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Old 18th March 2013, 06:55 PM   #71
Champ is offline Champ  Canada
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Originally Posted by Mooly View Post
Best bet I think for those

(for the sake of completeness (but don't feel you have to do this), it would be informative to know what those replaced diodes really did develop in the way of a volt drop. This shows the discrepancy in the marked voltages and the 1.4 volts that two diodes generate)
I would then
1. take a 4.7ohm resistor, attach it to one end of the diode.
2. attach remaining resistor lead to a 9V battery
3. attache VM to diode and then to the other terminal of the 9V battery.
4. Take reading which should be 9V - 1.4V for a total of 7.6V

Have I got that right.
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Old 18th March 2013, 07:32 PM   #72
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4.7K (4700 ohms)

4.7 ohms would draw half an amp if the battery could supply it, and probably zap the diode.

I'll draw it...
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Old 18th March 2013, 07:37 PM   #73
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Old 21st March 2013, 02:14 PM   #74
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Still have to get the 9V battery Mooly.

Run into a bit of trouble. I replaced the tants with 2 small lytics and all is good.
I have now moved into replacing the carbon resistors. After about half of them installed I thought I should test to see if thing are good. I get the old dim bulb tester to be on the safe side and presto a short.

I am using Takman metal film 1/2W resistors. These should be a good match. I have gone over all my solder joints and inspected for pulled wires, checked values and all seems to be good. What do I need to do to fix this?
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Old 21st March 2013, 02:18 PM   #75
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That could be anything.

What resistors have you replaced ? Have you been working on one or both channels ?

I would recheck all your work and check the new resistors are what you think they are value wise and that they are in the correct place in the circuit.
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Old 21st March 2013, 05:27 PM   #76
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OK! Nothing like slowing down and taking a pause. I checked it all and yes R110 and R210
call for a 47k and I had a 47R instead. I put the old ones back in as I have no replacements for them on hand. No wonder Mooly, that's a huge difference. Fired it up and the bulb went dim. I'll get the hang of this sooner or later. 110 and 210 are both out of spec though.
Just hope I haven't messed other things up.
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Old 21st March 2013, 05:55 PM   #77
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Its a good job you used the bulb tester.

R110/210 are part of the constant current source and "pull" current through the diodes you have just replaced. I would be inclined to replace those again after that because you are bound to have exceeded the maximum specified forward current. Nothing else will have suffered fortunately... which is good

When you say R110 and 210 are out of spec, do you mean the new or the old ? I'd be very surprised tbh if the originals had gone high.

Those 47 ohms that took all the current should be checked too.
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Old 28th March 2013, 05:34 PM   #78
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Its a good job you used the bulb tester.

R110/210 are part of the constant current source and "pull" current through the diodes you have just replaced. I would be inclined to replace those again after that because you are bound to have exceeded the maximum specified forward current. Nothing else will have suffered fortunately... which is good

When you say R110 and 210 are out of spec, do you mean the new or the old ? I'd be very surprised tbh if the originals had gone high.

Those 47 ohms that took all the current should be checked too.
I replace all the dubious resistors Mooly.

On another note, I decided to replace the old RCA inputs. There are 2 sets which is nice. While I was at it I replaced the signal wire with some Mogami shielded cable. This goes from the inputs to the source switch. This upgrade alone is probably the second most notable upgrade to the sonics I have done so far. Big difference. This bring me to this question, which maybe for another post, but here goes anyway. The manual says you can go direct with your source into the 2 inputs. There are L and R channel level controls. They don't use the term Passive Preamplifier, but in effect that is what this is if I am not mistaken. I have tried this with both the CDP and phono and am rather impresses with the sound. I have even more gain from the CDP which in effect is very loud indeed (2v out) and considerably more from the phono, which is nice since I was about half volume on my Krell KSP7B pre to get a decent level for listening and much less going direct.

So the question is, is there any way of upgrading the level pots to something higher end. alps ect. Should it be an attenuator or just a better quality pot, which I am having a hard time finding. 150ohm pot.

Last edited by Champ; 28th March 2013 at 05:37 PM.
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Old 28th March 2013, 07:20 PM   #79
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It's a 150K

That's interesting because today we would use much lower values due to preamps and modern source components having much better drive ability.

You can use anything value wise here. I would say 10 to 47K (50K) would be ideal. A real downside of high values is that the pot and circuit capacitance it sees on its wiper form a variable low pass filter (an R/C filter) that can affect the frequency response as the pot is rotated.

If you don't need two inputs then I would bypass the switching and route one of the inputs direct to the volume controls.
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Old 30th March 2013, 10:59 PM   #80
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I am having a hard time finding anything that is a step up from this from a local supplier here in Toronto Alpha Potentiometer
Pretty much what is already in the amp now, but at lower values. I see this Alps but the shaft is far too long, the 100K mono version. Too bad. controls_pot_alps

I would like to keep the two inputs as I am able to run a phono and CDP as well.
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