I'm considering building this very nice hybrid amp, Class-A 25W:
http://www.diyaudio.de/html/25_25w_hybrid.html
It has balanced inputs, Lundahl input and interstage transformers, Absolutely no capacitor in the signal path
Zero dB feedback and 2-stage current amplification using Hitachi® Mosfets as driver and Sanken® bipolar power transistors.
Any comments on the tube preamp section?
Seems a very nice desing.
Thanks for your comments.
Bye.
http://www.diyaudio.de/html/25_25w_hybrid.html
It has balanced inputs, Lundahl input and interstage transformers, Absolutely no capacitor in the signal path
Zero dB feedback and 2-stage current amplification using Hitachi® Mosfets as driver and Sanken® bipolar power transistors.
Any comments on the tube preamp section?
Seems a very nice desing.
Thanks for your comments.
Bye.
It looks involved, expensive and redundant. I'm not trashing it but, why go from tube to mosfet to bipolar. Aren't each one of these kind of a contradiction in sound. I mean if you like the sound of tube's then I could almost see the mosfets, but bipolars don't sound like either one of those. They are unique unto themselves aren't they? I am in no way questioning your taste, merely making some observations and asking some questions.
Maybe I'm too simple at times. Do you know anyone who has heard it? After all, that's what it's all about.
Maybe I'm too simple at times. Do you know anyone who has heard it? After all, that's what it's all about.
The follower of the follower...
Questions about sound a part (subjectives) ...the reason why the designer use a bipolar follower after a source follower is for to lower the output impedance..as the amp don't have overall feedback
For instance if the mosfet output impedance is 1 or 2 Ohms...after the bipolar folower this became the (current gain of the transistor times)..less..
Exe. output mosfet impedance mosfet 2 Ohms... current gain of the transistor 50...the output impedance become 2/50=0,04
PassFan said:
Questions about sound a part (subjectives) ...the reason why the designer use a bipolar follower after a source follower is for to lower the output impedance..as the amp don't have overall feedback
For instance if the mosfet output impedance is 1 or 2 Ohms...after the bipolar folower this became the (current gain of the transistor times)..less..
Exe. output mosfet impedance mosfet 2 Ohms... current gain of the transistor 50...the output impedance become 2/50=0,04
How does it sound?
Yes you are right. It is what i'm trying to find and no answer yet. Please any comment on this kind of hybrid desing will be appreciated.
I expect this desing to sound kind like a pathos hybrid, see http://www.pathosacoustics.com/classiceng.htm
I don't mind a complex project, see my dac: http://www.diyaudio.com/forums/showthread.php?s=&threadid=12464
This kind of coupling transfo are used (I think) inside the Nagra preamp...
Yes you are right. It is what i'm trying to find and no answer yet. Please any comment on this kind of hybrid desing will be appreciated.
I expect this desing to sound kind like a pathos hybrid, see http://www.pathosacoustics.com/classiceng.htm
I don't mind a complex project, see my dac: http://www.diyaudio.com/forums/showthread.php?s=&threadid=12464
This kind of coupling transfo are used (I think) inside the Nagra preamp...
I see capacitors everywhere...
Keep in mind that each stage has an AC current loop. The input stage has 4 capacitors (counting caps and bypasses caps as one) in the singnal path between the input and the interstage transformer. You have 2 cathode bypass caps and 2 power supply to ground caps.
In the output stage you have 2 caps/bypasses referencing the secondarys of the interstages to ground plus the final caps in the power supply.
All the numbers above are per channel.
Keep in mind that each stage has an AC current loop. The input stage has 4 capacitors (counting caps and bypasses caps as one) in the singnal path between the input and the interstage transformer. You have 2 cathode bypass caps and 2 power supply to ground caps.
In the output stage you have 2 caps/bypasses referencing the secondarys of the interstages to ground plus the final caps in the power supply.
All the numbers above are per channel.
Some Thoughts ...
Hi,
if I'm writing about no capacitors in the signal path I mean coupling capacitors.
Of course all capacitors in the power supply and decoupling capacitors are also included in the signal path.
The goal for these capacitors is to achieve a low or at least a uniformly constistent impedance over the frequency range.
It depends how you look at things ...
The reason why this unusual combination of MOSFET driver and bipolar power transistors has been chosen is to achieve a high input impedance with a very low input capacitance (compare 2SK213 vs. 2SK 1058) and a very low output impedance which can only be achieved with bipolars if you want to avoid paralleling.
Best regards,
Norbert
Hi,
if I'm writing about no capacitors in the signal path I mean coupling capacitors.
Of course all capacitors in the power supply and decoupling capacitors are also included in the signal path.
The goal for these capacitors is to achieve a low or at least a uniformly constistent impedance over the frequency range.
It depends how you look at things ...
The reason why this unusual combination of MOSFET driver and bipolar power transistors has been chosen is to achieve a high input impedance with a very low input capacitance (compare 2SK213 vs. 2SK 1058) and a very low output impedance which can only be achieved with bipolars if you want to avoid paralleling.
Best regards,
Norbert
fregrove's right, a cap is used for certain reasons. Why build something without caps? Why not build something without transistors and tubes? Hell, let's omit the resistors too, then it'd be alot better!
Without cathode bypass capacitors you'd get local negative feedback and have a lower gain, some people swear against negative feedback, some people swear against capacitors. Everything is a compromise. But in the end all that matters is if it sounds good. So I say give it a try...
Without cathode bypass capacitors you'd get local negative feedback and have a lower gain, some people swear against negative feedback, some people swear against capacitors. Everything is a compromise. But in the end all that matters is if it sounds good. So I say give it a try...
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