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Old 6th July 2005, 09:47 PM   #1
Bgt is offline Bgt  Netherlands
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Default UCD400 boxed

Just a picture of my just finished amp. Still a lot of fine tuning to do. The box is from audiokit/Italy. Rather small size. Cooling block is from schuro like the caps. Transfo. is a 300W(2x40V) toroid. No snubbers anywhere.
Just a quick scope measuring is 100V at 8 ohms both channels driven. Not bad.
Click the image to open in full size.
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Old 7th July 2005, 09:11 PM   #2
Bgt is offline Bgt  Netherlands
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well, after taking the input caps out and changing the gain smd resistor from 560 to 180 ohms, I find the gain far to low for any preamp system, I fired it up and found an unproper grounding of the heatsink where the UCD400's are mounted on. Humm all over. After making a hard connection to the zero of the cap. PCB its OK now. My tuner(aircaps.) was completely freaked out from the 400kc. Now...dead silent.
Sound is very nice. The only things that get burning hot are the 12V step down transistors. Hope this stays OK.
Channel separation at 15kc is a tad lower for the module where the input section is nearest to the power output coil. Would be better if they were separated a bit more. Ah well...have to built another one!
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Old 8th July 2005, 04:42 AM   #3
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by Bgt
well, after taking the input caps out and changing the gain smd resistor from 560 to 180 ohms, I find the gain far to low for any preamp system, I fired it up and found an unproper grounding of the heatsink where the UCD400's are mounted on. Humm all over. After making a hard connection to the zero of the cap. PCB its OK now. My tuner(aircaps.) was completely freaked out from the 400kc. Now...dead silent.
Sound is very nice. The only things that get burning hot are the 12V step down transistors. Hope this stays OK.
Channel separation at 15kc is a tad lower for the module where the input section is nearest to the power output coil. Would be better if they were separated a bit more. Ah well...have to built another one!

Are those transistors getting that hot??? I`ll try to measure it sometime, these guys do not have to handle that much current so expect it to be OK. Anyway, I`ll check sometime with my thermocouple.

Best regards

Gertjan
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Old 8th July 2005, 03:50 PM   #4
ghemink is offline ghemink  Netherlands
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Quote:
Originally posted by Bgt
well, after taking the input caps out and changing the gain smd resistor from 560 to 180 ohms, I find the gain far to low for any preamp system, I fired it up and found an unproper grounding of the heatsink where the UCD400's are mounted on. Humm all over. After making a hard connection to the zero of the cap. PCB its OK now. My tuner(aircaps.) was completely freaked out from the 400kc. Now...dead silent.
Sound is very nice. The only things that get burning hot are the 12V step down transistors. Hope this stays OK.
Channel separation at 15kc is a tad lower for the module where the input section is nearest to the power output coil. Would be better if they were separated a bit more. Ah well...have to built another one!

Hi Bgt,

I measured the temperature of those two transistors in my experimental setup. They get indeed quite warm, around 70C while the temperature in my room was 30C. This was for the UcDs with the OPA opamp. I have nor measured it for the AD opamp version.

I guess this is still well below what is safe for these transistors.

ABout the gain, I would say that the standard 26dB gain should be high enough for most preamps. In my case I have more than enough gain. If you have a preamp that gives 2V RMS out, then you can already drive them to max power.

Best regards

Gertjan
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Old 8th July 2005, 05:06 PM   #5
Bgt is offline Bgt  Netherlands
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Gertjan,

Thanx for measuring it. I did also and found 69C (with a small laser measuring device, forgot that I have 1) after warming up a bit. So that should be OK. Its a 8620 Type UCD. But it warms up the housing a bit which is a bit of a pitty with such a "cool"amp.
The housing is a bit smallish but that's what I like.
What I've found with the gain is that for 100V peak out you need 5v peak in. Well my tuner output is only 0.5V rms. My DAC(Elektor2000withAD8620's) is about 2V peak. Combined with the passive preamp, which has a gain of about 0.9x that leaves me with a very soft amp. if I don't change the gain. With the 180 ohm resistor I only need 1.4 V peak for 100V peak out.

KR, Bert
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Old 8th July 2005, 05:20 PM   #6
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It is adviced vertical mounting of the PCB and drilling holes to the box to allow convective air cooling to the parts (to wich the huge heatsink is not contributing, I guess)

At least that's what I'll do when my parts arrive.

Good luck

Mauricio
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Old 8th July 2005, 07:48 PM   #7
Bgt is offline Bgt  Netherlands
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Mauricio,

Concerning the position of the PCB, I tried to put it vertically but then 1 side of the T bone piece got too hot. The way it is now it is more evenly hot/cool on the PCB. There are cooling vents in the top and bottom cover just where the heatsink is positioned. Just look at the pic. Here you get your convection cooling airflow.
Click the image to open in full size.

Anyway, after having it on for 4 hours on average level(classical music) the 12V stabilizer transistors are about 74C and the output coil is 70C. The T bone piece is 50C. Inside the box 37C. Room temp is 24.

Click the image to open in full size.

It is very easy to tune now. Very easy to reach the parts.
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Old 8th July 2005, 08:28 PM   #8
Bgt is offline Bgt  Netherlands
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power consumption idle = 97ma
full power, 1 Kc sinewave@100V peak(just not visibly distorting) on 8 Ohms(both channels) = 1450 ma
Absolutely a more environment and wallet friendly amp. than my NAD C272.
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Old 8th July 2005, 09:18 PM   #9
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Very nicely done I wish i could do that good.
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Old 8th July 2005, 10:01 PM   #10
Bgt is offline Bgt  Netherlands
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Thx Tekko. Will make another 1. But now with the 180's. And a smaller housing!
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