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Old 18th April 2012, 12:55 AM   #1
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Default Adapting salvaged SS phono stage for use

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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File Type: jpg phono 002.JPG (84.7 KB, 160 views)
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Last edited by devilsindetails; 18th April 2012 at 01:02 AM.
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Old 18th April 2012, 01:18 AM   #2
KBK is offline KBK  Canada
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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.

Last edited by KBK; 18th April 2012 at 01:22 AM.
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Old 18th April 2012, 01:45 AM   #3
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Quote:
Originally Posted by KBK View Post
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?
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Old 18th April 2012, 05:19 AM   #4
Calvin is online now Calvin  Germany
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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 IŽd assume the supply voltage to be rather close to +30V.
But then again....a SM will give reliable answers

jauu
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Old 18th April 2012, 05:46 AM   #5
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To do this properly we need more information. Most importantly, the type numbers of the transistors / fets. Once we have these we can work out the ideal supply voltage from first principles.
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Old 18th April 2012, 05:55 AM   #6
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Quote:
Originally Posted by Calvin View Post
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 IŽd 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.
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Old 18th April 2012, 05:57 AM   #7
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Quote:
Originally Posted by Mark Kelly View Post
To do this properly we need more information. Most importantly, the type numbers of the transistors / fets. Once we have these we can work out the ideal supply voltage from first principles.
I'll check the receiver carcass and jot down some info...thks for responding
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Old 18th April 2012, 05:59 AM   #8
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I meant the ones in the phono module itself. They look like TO92 BJTs to me, if they are we just need to know whether they are PNP or NPN, which we can work out from the type number.
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Old 18th April 2012, 06:05 AM   #9
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Quote:
Originally Posted by Mark Kelly View Post
I meant the ones in the phono module itself. They look like TO92 BJTs to me, if they are we just need to know whether they are PNP or NPN, which we can work out from the type number.
Ok...I see..they are marked C1571 G-E7
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Old 18th April 2012, 06:09 AM   #10
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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.
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