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KG Balanced Dynahi build discussion thread

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I was able to get a set of bords for the Dynahi rev2 from Tran. Hopefully I'll get them in the next two weeks. Until then I have a few questions before I start to buy parts.

Would a pair of Sigma22's work for the power supply instead of the PSU borads that come with the set?

Could I drive a pair of 8 ohm monitors with this amp as well as headphones? If so how much power will it provide?

What are the reccomended specs for a power transformer if I'm going to drive speakers as well as headphones?

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sigma22's will work fine. Probably you want one power supply per channel.

I never tried to drive speakers with the balanced board, that would be the

equivalent of a 4 ohm load per side. Should work, might get very hot.

Probably something like 18 watts.

Birgir and I are working on a pure class A speaker amp (or lcd2/3,hf6)

thing that is 20 watts into 8 ohms. Its a krell ksa50 clone down graded a

bit but way more bias. All the new modern onsemi transistors.

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Using a Dynahi to drive speakers is a bad idea IMHO unless you have huge heatsinks and a PSU which can handle the load. Even two Sigma22's will struggle to keep up so why not just build a F5 for speaker use with its super simple PSU?

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It was just a thought. I was going to build something else for the speakers, but I thought it was worth an ask. I won't try to drive speaker with it then. So you think I would need a total of 4 sigma22's? One amp board is 2 channels right? Or did I misunderstand? I was thinking one sigma22 per board ie one for Left and one for Right.

I'm guessing 30VAC output on the transformer. How many voltamps?

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sigma22's will work fine. Probably you want one power supply per channel.

I never tried to drive speakers with the balanced board, that would be the

equivalent of a 4 ohm load per side. Should work, might get very hot.

Probably something like 18 watts.

Birgir and I are working on a pure class A speaker amp (or lcd2/3,hf6)

thing that is 20 watts into 8 ohms. Its a krell ksa50 clone down graded a

bit but way more bias. All the new modern onsemi transistors.

Sounds like a nice K1000 amp too.

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Have you been drinkin?

What is a quad amp three?

Or didja mean to say there?

I been drinkin. Jus strugglin to understan yer cryptic respons.blink.png

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I said too, so he said three. Not really that cryptic, well maybe if you're drunk.

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The plan is to introduce a relatively simple amp that can drive any headphone to destruction and be fully Class A. The EF-6 is a nice design for the price but we can't settle for something commercial.. azn.gif

For the transformer, bigger is usually better and with Class A amps you should spec at least double the max current draw. Be vary of the inrush current though.

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I would think that a transformer sized similarly to a beta22 would be sufficient. For my 2-ch Dynahi, I used a SumR 2x30V 120VA transformer, which would be overkill for a balanced Dynahi. I think 80VA is normally about what Amb recommends for a balanced b22?

EDIT: I don't have any problem with inrush current on this, but am using a single sigma22 with it, which starts up slowly. YMMV depending on what you are using for PSU(s).

Edited by Pars

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I just for fun finished testing the new balanced dynahi into 8 ohms, and it actually works

and works well. Unfortunately the power supply limits to about 1.5 amps, which ends up about

18 watts into the load, of which about 3 watts is pure class A. Everything gets very hot

doing this. So if you put monster heatsinks on everything and beef up the power supply

you can probably get more.

The other thing is going to also run at +/-30 volts, but will put out 20 watts pure class A into

8 ohms. The power supply for this is going to be substantial.

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Wow... Thanks for trying that. It's good to know that it doesn't blow up. Alas, I think I'll just build it with a case and PSU that will support headphones for now, but it's nice to know I could power speakers with it

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am I missing something or is the LSJ109 a single in a TO-92 package ? The board has it layed out for a TO-71. Was it available as a matched pair or something? Need some help on this part.

Also, I can find the LSK389 in a TO-71 package, but what grade or letter do I use A B or C?

Edited by sbelyo

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The LSJ109 hasn't been released yet. Don't get Kevin's BP up discussing this failure on Linear Systems part to come out with P-ch JFETs :)

Read the datasheet for the LSK389... I don't think the letters have anything to do with package type though. I think that is the IDSS grading.

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ah, ok that makes sense. As far as the LSK389 you're right, the pakage is the same I just don't know what grade to use.

Another question, the people out there with completed board are just using the 2SK170's and the 2SJ74's (matched pairs) ? If that's the case it's the only way to complete a board right now correct?

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Unless you happen to have 2SJ109s and 2SK389s around, yes. Linear does have the LSK170s, and had at least released samples over a year ago (IIRC) of the LSJ74s. Normally with the Toshiba parts (2SJ/2SK), BL grade was the norm. I'm not sure which Linear grade corresponds to that (I would guess the B designation). Note that the TO-71 packages is a -71 suffix on the PN, while the SOIC is a -SOIC-8 suffix.

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found:

8 2SK170

8 2SJ74

2 2SK389

All BL grade

I was planning on using vishay-dale resistors except for the resistors on the output transstors. Would it be worth it to replace those with PRP? I contacted them and they will sell me 64 20R 1/4 watt 50ppm 1% at about $1.25 a piece lead time 6 weeks. Couldn't find 20R at Partsconnexion or soniccraft. I could also get IRC 20 ohms from mouser at around the same price and they are in stock.

What do you all think?

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Michael Percy has the 20R PRPs...

I would personally build the whole thing with PRPs (or Roederstein MK3s)... that is what I did on my original dynahi boards. Not sure whether it really makes a difference or not.

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yep, they look to be almost the same size. max on the dales is 0.425 in length PRP is 0.400

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