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Noise in my DIY tube preamp
Noise in my DIY tube preamp
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Old 6th July 2018, 08:36 AM   #1
stenak is offline stenak  Norway
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Default Noise in my DIY tube preamp

The last months I have been building a diy tube preamp. It is not my first diy tube preamp, probably my 6th or 7th? All the others I have used point to point connection, and not pcb.
The Muffsy BSTRD - Class A Tube Preamp PCBs from muffsy on Tindie
I have build Remus(Swedish guy had an atricle in The Swedish Audio/Video around 1990?), ssss with ecc82, Forewatt srpp, and some other..
Have never had any problem with hum or noise, but today i fired up my "BASTARD" , yes its called that!, and it was like I was sitting near an old motorboat!, just noise...
What have I done wrong? I thought that to build with pcb-s was musch easier, nothing can go wrong? I think I have some skills, because I have been building tube preamps since the 1990s.
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Old 6th July 2018, 08:49 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Schematic?
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Old 6th July 2018, 10:15 AM   #3
stenak is offline stenak  Norway
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Here is a link to the schematic..

the bastard | theslowdiyer
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Old 6th July 2018, 10:17 AM   #4
stenak is offline stenak  Norway
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Maybe the tubes are faulty?. Bought some 6s26 from Ukraine. Have a pair of RCA 6j5 in metal can. I will try these later today

Last edited by stenak; 6th July 2018 at 10:30 AM.
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Old 6th July 2018, 10:50 AM   #5
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Ensure you have decoupled the HT for each section and the ground point are the same for each pre amp.
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Old 6th July 2018, 12:32 PM   #6
stenak is offline stenak  Norway
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I should have used point to point soldering on this project to..Pcb-s are not so easy work with when it comes to troubleshooting.
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Old 6th July 2018, 01:22 PM   #7
artosalo is offline artosalo  Finland
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Quote:
...and it was like I was sitting near an old motorboat!, just noise...
What is the "noise" in this case ?
High frequency hiss, 50 or 100 Hz based hum, slow frequency "motorboating" or what ?
Does the position of volume pot affect the noise level ?

One heater pin (7) is directly connected to GND. Are you using DC-heater supply ? With AC the hum is very likely.

Last edited by artosalo; 6th July 2018 at 01:36 PM.
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Old 6th July 2018, 03:01 PM   #8
huggygood is offline huggygood  France
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motor boating ?
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Old 6th July 2018, 06:15 PM   #9
PRR is offline PRR  United States
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Noise in my DIY tube preamp
Quote:
Originally Posted by stenak View Post
Here is a link to the schematic..
the bastard | theslowdiyer
Lot of stuff there, starting with a transistor scheme.

What would be better is a direct link to THE schematic, amplifier and power supply (since you say motoboating).

However this "seems" to be a stereo pair of 6J5 single-stage amplifiers. Such a thing can NOT oscillate (not even as a phase-shift oscillator), unless it is wired very wrong. So we need to see specifically what you have.
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Old 7th July 2018, 07:49 AM   #10
stenak is offline stenak  Norway
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Default The Bstrd..line amp

Yes, it was like sitting in an old motorboat with a one cylinder motor...
Here are schematics over the amp and psu. I have built the transformer into a seperate box.
Attached Images
File Type: jpg Bastard PCB.jpg (150.1 KB, 388 views)
File Type: jpg Bastard PSU PCB.jpg (194.9 KB, 383 views)
File Type: jpg Bastard psu.jpg (79.6 KB, 382 views)
File Type: jpg Bastard skjema.jpg (62.5 KB, 380 views)
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