JfetBOZ mods

[carawu]

Hm, what about a solid state aikido jfet gain block?


http://www.tubecad.com/2004/blog0013.htm

http://www.tubecad.com/2004/AikidoAmp12.gif



Carsten

[JPeitzman]

Kind of JBOZ/Pass, that is if you count it as a JBOZ with a buffer. Although an interesting circuit none the less. Maybe I will bread board this tonight along side my JBOZ and see what they sound like. I love my stock non-modded JBOZ, but the Aikido gets good reviews on the tube side...though it is no DHT

[JPeitzman]

Just built it but I only listened for about 15min since it is past my bed time . Keep in mind a few things:
1. I used what I had on hand and what was easy to reach, all the passives are right except a 3k3 at the drain of the input JFET and I am reusing the 22R from my JBOZ source. Because of this it has much more gain than the JBOZ.
2. I am using 2N4220's, they don't sound bad to me, but I am willing to bet that J310 or 2SK170's sound better...especially the 2SK's.
3. I am using a 24v regulated bench supply, most likely not the best for sound quality. iPod for a source, again not the best but it is always what I use.
4. I only have one channel so I can't get a super good feel for the sound.

Testing was done iPod -> line stage -> JLH Class-A Original -> speakers. Volume was controlled by the iPod, no pot robbed for this project just yet. Listened to: Ani Difranco, James Taylor, Hendrix, Stereo MC's, and a quick splash of Miles Davis. A lot of this was done just skipping around real quick, I'm tired.

Just real quick the bass seems a lot weightier than the JBOZ, but maybe not quite as controlled. It also seemed a bit more dynamic, it did however seem to get "lost" during complex rock passages. Ani Difranco live (Living in Clip) did sound good, but I feel that the JBOZ was just more natural. The J-Aikido sounded good with her, but with the JBOZ it just sounded a little more life-like, especially at the parts where she is just talking into the mic. Between her breathing into the mic, the acoustics of the concert hall, her un-miced drummer talking in the back ground, it was all there with the JBOZ. It was there with the J-A, it just didn't sound the same.

I am sure with some tweaks here and there the J-Aikido could sound very good. With unmatched FET's, a bench supply, and a handful of lose parts I wasn't expecting much with either circuit but I got a lot. In the next couple days I will play more with the gain, parts, and maybe try some NFb.

After an unfair (to the J-Aikido) and sleepy listen: J-Aikido -> 0 JBOZ -> 1 ...we will see what the weekend holds for these amps. I would still encourage the building of the J-A just for fun, it still sounds good!

Cheers

James

[carawu]

Hi James,

that´s really fast.
I hope, you build an 2sk170-Aikido and share your findings.

Carsten

[JPeitzman]

I have spent the past hour listening to the J-A and must say that it is really growing on me. I have to say that my previous review needs some amending as I was very tired and listened for a very short time, roughly 30min. I know to really comment on the sound I need to listen for longer even than just an hour, that will be tomorrows task. I will have time then to switch back between the J-A and the JBOZ.

Just real quick the bass seems a lot weightier than the JBOZ, but maybe not quite as controlled.

On the contrary after doing a little more listening the bass does seem well controlled. I can say it seems that compared to my JBOZ and my ESP P88 (using LM4562's) the bass is A LOT weightier. This thing really made my JLH sound like a new amp in the low mid and low range. Honestly in my setup I am saying kick in the teeth bass. The Aikido covered everything else quite well too. At times however I felt that the highs could get a little edgy or piercing. Of course the times it sounded piercing was when I had it turned up quite high. Thus far I have never had the JBOZ sound piercing or edgy, it is always laid back, warm, easy going, kind of like me. I personally feel that the bass on the JBOZ is a bit shy, though it is there. I feel too that it defiantly isn't at the same level as the bass in the Aikido. If you haven't guess yet the bass from this little monster really blew me away. The highs on the JBOZ are light and airy, I would say angelic. They are clean and clear yet fluffy, really quite nice. I feel to my ears the midrange is where the JBOZ really shines. Warm, liquid, psychedelic, I can say in honesty I prefer tubes, but the JBOZ comes close in this regard. When it comes to blues and jazz my weapon of choice for now (excluding the previous "I prefer tubes") is the JBOZ. After all the PSU noise and finicky behavior is worked out I think a well designed and built JBOZ could go toe-to-toe with a DHT line stage, or really any tube line stage. To add I think it could go toe-to-toe with any line stage and at the very least give it a solid run for it's money. I would say if the JBOZ is a DHT line stage, then I guess the J-Aikido is a...tube Aikido

It also seemed a bit more dynamic, it did however seem to get "lost" during complex rock passages.

This amp seems VERY dynamic and very fast. Like I mentioned above the bass has an authoritative slam that is quite controlled. The rest of the range is clean and detailed, focused. despite the bass nothing seems to really get over emphasized. As far a getting "lost", I can say now with almost 100% confidence this is not the case. I threw quite a bit at this line amp tonight, and everything pleased me. I gave it Massive Attack, Hendrix, Gorillaz, Bosten, Zeppelin, Stereo MC, anything I could think of to get the little electrons in this baby confused on their way out...nothing. Some of my "lost" before I figure/fear is just bad recordings on the source end. As far as I can tell the JBOZ does not exhibit any problems with getting "lost" either. I felt that the JBOZ was in fact very reveling and "invisible", what your source sounded like was what you got at your speakers. It was almost like the JBOZ wasn't even there so there was nothing for it to lose. At the same time though it was there, part of Papa's magic I guess.

