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Old 24th April 2012, 03:43 PM   #1
hesee is offline hesee  Finland
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Default Newbie looking for help, pre-out to tube amp.

I am planning to create pre-out to my tube amp. Unfortunally there wasn't any schematics around (Cayin A-88T) so i had to draw them myself.

Click the image to open in full size.

Amp uses 6SL7 and 6SN7 tubes in preamp and KT88/6550 tubes in poweramp. Allso poweramp sections is most likely push/pull setup.

I was planning to plug pre-out wires to right after volume control pot. Rest of the preamp section appears to be just for push/pull configuration. However that's just my guess, as i am good to soldering according to schematics, but i suck when i have to figure out how electronics work..

Would that be (after the pot in input to preamp stage) be best place for grabbing pre-out signal, or is there better one?
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Old 29th April 2012, 11:01 AM   #2
hesee is offline hesee  Finland
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I did create pre-out, by grabbing signal after volumecontrol, before first condensator. Seems to work just fine.
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Old 29th April 2012, 11:28 AM   #3
nazaroo is offline nazaroo  Canada
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Quote:
Originally Posted by hesee View Post
I did create pre-out, by grabbing signal after volumecontrol, before first condensator. Seems to work just fine.
Make sure you are not directing any DC high voltage out of the amp/preamp and into some other piece of equipment not expecting to have to block High Voltage.

Check for D.C. on the signal out you have created.

Even though the circuit might work for a while,
the voltage rating of the input cap in the other equipment
you want to plug into might only have a low voltage blocking cap in its input circuit.

Eventually the input cap on the other equipment will burn out and damage may ensue.

Its always good to have a cap in series out, with a resistor (or volume pot) across it to ground, to create a stable and high output resistance for the preamp to 'see'.

Then you take the signal out from the other side of the cap (and resistor) or from the wiper of the pot (if you put one in) to the new output jack.

That way, if there is any High Voltage DC where you are tapping it, it won't get into other equipment or hurt anyone.

Use a 600 volt output cap, say .1 uF and a 200k - 500k volume pot or resistor. If you aren't getting enough bass, just put two caps in parallel.
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Old 29th April 2012, 01:20 PM   #4
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Quote:
Originally Posted by hesee View Post
I did create pre-out, by grabbing signal after volumecontrol, before first condensator. Seems to work just fine.
Maybe works, but please realize that you are loading down your source (CD player or DAC), by making it drive two inputs (the input of the power amp and the input of the Cayin). Quite possibly your DAC can easily drive this, but still you need to consider it.
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Old 30th April 2012, 01:54 PM   #5
hesee is offline hesee  Finland
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I did check output for DC with multimeter, no leaks there and CD drives splitted input easily as does the dac. Atleast there's no changes in volume or sound quality with or without pre-out wires.

However i am i still not sure if i am going to keep that setup. It's used to drive subwoofer, but it adds slight humming sound (has allways been there) and i still have some issues in subwoofer integration.
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