The Multi Amp aka Dynalo Mk2

[jbozek]

can i maybe replace the jfets on original dynalo with that340? and what mods should i do? i think i must tune the ccs, and change pot from 50k to 10k. correct me if i am wrong

[GGW]

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!

[Pars]

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.

[GGW]

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

[jbozek]

thank you very much, all of you!

[GGW]

Thanks, @starcat 🤘

 

Does anyone have any leads on LSJ109?  (Side question, the LSJ109 doesn't look like a dual JFET so would I need a matched pair of these to replace a single 2SJ109?)

[Pars]

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

[Bespav]

Try here:
https://www.ebay.com/itm/Toshiba-2SJ74-2SK170-Quad-0-03-4-9-11-bl-B-/253517005056?_trksid=p2349624.m46890.l49292

[Pars]

^ Reputable seller of genuine devices.

[jbozek]

damn they are expensive

[jose]

Yes, this seller sells genuine sand. Highly recommended

[Pars]

14 minutes ago, jbozek said:

damn they are expensive

Yes, not cheap, but considering it is a matched quad, approx. $11@. And generally unobtanium. The diyaudio store charges $39 for a similar matched quad of the Linear Systems devices (2 N, 2 P).

[Bespav]

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.

[jbozek]

if i have a 50k pot, but need a 10k, can i put a 10k resistor parallel to amp input (or pot output)?

[GGW]

thanks all!  Does anyone have gerbers for the little adapter board to make the LS 170/74 JFETs work?

And gerber for adapter board for LSK489 / LSJ689 please  

[GGW]

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!

[Pars]

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.

[jbozek]

do you maybe sell LSK489 / LSJ689 ?

[Bespav]

Noob question but do you have to match across N and P channels for the input stage?

No, there are two different individually biased input stages and no need to match n- with p- devices.

[Craig Sawyers]

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

Try here:
https://www.ebay.com/itm/Toshiba-2SJ74-2SK170-Quad-0-03-4-9-11-bl-B-/253517005056?_trksid=p2349624.m46890.l49292

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.

[mwl168]

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...

 

Edited March 4, 2021 by mwl168

[RudeWolf]

I get unmatched 2x(2sk389/2sj109) from the EU for that money. I guess it's matching vs thermal bonding here.

[Pars]

1 hour ago, jbozek said:

do you maybe sell LSK489 / LSJ689 ?

Not sure who you are asking, but no, I don't have any, and they probably would not be for sale if I did.

[GGW]

Thanks everybody - super helpful!

@Pars - how did you hook up the LSK489 / LSJ689's to the THAT340 dip socket?  Bending like crazy? 

[Pars]

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 March 4, 2021 by Pars