and?
Babelfish F8 is better than Aleph Jzm is better than Aleph J
Babelfish F8 is better than Aleph Jzm is better than Aleph J
Biasing up now. One channel at 485mV on R16 with dead 0V offset. Other channel 485-495mV and can't trim below 65-70mV offset.
The channel with high offset started way up around 700mV and took a lot of turns to reduce.
Anything that needs to be addressed?
.. Per last 20 minutes a little higher at 85mV with temps up.
The channel with high offset started way up around 700mV and took a lot of turns to reduce.
Anything that needs to be addressed?
.. Per last 20 minutes a little higher at 85mV with temps up.
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So that is an Iq of approx 1.75A - now do you have the correct values of R6 and TP1 which adjusts the DC offset depending on Semisouths or IRFP in OS, according to the schematic in post #1?
My offset would dance up and down until the first hour of operation, starts at like 200 and then starts heading for zero ish after it gets good and hot. Speakers are dead quiet the whole time.
Yes the 500ohm trim pot and 330ohm resistor.
Was getting warmer on the table so backed off at 1.75A or so to start.
Did notice that if I brought Iq up towards 1.8 then offset would go down. Almost like maybe going to 1.9 would drop things down below 50mV or less.
What odds I just moved it into position.
Warming up the other recently completed project, my 4P1L DHT preamp. What a monster. I had to put off this cutover because I was having such a fun time with it.
And on that note, just flicked the power switch. Quick ground buzz and settled in to silence and the soft pings of a heating cathode.
DHTs and Power JFETs. I am in for a good evening.
Was getting warmer on the table so backed off at 1.75A or so to start.
Did notice that if I brought Iq up towards 1.8 then offset would go down. Almost like maybe going to 1.9 would drop things down below 50mV or less.
What odds I just moved it into position.
Warming up the other recently completed project, my 4P1L DHT preamp. What a monster. I had to put off this cutover because I was having such a fun time with it.
And on that note, just flicked the power switch. Quick ground buzz and settled in to silence and the soft pings of a heating cathode.
DHTs and Power JFETs. I am in for a good evening.
Uhmm, might have to see what ZM has to say. Although he would probably say 50mV DC offset is no worry. I am running mine with Semisouths at 1.4A Iq (smaller heatsinks), but the DC offset can be adjusted easily to near zero with an adjustment range +/- either side of 0mV DC.
if offset is positive, means lower output part isn't "open" enough, asking for higher Ugs
just put 1K trimpots in both channels
first pre-set them to mid position (confirm with ohmmeter), then solder in pcb
Amp running, sounds fantastic.
At speaker terminals with meter polarity matching speakers have -100mV.
Enjoying too much to worry about pulling trim pots at the moment. Next rainy day.
At speaker terminals with meter polarity matching speakers have -100mV.
Enjoying too much to worry about pulling trim pots at the moment. Next rainy day.
OK for the moment, but get the DC offset below 100mV when you get the chance. You will be very pleased with the amp.
if offset is negative, do nothing
trimpot is minimized, so no use of changing it
just leave it as is, better than changing drain resistor for input JFet, and decreasing OLG
I’m going to venture that you’ll have the same moniker I’ve given it: The Goldilocks amp.
I have a pile (just like most people in the Pass forum) and this one is by far the brings the best and some really great things for my ears and system. Truly phenomenal.
Well, this is one of the things that Papa wanted in the first place, not just explore how three transistor pins could be used but to give things that someone takes and improves.
This is truly a mature and phenomenal sounding design.
This is truly a mature and phenomenal sounding design.
All this repeated F8 “hoopla” has me twitching and scratching 😬😬😬
Has anyone who built this one also built the Babelfish J2?
Any comments or observations between the two? MZM?
I know I don’t need any more amps to build, but I have the Semisouths.
Re-reading Pa’s F8 article just made things worse.
I’ll go stick my head back in a speakerwhile I wait…
Has anyone who built this one also built the Babelfish J2?
Any comments or observations between the two? MZM?
I know I don’t need any more amps to build, but I have the Semisouths.
Re-reading Pa’s F8 article just made things worse.
I’ll go stick my head back in a speakerwhile I wait…
paraphrasing Papa, mine is to build them, not to judge between them
hardly that I can give you any objective comparison
pretty much they're all having dominant 2nd, they're all on high enough plateau of sound quality
if in doubt, just remember that I told many time - they're all sounding the same
