SEWA - Seven Watt Amplifier

[Vix]

Congratulations Zlati!
I bet that SEWA combined with a tube preamp is a real bang for the Buck! Hard to beat that price/performance ratio!

Nice

[Tyimo]

Thanks DJK for the info!

Tyimo

[Roscoe Primrose]

Looks like Digikey does business in Hungary, don't know what the shipping cost/time might be though...

DigiKey Corp. | Elektronikai alkatrészek forgalmazója | Magyarországi weboldal

Roscoe

[tiefbassuebertr]

Originally Posted by cumbb

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:

C.

I have observe the same by my investigations. Where is going the online schematic in the meantime (Ladislav Bunta's homepage) ?

Originally Posted by cumbb

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!

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.

Originally Posted by cumbb

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

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:
First taste of Papa's new devices
Successors for V-FET SONY-Yamaha-TOKIN 2SJ28, 2SJ18/2SK60, 2SJ26/2SK76 and 2SK180

Originally Posted by zlati84

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)

What means that? Please let us know the heatsink temperature above the ambient temperature (or you know also the ambient temperature at those days).

Originally Posted by zlati84

My SEWA become to a little hybrid amp with big sound
The tube preamp is E88CC SRPP, made by this schematics
Attachment 173494

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.

[osscar]

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!

[Jay]

Originally Posted by cumbb

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:

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.

Originally Posted by cumbb

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.

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.

[osscar]

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

[Roscoe Primrose]

Sounds like you either left out C2, or it's leaky....

Roscoe

[osscar]

Thank for the hint but i do not think that C is damaged - they are new and the problem is in both channels. Otherwise, the amp works and sounds good.I will try to take a look on output sine with scope.