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First Watt J2 single-ended, Class-A, all-J-FET amps

70.162.135.70

Posted on December 23, 2014 at 16:58:25
jeffreybehr
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Bought one to evaluate and then quickly another to power my 97dB-sensitive Serenity Acoustics Super-7s.
 photo 2014Dec23_Roompano_SAM0164_1800w_zps4bbcb1be.jpg

With Nelson Pass's approval, I wired the 2 channels in each amp in parallel; max. power went from 30WPC into 8 and 15WPC into 4 to 30 Watts into 8 and 60 into 4. Have added highest-quality powersupply-bypass caps--BlackGate FK 2200/35s and SoniCap 0.47uF Platinums--on the boards as close to the output transistors as possible...
 photo 2014Dec15_outputbypasses_1000w_zps775393b1.jpg
The BGs are visible hanging from the board but the Platinums are farther 'back' and not visible.

The longer I listen, the more convinced I am that this amp-and-speaker combination is the best I've ever had, and the amps I've had include WAVAC MD-805m and Coincident Frankenstein II SETs. This combination is VERY musical, full range*, and resolving.

I'm THRILLED.

* with response well into the bottom octave with their powered woofers

 

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RE: First Watt J2 single-ended, Class-A, all-J-FET amps, posted on December 26, 2014 at 08:46:52
AbeCollins
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Very nice!

I was looking at some First Watt amps but I recall that my Aleph 3 and Aleph 30 at 30wpc were marginal in driving my 91dB Tannoys. They played music beautifully but were a little dynamically constrained.

Your speakers appear to be much better suited for lower power amps. Nice room too!

 

RE: First Watt J2 single-ended, Class-A, all-J-FET amps, posted on September 28, 2016 at 19:42:28
bare
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Really? can only assume your Tannoys are either Damaged or Imposters.
Missing Dynamics ! really? Beyond my experiences Mate.
My Golds startle me with their dynamics, every time I fire 'em up... with the Lowish Power of my F6... it's Very Nice.
Better in fact than with Any other amp I've fitted to them over the last 42 years.
The above combo has eliminated ..any.. further upgrade lust.. likely to the end of my days.

 

Reading this months after it was written..., posted on March 6, 2017 at 15:26:20
jeffreybehr
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...your 'The above combo has eliminated ..any.. further upgrade lust.. likely to the end of my days.' comment mirrors how I feel about my current all-real*-triode output-transformerless poweramps, Atma-Sphere M69 Kk3.3s, slightly improved, of course.
 photo 2016Jun08_RC amp_2000w_zps9s1hjral.jpg

Rated at about 40 Watts into 4 Ohms, they sound fabulous with the Super-7s. The trio of Tung-Sol roundplate 6SN7GTs in each may have something to do with that.

* as opposed to triode-wired pentodes or tetrodes.

 

RE: Reading this months after it was written..., posted on March 6, 2017 at 17:48:08
coolhand28
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Looks like great work!What would you do to improve sonics on my pass xa 30.5?All i've done is change 5 ways that Pass uses to Furutech that he uses on .8 series.....Mike

 

TYVM, Abe. (NT), posted on December 26, 2014 at 10:31:29
jeffreybehr
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.

 

RE: First Watt J2 single-ended, Class-A, all-J-FET amps, posted on December 25, 2014 at 13:53:03
Ric Schultz
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I see you have removed the bolt from the transformer. This is good. If the screws holding down the diode bridges are magnetic then change them to brass hardware for better sound as well. Same with the washers and screws holding down the big transistors. Remove the indicator LEDs if you have not done so. They really mess up the sound. Remove all AC filters (thermistors, etc.)....they veil the sound. Put a top of the line Audio Magic fuse in it, bypass the binding posts, use better input wire, output wire, input jacks, power supply wire, better solder, resistors, smaller faster bypass caps (my modded Wimas for instance), damp the heatsinks, twist tightly the AC wires to and from the transformer.....plenty more to do after this too!

One does not need anyones approval to mod a piece of equipment. Once you own it you can do what you want. Obviously, mods can effect resale value.

