Krill output stage + tube preamp

kacernator · 24th September 2011, 01:36 PM

Hi,

I am going to build hybrid amplifier. I want to use 100W output stage from Krill amplifier. I have several questions about the output stage.

First, how should I modify the input of the output stage to make it work with external preamp and what is the input impedance of output stage?

Second, can I substitute drivers from 2SC5200 to MJ150030?

Third, can I substitute signal transistors to BD139 and BD140 - propably worse sound, but I already have them.

Thank you.

Steve Dunlap · 24th September 2011, 02:00 PM

Quote:

Originally Posted by kacernator

Hi,

I am going to build hybrid amplifier. I want to use 100W output stage from Krill amplifier. I have several questions about the output stage.

First, how should I modify the input of the output stage to make it work with external preamp and what is the input impedance of output stage?

Second, can I substitute drivers from 2SC5200 to MJ150030?

Third, can I substitute signal transistors to BD139 and BD140 - propably worse sound, but I already have them.

Thank you.

Are you saying you want to substitute a tube VGS for the VGS shown in your attached schematic?

The output stage will accept almost any transistor that meets the power and voltage requirements.

kacernator · 24th September 2011, 02:23 PM

Just to be clear...schematics attached.

heinz · 24th September 2011, 02:30 PM

I tried a Tube vgs : Krill construction thread - 100W version
Not 100W but sounds very good.

kacernator · 24th September 2011, 02:43 PM

I am curious how it will sound with aikido preamp. I too will not have 100W output power, because I will have lower voltage rails (30V), but want to use double output pairs to lower output impedance.

But how to modify the input transistors? Should I connect 1k in series and 47k to ground resistor from base of input transistors?

heinz · 03:09 PM

i just used two resistors to trim the base of Q7/Q10. One resistor was 680K, other one 1Meg Pot.
Tube is EF86 in Triode Connection. V=200V. All Values of Restistors and Caps are rough guesses ... :-)

Edit: Attachments

kacernator · 24th September 2011, 03:05 PM

680k trimpot for DC offset?
So you have about 1M input impedance of Krill output stage?

Bigun · 24th September 2011, 03:27 PM

You can probably get rid of one of the capacitors in the signal path - either the input cap or the inter-stage cap through a judicious choice of power rails for the tube.

Steve - correct me if I'm wrong - but I also believe you'll benefit if you can afford to add more output transistors. With no gnf the output will tend to have more distortion and lower damping factor than with gnf. Additional output devices will help you reduce the output impedance, they will also have less current variation through each one so lower distortion. And as far as I can see, the Krill output stage benefits even more from additional devices because more devices means more base-storage of minority carriers which is what is behind the distinctive non-switching / soft-switching characteristic.

kacernator · 24th September 2011, 03:36 PM

Can I change input transistors Q7/Q10 to BC550/BC560 ?

heinz · 24th September 2011, 03:42 PM

I dont know - I did use bd139/bd140 in that position

24th September 2011, 02:30 PM	#4
heinz diyAudio Member Join Date: Mar 2007	I tried a Tube vgs : Krill construction thread - 100W version Not 100W but sounds very good. __________________ (((---)))

24th September 2011, 03:27 PM	#8
Bigun diyAudio Member Join Date: Jan 2009 Location: K-W Ontario Blog Entries: 2	You can probably get rid of one of the capacitors in the signal path - either the input cap or the inter-stage cap through a judicious choice of power rails for the tube. Steve - correct me if I'm wrong - but I also believe you'll benefit if you can afford to add more output transistors. With no gnf the output will tend to have more distortion and lower damping factor than with gnf. Additional output devices will help you reduce the output impedance, they will also have less current variation through each one so lower distortion. And as far as I can see, the Krill output stage benefits even more from additional devices because more devices means more base-storage of minority carriers which is what is behind the distinctive non-switching / soft-switching characteristic. __________________ "The test of the machine is the satisfaction it gives you. There isn't any other test. If the machine produces tranquility it's right. If it disturbs you it's wrong until either the machine or your mind is changed." Robert M Pirsig.

24th September 2011, 03:42 PM	#10
heinz diyAudio Member Join Date: Mar 2007	I dont know - I did use bd139/bd140 in that position __________________ (((---)))

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24th September 2011, 02:43 PM	#5
kacernator diyAudio Member Join Date: Jan 2008	I am curious how it will sound with aikido preamp. I too will not have 100W output power, because I will have lower voltage rails (30V), but want to use double output pairs to lower output impedance. But how to modify the input transistors? Should I connect 1k in series and 47k to ground resistor from base of input transistors?

24th September 2011, 03:05 PM	#7
kacernator diyAudio Member Join Date: Jan 2008	680k trimpot for DC offset? So you have about 1M input impedance of Krill output stage?

24th September 2011, 03:36 PM	#9
kacernator diyAudio Member Join Date: Jan 2008	Can I change input transistors Q7/Q10 to BC550/BC560 ?

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