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Boyuu EL34 A9 Tube Amp
Boyuu EL34 A9 Tube Amp
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Old 7th December 2017, 07:26 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, 08:03 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, 10:23 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.
http://www.diyaudio.com/forums/attac...ods-rev1-2-pdf

Get back here if you want, I can do some measurements if you need.
Marcel
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Old 8th December 2017, 06:13 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, 11:28 AM   #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.

Marcel
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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Old 23rd December 2017, 01:32 PM   #316
PrebenDK is offline PrebenDK  Denmark
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Hi All
Iím new on here, an also new on tube amps. Searching on the Internet for a small beginner tube amps, I stomped over this thread. That was very interesting to read the whole thread (32 pages). Then I bought a pre-built Boyuu A9 EL34 from a stock in Germany. First thing I do, was open the tube amp, and check all connections and the value of all components. Insetting the tubes and slowly get power on with my vario-transformer (Nordmende RT 397/1). No smoke or explosion, just the warm glow from the tubes, and turning the volume up, music flows out of the speakers.
The schematic (originally posted by Celsius) is identical to my Boyuu A9 except from some value of components. My tube amp is build for AC240V. Here in Denmark the average voltage is AC230V. I have changed the values on the schematic, so you can see the values for my AC240V version. Resistor R107 and R108 are one resistor 500 ohm 6 watt. And the same for R207 and R208.
EL34SE 240V.jpg
I have measured some voltages at AC230V line in:
AC305V on the rectifier pin 4 and 6 according to ground (With AC240V line in, there is AC315V, as shown in the schematic).
DC320V on B1 (B+ on the PCB), and DC296V on B2.
DC310V on pin 3 (anode on tube EL34).
DC315V on pin 4 (grid on tube EL34).
DC22V on pin 8 (catode on EL34).
DC146V on pin 2 and 5 (anode on tube 6N9P).
DC1.5V on pin 3 and 6 (catode on 6N9P)

And here some photos:
My Boyuu front.jpg
Boyuu bagside.jpg
My Boyuu inside.jpg

And a Merry Christmas to all of you.

Last edited by PrebenDK; 23rd December 2017 at 01:43 PM.
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Old 23rd January 2018, 03:55 PM   #317
dmnstewart is offline dmnstewart
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Just built the A9 and have started checking DC voltages et with rectifier valve inserted and no load.
I have the version with r9 (39R) connecting rectifier pin 8 to choke and smoothing capacitors.
Upon switch on this resistor started to overheat.
I connected the resistor to pin 2 and got DC voltages.
Anyone know why this would happen?
Definatly shows pin 8 on the diagram.
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Old 24th January 2018, 07:06 PM   #318
MakW is offline MakW  Netherlands
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@Preben, nicely done, enjoy.

@Stewart: the tube bases are lousy in specs and tubes may be fitted wrongly without a sign ... until you switch on.
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Old 24th January 2018, 07:47 PM   #319
dmnstewart is offline dmnstewart
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Yes the tube bases are a pretty wide tolerance, which allows the valves to be be inserted incorrectly. Never happened to me in the past.
Amplifier working now but gain is low. Maybe need a pre amp
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Old 24th January 2018, 08:28 PM   #320
MakW is offline MakW  Netherlands
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what to you feed your amp? Source etc.
and how much do you need: modern speaker (in-) sensitivity is an issue with tube amps.
96db or something is nice.

This EL34 has already inspired my wife, supported by neighbours, to draft a declaration of war

gr. Marcel

Last edited by MakW; 24th January 2018 at 08:37 PM.
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