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Old 1st December 2009, 06:58 PM   #621
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I happen to have it in my HD, so here it is again not to be searching around.
Update required ?
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Old 1st December 2009, 08:54 PM   #622
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Just curious as to how the dcb1 compares to the Burson buffer?

Anyone care to comment?

Burson AB-160 Audio Buffer
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Old 2nd December 2009, 12:48 AM   #623
Salas is offline Salas  Greece
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Update required ?
Lets leave the building practice flow a bit and we will learn more, so to home in better to what may prove more popular to recommend or to explain better in a near future edit. 2SK117 can be added as a 2SK170 direct substitute for instance for all the regs area Jfets (not for the audio part). We came to that conclusion after Stormsonic reported they do OK (in the reg only thread) and the pinch off voltage is correct.
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Old 2nd December 2009, 09:17 AM   #624
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Em, well I had a slight "light-bulb-over-the-head-moment" last night. I got out the thermocouple for my dmm and powered up the DCB1. Temp on the fets was ~24degC. Then I left the thermocouple off for a while. Then I noticed that the air temp in the workshop was +5 degC (chilly here at the mo!). So it would seem that what I'm actually getting is about 20deg over ambient - and thats when screwed down to a heatsink plate. So in your average room, thats maybe 40degC when on a good heatsink.

So that would seem like a reasonable amount of heat!!!! Apologies for my doubts earlier. Shows how you can be misled by missing the obvious!!!


Anyway, next step is adding in the lightspeed. That will be interesting as right now, the stepped pot sounds great. All that sibilance stuff is pretty much gone. Looking back over the last week or so, it seems that the sibilance was cured by:

1. tidying input and output wiring (esp. dirty contacts)
2. Matching the 50k pot resistance to the 220K (ie changing them to 540k)
3. Changing the 220r in the B1 part from metal film xicons to metal film dales.
4. Possibly run in time.


Fran
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Old 2nd December 2009, 09:26 AM   #625
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All that sibilance stuff is pretty much gone. Looking back over the last week or so, it seems that the sibilance was cured by:
1.
2.
3.
4. Possibly run in time.
I wonder if there is a case for reforming all electrolytic capacitors before fitting them into our circuits.
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Old 2nd December 2009, 10:00 AM   #626
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Good point.
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Old 2nd December 2009, 10:33 AM   #627
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I wonder if there is a case for reforming all electrolytic capacitors before fitting them into our circuits.
I'd always regarded burn in of caps as a little on the voodo side, it is funny how a single sentence can change your opinion! Interesting food for thought Andrew!

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Old 2nd December 2009, 11:26 AM   #628
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I think that anyone that believes components need burn in is completely deluded.

All properly designed circuits should perform to specification within a few seconds and reach their best compromise of performance targets when the optimum design temperatures have been achieved, probably within 30minutes from a cold start up.

Changes that occur days and/or weeks after initial start up and testing must be due to changes in the components. The major culprit for this change is likely to be old stock electrolytic capacitors. The oxide film degrades rapidly after production. The manufacturers specify in detail the reforming that must be done to allow their caps to be specification checked in the factory. After they have been transported around the world and sat on the wholesalers shelves and then at the retailers shelves and finally on the DIYer's shelf, how can an electrolytic perform to specification if it is not reformed to the manufacturer's specification?

I have been promoting this culture for years, but the deluded stick to their beliefs.
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Old 2nd December 2009, 11:35 AM   #629
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Heres a story to back this up. Over in the analog section RJM came up with a new version of the phonoclone with improved power supplies. So, as I already had 2 phonoclones, I thought, hey why not a 3rd!! So I became a beta tester for the new boards. RJM was ahead of me a bit, but we both ended up testing at about the same time. Every day over a 3 week period, constantly powered on and playing say an hour a night, I could hear changes in this thing as it became smoother and smoother sounding. Stopped changing after about 3 weeks. RJM reported exactly the same with his - and he wasn;t bullshittng me, I just knew that from the way he said stuff in the emails. Anyway, a monthy or 2 goes by, and we are both happy. Then someone discovers a mistake on PCB silkscreen where 4 electrolytic caps are reversed - ie wrong polarity. None of the caps failed (very low voltage in the wrong direction) but all were bulging to some extent.

We put the changes in sound down to the caps changing properties over time. Seems like a most reasonable explanation. We fitted new caps, but the sound never changed........



Sorry for the OT post, but it kinda fits.


Fran
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Old 2nd December 2009, 11:41 AM   #630
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I replaced a capacitor on a chipamp the other day. It sounded a little harsh upon start-up, but this disappeared within a couple of minutes. It didn't get any better/worse after that period.
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