Pass Labs X2 REV1 Relays?


2002-09-12 11:14 am
Kermit said:
It's just a guess, but I think it's this one:
Same as is used in the Ono. I thinks Pass likes to buy big and use the same components in many of his products. Makes sense.

Cloning an X2 are you? Any plans for making pcb's? I'v been planing on upgrading my preamp, and X2 seems to be a good candidate.

Good guess! Thanks. Yes, I'm cloning an X2, and I will try to make as good a replica as possible, down to the pcb layout and component choices. I also feel the X2 to be a good candidate ;)
Nelson Pass said:

That is an SDS number.
Aromat is Panasonic, Panasonic is Matsushita.
SDS now being NAIS, or Matsushita if you prefer.
Matsushita has used licenses from SDS for decades, the S in SDS from the founder and relay designer Mr Sauer in Germany.
Ever go to Japan and you'll discover how big companies as Matsushita and Mitsubishi industries are.

The SDS DS2Y i started using 2 decades ago, it's a joy observing NP knowing the hardware so well.
Cool, thanks.

Now the next question - looking at the amp it seems a lot like
an unbalanced to balanced converter. Unless I'm missing
something it does not have the "supersymmetry" circuit.
Therefore, if one has balanced sources, wouldn't an Aleph P 1.7
be a "better" choice ? What would be the benefit of the X2 over
the P 1.7 ?

Is the X2 not a X?

No problem !

By the way, I have the same question popping up in my head last night, when I looked through the X2 service manual - I dont se the feedback resistor going from drain to gate of the FETs - so basicly, its two bosoz /BLS stages, where the first one is unity gain, and only handles the balanced input, and the second has 10/17 dB gain, and handles amplification and optional conversion from unbal. to bal.
Is it really true that the X2 is not a "X" ??

Conserning advantages of the X2, it may be the high output voltage swing, I seem to recal the distortion curves of the BLS "manual" showing the voltage swings effect on the FET distortion.

Cheers !

I made a X2 Rev1 preamp but I have an issue and need help if someone can help.

This is the PSU schematic (in red my voltages)

This is the input (in red my voltages)

This is the output (in red my voltages)

My problem is that R6 is very very hot (I installed a 10W 1K resistor because a standard resistor burn). And I don't have 60V and 40V on drain of IRF but 84V.
All other voltages seems ok.

I tried with Axicom 2K88 24V relays, and with 2x 3K2 resistors in place of relays.

Could someone confirm that PSU schematic is correct ? (i modified just primary from 120V to 220V E.U. standard, and C1, C2, C3, C4 are 4400µF and not 1000µF)
TH1 is 10 ohms 3A

Thank you


suddenly I have a doubt ! When on Nelson SM is noticed 1004 for a resistor, is the resistor a 1K004 or a 100x10000= 1 Mohms
If 1004 is 100x10000= 1 Mohms in the SM, i found my stupid error and now I know my problem.
In E.U. we use not really the same codification than in U.S. i think, and in this case I must check all resistors because the last number in the code is the multiplication coefficient.

Could someone confirm ?



with correct resistor I have correct voltages now.

But I still have an issue if someone can help.

The relay mute don't work. Relays don't engage. I have no voltage on relays pins.
On this schematic are all voltages from ground [IMGDEAD][/IMGDEAD]

I verified all connexions, and changed by security Q5/Q4 R9/R10 D1/D2 R6/R8

Could someone help me ?


Last edited:

I think that I found the solution. There is a mistake in the SM
On the schematic there is a 60V CT transformer, but it's ok for the 85V, not for the 95V version. For the 95V version we must use a 80V CT and not a 60V CT like it is noticed on the SM
With a 60V CT we have 100V unregulated and it is not enough to have a difference of 8V between regulated and unregulated voltages.
I have 100V for unregulated and 95V regulated, so I must find a transistor which conduct with only 2 or 3 volts difference.

Does somebody has an idea of which transistor I can use in place of IRF9610 ? It could help to solve this issue quick