Mezmerize DCB1 Building Thread - Page 32 - diyAudio
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Old 8th July 2011, 01:19 AM   #311
Salas is offline Salas  Greece
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There are 10 or 1 Ohm resistors under each K170 that feeds the strings of 5. Is there enough voltage drop across those resistors? That indicates the currents. Should be near 70% IDSS of the JFETS you used. Is it so? If yes, although I haven't heard of such a bug in the course of the threads before so to answer from experience, I would check the BC transistors and Mosfets also. Is there Vbe and VGS proper on all? You report small drops across R1, maybe the CCS MOSFETS are not OK?
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Old 8th July 2011, 04:24 AM   #312
orpheus is offline orpheus  United States
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Originally Posted by Salas View Post
There are 10 or 1 Ohm resistors under each K170 that feeds the strings of 5. Is there enough voltage drop across those resistors? That indicates the currents. Should be near 70% IDSS of the JFETS you used. Is it so? If yes, although I haven't heard of such a bug in the course of the threads before so to answer from experience, I would check the BC transistors and Mosfets also. Is there Vbe and VGS proper on all? You report small drops across R1, maybe the CCS MOSFETS are not OK?
Over the 10 ohm resistors, I get .042 volts on the positive leg, and 0 volts on the negative leg. I used 2SK170BL's, but I didn't measure the idss of them before installing them for the power supply. Both the 2SK170's in the power supply for the 5 led string were exchanged, so there have been two sets in there with the same problem.

Should I pull the mosfets and transistors and then measure them, or could I measure them in circuit to test them? What measurements would you like me to post?

Thank you so much for your help.
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Old 8th July 2011, 10:40 AM   #313
Salas is offline Salas  Greece
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The 0 reading on the negative leg 10R is tell tale there is no current for its leds. The positive leg indicates 4.2mA which can be coming from a 6mA fet or less (low end for BL), when tested for idss with a 9V battery. Where you got those K170BL? Pull the negative leg K170 and test for idss first. If its OK put it back. Having no current there with a good K170 means the negative side CCS will not give it any, or something draws all of it elsewhere. Do you get a cold negative side to the touch for both Mosfets? With complete circuit running, measure voltage between gate and source of each negative side mosfet, and between base and emitter of the BC transistor. Should be 3.5 to 4V and 0.6 to 0.65V.
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Old 8th July 2011, 04:11 PM   #314
AndrewT is offline AndrewT  Scotland
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Originally Posted by orpheus View Post
...........I am using a 12 volt transformer.

Here are some voltages:

output from Diodes: 11+, 9.9-
What does that mean or indicate?

for ~10V output from the Salas type regs, the DC input voltage when mains power is at lowest end of tolerance should be >=16Vdc.
When mains is at normal tolerance expect 17to 18Vdc.
When mains is at highest tolerance, you would expect the regulator to survive with upto 19 to 20Vdc at the input.

If you are only getting 11Vdc and 9.9Vdc at the inputs to the two Salas type regulators then your transformer is either broken or you have wired it up incorrectly.

The DCB1 works well with a 30Vac centre tapped transformer, i.e. 15,0,15Vac
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Old 25th July 2011, 12:16 AM   #315
Frosteh is offline Frosteh  United States
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Does anyone know the price of the matched JFET's? I'm also looking for a PCB, but that seems to vary more since I'll have to find one that someone didn't want since I missed the last GB.

EDIT: Never mind. Found these on ebay. Will these work? I only need 2 matched pairs, not 4 matched, right?

Last edited by Frosteh; 25th July 2011 at 12:21 AM.
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Old 25th July 2011, 12:54 AM   #316
Salas is offline Salas  Greece
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You need 2 matched pairs in the 7-8ma region. Each pair can be a bit different, you don't need 4 in same IDSS. The bags look Toshiba to me in that link. Also Andrew has very well matched LSK170s (excellent American clones).
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Old 25th July 2011, 01:46 AM   #317
Frosteh is offline Frosteh  United States
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Originally Posted by Salas View Post
You need 2 matched pairs in the 7-8ma region. Each pair can be a bit different, you don't need 4 in same IDSS. The bags look Toshiba to me in that link. Also Andrew has very well matched LSK170s (excellent American clones).
Is there something wrong with the Toshibas? $3.10 for 4 is quite cheap. Any advantage to using the LSK170's (other than supporting a fellow DIYer and faster shipping from the UK than Israel)?

Last edited by Frosteh; 25th July 2011 at 02:00 AM.
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Old 25th July 2011, 02:13 AM   #318
Tea-Bag is offline Tea-Bag  United States
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you can't guarantee what matching level this guy provides, but you could ask.

Ed Lafontaine and Blues are two other guys who might be able to sell you this stuff stateside, and then you get matched quads. Dont forget you need 6 additional ones to complete the power supply section. They do not need to be matched.
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Old 25th July 2011, 03:17 AM   #319
Frosteh is offline Frosteh  United States
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Originally Posted by Tea-Bag View Post
you can't guarantee what matching level this guy provides, but you could ask.

Ed Lafontaine and Blues are two other guys who might be able to sell you this stuff stateside, and then you get matched quads. Dont forget you need 6 additional ones to complete the power supply section. They do not need to be matched.
This is what he quotes: "I declare +/-2% to be on a safe side but really I select no more than +/- 1% (Vgs = 10V)." What exactly does this mean? I'll pm Ed and Blues to see what they'd want for a couple matched ones.
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Old 25th July 2011, 03:35 AM   #320
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I'd be glad to assist if I may...

Omron G6H-2 12VDC relays

If a set of "matched" devices varies 0.08/8.00, that is 1%. I have never sent out a set with more than 0.04 variance. I have sent out quad sets above the 7-8 mA range... I do give the greater emphasis to channel-channel matches.

I may find a Mesmerize board as well.

Last edited by Ed LaFontaine; 25th July 2011 at 03:41 AM.
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