Original schematic without feedback

Kostya-M · 10th April 2008, 10:59 PM

It was one dispute, what solid amplifier can’t be made without feedback in signal path. After several tests I devised balanced topology that works well. I made more then ten copies of such amplifiers with different power supplies, servo and variations. My last variant has no any servo. But it demand of accurate selection of transistor in pairs.

Kostya-M · 11th April 2008, 10:09 PM

I add several information
Max output power of this amplifier is 20-25 W
Damping factor = 4
Frequency response 5 Hz - 67 kHz by -3 dB
1% harmonic distortion is reached on 7 W
Harmonic level and spectrum is not depend on frequency.
THD level as function of frequency on different levels represents on figure

KSTR · 11th April 2008, 10:43 PM

Nice tube-style amplifier!

Can you give some details on VT5 & VT6? Are those really high-voltage high-power JFETs? And the FETs in the driver stage, what are their specs?

- Klaus

bigwill · 11th April 2008, 10:50 PM

I bet it sounds nice

Kostya-M · 11th April 2008, 11:42 PM

VT5 and VT6 are static induction JFET with max drain voltage 450V.
VT1 and VT2 are middle power HF JFET

And photo of the amplifier

Kostya-M · 12th April 2008, 07:23 AM

bigwill, yes it has sound likes very good triode PP amplifier in class A, but without tube's colour.

Parameters of transistors:
2Ï903
power disipation - 6W
max ds voltage - 20V
S=50-60mS (Id = 50mA)
Cgd=13pF
Cgs=15pF

2Ï926A (SIT, triode characteristics)
power disipation - 50W
case - TO-3
max Uds - 450V
Ri = 270 Ohm

lumanauw · 12th April 2008, 08:22 AM

The inductors/transformers, we can buy them or we have to DIY?

Kostya-M · 12th April 2008, 06:40 PM

Output transformers and interstage inductors we made in our laboratory (www.lampovik.ru). Power transformers and power inductors made in Russia by order. Input transformer-attenuator made in Moldova by Vorobiev, it's analog of Sowter 9335. Transformer after attenuator for variable output is Sowter 3575.

h_a · 15th April 2008, 12:53 PM

My congratulations! What an exotic amp!

All the best, Hannes

KSTR · 15th April 2008, 03:12 PM

... and take a look at the other great projects of these guys! Big bottled tube stuff, tesla coils, all beautifully handmade and packaged... impressing....

- Klaus

15th April 2008, 12:53 PM	#9
h_a diyAudio Member Join Date: Sep 2006 Location: Graz, Austria	My congratulations! What an exotic amp! All the best, Hannes __________________ fresh matched IRFP240/IRFP9240 fets \|\| AlephJ/JX-kits F5 transistor kits \|\| Burning Amp BA-1/2 transistor kits

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11th April 2008, 10:43 PM	#3
KSTR diyAudio Member Join Date: Jul 2007 Location: Central Berlin, Germany	Nice tube-style amplifier! Can you give some details on VT5 & VT6? Are those really high-voltage high-power JFETs? And the FETs in the driver stage, what are their specs? - Klaus

11th April 2008, 10:50 PM	#4
bigwill General Nuisance diyAudio Member Join Date: Dec 2004 Location: UK	I bet it sounds nice

12th April 2008, 07:23 AM	#6
Kostya-M diyAudio Member Join Date: Jun 2005 Location: Korolev near Moscow	bigwill, yes it has sound likes very good triode PP amplifier in class A, but without tube's colour. Parameters of transistors: 2Ï903 power disipation - 6W max ds voltage - 20V S=50-60mS (Id = 50mA) Cgd=13pF Cgs=15pF 2Ï926A (SIT, triode characteristics) power disipation - 50W case - TO-3 max Uds - 450V Ri = 270 Ohm

12th April 2008, 08:22 AM	#7
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	The inductors/transformers, we can buy them or we have to DIY?

15th April 2008, 03:12 PM	#10
KSTR diyAudio Member Join Date: Jul 2007 Location: Central Berlin, Germany	... and take a look at the other great projects of these guys! Big bottled tube stuff, tesla coils, all beautifully handmade and packaged... impressing.... - Klaus