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Per-Anders Sjöström

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Phono RIAA amplifiers / Re: QSXM2 problem
Last post by zayance - December 31, 2020, 10:56:08 AM
Hi Per,

As you know i left this one aside for some weird probs concerning the build for years;
I'm taking my time and try to give it another chance.
I've desoldered everything on one channel, and kept preamp stuffed on LEFT Channel, stuffed with BC550/560 transistors (the circuit that wasn't quit working right).
The Right Channel is stuffed with SMD BS850/860 and all BC847/857BS.
This for giving me a comparison, because i suspected that my batch of BC550/560 might be causing some problems, so tought of comparing with smd ones, might be stupid, might be a good idea, will see.....
Anyway, still didn't powered and started the test according to your build, and didn't stuff the RIAA, going step by step for now.

I just wanted to clarify some infos on the build, because circuit description on your website and the infos provided on the Schematic confuses me a little, if you can just confirm these:

From Circuit description on your website:
R1 + R97 are the values that should match the MM pickup
R3 + R97 are the values for matching  MC Pickup

Info On Schematic:
R2 Resistor for MM pickup ?  (circuit description gives this one in addition to C2? as EMI filtering)
C1 for MM
C52?  typo prob on the Schematic?. for MC

Thanks for your help and clarifications...

Will ask questions or update on the old forum thread if this comes to an end haha.


Phono RIAA amplifiers / Re: QSXM2 - news and question
Last post by fantast - November 08, 2020, 11:40:35 AM

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,
Phono RIAA amplifiers / Re: QSXM2 - news and question
Last post by peranders - 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.
Phono RIAA amplifiers / QSXM2 - news and question
Last post by fantast - 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,
Power supplies / Re: SSR03 (AD825, LM431, +-15V...
Last post by peranders - March 31, 2020, 07:01:07 PM
Sorry for the late response. Do you get a stable output voltage now?
Power supplies / Re: SSR03 (AD825, LM431, +-15V...
Last post by minionas - March 14, 2020, 02:06:52 PM
Ive installed R9 and R10 1 ohm resistors. Had some fun with one new resistor so had to open the schematic and look for problems why one LED does not emitt light on second power on while it did lit on first power on. And finally found one of new 1 ohms resistor faulty. Changed it again and now both LEDs are lit brightly.

Ignore my dumb measurement as i was not aware that pins of LM317 and 337 are alocated differently, therefore input is the same for both of them - ~25V.

Also ignore my dumb question/statement that i get different voltage after rectifier bridge, as it is the same for both sides as after inspecting schematics now i know where to measure :)

Power supplies / Re: SSR03 (AD825, LM431, +-15V...
Last post by minionas - March 13, 2020, 07:14:58 AM
I'll try that on the weekend.

Why do you think im getting 24+V on the positive side of the power supply while 17,9V on negative side after rectification..?
Power supplies / Re: SSR03 (AD825, LM431, +-15V...
Last post by peranders - March 13, 2020, 06:29:46 AM
I suggest that you reduce the R9 and R10 to 1 ohm. You could also place a wire jumper there. Both LED's should lit also. That is a sigh that you will get a proper regulation.
Power supplies / Re: SSR03 (AD825, LM431, +-15V...
Last post by minionas - March 12, 2020, 09:33:58 PM
AC input is ~21.4V.
Load is ~3-400ma per side.
Power supplies / Re: SSR03 (AD825, LM431, +-15V...
Last post by peranders - March 12, 2020, 09:30:21 PM
How high is your input AC voltage? How much do you load with? Current?