Spectral DMA180 - multiple issues

[NoSoundAtAll]

Hello all,
I have bought second hand DMA180 series 1 amplifier. Nice piece of equipment. Sound is really nice, even with issues listed bellow!

So issues,it is working and producing sound, however there are several isues i need to fix, and looking for advice of anybody who was servicing the unit:

• Both sides of amplifier are looking as beeing made in different time. On one side, for example, has main capacitors on one side 10000uF and second side 6800uF, etc. Both sides looks like factory originals.
  
• Left channel - DC offset on output terminal is drifting from -30mV to +50mV. I would expect it to be more stable around 0mV.
  
• Left channel - THD is around 0,7% - 2%, which is way out of spec. Any idea where to start looking for? Noisy small transistors?
  
• Right channel - THD is within spec, but there is DC offset of 600mV.
  
• There are 6 trim pots on each board, but seems it is just 6x transistor bias pot. There are also 2 additional trim pots...hopefully DC offset trim pot. Wil try later.
• There are some thermaly glued transistors with copper foil arround. Anybody know, what transistor types they are?
  
• There are some semiconductors, which i cannot find anywhere on internet according to their ID. Seems to be transistors in metal case. See the picture, 4x close in the middle. If anybody know, what type of semiconductor it is, please let me know. And again, they have different number on one Left channel and different on right channel SIVN 0116N2 and SIVN 1316N2. Seems like backward written 2N6110 and 2N6131 in metal case. But kind a strange

Thank you for any advice. Will keep you posted on my progress, seems to be a lot of work with restoration...

 

[Lavane]

I'm seeing more than just a cap value difference. Resistors, resistor count between the two boards are different between them. There is a film cap missing on the left side in the picture, different IC chips, an extra chip on one board, film caps on one board where there isn't any place to mount them on the other, red LED's on one board, green on the other.
Left side has "series 1" printed on it, the other doesn't.
Maybe someone put a series 2 board on one side as a replacement?

 

[Ds2000]

Hello all,
I have bought second hand DMA180 series 1 amplifier. Nice piece of equipment. Sound is really nice, even with issues listed bellow!

So issues,it is working and producing sound, however there are several isues i need to fix, and looking for advice of anybody who was servicing the unit:

• Both sides of amplifier are looking as beeing made in different time. On one side, for example, has main capacitors on one side 10000uF and second side 6800uF, etc. Both sides looks like factory originals.
  
• Left channel - DC offset on output terminal is drifting from -30mV to +50mV. I would expect it to be more stable around 0mV.
  
• Left channel - THD is around 0,7% - 2%, which is way out of spec. Any idea where to start looking for? Noisy small transistors?
  
• Right channel - THD is within spec, but there is DC offset of 600mV.
  
• There are 6 trim pots on each board, but seems it is just 6x transistor bias pot. No DC offset trim pot. So im expecting to deal with DC, there are some mismatch transistors on board somewhere... Maybe the thermally coupled once? Seems they are glued together and put copper foil arround. Anybody know, what transistor types they are?
  
• There are some semiconductors, which i cannot find anywhere on internet according to their ID. Seems to be transistors in metal case. See the picture, 4x close in the middle. If anybody know, what type of semiconductor it is, please let me know. And again, they have different number on one Left channel and different on right channel SIVN 0116N2 and SIVN 1316N2. Seems like backward written 2N6110 and 2N6131 in metal case. But kind a strange

Thank you for any advice. Will keep you posted on my progress, seems to be a lot of work with restoration...

There are quite a few differences between the boards. And Spectral does not give up their IP, i.e. service manuals.
This will be a tough one, I wish you the best of luck.

 

[NoSoundAtAll]

I'm seeing more than just a cap value difference. Resistors, resistor count between the two boards are different between them. There is a film cap missing on the left side in the picture, different IC chips, an extra chip on one board, film caps on one board where there isn't any place to mount them on the other, red LED's on one board, green on the other.
Left side has "series 1" printed on it, the other doesn't.
Maybe someone put a series 2 board on one side as a replacement?

I didnt want to write down all differences, but there are definitelly some
Both of them are Series 1 and PCB are similar. You need to rotate one board 180 degree, then they match. And both look like factory originals. So one side is just other revision.

One curiousity of design, and why some ICs are different. On one side are EN2016CN (NPN transistor array) ICs and 2N6131 and on second channel are EP2015CN (PNP transistor array) and 2N6110. So one channel driver stage is based on NPN transistors and second channel on PNP transistors.

It seems, ouput power stage is standard Push Pull design, but driver stage can be complementary symmetry circuit on one channel fully from PNP and on second channel fully from NPN. Never heard of such design with any other amplifier. Will try to dig deeper to circuitry later. This is just quick first observation.

 

[NoSoundAtAll]

Im also curious, there are on each board red and green led diode. Red glows, but green do not light at all on both boards same.

 

[Edmund Chan]

Hi ,there are 6 pots on each PCB, and soldering points next to each pot. I checked with DC voltmeter, measurement is around 0.5-0.6 V and -2V on the pots. Is it noraml or what is the correct voltage on each measuring points? Any idea? Thanks you!