Had some time today to test the MB, which appears to be working. I am using one of the DC-DC converters that have been mentioned. Got the B+ on the board dialed in at 48vdc with about .25mv ac ripple, really nice and clean design.
Thanks all.
Thanks all.
yep both sets (low and high gain) are completed. Do some bench testing today and then start the case build.
Thank you all. I just tested both pairs of DB playing into one A7 speaker. Everything working as it should.
A testament to the design and layout folks that made this project so successful.
Now on to mounting it into the final cabinet.
A testament to the design and layout folks that made this project so successful.
Now on to mounting it into the final cabinet.
Almost X. I have three builds, ImPasse, MoFo and AKSA preamp in the final stages of drilling holes and cases for each. So very close now to finishing all three and then photos.
I have been using the Impasse since it is mostly built to feed the Mofo which is also mostly built, sounds really nice.
Looking forward to having the ImPasse, AKSA and BA-3 preamps to play with, using the MoFo and two F4 amps.
Thanks to all for such neat and fun projects.
Regards,
David
I have been using the Impasse since it is mostly built to feed the Mofo which is also mostly built, sounds really nice.
Looking forward to having the ImPasse, AKSA and BA-3 preamps to play with, using the MoFo and two F4 amps.
Thanks to all for such neat and fun projects.
Regards,
David
Well finished the case yesterday, assembled, with all of the wiring in place. Turned it on and yes, it works (also worked bench testing earlier). Started changing out DBs and now no amplification.
So started trouble shooting each side with a different DB (I built both high and low gain versions), nothing. The signal will pass through the circuit without the preamp being turned on. Same level in equals same level out. Also the pot has no effect on the signal whether the preamp is on or off.
Not sure what I did. I removed the active devices from both the MB (only two there) and the ones on a DB and checked them, all are working.
Checked the DC-DC converter, ok there. Output of the Cap MX, also working, ripple still holding at around .3mvdc.
At loss here.
After several hours I am thinking perhaps just order more boards and start over.
Thoughts, suggestions
Thanks
David
So started trouble shooting each side with a different DB (I built both high and low gain versions), nothing. The signal will pass through the circuit without the preamp being turned on. Same level in equals same level out. Also the pot has no effect on the signal whether the preamp is on or off.
Not sure what I did. I removed the active devices from both the MB (only two there) and the ones on a DB and checked them, all are working.
Checked the DC-DC converter, ok there. Output of the Cap MX, also working, ripple still holding at around .3mvdc.
At loss here.
After several hours I am thinking perhaps just order more boards and start over.
Thoughts, suggestions
Thanks
David
So none of the DB’s work now? Is there any noise or hiss at all or silence? With DB’s installed and amp turned on, is there any bias current flowing? Check by measureinf voltage across R14 or R15 on the TH DB. On SMT board it is R116 and R117.
If there is current flowing but no sound - check on MB if your audio in vs audio outs have been switched. The inputs are on the inside of the 8pin connector and outputs on the outside. Half of them are GND on side closer to volume pot.
The signal should not pass through the circuit without amp being turned on. That sounds like you may have wires on 8 pin connector backwards. Signal is on ground which is all connected together.
If there is current flowing but no sound - check on MB if your audio in vs audio outs have been switched. The inputs are on the inside of the 8pin connector and outputs on the outside. Half of them are GND on side closer to volume pot.
The signal should not pass through the circuit without amp being turned on. That sounds like you may have wires on 8 pin connector backwards. Signal is on ground which is all connected together.
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Well X, it turned out to be none of the above. Been spending a bit of time trouble shooting individual channels and discovered why the preamp worked when I completed it yesterday.
In the process of changing the RCA cable going the amp, I moved the Left channel RCA chassis connector and those little plastic collars that are supposed to keep the connector body from touching metal did, just enough to cause an intermittent short to ground.
Bang head slowly on wall!!!
Thanks for being there
In the process of changing the RCA cable going the amp, I moved the Left channel RCA chassis connector and those little plastic collars that are supposed to keep the connector body from touching metal did, just enough to cause an intermittent short to ground.
Bang head slowly on wall!!!
Thanks for being there
Yes finally got everything sorted, buttoned up the case and now enjoying music through the Pass F4s
Yes a really nice preamp. I will in the future play with some of the caps, for now just enjoying.
Thanks to all.
David
Yes a really nice preamp. I will in the future play with some of the caps, for now just enjoying.
Thanks to all.
David
Attachments
Very nice work DrPro! Beautiful fit. Congratulations!

So you are the first to try with F4 which was probably the target “audience” for this Preamp. Please share your listening impressions when you have more time clocked on the amp.
Cheers,
X

So you are the first to try with F4 which was probably the target “audience” for this Preamp. Please share your listening impressions when you have more time clocked on the amp.
Cheers,
X
Will do, it's playing now at the moment. My homage to Nelson is the blue LED on the front, not very clear in this photo, but yes it is blue.
Yes finally got everything sorted, buttoned up the case and now enjoying music through the Pass F4s
Yes a really nice preamp. I will in the future play with some of the caps, for now just enjoying.
Thanks to all.
David
That looks great!
Is that a commercially available case? looks like it's the perfect size.
Cheers,
Gable
Thanks Gable. It is, came off of Allie Express. I bought it for my ImPasse build and those that know tubes better than I said it would be a bit tight with the transformer, PS, and preamp board so close together. Hum and such would occur. So I saved it for later. I had to cut the sides and front and rear panels down by about 2" and drill new holes. Never again, too much time and my fitment of the holes is awful.
You might check the cases on that site, very reasonable even with shipping costs added. My cut down exterior dimensions are 12"x8.5"x3 (LxWxD). The various other bits came from Apex Jr. and Parts Express.
David
You might check the cases on that site, very reasonable even with shipping costs added. My cut down exterior dimensions are 12"x8.5"x3 (LxWxD). The various other bits came from Apex Jr. and Parts Express.
David
Thanks Gable. It is, came off of Allie Express. I bought it for my ImPasse build and those that know tubes better than I said it would be a bit tight with the transformer, PS, and preamp board so close together. Hum and such would occur. So I saved it for later. I had to cut the sides and front and rear panels down by about 2" and drill new holes. Never again, too much time and my fitment of the holes is awful.
You might check the cases on that site, very reasonable even with shipping costs added. My cut down exterior dimensions are 12"x8.5"x3 (LxWxD). The various other bits came from Apex Jr. and Parts Express.
David
That is a lot of work! I'm still planning my build for now, I'll poke around for similar cases.
Thanks!
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