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Old 17th June 2013, 02:02 AM   #3631
6L6 is offline 6L6  United States
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Bigun - I like that idea! Do you have any example schematics? Something with the general configuration?
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Old 17th June 2013, 02:41 AM   #3632
Bigun is offline Bigun  Canada
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I have had a couple of different ideas in mind for awhile but I haven't built one yet - not having had an F4 handy being the main limitation (if I knew it'd sound pretty good in Class AB for summer use I'd put it on the active project list). Anyhow, the obvious starting point is a matched pair of p-type semiconductors in an LTP configuration driving a triode VAS with feedback from the plate to the LTP to lower the overall output impedance. I figure this would be enough to drive the high input impedance of the F4. The more linear the tube the cleaner the sound so the anode load would be best to be high impedance which also improves PSRR.

Next up you might think about a hybrid based on a simple Aleph front end. Some people prefer Singleton inputs to an LTP, which is another option here.

You need to plan out the voltages carefully, use the right tubes - and dc coupled where possible. The 6DJ8 and modern relatives might be reasonable choices and ECC99 is rumoured to be very happy with lower (by tube standards) voltages and can be very linear.

If / when I build an F4 I'll start a thread on a pre....
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Last edited by Bigun; 17th June 2013 at 03:03 AM.
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Old 21st June 2013, 10:15 AM   #3633
generg is offline generg  Germany
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Quote:
Originally Posted by generg View Post
I liked the F4 extremely combined with pumpkin or aleph p........

Just an idea, I will do myself, replace the Toshibas by the 610/9610 combo in the BA-3.
O.K. I did the unnecessary.....

I changed the Toshibas in the BA-3 Frontend against the old 9610/610 combo.

I had to add 220R to each 5k pot to get the higher Vgs and cut some traces etc.

Distortion values were ugly higher than the Toshiba values if I checked right, but there was another problem with my setup so I am not quite sure....

But the sound rembers me very much of good old Pumpkin/f4 combo.

Because of K2 dominance more body and punch, not so detailed but you get a very natural and pleasant sound.

So can recommend to try it if you find the standard BA-3/F4 combo a bit disappointing why ever...

I will look at the distortion values and I have impression that P3 is working no more. Too much distortion in the 610/9610 combo.....?
Will inform you.....
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Old 21st June 2013, 10:20 AM   #3634
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What if I told you I think big TO220 may sound better than small sot223 in preamp you keep complicating my life, but at least these fets are easy to get.
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Old 21st June 2013, 10:25 AM   #3635
generg is offline generg  Germany
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Hi buzz,

what types did you compare? the ZVN/P against the Toshibas in your BA-3 variation?
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Old 21st June 2013, 10:29 AM   #3636
lohk is offline lohk  Europe
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I will sell my unused and shiny Peter Daniel F4 boards (two channels), also possibly with some selected Mosfets too. I get lost in all Pass projects and will not have time to make an F4.
Any interest?
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Old 21st June 2013, 10:32 AM   #3637
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Yes. Initial impressions are similar to yours. Bigger fets seem to be more full bodied, but I want to try to get spectra close and listen. I am also trying different loading and feedback schemes. I know you don't need the power, but balanced is the way to go, IMO hope to have pics by the weekend.
Lohk,
6l6 might be interested in those boards.
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Old 21st June 2013, 01:41 PM   #3638
6L6 is offline 6L6  United States
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lohk - Yes, I am interested, please check your PM.
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Old 23rd June 2013, 11:09 AM   #3639
lohk is offline lohk  Europe
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sorry, the boards are already sold
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Old 23rd June 2013, 12:18 PM   #3640
Zen Mod is offline Zen Mod  Serbia
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nobody tried IRFPs in output of BA3 , yet ?

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