Increasing the bias current on my NAKSA80s & Sorayas ... seems to be a good thing!! - Page 2

xrk971 · 12th October 2017, 09:45 PM

I recently did something similar but took it all the way to its maximum: full Class A. I had an old Apex FX8 (Bimo mod) Class AB that uses lateral FETs that was gathering dust on the shelves. Since I had made a new Class A case and PSU, I decided to install the FX8, but run it in full Class A. Normally bias would be set around 80mA to 120mA. I cranked the bias adjust pot up and up and up. I could hear the trafo start to hum, yikes so backed off to 1amp. It ran fine and sounded better than it ever had. A few days later, I took it to 1.25 amps. Now there is stays and I must say I enjoy the sound. I am told by Bimo that I should be able to get 16w at 8ohms in Class A with 24v rails. This was a successful and safe experiment as these were lateral FETs. I can't say I would do this with my hexFET Class AB amp. It probably would have run away and magic smoke would have resulted. Anyhow, wanted to chime in with my limited experience of pushing an amp to the max bias. Heat = Fun

Sjef · 13th October 2017, 05:05 PM

Funny thing I bought the Naksa's as a cool running replacement for my claase A mid amps and single ended truode tweeteramps.

Sjef · 13th October 2017, 05:07 PM

Funny thing I bought the Naksa's as a cool running replacement for my claase A mid amps and single ended triode tweeteramps.

AKSA · 14th October 2017, 08:58 AM

Sorry, late Sjef, my daughter was married in Manhattan today and I watched on Skype!!

Yes, the NAKSAs are all Class AB but designed to sound a bit Class A due to the harmonic profile created in the first and output stages.

It is actually a huge tribute to them that you consider them in such rare company; a single ended triode is my idea of the perfect musical sound, but I has many, many technical issues, particularly transformers, filaments and low power.

Hugh

Sjef · 14th October 2017, 12:59 PM

To be honoust the single ended triode sound a bit better but they produce a lot of heat, consume a lot power and not to mention expensive tube replacement, specially in a system that's being used by the whole family and therefore runs many hours a day. The Naksa's do share some of it's sound character, at least more then most transistor amps. I stopped using the triode amps after the second 500 euro tube replacement. The Naksa runs cooler and are more worry free and cheaper in the long run.

saf · 17th October 2017, 05:34 PM

I have found that the same amp can run hot or cool, solely on the speaker its connected to.

I have a Maya connected to a Sonus Faber Amati ( 80Kg monster speaker 4ohm/92dB) and it probably runs at 10 to 15 above ambient temperature.

On the other hand, i have another Maya connected to a Sonus Faber Elipsa Auditor ( mini monitor speakers 4ohm/89db) and this amp GETS HOT ! I mean very HOT like 30 degrees above ambient !

andyr · 17th October 2017, 08:20 PM

Quote:

Originally Posted by saf

I have found that the same amp can run hot or cool, solely on the speaker its connected to.

I have a Maya connected to a Sonus Faber Amati ( 80Kg monster speaker 4ohm/92dB) and it probably runs at 10 to 15 above ambient temperature.

On the other hand, i have another Maya connected to a Sonus Faber Elipsa Auditor ( mini monitor speakers 4ohm/89db) and this amp GETS HOT ! I mean very HOT like 30 degrees above ambient !

How very interesting. Are these Mayas rated at the same output power?

Andy

AKSA · 17th October 2017, 10:39 PM

Yes, Andy, and it's very interesting.......
It tells me that the crossover on the first speaker is probably series, and the second, shunt, and maybe also the second speaker has lower sensitivity.

Thanks Filipe, useful information for the amp and the speaker!!

Hugh

bogdan_borko · 18th October 2017, 11:22 AM

Quote:

Originally Posted by saf

I have found that the same amp can run hot or cool, solely on the speaker its connected to.

I have a Maya connected to a Sonus Faber Amati ( 80Kg monster speaker 4ohm/92dB) and it probably runs at 10 to 15 above ambient temperature.

On the other hand, i have another Maya connected to a Sonus Faber Elipsa Auditor ( mini monitor speakers 4ohm/89db) and this amp GETS HOT ! I mean very HOT like 30 degrees above ambient !

