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The Multi Amp aka Dynalo Mk2


spritzer
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Hi All,

After reading this entire thread, it seems there are a number of options for transistors to use in place of THAT340 on the input stage (if you can source them).

Please could someone help rank the below in order of preference?

 

- 2SJ109 / 2SK389 appear impossible to source

- LSJ109 / LSK389 (LSJ109 also looks hopeless unless you roll the dice on ebay / aliexpress)

- 2x Matched pairs of LSJ74 and LSK170

- 2SC3381 / 2SA1349

- LSK489 / LSJ689

- Anything else?

 

Or just go with THAT340 and live with the low input impedance that seems to be a minor issue?

Thanks!

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Sound-wise, any of the JFET options are preferred. If you can find them, the Toshibas would probably be preferred (2SJ / 2SK parts). I have used the Linear Systems LSK489 / LSJ689 and didn't notice a difference from the Toshiba devices, but I have read that some prefer the Toshiba. The BJT devices (2SA/2SC or the THAT part) to me don't sound as good. Not bad, but not as good. And that is with 10K pots. I think the 2SA / 2SC sounds a little better than the THAT part, but not up to the level of the JFETs.

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Thanks, Pars!  Very much appreciated! 😬

Was quietly hoping you would respond as you have clearly tinkered more than anyone else on the thread when it comes to transistors used for the input stage

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The LSJ109 is (was?) a dual JFET, but not in the same package as the Toshibas were. For thru-hole, it is available as a TO71 can package with 6 leads. It seems as though these are either discontinued or just not available. Your alternatives are to use the LSK489 / LSJ689, or use the singles. The 489/689 is what I have used. The diyaudio store sometimes has the singles: https://diyaudiostore.com/collections/parts/products/linear-systems-matched-jfets

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damn they are expensive


Since you're on the audio slippery track there are no ways to turn off.
Yes, you can use bc850c/bc860c or even cheap as dirt 2n3904/2n3906 on the input stage and obtain similar **measurable** performance. But JFET input stage sounds better. It's like to changing Samwha capacitors to a purebred Elna Silmic.
Really we don't understand what to measure to obtain sonic-correlated ruler/scale.
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Noob question but do you have to match across N and P channels for the input stage? Or just within N and within P if you go the single JFET route?

I.e. if I go for, say, 2 x LSJ74 and 2x LSK170 - do they ALL have to be matched or only the 74s with each other and the 170s with each other?  If the latter, then no need to buy plenty  LSK489 / LSJ689 and match them?

Thanks!

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When I used the Linear duals, because of cost, I didn't bother matching them N to P. Kevin has said the CCS takes care of it anyway. If doing singles, if you can get them matched including N-P without a huge premium, I'd do it.

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On 3/2/2021 at 4:30 PM, Bespav said:

Well that is interesting. The killer, however, if these came from the US to the UK is (a) $18 shipping and (b) They would get stopped for VAT and a clearance fee of UKP10. So the actual price per quad is about doubled.

But the same thing happens for the DIYAudio linear systems ones. All part of rip off Britain.

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Matching P channel and N channel is very challenging even you have a large supply of both. Agree with Pars that it's not really required for this application. 

If you already use dip socket for the THAT340 you can simply plug in the SK170/SJ74 into the dip socket with some leg bending. There should be some photos showing how this is done in the Balanced Dynahi build thread. 

found the photo so I'll show it here...

 

JFET replacing THAT340.JPG

Edited by mwl168
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Adapter boards that I layed out and were in one of the GBs.

I think you could just plug them into a 14 pin socket with no lead bending, but if I recall correctly, one of the JFETs would be backwards. No big deal on the Toshibas, at least according to John Curl. I presume the Linear Systems would be OK as well.

Edited by Pars
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