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SuSy dynahi v2

Kevin Gilmore's higher-powered version of the dynalo

Re: SuSy dynahi v2

Postby mloutfie » July 6th, 2015, 2:49 am

So signal connected to + and ground connected to ground and -? then trs ground sleve connected to power supply ground?

If that's the case the 4PDT switch that I use to switch the input won't be enough i need to use something else to do the switch I guess

To previous builder how hot does your case get. For me get as hot as 50 degrees C
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Re: SuSy dynahi v2

Postby amb » July 6th, 2015, 2:59 am

A 4PDT switch will work for both channels. Here is a diagram of one channel (it says beta24, but would be the same as any fully-differential or fully-balanced amp):

Image

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Re: SuSy dynahi v2

Postby mloutfie » July 6th, 2015, 3:09 am

I see.... Didn't think of that. Thanks so I just need to wire another connection direct from rca and balance ground straight through amp ground. Thanks a lot will try that.
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Re: SuSy dynahi v2

Postby mloutfie » July 6th, 2015, 3:16 am

BTW been using the amp with the case close for an hour it does get quite hot the caae is barely touchable now. The case is sealed full aluminum with no ventilation. Looks like I need to drill holes for ventilation. Or is it okay to leave it as it is. Considering the full aluminum case will act like a big heatsink. The case is 3u rack case but I am putting 2 amp board and 2 sigma22 board in it. To its packed. I put the transformerin. Another case
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Re: SuSy dynahi v2

Postby amb » July 6th, 2015, 4:04 am

A totally enclosed box traps the heat inside, and does not act as a heatsink because air is not a good heat conductor. Let it warm up fully with the cover closed. Then remove the cover and quickly check the heatsink temperatures with an IR thermometer, before they get a chance to cool down. If you get anything higher than mid-60s °C then you need additional ventilation. Or you could run with less bias.

Too much heat could reduce the life of parts, not just the transistors themselves, but other parts such as electrolytic capacitors too.
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Re: SuSy dynahi v2

Postby mloutfie » July 6th, 2015, 5:18 am

I haven't got an IR thermometer so I guess drilling holes is much easier since the top aluminum is quite thin and easy to drill.
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Re: SuSy dynahi v2

Postby DEFL » July 7th, 2015, 4:39 pm

DEFL wrote:
amb wrote:If you can find the 2SC5171/2SA1930, they're worth a try.

Thanks, ordered 50 pcs of each. The rest will go for Krell KSA5 clone.

Ok, received them all week ago. Found time to proceed to matching. Also purchased this device which is worthy to have:
http://www.ebay.com/itm/261034173174
It has capability to test transistors at higher current than Atlas DCA75. I will use it with external DC 6C-2A adapter. Options available are 10uA, 1mA, 10mA.
What is the closest value to real life operation? With current, Hfe varies significantly, and so does heat output.
Quick test of 2SC5171 showed: Hfe ~195, ~220, ~90 respectively.
And 2SA1930: ~190, ~215, ~100.
Those are just one random item.
Waaaay better than MJE15030/15031.
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Re: SuSy dynahi v2

Postby DEFL » July 7th, 2015, 11:32 pm

Since we are aiming at 75mA and 75mV of bias voltage, I think 10mA setting on DY294 is a proper value to match them. Is my assumption correct? Want to avoid mistake as much as possible and shorten life of the transistors, cause they get quite hot quickly at 10mA.
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Re: SuSy dynahi v2

Postby mloutfie » July 8th, 2015, 1:02 am

We should be aiming 750mV of bias voltage actually not 75mV. I read in some post that says 75mV which is wrong and led me to a wrong path when I started building mine.
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Re: SuSy dynahi v2

Postby amb » July 8th, 2015, 1:06 am

DEFL, if the intended in-circuit operating current is 75mA, then it's best to measure the hfe at the same current. However that might be tricky as the transistor will heat up quickly and affect the readings (BJTs have a positive temperature coefficient). If the transistor has a relatively flat hfe vs. Ic curve, then measuring at a lower current might be easier and still give good results.

mloutfie and DEFL, don't confuse bias current from the voltage drop across the output resistor, which is a way to measure the bias current. One is in mA, the other in mV. Let's say you have 750mV voltage drop across a 10 ohm resistor, then the actual bias current is I = V/R = 75mA.
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