When SITs sit in my drawer

[ripson]

Hi guys, I am in DIY audio for some time and realised that what works best to me is minimalism. In my case: I steal I2S signal from modified Squeezebox Dual and provide it to the Soren DAC connected directly to power amp: Firstwatt F5, Harman Kardon 402 power amp or EL84 (as a pentode) with 12AU7 as a driver at a few mA with no global NFB and no cathode resistor just 8-9V negative voltage on the gate, volume is regulated in the digital domain. It's great, there is magic, listen to Macy Gray, album Stripped at 24bits and 96kHz and it sounds wonderful, I am really happy with it… but you know, there is always possibility that maybe… there is something more magical and it’s not the end of the journey 😕


I am lucky enough - not that I'm bragging - to own two matched pairs of Semisouth JFETs that I purchased a few years ago. Initially I was planning to build FirstWatt F6 - I have all the parts including transformers… but… I am happy with F5 and I don’t think that F6 will make a huge difference.

However recently I have read about F1J and F2J and this is completely new concept to me. I own a pair of Markaudio Alpair 12P so happy to build horns but not sure if these drivers is good match for these unusual amplifiers…

Guys, any magical experience with F1j or F2J? If so what speakers are you using with them? Or maybe you have other idea how I could use these two pairs of JFETs.



P.S. I need to mention that I have also some 2sk82 and 2sj28 that are still waiting to be used in some exciting project 🙂

cheers

 

[Zen Mod]

it really depends of room size, preferred type of speakers and SPL habit, which is - at lest for me, of utmost importance ..... so speakers having greatest role in overall sound

anyway, decide that, then amplification dilemmas

please, toobz are having Grid, not Gate

Gate are having these multilegged fuses

 

[ripson]

grid of course 🙂 by the way recently I have used your idea of curing 50 years old speakers with two layers of dammar varnish. What a difference! thanks for that! 🙂

 

[codyt]

Beyond the F1/F2j’s, another idea would be to use a pair on the bottom in ZM’s babelfish J2, which leaves you with an extra pair. They sound good in Aleph J too.

 

[Zen Mod]

glad that you found it useful 🙂

though, hardly that idea is mine ...... I read about Dammar for speaker cones eons ago

btw. they'll sound even better after some burning in, but you probably already know that

 

[ripson]

Thank you codyt, I'm goint to check out the Babel-fish project for sure.


but... I am still very curious about this power current source amplifiers 🙂

 

[Zen Mod]

that - only if you have efficient and sensitive FR or ER speakers

no particular use of current source amps with speakers made primarily for voltage amps (main difference is in xover)

 

[ripson]

yes, I understand, my only full range speakers are Markaudio Alpair 12P in Pencil and Karlsonator 0.53x with dual 3FE25-16. I have dammar treated EMI coax but with 2nd order XO on the tweeter, none of them are super efficient - around 92dB.



If someone own F1/F2/F1J/F2J and is more than happy pairing with some particular speakers please let me know. I am curious about your experience/thoughts. I like to explore new ideas.



Regarding room... not worried about it, have different rooms

 

[Zen Mod]

92db is OK

xover is not so critical if not complicated

 

[ripson]

OK then, cool, thanks, I am going to build F2J (probably I would need to design PCB - not sure if I remember the EAGLE), but first step LTSpice 🙂


I will report in next few months/years 🙂

 

[adason]

or build F1J, the boards may still be available
there was second group buy recently

 

[ripson]

works cool on the sim, the quiescent current of 2.63A flows through the transistors 😎

 

[Zen Mod]

2A63 is bit overoptimistic, when you don't need it - even for 4R spks

 

[indra1]

my only full range speakers are Markaudio Alpair 12P in Pencil and Karlsonator 0.53x with dual 3FE25-16. I have dammar treated EMI coax but with 2nd order XO on the tweeter, none of them are super efficient - around 92dB...

Perhaps it is a good idea to read or re-read the Current Source Amplifiers and Sensitive / Full-Range Drivers article. Out of the many drivers tested, the Jordan J92S would be the one most similar to the Alpair.

 

[ripson]

Perhaps it is a good idea to read or re-read the Current Source Amplifiers and Sensitive / Full-Range Drivers article. Out of the many drivers tested, the Jordan J92S would be the one most similar to the Alpair.

Thank you, I think I am going to build F2J anyway, it's relatively simple and quick to build (apart from designing PCB), I like the fact that the amp has no NFB which I guess results in having super clean treble (no phase shifts injected to the input and so on), not sure about the base with such damping factor, but hey, I will experiment with different speakers.

I understand that with the pot we set the symmetry until both peaks clip at the same time and with the MOSFET source resistor we can adjust the Id current. I guess it won't be necessary.

I think I feel something like excitement, the excitement caused by slowly approaching extraordinary musical and audiophile experience.

 

[indra1]

IIRC the Jordan has a slight 3dB bass boost.

 

[ripson]

I'm more concerned about the precision, tightness of the bass, not its "amount". We will see 🙂

 

[ripson]

I'm playing with F2J in LTSpice and I have added some non-resistive load and got ugly overshoots in 1kHz square voltage response... however the current running through the speaker is nice and square. Cool! 😀


EDIT: PS. Probably my SJEP120R100 spice model is not very precise.