Project: Pioneer SA-900

[Super Noob]

Picked up an older Pioneer AMP. It is an SA-900 with cap coupled outputs. Works but needs some love on push buttons switches (sticking) - I have them working albeit not ideal yet. The plastic housing was broke and they wouldn't latch. Working - but anyways, I just wanted to know if any of you were rebuilding one of these, what might you change or alter on my rebuild list? Like increasing some of the values - specifically power supply main filters and main speaker coupling caps?

Thanks in advance for your thoughts.

 

[RobinTW]

It makes sense to replace all the electrolytic caps due to aging, but I don't know why you also want to replace some diodes and transistors. Are they also bad? I would keep them if they don't show any sign of aging. They should have very long service life.

For power supply board D1~D4, if I am to replace them, I would go even higher amp rating diodes. Then I can use a big main filter cap. Your planned 3300uf looks very small to me. It's a 50W+50W amp. Sansui AU-777 is a 25W+25W also cap coupled amp and it uses 4000uf. I would use at least 6800uf.

 

[Super Noob]

Robin Thanks For Your Comments and Looking at the PDF.

The diodes are 2 amp variant (fast recovery).... compared to 1 amp in there now. I use to retain the diodes on my 10-15 rebuilt units, but I started changing these these (they are cheap). Many of the diode / transistors that have tarnished legs in the older units, and I look to replacee. I typical replace as many small transistors as possible (T0-92 style) on the recommendation of others before, and they do improve the sonics. KSC1845 / KSA992 are very good and cheap to replace when you buy them 100 at a time. Keep main outputs unless they are mismatched. Guess I have done both many times.

I typical increase main filter caps (on non-cap coupled) by about 20-40%.... and various coupling caps where others have documented rebuilds.

I will jump up the filters some more based on your recommendation. 2200 to 6800 and 470 to 1000.

Thanks again.

 

[gslikker]

I refreshed my SA900 http://members.quicknet.nl/gerard.slikker/pioneer-sa900.htm

I have no list since it was more a tinkering thing, whether or not according AK consensus approved component replacement practices but it ended up as a very nice amp.

Interesting was Pioneer did put in wrong caps in the control amp, they suffered overvoltage.

 

[Super Noob]

I saw that rebuild... a bid more exotic than I typical do. Looked really nice. Good work.

 

[RobinTW]

@gslikker

Strange. You seem to replace these two potentiometers with regular resistors. Why?
Then how do you adjust center voltage? BTW, how do you set the DC bias?

 

[gslikker]

@gslikker

Strange. You seem to replace these two potentiometers with regular resistors. Why?
Then how do you adjust center voltage? BTW, how do you set the DC bias?

View attachment 1509583

I forgot. According the comment above picture I found the 50k pots at end of range already and those resistors are 51k. As you can see on the big bottom side picture of almost finalized amp there are the 100k pots now on the solder side of the circuit card. I probably could not reach wanted voltage keeping things original.
Bias pots settings I just measure voltage over one of the big emitter resistors each channel to determine current.

 

[liemjerry]

how the sound like after you've finished your restoration?

 

[Super Noob]

It sounds really nice.... been listening for a few days. I will post the rebuild details in the next day or so.

 

[Super Noob]

Here is my rebuild sheet that I used for the most part = hope it helps someone out in the future.

https://drive.google.com/open?id=1GyxYcSayrvvLZ9Z3apswVuyfZ3iZFNHy

The posts will follow on the board rebuilds and the process.... thanks for viewing.

 

[Super Noob]

Power Supply Board (W16-017)
C3 - Original 100uF 50v / Now 100uF 63v (UPW 105 degree)
C5 - Original 220uF 25v / Now 220uF 35v (UPW 105 degree)
D1 - D4 – Original SR1DM-8 / MUR220RLG (On-Semi 2A Fast Recovery)
D5 – 1S338Q Zener / BZX85C13 (OnSemi 13v 1A)
Q3 - Original 2SC905 / Now KSD1616AGTA (On-Semi)

Managed to miss the Zener on my Mouser order.