The J-Aikido sounded good with her, but with the JBOZ it just sounded a little more life-like, especially at the parts where she is just talking into the mic. Between her breathing into the mic, the acoustics of the concert hall, her un-miced drummer talking in the back ground, it was all there with the JBOZ. It was there with the J-A, it just didn't sound the same.

I am not sure about this now, it all sounds very good on the Aikido. I will say that to my ears the JBOZ does sound warmer and smoother, liquid almost, not sure if it is 71A liquid...I hear very liquidy things about this tube...another time. But in all seriousness the JBOZ does sound much more like a tube than a FET. Nice warm yet clean mids with good clean highs, a little shy at the low end. Sounds like general tube banter huh, of course tubes can sound however you want them too. I am very attracted ( ) to the magic, warmth, and sound of the JBOZ. With enough time and some better listening though I think the Aikido could grow on me. I really like the sound of Miles Davis on the JBOZ, very liquid. Makes me feel as if I am sitting in a smoky jazz club or in a studio right there with everyone. It just wasn't quite the same with the Aikido, but it was close I can say. Maybe if I listen more and/or different parts with burn in it will take on a new sound. I added in a little "Riding with the King" (Clapton and BB King) just for a listen and I feel the same way. I don't know what it is for sure but for blues/jazz I like the JBOZ better. The second re-listen of James Taylor makes me think that acoustic guitar sounds better on the JBOZ too. I listen to acoustic a lot and play a little (try to very poorly), it just sounds more real on the JBOZ.

Maybe that is how it breaks down, JBOZ = Acoustic/Jazz/Blues ; Aikido = Rock/Techno/Movies (dynamic)/Rap( )/Pop( )/... I haven't listened to any classical/orchestra/large concert works yet so I am not sure how they would fit in here. I would guess it would go either way. The Aikido may pick a few more clean details out of the piece, but the JBOZ may be more smooth and natural. It seems too that after reading some reviews and thoughts on the tube Aikido that the JFET version carries a lot of the same traits. The tube version is often described as being focused and clean with huge bass slam. Also often said to be very fast. Now I am interested to build the tube version to see how it sounds and compares.

Keep in mind:
1. My setup, like other DIY'ers, is a build in progress and currently a slight mess.
2. These (the two line amps) are just bread boarded using cheap parts. Nothing is matched, the resistors are a mix of general purpose 1% and 5% metal films and 5% carbon comps. The caps are nothing special, Panasonic electrolytic's and film's, the exception is that the JBOZ uses big huge 10uF oil caps at the output. I didn't hook it up to a scope first, simulate it, I didn't even reach for my meter, I just built it, closed my eyes, and hit the switch. **I do not condone these actions, untested and double checked circuits could damage your system. Good idea to double check wiring and poke around with a meter a little first.** Another note on this though, I never sim. I don't own or have a single piece of simulation software. I do pen and paper and bread board, I am old school but I'm not old enough to be old school.
3. I am new still to audio so I haven't had a good chance to listen to other systems and compare a large range of units.
4. I am not a reviewer, I try to use words often used by reviewers to the best of my ability. I am trying to describe how it sounds to me, bold face me, it could and will sound different to different people. My system is different than others and my brain and ears work different than others.

Hopefully that was useful to at least one person, otherwise I guess my fingers got a good work out. As a final word, I would build both and see how they sound, but I would really say build the JFET BOZ. With 7 passives, a pot, and a JFET, add in parts for a real basic power supply and you are looking at about $25 or less if you already have a transformer. You could go up from there with Caddocks and Teflon caps...but with how good it sounds with lose and recycled parts I am sure some Wima's and Vishay RN's would be fine. I built mine in about 5min, hooked it up and it worked, no pops, clicks, bangs, booms, fires, blackouts. I can say that my LM4562-based P88 sounds very good, especially with movies and compared to my Sony theater in a box. But to my ears the JBOZ walks all over the P88 almost no contest. Just a word for those looking with hungry eyes at the J-Aikido, I feel that it beat my P88 too.

Cheers

James

[carpenter]

I simmed the F4 with my version of a choke loaded Jfet BOZ. Input is 1.5 volts. R29 represents a 4 ohm speaker load:

[carpenter]

Here's a close-up of the graph. Probe 2 is the voltage output of the JfetBoz; R29 node is the current available from the F4; D4-N is the voltage available from the F4. These measurements were taken with a 1.5 volt/1000Hz input into the Jfet BOZ.

[carpenter]

Ha.... a little bit of ZV7-T

[JPeitzman]

Sorry to sort of thread jack Carpenter. I just thought some people might want a quick and dirty comparison. I will have to try the choke loaded JBOZ, seems interesting.

[carpenter]

You're doing fine! I enjoyed reading about your experiment.

I'm having fun, too. The choke darn near doubles the JfetBOZ output; this is what I'm after in order to make an integrated JfetBOZ/F4. The simulation software is such a blast once you become acquainted with its personality. I'm thankful that Nelson suggested that I apply myself and enjoy the benefits!

I'm learning how to use the jfet single-ended and balanced. This way I can operate the hf horns single-ended and the midbass balanced (which means coupling two F4 in balanced mode--mo' power).

Gotta love DIY audio!

John