Both Sonus Faber models have impedance drop to 2.5 ohms at certain freq.range (you could see the graphs in stereophile) so if you listen at loud levels it's normal that the amp is hot.

andyr · 18th October 2017, 12:35 PM

Quote:

Originally Posted by bogdan_borko

Both Sonus Faber models have impedance drop to 2.5 ohms at certain freq.range (you could see the graphs in stereophile) so if you listen at loud levels it's normal that the amp is hot.

Sure, b_b ... but the interesting thing is ... that for 2 identical power-output Mayas:
* the larger S-F speaker causes the Maya to run warm, whilst
* the smaller S-F speaker causes it to run hot.

Andy

12th October 2017, 09:45 PM	#11
xrk971 Got Foam? diyAudio Member Join Date: Oct 2012 Location: Metro DC area	I recently did something similar but took it all the way to its maximum: full Class A. I had an old Apex FX8 (Bimo mod) Class AB that uses lateral FETs that was gathering dust on the shelves. Since I had made a new Class A case and PSU, I decided to install the FX8, but run it in full Class A. Normally bias would be set around 80mA to 120mA. I cranked the bias adjust pot up and up and up. I could hear the trafo start to hum, yikes so backed off to 1amp. It ran fine and sounded better than it ever had. A few days later, I took it to 1.25 amps. Now there is stays and I must say I enjoy the sound. I am told by Bimo that I should be able to get 16w at 8ohms in Class A with 24v rails. This was a successful and safe experiment as these were lateral FETs. I can't say I would do this with my hexFET Class AB amp. It probably would have run away and magic smoke would have resulted. Anyhow, wanted to chime in with my limited experience of pushing an amp to the max bias. Heat = Fun __________________ XRKaudio https://www.etsy.com/shop/XRKAudio

14th October 2017, 08:58 AM	#14
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Sorry, late Sjef, my daughter was married in Manhattan today and I watched on Skype!! Yes, the NAKSAs are all Class AB but designed to sound a bit Class A due to the harmonic profile created in the first and output stages. It is actually a huge tribute to them that you consider them in such rare company; a single ended triode is my idea of the perfect musical sound, but I has many, many technical issues, particularly transformers, filaments and low power. Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

17th October 2017, 10:39 PM	#18
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	Yes, Andy, and it's very interesting....... It tells me that the crossover on the first speaker is probably series, and the second, shunt, and maybe also the second speaker has lower sensitivity. Thanks Filipe, useful information for the amp and the speaker!! Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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13th October 2017, 05:05 PM	#12
Sjef diyAudio Member Join Date: Jan 2003 Location: Amsterdam	Funny thing I bought the Naksa's as a cool running replacement for my claase A mid amps and single ended truode tweeteramps.

13th October 2017, 05:07 PM	#13
Sjef diyAudio Member Join Date: Jan 2003 Location: Amsterdam	Funny thing I bought the Naksa's as a cool running replacement for my claase A mid amps and single ended triode tweeteramps.

14th October 2017, 12:59 PM	#15
Sjef diyAudio Member Join Date: Jan 2003 Location: Amsterdam	To be honoust the single ended triode sound a bit better but they produce a lot of heat, consume a lot power and not to mention expensive tube replacement, specially in a system that's being used by the whole family and therefore runs many hours a day. The Naksa's do share some of it's sound character, at least more then most transistor amps. I stopped using the triode amps after the second 500 euro tube replacement. The Naksa runs cooler and are more worry free and cheaper in the long run.

17th October 2017, 05:34 PM	#16
saf diyAudio Member Join Date: Sep 2009 Location: Porto	I have found that the same amp can run hot or cool, solely on the speaker its connected to. I have a Maya connected to a Sonus Faber Amati ( 80Kg monster speaker 4ohm/92dB) and it probably runs at 10 to 15 above ambient temperature. On the other hand, i have another Maya connected to a Sonus Faber Elipsa Auditor ( mini monitor speakers 4ohm/89db) and this amp GETS HOT ! I mean very HOT like 30 degrees above ambient !

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