 

[Super Noob]

Main Amp Board (W23-010)
C1 - Original 100uF 25v / Now 100uF 35v (UKL1V101MPDANA)
C2 - Original 100uF 25v / Now 100uF 35v (UKL1V101MPDANA)
C3 - Original 10uF 10v / Now 10uF 25v (UKL1E100MDDANA)
C4 - Original 10uF 10v / Now 10uF 25v (UKL1E100MDDANA)
C5 - Original 22uF 25v / Now 22uF 35v (UKL1V100NDDANA)
C6 - Original 22uF 25v / Now 22uF 35v (UKL1V100NDDANA)
C7 - Original 47uF 3v / Now 47uF 25v (UKL1E470KED)
C8 - Original 47uF 3v / Now 47uF 25v (UKL1E470KED)
C11 - Original 100uF 3v / Now 100uF 25v (UKL1E101MPDANA)
C12 - Original 100uF 3v / Now 100uF 25v (UKL1E101MPDANA)
C13 - Original 100uF 50v / Now 100uF 63v (UPW1J101MPD)
C14 - Original 100uF 50v / Now 100uF 63v (UPW1J101MPD)

Q1 - Original 2SC870 / Now KSC1845FTA
Q2 - Original 2SC870 / Now KSC1845FTA

VR1 – 50K Ohm / Now 3386H-1-503LF (Bourns)
VR2 – 50K Ohm / Now 3386H-1-503LF (Bourns)
VR3 – 50 Ohm / Now (Bourns)
VR4 – 50 Ohm / Now (Bourns)

Managed to order VR3-VR4 as 50K... but had some spares in stock (mounted them on the bottom of the board due to configuration of the VR - turned out fine as they are easy to access at the bottom).

VR1-V2 as indicated earlier by others - the pots need more resistance. I put a 30K resistor in series.

Cap coupled amp so the common collectors on the output transistors were set to 50% of rail voltage. Bias was dialed up to 10mV (for 20ma) measured across one emitter resistor in each channel.

 

[Super Noob]

Filter Caps for Power Supply & Output Caps
C35 - Original 2200uF 50v / Now 2200uF 50v (LKG1H222MESABK)
C36 - Original 2200uF 50v / Now 2200uF 50v (LKG1H222MESABK)
C37 - Original 470uF 100v / Now 1000uF 100v (EKMH101N102MQ30S)
C38 - Original 2200uF 100v / Now 6800uf 100v (ESMH101VSN682MA50T)

I removed the tabs off the old caps, mechanically secured them to the snap in tabs, and soldered in.

 

[Super Noob]

Filter Unit (W15-059)
C1 - Original 1uF 25v / Now 1uF 63v (WIMA – MKS2C041001FJC00)
C2 - Original 1uF 25v / Now 1uF 63v (WIMA – MKS2C041001FJC00)
C3 - Original 3.3uF 50v / Now 3.3uF 63v (WIMA – MKS2C043301K00KSSD)
C4 - Original 3.3uF 50v / Now 3.3uF 63v (WIMA – MKS2C043301K00KSSD)
C9 - Original 3.3uF 50v / Now 3.3uF 63v (WIMA – MKS2C043301K00KSSD)
C10 - Original 3.3uF 50v / Now 3.3uF 63v (WIMA – MKS2C043301K00KSSD)
C15 - Original 1uF 25v / Now 1uF 63v (WIMA – MKS2C041001FJC00)
C16- Original 1uF 25v / Now 1uF 63v (WIMA – MKS2C041001FJC00)
C17 - Original 3.3uF 50v / Now 3.3uF 63v (WIMA – MKS2C043301K00KSSD)
C18 - Original 3.3uF 50v / Now 3.3uF 63v (WIMA – MKS2C043301K00KSSD)
C19 - Original 100uF 35v / Now 100uF 50v (UPW1H101MPD)

Q1 - Original 2SC871 / Now KSC1845FTA
Q2 - Original 2SC871 / Now KSC1845FTA
Q3 - Original 2SC871 / Now KSC1845FTA
Q4 - Original 2SC871 / Now KSC1845FTA
Q5 - Original 2SC871 / Now KSC1845FTA
Q6 - Original 2SC871 / Now KSC1845FTA

 

[Super Noob]

