15
luvrockin is offline luvrockin
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I believe I do. I will dig when I get home. I don’t remember what there were offhand but I do know that after I built it and when troubleshooting the noise problem confirmed the B+ voltage was in spec. I will check when I get home after work.
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Old 14th January 2020, 09:10 PM   #16
IEales is offline IEales
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The issue likely the same as I had with VTA built M-125s.

See teaching the VTA M-125 to sing

If you use a Y cord with a shorting plug or just plug 1 RCA cable into both amps, they will likely hum due to the fact that the M-125 has a 9 point ground tied to Earth Safety.

I quietened my M-125s by nearly 40db. I now have to look at the tubes to see if the amps are on.
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Old 14th January 2020, 10:43 PM   #17
IEales is offline IEales
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Default SHORTED RCA cable

OOPs. I meant SHORTED RCA cable above ^^^
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Old 16th January 2020, 02:15 PM   #18
claudiomas is offline claudiomas  France
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long time ago my customer built this kit
and there was hiss noise or something like this
parallel a X nF cap on input tube anode resistor
i send informations to Roy @ this time....
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