 

It would be interesting to hear what Nelson Pass might say..., posted on December 26, 2014 at 02:12:03
... about some of your ideas. I would imagine that he's aware of what some hobbyists are doing with his stuff. I would also imagine that he is a pretty liberal or open-minded guy when it comes to new ideas, so long as they rest upon a firm scientific and audible basis.

To your knowledge, has Pass ever personally chimed in to approve or disapprove of anything proposed by various tweakers on audio boards?

 

RE: It would be interesting to hear what Nelson Pass might say..., posted on December 26, 2014 at 19:09:41
Ric Schultz
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"While I don't pursue the same methods, you are correct that playing with the circuit while listening yields a lot of benefits. I like to concentrate my efforts in my particular style - I leave others to pursue it in their own way.

You are of course free to play with my designs as you like."



The above is the exact email Nelson sent me when I informed him of my intentions to offer mods on the First Watt amps. Basically, what he is saying is that he is not interested in parts and execution.....only circuit design. Once he said that people would send him different caps and resistors to play with and his comment was "why don't they send me better transistors?". He has the world's only stash of power Jfets and had his SITs made custom for him. He likes devices and circuits. Not interested in wires, caps, damping, solder, sound of LEDs, etc. His products sound great because they are made well and the circuits are fantastic and simple and pure......but circuits are only 50%. The other 50% comes from execution. You would die and go to heaven if you heard one of his circuits (or any great circuit) executed to the max.

I have had zero people send me First Watt amps to mod....a couple of people said they would but never did. I mean, you spend $3000 on a low power amp that you may sell shortly (you know, you are looking at less sensitive speakers, whatever) so why invest in an amp that will lose resale value because some "tweaker" made it sound better?

Back in 98 I was going to produce an all out class A amp but could not find the means to get heatsinks and chassis in small quantity with large enough heatsinks......now there are chassis from Italy and China that are made for Class A circuits. So, I have decided to make my own Class A amps now....now finally, people can hear a great class A amp done with great execution. Should be fun.

 

RE: Your own class A amps, posted on December 27, 2014 at 07:37:21
Sounds good, I'm sure you'll find many here who will be interested in your products.

 

Two things, posted on December 27, 2014 at 06:05:12
1973shovel
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"[Nelson's] Not interested in wires, caps, damping, solder, sound of LEDs, etc."

I'm not a Pass devotee*, but I do admire the respect he garners among those who truly know amplifier circuits. I will take a slight exception to the above statement, only because I read a post somewhere of Pass recommending Elna Silmic electrolytic capacitors for their sonic quality. It's a minor quibble though, and in general, your point is well taken.

"why invest in an amp that will lose resale value because some "tweaker" made it sound better?"

I'm not an equipment flipper, so I ask myself, "Why not get all I can out of my F1?" (upgraded to F1J by Pass). But, even though I have little doubt that it could be sonically improved, I baulk because of the resale value. If I'm going to keep the amp, it makes little sense, I know. Maybe if there were 1001 or even better, 10,001 of them made, I might be more willing. But with only 101 of them out there, I'm far more cautious of doing something I'll regret.

*Some of his followers call him "Papa", which kinda gives me the creeps.



 

Pass does participate in the DIY Audio Pass Labs forum., posted on December 26, 2014 at 10:26:49
jeffreybehr
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http://www.diyaudio.com/forums/pass-labs/

Since I can't get a schematic for this amp, I've e-mailed him several times to discuss the functions of various devices in these amps. He's been informative, helpful, and, if not exactly encouraging, at least not discouraging at my intentions.

 

RE: Pass does participate in the DIY Audio Pass Labs forum., posted on December 26, 2014 at 10:39:29
A.Wayne
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NP,

Is one of the great guys in audio, not only exceptionally talented as a designer , but well respected and respectful as well , I'm a big fan and always have a few of his offerings at one time or the other on hand...

