Adapting salvaged SS phono stage for use

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I pulled a (Moving Magnet) phono-stage out of a deceased SS Yamaha receiver with the hope of adapting it for use with a little SE tube amp I've restored.

I want to use this an interim measure while I come up with a DIY phono preamp once I gain enough confidence and experience.

But I don't know the required B+ voltage for this board...how do I estimate?

I see that the caps on the board have voltage ratings between 35vdc and 50vdc, but those are simply maximums, correct? And I am assuming that the lowest rated caps would mark the upper limit of DC voltage this circuit could tolerate?

Any ideas of a good starting point for me to try and power up this board? 9vdc. 12vdc.

Also, where would I run the negative lead from my DC power supply?

Thanks. Leon
 

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the b+ line coming in should be connected to the positive terminal of a local buffer capacitor.

Try starting at half that DC value. If it is a 35vdc cap, try 20vdc. something like that.

Best bet, by far, is to go back to the scrapped Yamaha,and figure out the correct voltage from that unit's internals.... or use it's model number, and maybe find the schematic.

the big light blue cap in the corner seems to be the B+ buffer cap. That cap's voltage value should be quite telling.

The output of the board also looks like it wants to see a fairly high impedance, on whatever you feed it into.
 
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the b+ line coming in should be connected to the positive terminal of a local buffer capacitor.

Try starting at half that DC value. If it is a 35vdc cap, try 20vdc. something like that.

Best bet, by far, is to go back to the scrapped Yamaha,and figure out the correct voltage from that unit's internals.... or use it's model number, and maybe find the schematic.

the big light blue cap in the corner seems to be the B+ buffer cap. That cap's voltage value should be quite telling.

The output of the board also looks like it wants to see a fairly high impedance, on whatever you feed it into.

Thanks...That larger (buffer) cap reads 35vdc....so 20vdc should be ok to start?

Just so I know we are looking at and talking about the same thing....the two rca's in the pic are the inputs from the turntable, so when you say that the output of the board looks like it wants to see fairly high impedance, why do you say that?

Also....where would I feed the negative lead from my DC power supply?
 
Hi,

looks pretty much like a single supply stage to me.
+B : positive supply voltage
E: earth/GND/Power supply return
RO: Right channel Out
Lo: Left channel Out
The most reliable information would come from a Service Manual. With a little googling You probabely will even find a manual for free.
other than that You can only assume the siupply voltage to be considerably lower than the 50V-specced Caps (typical voltage classes for caps are ...16, 20, 25, 35, 50, 63, 80, 100V....). As a wild guess I´d assume the supply voltage to be rather close to +30V.
But then again....a SM will give reliable answers

jauu
Calvin
 
Hi,

looks pretty much like a single supply stage to me.
+B : positive supply voltage
E: earth/GND/Power supply return
RO: Right channel Out
Lo: Left channel Out
The most reliable information would come from a Service Manual. With a little googling You probabely will even find a manual for free.
other than that You can only assume the siupply voltage to be considerably lower than the 50V-specced Caps (typical voltage classes for caps are ...16, 20, 25, 35, 50, 63, 80, 100V....). As a wild guess I´d assume the supply voltage to be rather close to +30V.
But then again....a SM will give reliable answers

jauu
Calvin

No service manual available for this very old receiver so I will trace back some wiring on the old receiver carcass and see if I can find out some more information. Thanks for your reply.;)
 
Are you sure that this is the entire phono part?

Using only 2 transistors for a full RIAA-circuit is possible, but untypical due to the many compromises to be made.

Hannes

PS: no need to worry much about the supply voltage; simply use 15-20V and be set. Any average TO-92 transistor takes 100mW power dissipation (rather some more), which means 5mA bias current which is much larger than the typically used values are.
 
Are you sure that this is the entire phono part?

Using only 2 transistors for a full RIAA-circuit is possible, but untypical due to the many compromises to be made.

Hannes

PS: no need to worry much about the supply voltage; simply use 15-20V and be set. Any average TO-92 transistor takes 100mW power dissipation (rather some more), which means 5mA bias current which is much larger than the typically used values are.

Yes that's it. It was taken out of a very ordinary little receiver built in the early 70s....I believe there are a total of four transistors on the board....two per channel...does that sound a little more par for the course?
 
Ok...I see..they are marked C1571 G-E7

In that case I assume they are BC157, a PNP BJT. If so the leg nearest the front edge in phot 1 is the collector, with the opposite leg the emitter.

The ideal supply voltage will be the value at which the collector DC value on the output transistor (the one on the left side of the board in the phot) is half way between the emitter DC value and ground.

I'd start at 12V and go up until you reach this value. If it doesn't occur before 24 V then I'm wrong.
 
Thanks Mark and all....I'll let you know if I am successful.

One question however. ( I know eyes may roll in some quarters) but hey, I'm still learning:guilty:

The LO and RO (hot leads) and the E's earths are destined for R & L input RCAs of my amplifier but where does the negative from my DC power supply go to on this board?....to one of the screws that hold down the board?
 
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Yes, good call, that's much more likely in a Japanese component.

In that case ignore what I said, it's an NPN transistor and the pinout is different.

The principle, however is the same - you want the collector sitting halfway between the emitter and the power supply rail (in the case of NPN it's the positive rail)
 
Finally got around to applying some DCV to this little board. Although my voltage options were limited I managed to get the circuit energized at about 16VDC via an old HO Train Transformer (my dedicated adjustable DC voltage source only goes from 0-10VDC).

While the phono-signal amplification seemed spot on there was a fair amount of hum...however, I noticed that the moment I disconnected either one of the + or - DC leads the hum disappeared and the signal was clean as the circuit de-energized and then collapsed.

I checked the ground on my turntable connection firm, and the continuity connections on my cartridge/headshell are also a-ok, as is the wiring of the arm.

As a test, I disconnected the ground wire from my turntable and noted that this hum was a different frequency than that of noted above. So I am assuming that the intitial hum I heard is a product of the DC power supply?

Any ideas on how I can eliminate this? I connected the negative lead from my DC voltage source to several negative spots on the board with no change in the hum.

Would the use of a 16VDC battery pack help to eliminate this?
 
Your old HO train transformer likely has no output smoothing at all , you would probably get less hum by using a DC Wallwart , but this also falls way short of what you require . You could try adding a pi type smoothing filter network to the output of the "HO"........1000uF in parallel,100ohms in series , then another 1000uF in parallel......then connect to the pcb .

Powering from a battery is going to be the quietest.

PS the HO train transformer may be totally inadequate......it could be 1/2 wave rectified....making it even harder to smooth.
 
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Your old HO train transformer likely has no output smoothing at all , you would probably get less hum by using a DC Wallwart , but this also falls way short of what you require . You could try adding a pi type smoothing filter network to the output of the "HO"........1000uF in parallel,100ohms in series , then another 1000uF in parallel......then connect to the pcb .

Powering from a battery is going to be the quietest.

PS the HO train transformer may be totally inadequate......it could be 1/2 wave rectified....making it even harder to smooth.

Thanks for answering epi...will give it a go...you've confirmed a few of my hunches but wanted to see if I was on the right track.
 
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