SEWA - Seven Watt Amplifier

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#924
cumbb said:
Hello.

I suggest the same modification on the sewa as Ladislav Bunta did on the power Follower of Pavel Macura. The Bipolar Transistor. The sound will be more relaxed and fine:

An externally hosted image should be here but it was not working when we last tested it.
C.
Click to expand...
I have observe the same by my investigations. Where is going the online schematic in the meantime (Ladislav Bunta's homepage) ?
cumbb said:
Hello.
The sound of the sewa in general comparision to the power follower of Macura (in my mind!):
It seems, the sewa has more „black“, more focus, he is more present and living, but he is a little bit restless, „brittle“, scruff.
The Macura seems to be more relaxed and quiet, more fine and clear, extended, but not so present and alive.
But this is only my experience!
Click to expand...
Also this I can confirm. The reason are the lower values for the input-, output- and reverse capacitance of Ladislav Bunta's discrete IGBT resp. CFP/sziklai darlington.
cumbb said:
Hello.my proposals:
Connect the grounds of the Q2 of the sewa.
Do not use channel separate PSUs. Never and nowhere. C.
Click to expand...
I don't understand the advantages of only one PSU for both channels.

Now an other question: what are the audible sound differences, if there are V-FET's and SIT's in use instead normal MOSFET and discrete IGBT ?? Are there really additional great advantages in sonic quality by the use of this semiconductors in this both unity gain power followers?
check in this case also this thread:
http://www.diyaudio.com/forums/pass-labs/188066-first-taste-papas-new-devices.html
http://www.diyaudio.com/forums/soli...kin-2sj28-2sj18-2sk60-2sj26-2sk76-2sk180.html
zlati84 said:
My amp works on 32V supply, 2.5 amps bias, temperature of the heatsinks is about 62 degrees C. ( Power is in a separate box)
Click to expand...
What means that? Please let us know the heatsink temperature above the ambient temperature (or you know also the ambient temperature at those days).
zlati84 said:
My SEWA become to a little hybrid amp with big sound😀
The tube preamp is E88CC SRPP, made by this schematics
View attachment 173494
Click to expand...
I want to know a solid state front end with a sound character as close as possible to that one of this tube SRPP topology.
 
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#925
I have always wanted to try the SE SS amp. I have pair of ixys depletion mode Mosfets - but the PSU will be more expensive for high-voltage de-light amp, so i will go for Sewa with irfp 150 .
My SEWA is slowly being created, thanks to the author - for the PCB layout and circuit ! my progress in the attachment!
 

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#926
cumbb said:
I suggest the same modification on the sewa as Ladislav Bunta did on the power Follower of Pavel Macura. The Bipolar Transistor. The sound will be more relaxed and fine:
Click to expand...

Relaxed sound is usually boring. Such is usually true with that kind of addition to the mosfet. Not my cup of tea I believe. Just a guess.

cumbb said:
It seems, the sewa has more „black“, more focus, he is more present and living, but he is a little bit restless, „brittle“, scruff.
The Macura seems to be more relaxed and quiet, more fine and clear, extended, but not so present and alive.
Click to expand...

From your description of the sound, it seems you are comparing a Mosfet to a Bipolar. Actually I have built both amps at different times and so never tried to compare the sound, but I think I have the same impression about the sound.

I prefer to use a lower capacitance mosfet and intuitively select a better transconductance Mosfet (due to mismatch for example) to be put in the current source (bottom mosfet).

MAY BE the bipolar used in the current source will also have effect to the sound. I will try different types of bipolar anytime, to see if the sound "changes". I used a low Cob bipolar here, but have no idea with temperature characteristics.
 
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#927
Hi ,
I preform today the first Sewa amp (standard rev1 with irfps150 and bc 550c) tests (using positive rail from existing PSU in my F5 amp) . without the signal source is everything fine - bias approx. 2 A - 0.64V across Source resistors. But when i connected source (SS preamp or CD player) - bias immediately falls to 1 A or 0.3V across resistor and remains stable at 1A.when i disconcerting the signal source - instantly jumps to 2A.
I do not understand where there might be a problem
 
#932
cumbb said:
Hello.

I suggest the same modification on the sewa as Ladislav Bunta did on the power Follower of Pavel Macura. The Bipolar Transistor. The sound will be more relaxed and fine:

An externally hosted image should be here but it was not working when we last tested it.


And my proposals:
Connect the grounds of the Q2 of the sewa.
Do not use channel separate PSUs. Never and nowhere.

The sound of the sewa in general comparision to the power follower of Macura (in my mind!):

It seems, the sewa has more „black“, more focus, he is more present and living, but he is a little bit restless, „brittle“, scruff.
The Macura seems to be more relaxed and quiet, more fine and clear, extended, but not so present and alive.

But this is only my experience!

Best regards.
C.
Click to expand...

This diy amplifier I get for service.
Do you know the formerly URL, where to find is this circuit?
Then I will try to find it about webarchive.
 
#934
lineup said:
The MOSFET Power Follower of Pavel Macura (PMA)
can be found here:
Mosfet Power Follower and other projects

And here below is the schematic from the original circuit.
Click to expand...
Thank you. This link and this circuit I have. Unfortunately the schematic from post #892 isn't to find there.
But this schematic I need in high resolution (Ladislav Bunta's advanced circuit).
 
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#935
Hi there,
Coming to this low power solid state amp thing very late in the day, having generally used tube amps or hybrid (tube/SS) to drive Fostex 206En in BLH cabinet.
Does anyone know of any PCB's (Rev B or C) that are going spare?
Or a revised design of SEWA or alternate design for which PCB's are available?
I've tried point-to-point wiring and it's not a pretty sight, and I am not confident enough (in DIY terms) to fill in any gaps in circuit designs, i.e. I need to use a fully resolved design!

Thanks for any suggestions/links
J
 
#937
tiefbassuebertr said:
Thank you. This link and this circuit I have. Unfortunately the schematic from post #892 isn't to find there.
But this schematic I need in high resolution (Ladislav Bunta's advanced circuit).
Click to expand...
The wanted schematic is here:
ImageShack® - Online Photo and Video Hosting
Imageshack - p83f3gb0.gif
http://www.diyaudio.com/forums/attachment.php?postid=1563709&stamp=1216269919
go also to post 27 under
http://www.diyaudio.com/forums/soli...uras-mosfet-power-follower-3.html#post3804254
 
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#940
I just saw this thread and amp for the first time. Nice amp, Lineup! I love SE Class A single transistor amps. Hugh and I recently came up with a preamp that might be a good fit here. JPS64 did a fantastic job on the layout.

AKSA's Lender Preamp with 40Vpp Output

I think I may have inadvertently built this amp in making my MoFo, I had a load resistor in place of the choke for a while.
 
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