NP telling you to give it a go is not unexpected , he welcomes your discovery ..:)

Regards

 

RE: Pass does participate in the DIY Audio Pass Labs forum., posted on December 29, 2014 at 01:16:38
morricab
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WHat? No bashing of his horribly underpowered clip machines?!?!? Aren't you going to tell him how his 25 watt distortion generators will be clipping continuously and that he must love the sound of distortion?? No...hypocrisy is a word I guess you are familiar with.

 

Who is 'him'? We were discussing Nelson Pass., posted on December 30, 2014 at 21:09:30
jeffreybehr
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And if your note is what passes as a helpful comment from you, then I agree with Mr. Wayne--you better adjust your meds.

 

RE: Morri Please up the meds ... , posted on December 29, 2014 at 13:56:50
A.Wayne
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Morri,

Err, Hmmm, Please ask your helper to read the OP, they are bridged , lot more than 25 watts and look at that, 97db sensitive speakers to boot, get a hold of yourself man.


 

Paralleled, Mr. Wayne, paralleled, not bridged., posted on December 30, 2014 at 21:12:08
jeffreybehr
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When paralleled, two channels double current compared with one channel. When bridged, they double Voltage.

 

RE: Paralleled, Mr. Wayne, paralleled, not bridged., posted on September 27, 2016 at 17:09:03
cin5
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Congrats Jeff with all of your audibly successful mods on the J2 amps. I also have a J2 amp and will use it to drive clones I'm building of a very successful two-way hybrid horn system. Designed by Gary Dahl and Lynn Olson, the mains are Radian 745 Neo/Be drivers in Azura 425 horns. They are passively crossed to a pair of GPA Altec 416-B midwoofers. The sealed cabinets cut the midwoofers off at just below 70Hz, where my pair of Rythmik 12" sealed servo subs take over. System sensitivity is 97db and impedance is between 8 and 7 ohms. My room is only 14 ft x 19 and my average listening levels will probably be between 68 and 75db @ 70Hz at 11 feet, before my subs kick in. https://en.wikipedia.org/wiki/Fletcher%E2%80%93Munson_curves So the J2 would hardly break a sweat pushing these speakers.

Two questions.

1.) Sadly, things have changed and after completing these speakers I won't be doing much more DIYing. But as you are clearly thrilled with the increased sound quality from your modded J2, might you or someone you know do these J2 mods to order? I'd want the mods that would most contribute to the improved sound.

2.) Have you ever heard the Pass XA30.5? If yes, how would you compare its sound to that of a stock J2 amp? More precisely, how would compare their sound when the XA30.5 is under load such that the needle of its front panel ammeter is very close to its center position-that is, where the amp is operating within its Class A bias region?**

Bigger soundstage in all dimensions? Deeper more robust midbass and low bass? More 3D imaging. More lifelike midrange? More extended and sweeter sounding highs? Better micro and macrodynamic detail? Better overall tonality?

Also, perhaps a rather silly question, but I am curious about which amp makes a better space heater.

** The Pass XA30.5 does 30 wpc and can handle 60 watt peaks, all in Class A. Beyond this output level it moves into Class AB where it does > 100 wpc.


 

I've never heard ANY Pass Labs amps AFAIK., posted on September 30, 2016 at 17:18:30
jeffreybehr
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Most-probably, Jeffrey Glowacki of Sonic Craft could and would perform the upgrades that I did on mine.

 

RE: I've never heard ANY Pass Labs amps AFAIK., posted on October 2, 2016 at 16:00:19
fantja
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Are you out there?

 

RE: I've never heard ANY Pass Labs amps AFAIK., posted on October 1, 2016 at 05:30:46
fantja
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Good to see you- Jeffrey

please post some current pics of your system! Any new gear arriving to you this Fall?

 

RE: Paralleled, Mr. Wayne, paralleled, not bridged., posted on December 30, 2014 at 22:00:00
A.Wayne
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Yes , correct , i had missed you saying parallel as opposed to bridge ....




Regards ...

