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Old 10th June 2008, 07:17 PM   #1
Kippy is offline Kippy  Netherlands
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Default Music angel XD-SE EL34

Sorry for my not to gread englisch but I will try my best to explain my problem.

I heve bought a music angle XD-SE tube ampliefier with EL34 end tubes. So far so good, it sound's good, but ik could sound bether. Ik have fount the scematic of this amp in an other thread on this forum My Experience with "Music Angel" EL34 PP

This scematic is nog very eary to read becouse of the poor quality so i opened my amp and drown the scematic form the ciruit boards. This is what i got:

[img width=600 height=453]http://home.xmsnet.nl/bjaspers/100_0623_6002.jpg[/img]
Hier staat de grote verzie

It is not looking verry bad but is could be bether, and there are some strange resistor valuse:
  • R24/R25 3K --> In the most el34 push pull amps they are not 3K but 100Ohm
  • The 2 x 22 Ohm resistor between El34 pin 8, Normal 12 Ohm
  • R19 - R20 / R16 - R17 --> Together 78K, Normal 1K and some times compleetly removed
  • An other strange thing is the feedback from 6N1 throug the R3/R4 resistor devision withr the 10K sery rezistor
  • And the circuit of R10 and R11 I don't understand

There will probebly be more strange things in the circuit, but this are the things that i can find with my limmeted tube knowledge.
I think i would be best to remove R19, R16, R1. And replace R24, R25 with 100Ohm resitors. And replace the 22 Ohm resitors for 12Ohm ones.

Ill change the 0,33uF capasator's that are in the signal way for JJ capasators and change the potentiometer for an Alps one.

Do you think that this is a good idea for improving the sound? And are there other things that i can remove ore change to improve the sound?
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Old 10th June 2008, 08:19 PM   #2
Svein_B is offline Svein_B  Norway
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Glad to hear that your amplifier sonds good
There are actually quite a few owners that seem quite pleased with the sound of the the M.A. amplifiers.

As you have observed there are however a few unusual component choices, such as the unusually large grid-stoppers. This could be because the builders do not know what they are doing, or it could be that they have reached their choices based on listening tests.

- R24/R25 3K --> In the most el34 push pull amps they are not 3K but 100 Ohm
Yes, large value screen stopper resistors.

- The 2 x 22 Ohm resistor between El34 pin 8, Normal 12 Ohm
Two 22 ohm in parallel makes 11 ohm. Not so bad. Actually the cathode resistors could be 1 ohm or 10 ohm without making much difference. Their main purpose is to create a small voltage drop to measure the current.

- R19 - R20 / R16 - R17 --> Together 78K, Normal 1K and some times compleetly removed
Yes. unusually large grid stopper, and actually a voltage divider network
The resistors do however seem to be of the "ear-friendly" carbon composite type.

- An other strange thing is the feedback from 6N1 throug the R3/R4 resistor devision withr the 10K sery rezistor
The feedback ratio looks very low. May be OK for triode operation, but questionable for pentode mode.

And the circuit of R10 and R11 I don't understand
Probably just a voltage drop of the B+ for the driver stage. Not sure your circuit is exact here.

This guy Lukasz Fikus, seem to share your idea that a lot of components could be removed in some of these amps
http://www.lampizator.eu/AMPLIFIERS/AMPS.html

Myself I am not yet sure, but I was qurious enough to buy the bigger bottle KT88 version a few weeks ago to do some measurements and experimentation. So far I have only listened to some music. It sounds quite pleasant, and responds well to some premium NOS tubes.

SveinB.

Edit: a direct link to Kippy's traced diagram: http://home.xmsnet.nl/bjaspers/100_0623_600.jpg
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Old 10th June 2008, 09:15 PM   #3
Kippy is offline Kippy  Netherlands
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Something went wrong with the images of the scematic, and i can't edit my post so, here are the good ones.

Click the image to open in full size.
big version
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Old 10th June 2008, 09:56 PM   #4
Kippy is offline Kippy  Netherlands
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@Svein_B

Thanks for the respons.

The link http://www.lampizator.eu/AMPLIFIERS/AMPS.html explains exacly why i want to remove all the unnessesery components. That is also the reason for this topic.

But is it is dificult to determen what components are wrong or can be conpleetly removed. That is why i need your help and the help of the other forum members to give me a push in the right derection.

Things that i'm going to do first are:
- Replacing R4/R25 with 1K resisors for bether sound in triode mode
- Removing R19 and R16
- Replacing R17 and R20 with 1K resistors
- Removing R1 and R2
- Replacing the potentiometer with a 100K potentiometer from ALPS
- Replacing the 0,33uF capacitors in the signal paths

But if i look at the lampizator site there are more things i can remove for a bether sound. So what are the other options?
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Old 11th June 2008, 10:01 PM   #5
Kippy is offline Kippy  Netherlands
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I have drawn the scematic again, but now with the good symbols. So now it will be a little easer to understand.
Click the image to open in full size.
http://home.xmsnet.nl/bjaspers/100_0631_V2.JPG
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Old 2nd September 2008, 02:35 AM   #6
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Hello,

This is my first post so I hope the picture below comes through.


I also have a music angel el34 push pull amp, specifically the XD 500 Mark III. From your schematics, as well as other on the web, I can tell that every version from music angel is different. My version does not have ANY grid stop resisters, which i found very suprising. I have posted a PDF of the diagram I put together over the afternoon. I will also try to post the power supply stages shortly.
Attached Files
File Type: pdf music angel xd 500 mark iii - audio stages.pdf (14.7 KB, 501 views)
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Old 2nd September 2008, 02:35 AM   #7
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The schematic below is the power stages of my amp.

I am planning on reworking this amp from the power stages back. The first thing that will need replacing is the electrolytic. Music Angel (MA) seems to be using second hand components. My PS caps have physical damages(tears in the insulation) and visable rust even though the rest of the amp is clean.

I have parts on order and will recap the PS with Panasonic TS-ED, change out all diodes to FREDs, and convert to DC filament supply. In a few cases they have the heater wires parallel with the the grid bias and negative feedback wires. I assume this is the source of most of the hum.

The parts will arrive in a week or two and I will let you know how the PS upgrades go. (i am upgrading one channel at a time.)

Erik
Attached Files
File Type: pdf music angel xd 500 mark iii - ps stages.pdf (17.9 KB, 289 views)
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Old 20th July 2009, 07:27 PM   #8
JackM11 is offline JackM11  United States
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Thanks everyone for sharing the schematic and information. My EL34 is the same as Kippy's. After a bias adjustment, I set the bias to be about 40ma. The resistor is 22 ohm(one for each El34 tube) so the reading is about 0.88V across it. I guess I have one weak tube as the voltage was 0.67v before but the bias adjustment took care of it. The amp sounds pretty good.
I noticed that the version posted by Erick is very different. Some resistors values are in hundred ohms instead of thousands ohms.
I noticed that the ground pin on the power receptacle is not wired. Should I wire it to the chassis? Can I get better performance if I remove the 6E2 magic eye tubes? I am new to this so any suggestions would be appreciated.
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Old 25th November 2009, 03:49 AM   #9
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Default Change tubes

Hi just wondering if i could change the tubes in this Music Angel XDSE EL34 to any other kind eg. KT77 or 6L6 or any other descent tubes
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Old 10th January 2011, 05:37 PM   #10
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I've been thinking of buying a Music Angel XD 500 MKIII Amplifier.
It will cost me around 700-750$. It is two years old, not used the last year. Tubes have been running 150-200 hours and one of the tubes at the back is pulsating a little slower than the others. What does that mean?
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