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Old 28th October 2011, 02:48 PM   #1641
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Soldered resistors in the VSPS last night. I used sockets at R2 and R3 so I can change resistors without desoldering and resoldering. Hope that works OK. Those boards from RJM took a little getting used to since they are thick and gold plated. They heated up a lot slower than the component legs so adjustments to my soldering style was in ordered. Finally got it sorted I think.
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Old 31st October 2011, 03:18 AM   #1642
pfcs49 is offline pfcs49  United States
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I finished my phonoclone tonight.
It works but has major hum turned up.
It sounds pretty good.
With TT disconnected, can turn volume fully up and hear fairly faint white noise and hum, 50/50 (acceptable)
With inputs shorted, has major hum turned up. (same as w/24ohm cart across it)
Surprisingly, when I touch the input pin (no TT connected) it doesn't cause a scare you shitty hum.
The problem is equal for both boards/channels.
When the 2 boards were completed, I checked current draw for +/-, both boards; the positive side drew ~250mA/negative side ~50mA, (both boards).
All 4 power supply opamps get very hot-too hot to keep a finger on them very long. Q1 and Q2 are cool.
I'm using it w/.8mV/24ohm Benz cart and set the gain @~42db to tame it down a little and match my B&O MI levels on 2nd TT, so R1=24ohm/R2=100ohm.
What could I have overlooked/screwed up on both boards to cause this?

Last edited by pfcs49; 31st October 2011 at 03:21 AM.
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Old 31st October 2011, 07:40 AM   #1643
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The power draw for the op amps is in the region of 5 mA each, circuit draw is about 20 mA per channel. 250 mA indicates a serious problem.

Disconnect the cart and move the phonoclone away from any audio equipment, to avoid damaging anything expensive.

Check you have right voltages at all the op amp pins. Should be about 9-12 V.

Both channels doing the same thing suggests a mistake in part placement. No smoke and a basically operating circuit suggests the error is a resistor with the wrong value rather than an improperly connected electrolytic capacitors or transistor. Not sure without more info, however.
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Last edited by rjm; 31st October 2011 at 07:43 AM.
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Old 31st October 2011, 10:29 AM   #1644
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by rjm View Post
The power draw for the op amps is in the region of 5 mA each, circuit draw is about 20 mA per channel. 250 mA indicates a serious problem.
Can you confirm that 5mA is the Power draw, or the quiescent draw when no output current is flowing?

If a 5mA Iq opamp is outputting 10mAac to a load, then the supply rails will pass ~19mApk each, but alternately. Double that output loading to 20mAac (still within the limits of some opamps) then the supply rail current becomes ~32mApk.
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Old 1st November 2011, 04:05 AM   #1645
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That's typical DC current draw with the phonoclone circuit at zero output, but passing 2V rms to a 10k output load (typical operation) is not going to influence this estimate significantly. Anyway although 50 mA might be reasonable for the stereo pair, 250 mA is definitely not.
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Old 1st November 2011, 11:59 AM   #1646
pfcs49 is offline pfcs49  United States
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Q1 and Q2 are reversed. Somehow I assumed all 4 were the same.
They are physically oriented properly but Q1 is in Q2 socket and Q2 is in Q1 socket.
All caps are correct/all resistors.
Should this resolve the issue?
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Old 1st November 2011, 11:16 PM   #1647
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It's hard to predict in advance, but clearly the first step is to fix any mistakes in the parts placement. One or both of the transistors are possibly blown, it is unlikely any other parts were damaged.
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Old 2nd November 2011, 12:14 AM   #1648
pfcs49 is offline pfcs49  United States
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I tested them & all are OK.
Waiting to have some time to clean up the board and re-install them/see if all is OK. Will report then. Thanks.
PS-they weren't the least bit warm but the 2 opamps in the pwr supply were toasty.
Also-before prev post I checked all in & outputs for AC/DC: .000V

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Old 2nd November 2011, 05:32 AM   #1649
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The reason the op amps got toasty is that the emitter-base diodes were reversed, blocking any current flow in the pass transistors. The x-reg op amps were left to provide the circuit current, instead of just the control current. 24 V on the op amp, 20 mA current, that's half a watt and with no heatsink a DIP8 package is going to get too hot to touch... though not hot enough to be damaged, I don't think.
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Old 2nd November 2011, 07:07 PM   #1650
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Default Wire Routing Suggestions

I've got almost everything in place but need some advice as to how to run the ground wires from the boards to the case/turntable ground. Should I twist up a pair and have them split into 2 separate wires at the center of the boards? Should I just run single wires around the case to the ground? Can I just run a jumper from 1 ground lug to the other and then run a single wire to the case? Are the grounding wires prone to pick up hum or am I worrying about nothing? I'm planning on grounding near the input jacks (bottom of the photo) so fewer cables have cross to opposite sides. Thanks in advance.
Dave
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