 

Thx for the further suggestions. I'm sure I'll do at least..., posted on December 25, 2014 at 23:55:05
jeffreybehr
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...some of them. :-)

I removed that power-transformer screw because in this later-of-the-two amps the PT is silicon-sealed to the floor of the amp. In the earlier amp, the PT is not glued in and I'll be replacing the screw/nut/washers with brass stuff.

 

RE: First Watt J2 single-ended, Class-A, all-J-FET amps, posted on December 25, 2014 at 17:47:27
fantja
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Agreed- RS.

 

RE: First Watt J2 single-ended, Class-A, all-J-FET amps, posted on December 25, 2014 at 12:24:06
A.Wayne
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Congrats on the setup jeff are your speakers 98dB/w/m ..? if so i can imagine a good match if above 4 ohms ...


Enjoy..

Regards...

 

Speaker sensitivity is 97dB broadband. (NT), posted on December 25, 2014 at 23:49:46
jeffreybehr
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.

 

As one First Watt owner to another, posted on December 25, 2014 at 09:34:25
1973shovel
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Thanks for your detailed post.

I have a First Watt F1J which I've considered tweaking. How did you get Nelson Pass to bless your hot soldering iron? And my second question would be, did you come up with a focus area for the improvements yourself, or did you seek guidance?

Thanks again for posting.

 

Pass didn't bless my improvements project..., posted on December 25, 2014 at 23:48:41
jeffreybehr
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...he blessed my wiring the two channels in parallel.

First, I don't change the circuitry, only the parts, usually like-for-like values. I tend to want LOTS-higher-quality parts in my equipment than the manufacturers install. Altho these amps retail for $4K each, they still have some inexpensive parts in them. I also tend to add the highest-quality stuff I can buy in the main-left/right channels, and I also believe in Steve McCormack's (and now c-j's, too) 'DNA'--Distributed Node Architecture--filosofy, which would be more-accurately named distributed powersupply architecture or DPSA. This adds small powersupply caps and film-type bypasses very close to the output transistors.


So I added highest-quality DPSA caps first and also replaced four small 'lytics on the boards with BlackGates and the binding posts with Cardas CCGRs. Soon I'll replace the RCA jacks with Furutech FP-901(R)s. Both of these connectors are singles since both amps are now monoamps. Will replace ALL the rectifiers and PS caps and resistors with the best I can buy.

I believe Pass designs excellent circuits and definitely has one great idea (among MANY others, I'm sure), that being the use of nonmagnetic parts.

What little I know about all this comes from decades--remember Peter Moncrieff's WonderCaps of the very early 1980s?--of DIYing this kind of stuff, sometimes not too well and learning from my mistakes. The last maybe-decade I've fallen under the influence of Jeffrey Glowacki of Sonic Craft, still the only audio advisor who has a 100%-correct record with me. What that means is what he recommends I do always works sonically, and what he recommends against but I did anyway is MUCH less successful. Glowacki definitely helped on this project.

FWIW, I also tend to pay no attention to whether the manufacturer's warranty is voided by my improvements--I simply do what I think I ought to do. Generally, I'm fortunate to be able to write that my results have turned out to be excellent.

 

RE: Pass didn't bless my improvements project..., posted on December 30, 2014 at 23:16:24
pictureguy
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Don't forget, Jeff, that even a NON-magnetic metal, when in a magnetic field or conducting a current WILL have an induced current (and a resultant magnetic field). I've made a demonstration Shaded Pole motor using an ALUMINUM pie tin!
The only way to avoid that is to go to PLASTICS which don't conduct.
Too much is never enough

 

Ahh, I see, posted on December 27, 2014 at 06:23:52
1973shovel
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"FWIW, I also tend to pay no attention to whether the manufacturer's warranty is voided by my improvements"

I admire your attitude, and admit I'm cautious in this area. Not that my F1J amp has a warranty. But, as Ric Schultz commented in another post in this thread, "He [Pass] has the world's only stash of power Jfets", so I'm less inclined to dive in than if I could order replacement parts from Mouser or Digi-Key.

