Thorens restec V1 preamplifier - diyAudio
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Old 8th March 2011, 09:11 AM   #1
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Default Thorens restec V1 preamplifier

Hello
My Frend have one and dont have a trafo or power supply.
Someone maybe know that what is the voltage for power preamplifier.
Preamplifier have 4 contact for power suplly, and i dont have circuit diagram or rectifier because i dont know what is the voltage.
please help

thanks
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Old 8th March 2011, 02:10 PM   #2
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Hello again
I open the Case of preamp and found 2 regulator 7815 and 7915, i think that trafo 12V-0-12V be enough to drive preamplifier
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Old 9th March 2011, 05:08 AM   #3
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You will have to use 2 x 15VAC transformer with split secondaries = 4 wires (not the one with center taped - 3 wires) if the preamp uses 2 diode bridges for convetring AC to DC. Math...15VAC x 1.41 = 21,15VDC....21,15VDC - 2 x diode voltage drop (depends on current draw and type of diodes used in diode bridges) = ~19,65VDC so you will have ~4,65VDC difference from input to output of LM7815/7915 as they need Vdrop=2VDC min. for proper operation.
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Old 9th March 2011, 02:24 PM   #4
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Thanks but
Preamp on the back side have 3 wires ( one wires to 1 leg of 7815 , another leg to 7915 and 3 leg for the central ground ) for power supply and dont have any rectifier inside
in orginal power supply ( another box that my frend dont have ) have rectifier and trafo and nothing else
i build power supply whit trafo 9,7-0-9,7 AC for test only and preamp work but dont have sound because relay on the output is 24V ( 2 pieces ) and on the output opamp ( ne5534 ) leg 7 voltage is 1V
relay is not working because voltage is to small
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Old 9th March 2011, 04:51 PM   #5
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You could make voltage doubler circuit and use the transformer you already have if VA rating is sufficient. Also, you will have to watch a dissipation over LM7815/7915 since in case of voltage doubler circuit, output voltage will be 2 x (9V7 x 1,41) - voltage drop over diode bridge = ~ 26VDC. Furthermore, you could use RCRCRC filtering after voltage doubler circuit to drop some volts before LM7815/7915 in order to lessen dissipation.
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Old 10th March 2011, 12:11 PM   #6
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thanks
by lm7815 and 7915 is elko 1000uF/25V and i dont whant to change this parts :-)
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Old 10th March 2011, 12:41 PM   #7
GoranB is offline GoranB  Poland
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You will need a trafo 15-0-15 if You want 7815 and 7915 to work as they should. For the relays as u said they are 24V. I think You should follow the power supply input pins where they lead. According me You will need another voltage for relays, separated from those for 7815 and 7915.
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Old 10th March 2011, 12:47 PM   #8
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Quote:
Originally Posted by vksamael View Post
thanks
by lm7815 and 7915 is elko 1000uF/25V and i dont whant to change this parts :-)
OK, then measure current draw from LM7815/7915 (probably few tens on mA, say 50mA). Now, since you will have ~26VDC after voltage doubler, and you want, >/=18VDC in front of LM7815/7915, just stick a resistors of (26-18)/50mA = 160R or so in series between voltage doublers and LMs. Now, you will have RC filter with your treasured vintage capacitors, and less dissipation over LM's.
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Old 10th March 2011, 01:07 PM   #9
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thanks aparatusonitus i think that will be just fine

GoranB i dont need another supply because connector for power supply have 3 wires and original power supply have only 3 wires for power ( unfortunately my frend dont have orginal power supply)

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