Control Amp (W15-050)
C1 - Original .1 uF 25v / Now .1 uF 63v (WIMA - MKP2C031001F00JSSD)
C2 - Original .1 uF 25v / Now .1 uF 63v (WIMA - MKP2C031001F00JSSD)
C3 - Original 30uF 6v / Now 33uF 25v (UKL1E330MED1TD)
C4 - Original 30uF 6v / Now 33uF 25v (UKL1E330MED1TD)
C5 - Original 39pF 50v / Now 39pF 100v (C0G - FG18C0G2A390JNT6)
C6 - Original 39pF 50v / Now 39pF 100v (C0G - FG18C0G2A390JNT6)
C7 - Original 30uF 6v / Now 33uF 25v (UKL1E330MED1TD)
C8 - Original 30uF 6v / Now 33uF 25v (UKL1E330MED1TD)
C9 - Original 470pF 50v / Now 470pF 100v (C0G - FG18C0G2A471JNT00)
C10 - Original 470pF 50v / Now 470pF 100v (C0G - FG18C0G2A471JNT00)
C11 - Original 10uF 25v / Now 10uF 35v (UKL1V100NDDANA)
C12 - Original 10uF 25v / Now 10uF 35v (UKL1V100NDDANA)
C13 - Original 10uF 25v / Now 10uF 35v (UKL1V100NDDANA)
C14 - Original 10uF 25v / Now 10uF 35v (UKL1V100NDDANA)
C15 - Original 50uF 25v / Now 47uF 35v (UKL1V470KPDANA)

Q3 - Original 2SC945 (not 2SC369 or 2SC458LG-C)/ Now KSC1845FTA
Q4 - Original 2SC945 (not 2SC369 or 2SC458LG-C) / Now KSC1845FTA
Q5 - Original 2SC945 (not 2SC369 or 2SC458LG-C) / Now KSC1845FTA
Q6 - Original 2SC945 (not 2SC369 or 2SC458LG-C) / Now KSC1845FTA

All KSC1845FTA were HFE matched and installed in parts on all boards.

 

[Super Noob]

Head Amp (W15-056)
C1 - Original 2.2 uF 50v / Now 2.2 uF 63v (WIMA – MKS2C042201K00JC00)
C2 - Original 2.2 uF 50v / Now 2.2 uF 63v (WIMA – MKS2C042201K00JC00)
C3 - Original 10uF 10v / Now 10uF 25v (UKL1E100MDDANA)
C4 - Original 10uF 10v / Now 10uF 25v (UKL1E100MDDANA)
C5 - Original 10uF 25v / Now 10uF 35v (UKL1V100NDDANA)
C6 - Original 10uF 25v / Now 10uF 35v (UKL1V100NDDANA)
C17 - Original 220uF 25v / Now 220uF 35v (EEU-FM1V221L)

Q1 - Original 2SC871 / Now KSC1845FTA
Q2 - Original 2SC871 / Now KSC1845FTA
Q3 - Original 2SC871 / Now KSC1845FTA
Q4 - Original 2SC871 / Now KSC1845FTA
Q5 - Original 2SC871 / Now KSC1845FTA
Q6 - Original 2SC871 / Now KSC1845FTA

 

[Super Noob]

MC Amp (W15-058)
C1 - Original 100uF 3v / Now 100uF 25v (UKL1E101MPDANA)
C2 - Original 100uF 3v / Now 100uF 25v (UKL1E101MPDANA)
C5 - Original 100uF 3v / Now 100uF 25v (UKL1E101MPDANA)
C6 - Original 100uF 3v / Now 100uF 25v (UKL1E101MPDANA)
C9 - Original 330uF 16v / Now 330 25v (EEU-FM1E331L)
C10 - Original 330uF 16v / Now 330 25v (EEU-FM1E331L)
C11 - Original .47uF 50v / Now .47uF 100v (WIMA –MKS2D034701E00JI00)
C12 - Original .47uF 50v / Now .47uF 100v (WIMA –MKS2D034701E00JI00)

Q1 - Original 2SC871 / Now KSC1845FTA
Q2 - Original 2SC871 / Now KSC1845FTA

 

[Super Noob]

Here are some completed pics:

 

[Super Noob]

I will replace one set of the proprietary speaker connectors tomorrow.

Here she is on the Pioneer stack...

 

[gslikker]

You will end up with a complete rebuild guidance document