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SuSy dynahi v2

Kevin Gilmore's higher-powered version of the dynalo

Re: SuSy dynahi v2

Postby DEFL » June 5th, 2015, 12:45 am

Checked bunch of THAT340 chips which is 2 Matched NPNs and 2 PNPs. This is input device of the latest revision of Susy Dynahi and other latest KG's amps. He says he likes it very much.
Hfe of NPNs is ~270, Hfe of PNPs is ~100.
However, Vbe is very, very consistent among all 4.
What's more important in this application: Hfe or Vbe?

Theoretically, FETs can be put into socket of THAT340, and it will work, but I don't want to do it. I've already deviated from Onsemi/Motorola to Toshiba output transistors. If now change input sand, it will be kind of better I had gone all Toshiba Dynahi from the very beginning.
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Re: SuSy dynahi v2

Postby amb » June 5th, 2015, 3:47 am

When it comes to matching input BJTs people generally match for hfe. But in a circuit like the dynahi's, it's more important to have the NPNs match each other (and the PNPs), but less important to match across NPN and PNP. Vbe is also sometimes used as a matching criterion, but usually in conjunction with hfe, not instead of it. Here too I don't think it's that important for the dynahi.
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Re: SuSy dynahi v2

Postby mloutfie » June 7th, 2015, 5:10 am

amb wrote:0.22A sounds low. Each output bank should draw about 300mA when biased properly, and there are two banks per channel.
1.2A is a bit much for a single σ22 with the standard PCB-mount heatsinks.

The amp's gain has nothing to do with power supply current draw.


I have been trying to set the bias to 75mV didn't realize that in your guide was actually 0.75V. I'm trying to set the bias to 750mV but increasing the bias also increase offset at the same time. After I got the bias to 700mV the offset was 24V. Yikes.

I reset all the trimpot to their original possition to retry. But something really odd happen. Even with the trimpot in their original possition the offset at output pin still shows 24v and the first 2 most left right 20ohm resistor shows it has 4V and the right pair of heatsink gets really hot also the mpsw56 gets really hot also.

The board now draw 0.6A. How can I increase the bias but keep offset at output low? Because when I increase the bias that high output offset increases also
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Re: SuSy dynahi v2

Postby amb » June 7th, 2015, 12:32 pm

With the SuSy design you're having to juggle between four trimpots per channel. Are they all set back to their initial position?
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Re: SuSy dynahi v2

Postby mloutfie » June 7th, 2015, 3:49 pm

yes they are back to default value now. the trimpot next to THAT chipis in midpoint. and trimpot next to the servo is on max. the voltage seems to be unmovable now
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Re: SuSy dynahi v2

Postby amb » June 7th, 2015, 5:52 pm

Maybe something got fried.
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Re: SuSy dynahi v2

Postby mloutfie » June 7th, 2015, 6:06 pm

Yeah that's what I think. my other board is fine. I changed the 500ohm resistor to 680ohm to reduce the bias as low as 75mV looks like I have to switch it back to 500 Ohm because I can only raise the bias to 400mV now.

Man this is hard.... compared to making tube amp like bottlehead crack this is a whole different level.
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Re: SuSy dynahi v2

Postby mloutfie » June 7th, 2015, 8:30 pm

Yeap the + bank of MJE15030 and MJE15031 are fried. This onboard heatsink will be a pain to undo to replace those. :(
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Re: SuSy dynahi v2

Postby DEFL » June 8th, 2015, 12:12 am

mloutfie wrote:yes they are back to default value now. the trimpot next to THAT chipis in midpoint. and trimpot next to the servo is on max. the voltage seems to be unmovable now

No, at initial position trimpots next to servo must be one on max, the other on min (don't remeber which is which, not at home right now). So you should rotate them in opposite direction.
Setup is VERY tricky and not straight forward. Large factor of randomness. Patience is required. DC offset may change rapidly so turn all trimpots slowly.
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Re: SuSy dynahi v2

Postby mloutfie » June 8th, 2015, 12:31 am

DEFL wrote:
mloutfie wrote:yes they are back to default value now. the trimpot next to THAT chipis in midpoint. and trimpot next to the servo is on max. the voltage seems to be unmovable now

No, at initial position trimpots next to servo must be one on max, the other on min (don't remeber which is which, not at home right now). So you should rotate them in opposite direction.
Setup is VERY tricky and not straight forward. Large factor of randomness. Patience is required. DC offset may change rapidly so turn all trimpots slowly.


By max I meant max resistance value. But if you mean turning wise you're right the one next to the servo is max counter clockwise and the other side max clockwise then I turn the clockwise on the one next to the servo and counter clockwise on the other one.

Well now time to replace those transistor for me. That would be interesting considering I'm using on board heat sink. Would be tricky to replace them with the heatsink in place. Don't really want to use blow torch to remove the heatsink :)
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