Sjöström Audio DIY forum

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.

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

Sorry for the late response. Do you get a stable output voltage now?

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 :)

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..?

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.

AC input is ~21.4V.
Load is ~3-400ma per side.

How high is your input AC voltage? How much do you load with? Current?

Lm317 has 24.5V at input and Lm337 has only 17.9V..

The AC voltage should be a few uV but this must be measured with special equipment. Check first the incoming voltage. It should be at least 4 volt more than the output voltage, in your case 19 volts. Measure at the input of the LM317/337.