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Old 25th April 2010, 09:10 PM   #1381
ra7 is offline ra7  United States
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Guys,

The leds are very of good tolerance... I can almost pick any 5 from the lot and they measure about the same.. although, I don't think this is what Salas is refering to. Also, the jfets used in the CCS portion are suspect types. They have GR marked on them, but they measure 8-10ma Idss. I discussed this a few pages back with Salas. Anyway, I took a chance and it is working... although, haven't tested the sound yet. I have a pretty transparent system, so any oddities should show up.

Will post pics of my led mishap soon.
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Old 25th April 2010, 09:28 PM   #1382
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Default led orientation pain

Yes, even after reading some things on orienting the leds properly, I managed to orient all of them in the exact opposite direction. Here are some pics.

I fixed it by chopping off the tops and re-soldering new ones on the top side of the pcb, although this was not my initial plan. At first, I tried to desolder a couple of the leads of left in the holes, but the pads themselves started lifting. This can be seen in pic 1. So, I used the top side instead. Pic 2, shows the solution to pads that were lifted..... just solder the successive leds' legs to each other.

I hope this helps some other unfortunate soul who might make such a mistake. More pics when final build is done.

(the power led is yet to be fixed )
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File Type: jpg IMG_5853[1].JPG (812.2 KB, 405 views)
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Old 25th April 2010, 11:57 PM   #1383
ra7 is offline ra7  United States
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Salas,

For the input selector, the switching is happening simply by switching to ground? I'm not seeing any other connections to be made. Also read your comments in the GB thread.

So, just connect 1-6 for the inputs on the switch and then connect ground to switch output?
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Old 26th April 2010, 12:09 AM   #1384
Salas is offline Salas  Greece
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I take it you use a Mezmerize, right? Yes you describe it rightly in that case.
The output closes a simple DC circuit to ground one by one for each relay's coil.
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Old 26th April 2010, 12:23 AM   #1385
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Quote:
Originally Posted by Salas View Post
One way to get closer than norm, is to have a weaker idss JFET in the plus side. Another way is if the particular Leds are stiff and don't translate easy to significantly more Vf for 5-10mA running current differences. Those Jfets do work both ways but the unorthodox way is normally stronger for self current and worse for regulation. In hot rod CCS currents environment the subjective benefit in THD profile is filled out by the stronger tone and details. In Blue the orthodox will be standard since its reinforced everywhere for hotrod. But unorthodox it helps tone with small currents. Helps with offset too if the audio fets are not that well matched also. Did you measure your offsets BTW?
My gut feeling is that it is likely stiff LED's because the Jets are idss matched between the 2 rails. The jets in the B1 are all at 9ma, and the shunt's are around 7ma. For the time being, I am using 2 wirewound 50R pots to dial the CCS to around 125ma at each rail. The offsets are -1mV and -2mV respectively. No sound yet as I haven't wired the pot and input RCA's. Hopefully, I will be able to hear the nice sound this evening.

Thanks for your support!!
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Old 26th April 2010, 04:14 AM   #1386
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Worry is over, it has been singing for 2 hours with my workbench gears. It replaces a passive preamp by Scott Nixon that I bought a few years ago. The first impression was very positive, the added dynamic and the revealing of the detail were quite noticeable.
I will let it run for the rest of the night to break in.

Thanks Papa, Salas, and TeaBag to make this possible!!
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Old 26th April 2010, 04:21 AM   #1387
Salas is offline Salas  Greece
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The pleasure is our's sir. Happy listening.
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Old 26th April 2010, 05:03 AM   #1388
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Mine is up and running too... first impression is very quiet background and very melodious! Its late here and I can't crank it up. More tomorrow.
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Old 26th April 2010, 05:19 AM   #1389
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Thank you, Salas.
Here are a couple pictures taken while it was singing. I am not even close to finish. Next will be the chassis which used to host a couple SCSI hard drives ...
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File Type: jpg P4250028.JPG (156.0 KB, 369 views)
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Old 26th April 2010, 05:23 AM   #1390
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I dig the op amp base for evaluating Vref bypass caps. Cool.
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