FirstWatt J2

[Zen Mod]

The one driver that didn't play nice was the Lowther PM6C

I have a vision!

altering Aleph AC gain makes wonders .......

 

[oltos]

clever

Okay, but will doing so

I'm not sure a soft start is necessary but I'm sure others will chime in, possibly Nelson himself.

If the old caps short out and hit my speakers with a spike I'd likely be badly screwed because my vintage Yamaha JA6681B drivers have no replacement diaphragms. Thus, assuming that the safest route is to replace all of the electrolytics in an amp this old, do Pass Labs or another company offer cap replacements on the J2?

 

[Ylab]

I would be surprising if the « old » caps short out. Just power it without no speaker or with a cheap speaker pair wired to it. If no boom and music you are good to go. It’s not a vintage amp from the 70s. It’s a top of the line amp with very good quality part. If the power supply caps have somehow degraded, it will not go boom on your speaker, most likely just a little hum. Maybe

 

[Marcus Halberstram]

If the amp hasn’t been powered for 8 years, it certainly wouldn’t hurt to bring it up slowly on a variac, as you initially suggested. That’s pretty much normal practice. Sleep better at night

 

[adason]

I would put cap (bipolar, few hundred uF) first between amp and speaker, run it with cheap bookshelfs for few days, if its fine, it will ok.
It helps to bring it up slow, but i would not change filter caps, likely good still. Waste of money.

 

[WBS]

The best information is available at the source. Go to their website and follow the pull down menu to "Support" and ask your question about caps.

Cheap "donor" speaks would be the way I'd go.

 

[labjr]

Just plug it in already! The suspense is killing me!

 

[Blues]

I have an original Aleph 3 from 1998 with original ps caps...I use it on 95 dB speakers.

 

[adason]

Just plug it in already! The suspense is killing me!

...or send it to me

 

[oltos]

BINGO! Forgot about my cheap pair of Panasonic speakers. Using those together with the Variac for a few hours should prove a good test.

Sorry, no can do adason. With the average system impedance and sensitvity of my new speakers, the J2 is probably about the best match I'll ever find for them. https://www.stereophile.com/content/first-watt-j2-power-amplifier-measurements

Thanks all.

 

[Nelson Pass]

Not too long ago I did repair work on a pair of Stasis 1's (corrosive water damage). The 45 year old caps fired up and still met mfr's spec and I haven't seen much in the way of failed caps except obvious abuse - excessive current, voltage or temperature.

.

 

[awc]

Does anyone have any PCB for J2 I can buy please ?

 

[AllenB]

Some substitute links for the first post..

https://www.firstwatt.com/j2.html

https://www.firstwatt.com/pdf/prod_j2_man.pdf

https://www.firstwatt.com/wattsnew.html

http://www.6moons.com/audioreviews/firstwatt10/j2.html

 

[EUVL]

https://www.diyaudio.com/community/...fier-lm317-efficient-and-simple.402477/latest

A clever use of LM317.
But you will need LM317HV with booster in the J2.
Or 2~3x 317HV in parallel. At least 50V, 3A.

Or LM338 TO3, if you can live with 20V rails.


Patrick

 

[EUVL]

Just to illustrate :

Patrick

 

[PKI]

Just out of curiosity, what is the advantage compare to original topology?

 

[EUVL]

Much simpler, standard, low-cost components, no unobtanium,
not dependent on optocoupler Vf and CTR tolerances (i.e. identical channels).


Patrick

 

[Blues]

Early on when we were still trying to figure out the J2, I shared a similar "J2" circuit with TL431 to set the bias...

 

[vdi_nenna]

Hi Patrick, is the above a simplified schematic or can a circuit be built as is?

Thanks.

 

[EUVL]

Should work as is, but I haven't build.
If you want to try, suggest you use a MOSFET instead of Semisouth first.
If it works fine, then change.
Won't cost you much.


Patrick