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Boyuu EL34 A9 Tube Amp
Boyuu EL34 A9 Tube Amp
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Old 7th December 2017, 08:26 AM   #311
Mooly is offline Mooly  United Kingdom
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Boyuu EL34 A9 Tube Amp
Hum can be difficult to trace and eradicate. Pure 50Hz hum (a pure deep tone) suggests it could be being induced into wiring, or perhaps a ground loop. If it is a harsher buzz then it is more power supply related.

Does it hum with the inputs shorted ? and does the hum alter with volume ?
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Old 7th December 2017, 09:03 AM   #312
Vbonnet is offline Vbonnet  France
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The hum disappears when I ground the input pin on the preamp tube.
I have tried disconnecting the potentiometer from it, without any change, which suggests the hum would appear somewhere around the valve.
It is equally present on both channels.
At the moment I am measuring 630mV at the speaker connector, with no source signal.
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Old 7th December 2017, 11:23 AM   #313
MakW is offline MakW  Netherlands
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Nice to hear your tube amp works. 50Hz Hum is much debated in de 310 long tread...
Does the hum change when you change volume?
Please read / search for suppressor resistor.

The schematic by DMAXY of post #225 shows mods to kill hum, results are very positive.

Get back here if you want, I can do some measurements if you need.
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Old 8th December 2017, 07:13 PM   #314
Quad ii is offline Quad ii  France
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I wanted to thank all the contributors of this thread, I finished this amp using a lot of advices ! There are still some problems of hum, a kind of distortion in the high medium (specialy with high pitched voices, piano, natural strings). But the sound is not bad and I don't have made all the possible improvement.
I bought this kit to have a base of experimentation in SE, but for this price the sound is not bad. I have only changed the signal capacitors for russian PIO models, potentiometer for an ALPS and the cheap rear selector.
After some breaking time I would experiment the changes provided by DMAXY.
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Old 10th December 2017, 12:28 PM   #315
MakW is offline MakW  Netherlands
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DMAXY was drawn by hand if I rememeber and schematic has used the 100K resistor for R103/203 as in the KIT, but does NOT have a surpressor R. All other schematics (GIDO, Geekstuff and others) have a 75K resistor for R103. Does this effect the schematics /function at all? Can I change R103 in Geekstuff schematic?

Hum/50Hz noise: Triode Dick (contemporary Dutch tube amp designer) takes a bit hum out by upgrading the selector in ALL designs: "Een hele hete tip is: schakel niet alleen de signaalweg, maar ook de afscherming."

My experience: take the time to burn in the tubes seriously. I can hear more high comming in and less fluttery (if that is a word) while deep bass straightens out @around 100 hours music, going on to present @150 hours. The only stable sound aspect is the 50hz hum in the beginning
This implies that if you start to change things early (<100 hours) it will be very difficult to know (hear! or measure)) what changes do with the music and therefor obscuring your optimal path to the best sound experience.
The 7T law: Tuning Tubes To The Top Takes Time.

PS. Triode Dick sais: use a selector with 4 poles and thus cut schielding (L+R) as well as signal (L+R) to prevent noise from other apparatus to get in the amp via shielding. Makes sense to me.
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