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Old 14th July 2010, 08:48 PM   #1
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Question Off board MOSFET's & CCS voltage regulator

I have a Szekeres design Class A single MOSFET (IRF513) headphone amp which has a constant current source based around an LM317 voltage regulator. It sounds fantastic, but I want to try and incorporate it into my Gainclone pre amp (passive attenuator), with a selector switch between power amp out and headphone amp. This will allow me to use the attenuator and selector switch of the pre (2 sources) for both the Gainclone and Szekeres amp

It is in a fairly large case at the moment, which allows the MOSFET's and voltage reg's to be mounted on heatsinks on the PCB. My plan is to move it to a smaller case which means I would have to mount the MOSFET's and voltage reg's to the inside of the case.

As long as I insulate the devices and mount the gate resistors (Rg) at the MOSFET terminal, will it be Ok to do this.

Chris.
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Old 14th July 2010, 09:36 PM   #2
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Hello.

Of course it is perfectly alright.
As long as the electrical connections are done properly. Insulation.

One thing is the MOSFET gate resistor, Rg
This should be put close to MOSFET G-pin.
So if you put MOSFET a bit from PCB,
then you let the Rg go with the MOSFET.
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Old 14th July 2010, 10:02 PM   #3
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Thanks Lineup.

Chris.
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Old 15th July 2010, 12:24 AM   #4
lineup is offline lineup  Sweden
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I think also Rref (sets the current)
should be close to the Vo pin of regulator.

Now afterwards I see you mention the gate resistor in your first post.
So, you already were aware of.

Otherwise, keep wires short.
As short as possible, but with some slack to avoid too tense wires.
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Old 16th July 2010, 10:32 PM   #5
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One channel built and tested. Volume a little low (using the analogue output of a DVD player), but the amp doesn't get too warm. The input resistor is 4.7K I used a 100k trim pot for R2 & 220K for R3. Rg is 220R and the CCS is set to 250mA. C2 is 470uF with no bypass cap (although a 1uf will be fitted on final assembly). I am using my passive attenuator (50K dual log/47K shunt) at the input. There is some noise (hum, which increases with volume adjustment), but I think this may be a grounding/shielding issue with the test set up.

It is being tested with 24ohm headphones (16Hz to 22kHz).

Any ideas on increasing the volume?

Chris.
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Old 20th July 2010, 09:33 PM   #6
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Both channels built and tested (bypass caps fitted).

Grounding issue traced to a PCB standoff, with a brass insert shorting one of the stripboard tracks!

It sounds lovely. Clean and detailed, just the way I like it. Can't wait to test it with some decent phones.

It's had 10 hours of running with no issues, which is pleasing. I can now impliment it into my system (LM3875 dual mono gainclone).

Chris.
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Old 21st July 2010, 01:27 AM   #7
lineup is offline lineup  Sweden
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Good!
Szekeres is a nice headphone amp.
Straight forward and no unnecessary hussle.
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