Does anybody know what the output transistor temperature is in a stock 252?
Just curious.
Just curious.
small transportable Stax amplifier Modification thread
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the calculation:
(2.5v-0.6v)/1200r=0.00158A
the 0.6v is the Vbe
but the actual Vbe is a little higher than 0.6v.....voltage measured across R23/24 is actually 1.80~1.82v,
1.8v/1.2k=1.5mA
I don't think r25 needs to be changed in this case.
(2.5v-0.6v)/1200r=0.00158A
the 0.6v is the Vbe
but the actual Vbe is a little higher than 0.6v.....voltage measured across R23/24 is actually 1.80~1.82v,
1.8v/1.2k=1.5mA
I don't think r25 needs to be changed in this case.
Does anybody know when (serial range) did 252s switch to the new boards? ( with non-insulated output transistors)
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google images show blue pcb with insulated TO-220 (same transistor arrangement as in 212), and green pcb with non-insulated TO-220 (arranged differently). I suppose the green one is the newest? when did they start using that?
blue pcb:
https://elchika.com/article/89649eab-0f98-44b8-b201-d21da4bdb419/
green pcb:
https://www.reddit.com/r/EarSpeakers/comments/5nkble/stax_srm252s_amp_in_the_srs3100_package/
blue pcb:
https://elchika.com/article/89649eab-0f98-44b8-b201-d21da4bdb419/
green pcb:
https://www.reddit.com/r/EarSpeakers/comments/5nkble/stax_srm252s_amp_in_the_srs3100_package/
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main components in green PCB srm-252s, serial # D2S-103xx, was part of a srs-3100 set.
PCB markings:
" PB-201
08451-20010 "
power supply section:
IC31 SG3524
Q31/32: K975 (Id=1.5A)
(212 uses K940, Id=0.8A; blue PCB 252 supposedly have K2961, Id=2A)
amp section:
Q9/10/11/12: A992
Q13/14/15/16: A1156
Q17/18/19/20: C2752
Q21/22/23/24/25/26/27/28: C5502
C5502 is said (per Spritzer) to be not as good as the old C5466 (output capacitance spec: 60pf for KSC5502; 2.2pf for C5466).
Maybe I should have bought a 252A instead...
power draw, using a regulated 12v supply (7812): --> 0.37A @ 11.9v
output transistor temp, measured at Q27 metal tab; with enclosure fully closed and screws installed, ran over-night: --> 68C (room temp 18c)
PCB markings:
" PB-201
08451-20010 "
power supply section:
IC31 SG3524
Q31/32: K975 (Id=1.5A)
(212 uses K940, Id=0.8A; blue PCB 252 supposedly have K2961, Id=2A)
amp section:
Q9/10/11/12: A992
Q13/14/15/16: A1156
Q17/18/19/20: C2752
Q21/22/23/24/25/26/27/28: C5502
C5502 is said (per Spritzer) to be not as good as the old C5466 (output capacitance spec: 60pf for KSC5502; 2.2pf for C5466).
Maybe I should have bought a 252A instead...
power draw, using a regulated 12v supply (7812): --> 0.37A @ 11.9v
output transistor temp, measured at Q27 metal tab; with enclosure fully closed and screws installed, ran over-night: --> 68C (room temp 18c)
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what serial # range?
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some serial #'s found on the web:
D2S-323x, 252a, assume blue PCB
D2S-503x, 252s, not sure which board
D2S-705(?), 252s, blue (can not tell if serial was 3 or 4 digit)
D2S-797x, 252s, green
D2S-090xx, 252s, green
D2S-103xx, 252s, green
D2S-323x, 252a, assume blue PCB
D2S-503x, 252s, not sure which board
D2S-705(?), 252s, blue (can not tell if serial was 3 or 4 digit)
D2S-797x, 252s, green
D2S-090xx, 252s, green
D2S-103xx, 252s, green
timb5881
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Nice thread
timb5881
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I found a battery (USBx2, 110 AC, 12v DC outputs), and with the correct cable it works. I just got it so I am charging overnight. I will let everyone know how long it can power the STM 212 out of the 12 volt DC out.
ludoo
1000+ Head-Fier
Reviving this thread as I just finished working on a green board SRM-Xh to replace caps, and enable the normal bias output by populating two missing components on the board. I replaced the pro bias socket with a normal bias one from an SRD-6 (I have too many of those) which is a perfect fit.
I still plan to replace or bypass the volume pot, but listening impressions so far are not bad: soundstage is much smaller than my SRM-313 but that's the main difference in sound on a quick listen. This amp will also be very easy to power from a USB PD power bank with a USB PD 12V cable.
This is the board with the missing capacitor and resistor that need to be filled in for normal bias, and the LO hole for the normal bias wire to the socket
What I used for cap replacement
- for the 6 22uf 250V I used 33uF 250V (DigiKey pn 493-16294-ND)
- for the 1uf 50V I used 2.2UF 50V (DigiKey pn 493-15488-ND)
- I left the 33uf 16V capacitor alone as it's tiny and very close to other components
- to enable normal bias I added a 2.2M 1/2W resistor, and a generic non polarized 0.1uf 630V capacitor
I would not mind adding a switch to flip from normal to pro bias, but am having trouble finding one with the right specs. Any suggestions appreciated.
Here is a pic of the patient undergoing operation
I still plan to replace or bypass the volume pot, but listening impressions so far are not bad: soundstage is much smaller than my SRM-313 but that's the main difference in sound on a quick listen. This amp will also be very easy to power from a USB PD power bank with a USB PD 12V cable.
This is the board with the missing capacitor and resistor that need to be filled in for normal bias, and the LO hole for the normal bias wire to the socket
What I used for cap replacement
- for the 6 22uf 250V I used 33uF 250V (DigiKey pn 493-16294-ND)
- for the 1uf 50V I used 2.2UF 50V (DigiKey pn 493-15488-ND)
- I left the 33uf 16V capacitor alone as it's tiny and very close to other components
- to enable normal bias I added a 2.2M 1/2W resistor, and a generic non polarized 0.1uf 630V capacitor
I would not mind adding a switch to flip from normal to pro bias, but am having trouble finding one with the right specs. Any suggestions appreciated.
Here is a pic of the patient undergoing operation
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