Thank you again for posting about your work, and your results. Even if I keep my soldering iron cool for my F1J, and only heat it for my tube amps, I really enjoy reading about your process.

Thanks!

 

RE: Pass didn't bless my improvements project..., posted on December 26, 2014 at 20:51:15
Ric Schultz
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The hardware may be non magnetic, but all those large Panasonic ten cent 3 watt resistors all have steel end caps.

 

Yup, but the Mills MRA-12s to be installed aren't magnetic. :-) (NT), posted on December 26, 2014 at 21:56:37
jeffreybehr
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.

 

RE: Yup, but the Mills MRA-12s to be installed aren't magnetic. :-) (NT), posted on December 26, 2014 at 23:53:58
Ric Schultz
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Smaller parts sound better....use the 5 watt Mills or parallel them if you need more wattage. If they are feedback resistors then use 1 watt PRPs....even better. You can also bypass Mills or large resistors with nude Vishays of much higher value. If you need a .47 ohm resistor then bypass by a 20 ohm nude Vishay.....better sound and the 20 ohm will only lower the value a tiny bit (.459 ohm)

 

RE: Yup, but the Mills MRA-12s to be installed aren't magnetic. :-) (NT), posted on December 27, 2014 at 03:51:43
fantja
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Interesting stuff guys!

 

RE: First Watt J2 single-ended, Class-A, all-J-FET amps, posted on December 24, 2014 at 04:55:02
fantja
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Excellent pics! Jeffrey.
How long have you owned the First Watt amps?

 

TYVM for your kind words. I bought the J2s in late October..., posted on December 24, 2014 at 11:54:47
jeffreybehr
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...from Reno HiFi.

 

RE: TYVM for your kind words. I bought the J2s in late October..., posted on December 24, 2014 at 12:20:20
fantja
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Yes, Reno hifi is well regarded.
Earlier this year I got my 1st taste of Pass Labs and want some more...

Which brand(s) cables & power cords are you using in your system?

 

Main powercords are DIY, all from Sonic Craft--Neotec UPOCC wire..., posted on December 24, 2014 at 15:56:05
jeffreybehr
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...of 13g. (for frontend stuff) or 11g. (for poweramps). Ends are Furutech--25(R)- or (mostly) 28(R)-series, altho the new looong cords for the J2s--fed by the main c-con, an Audience aR12 (Imp.)--will use the new 48(R)-series ends.

Feeding the Epson projector and the MET150 poweramp--both from the aR12--are 2 fairly long lengths of DH Labs PowerPlus cable with 25- or 15-series Furutech ends. The Crown SuperSubs amp, a CDi2000, is fed by a Pangea-9. The Super-7's bassamp PCs are now cheap no-brand stuff; I'll soon be building a long 10g. extensioncord--from the aR12--to feed those 2 plus the Crown and probably will build, using a stub of DH Labs wire, short PCs to feed the S-7 bassamps.

IC--The two long pieces--white with green stripe--feeding the J2s are Neotec solid-UPOCC-silver cables (NEI-1002). The frontend cables for the front-three channels are Audioquest Niagara with solid-silver conductors. IC for the surrounds and Crown SuperSubs amp are inexpensive AQ stuff.

It's quite a mish-mash, with quality ranging from the best I can buy (IMO, of course...:-)...) to barely-hi-end stuff. The entire system is quite complicated* for a hi-end system, and often I'm amazed that it sounds as good as it does.

Hinted at above is my current project--recabling power to feed ALL 14 pieces of equipment in the system from the main Audience p-con. Currently I have four p-cons--two from Audience (the aR12 and an aR2P-TO feeding the J2s)--plus 2 inexpensive Tripp-Lite isolation-transformer-based units in the system. Within a month or two I plan to buy a high-current--powered by 240VAC--Equi-Tech balanced-power p-con.

* For example, there are 21 ICs plugged into the back of my c-j 6-channel preamp...
Rear of MET1 photo 2014Dec24_rearofMET1_1200w_zpsf7980605.jpg
...and 13 channels of power-amplification functioning as 10 active channels.

 

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