Could a bad cap cause this? The 10uF are Panasonic FC from 10 years ago (stored in sealed bags) but I measured them and they measure very well still so I used them. All the other caps are new.
Page 7 of the pdf shows the pin 1 ID.
It is as the third diagram of Zen Mod's attachment - the line parallel to the edge indicates the side where pin 1 is located.
Thanks ZM and Ben!
Update:
I removed the boards from the chassis to inspect them and then reinstalled them so I redid the input and output connections and re-grounded the input+ for both channels and it's being well behaved now. I put dummy loads on output and disconnected input+ from ground and it's still stable so crossed fingers and connected to speakers.
It's playing music now and sounds great so far but I get a slight buzz on one channel when I touch volume know on preamp (!!!). The boards are installed in test bed so this chassis/PSU is well tested ...
I may revisit how my ground connections are done on the boards. Right now I have OUT- | PSU GND | IN GND | IN- | IN+
Damn gremlins!
Anyway, happy to report that no magic smoke seems to have been released and I have music in my room thanks to ZM and Papa once again!
Update:
I removed the boards from the chassis to inspect them and then reinstalled them so I redid the input and output connections and re-grounded the input+ for both channels and it's being well behaved now. I put dummy loads on output and disconnected input+ from ground and it's still stable so crossed fingers and connected to speakers.
It's playing music now and sounds great so far but I get a slight buzz on one channel when I touch volume know on preamp (!!!). The boards are installed in test bed so this chassis/PSU is well tested ...
I may revisit how my ground connections are done on the boards. Right now I have OUT- | PSU GND | IN GND | IN- | IN+
Damn gremlins!
Anyway, happy to report that no magic smoke seems to have been released and I have music in my room thanks to ZM and Papa once again!
Congrats! FWIW, my build was very picky about ground arrangements and definitely picked up on some inadvertent ground loops I’d created. Since I’ve addressed them, it’s been quiet as a mouse.
It feels like Diana Krall is singing in front of me but breathing on the back of my neck ... 
It's too soon to try and imitate Srajan until I get more hours but so far it's definitely worthy of building and the best/worst part is it's only the IRFP150 version so far. This will be fun toy for sure! F6 was too restricted to even try Cree but this one definitely works!!!
It sounds sweet and very clean at the same time. Similar to amp that lived in test bed just before that uses small number of parts and Renesas Laterals. I am playing through FrugalHorn v1 with Fostex Fe126 and ARC LS7 in front. Source is CD with Denafrips Ares 2 DAC.
I was talking to that Dennis guy a couple of weeks back and we agree that we need to find what 'normal' amp sounds like because we are treated to Papa amps for so long. Spoiled for choice for sure!
Babelfish treatment is extra on top! Thank you ZM!
It's too soon to try and imitate Srajan until I get more hours but so far it's definitely worthy of building and the best/worst part is it's only the IRFP150 version so far. This will be fun toy for sure! F6 was too restricted to even try Cree but this one definitely works!!!
It sounds sweet and very clean at the same time. Similar to amp that lived in test bed just before that uses small number of parts and Renesas Laterals. I am playing through FrugalHorn v1 with Fostex Fe126 and ARC LS7 in front. Source is CD with Denafrips Ares 2 DAC.
I was talking to that Dennis guy a couple of weeks back and we agree that we need to find what 'normal' amp sounds like because we are treated to Papa amps for so long. Spoiled for choice for sure!
Babelfish treatment is extra on top! Thank you ZM!
Great review twitchie. I need to get crackin on re-matching my 2sk2145. About half way through 100 jfets. The new setup with the jig is much more reliable/repeatable in terms of results but I can't find enough time to sit in front of it waiting for each jfet to stabilize.
I also have a test bed with small number of parts and with Exicon laterals right now. I love the sound of that amp, so this is even more exciting.
I also have a test bed with small number of parts and with Exicon laterals right now. I love the sound of that amp, so this is even more exciting.
It feels like Diana Krall is singing in front of me but breathing on the back of my neck ...
Similar to my experience with Led Zeppelin and the Babel J2. 😱
Congratulations!!! 🙂 🙂 🙂
Another Babelfish J2 sings!
First sound on the right channel! Or is it the left channel???? No, right channel
This is with Semisouth SEJP120R063 down and IRFP150 up. I’m getting about 720mV with P202 maxed out. It’s not fully cased yet so final adjustments remain. Playing a few quick tracks with an Amazon Echo Dot as a source it’s sounds REALLY good so far. Really looking forward to getting the other channel finished.
Thanks ZM!!!
First sound on the right channel! Or is it the left channel???? No, right channel
This is with Semisouth SEJP120R063 down and IRFP150 up. I’m getting about 720mV with P202 maxed out. It’s not fully cased yet so final adjustments remain. Playing a few quick tracks with an Amazon Echo Dot as a source it’s sounds REALLY good so far. Really looking forward to getting the other channel finished.
Thanks ZM!!!
Attachments
Last edited:
Awesome - congrats! Using the SS’s I also topped out my bias pot around 750mv/1.5Iq. I believe it’s an easy resistor tweak if you’d like to get more out of it. I’ve been playing around with MOX values and that’s bought me a little more current, so I’ve not swapped any resistors. That said, I did have to make a resistor swap to get my offset to 0. Guess it’s a small price to pay for a listen to those sweet semi’s 😀 My absolute favorite amp, hands down!
Thanks Cody! So far it seems like P201 has enough adjustment to get the offset to 0mV. So the chassis is from an F7 clone. It is the 4u/300. The sink was getting pretty toasty after about 15 minutes. I wouldn’t want to take the bias up any higher, but I have a 5u/400 waiting on the shelf for this amp. 😀 Just didn’t have the time to build up a new power supply yet before the basement starts construction on Monday.
So ZM, what is the best tweak to increase bias a bit?
So ZM, what is the best tweak to increase bias a bit?
P102 is for Iq set, while P101 is for output DC offset chase
if you need more of any, just increase resistor in series with trimpot
for instance, R123 goes to 510R, R118 goes to 1K2
do not forget to go back with trimpot before powering up
everything referring to schm in post #1
if you need more of any, just increase resistor in series with trimpot
for instance, R123 goes to 510R, R118 goes to 1K2
do not forget to go back with trimpot before powering up
everything referring to schm in post #1
Thanks for the guidance ZM. I’ll hold off on any changes until I get both channels up and running in the larger chassis. Hope to post some listening impressions very soon.
