Author Topic: QSXM2 - news and question  (Read 136 times)

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Offline fantast

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QSXM2 - news and question
« on: October 26, 2020, 08:01:49 PM »
Hi PA,

still so happy with my MM phonopre.
My news is, that I made it a symmetric output, using the FUNK SSOM-03b.V2 modul.
It works perfect with your pre, can be directly attached and I can really recommend it (i.p. if the remaing part of the system is symmetric ..)

On the other hand I am still building a solely MC version of the QSXM2 with MAT02/03. I would like to use two pairs of MAT02/03.
Just now, I have only one pair connected with the emitter resistor R17/R16. (3.6k each).

If I would like to use two pairs, I will double the emitter resistor values (7.2k for R16/R17/R18/R19) but I will need to increse current through the transistors as well.

In "circuit descripion" you gave the advice to decrease R31 & R25 (R26 & R24) apropriately and to increase C7 (C8).

In "basis layout" the current is about 0.75mA. I think 1.5mA per MAT02/03 could be could? That would mean I will try to increase the current by a factor of 4 to drive two pairs of MAT02/03, having 1.5mA per MAT.

Is that linear? - Meaning - should I reduce R31&R25 by 4 and increase C7 by 4? Reducing the resistors by 4 should give 4 times more current? R*C (R31*C7) will remain equal.

Will it work - or do I need to tweek some other areas of the amp as well to make it work?

Kind regards,
Claus
 

Offline peranders

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Re: QSXM2 - news and question
« Reply #1 on: November 01, 2020, 01:21:40 PM »
The easy way to replace the BC5xx transistors is to have the same total current and also the same voltage drop across the emitter transistors.If you want to change the DC currents then you should keep DC levels the same and correct any compensation capacities values, C7 for instanse.

Notice that one pair of MAT's will create a very good S/N ratio even for MC cartridges and added a pair lower the noice 3 dB which you probably won't hear.
/Per-Anders Sjöström, owner of this forum

Homepage with my DIY hifi stuff

Offline fantast

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Re: QSXM2 - news and question
« Reply #2 on: November 08, 2020, 11:40:35 AM »
Hi,

I have tried with one pair of MAT's - and you are perfectly right. It is already very good and pleasent. No need to activate the second pair...
Much impoved S/N than my MM with the BCCs..
I feel, it will also work with LI MCs in the range of 0.2mV.

Best regards,
Claus