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Old 15th November 2013, 08:44 PM   #1141
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Quote:
Originally Posted by AKSA View Post
Andrew,

I'm embarrassed to answer this because I've not tried it. When you work with an amp productionising and filling the documentation, you don't examine all the options. I don't believe Greg, Lineout and Mikelm did it either, but you'd have to ask them. Significantly you are asking me now, more than two years later!

I always had one comment about the FetZilla - that is lacks depth of image. This is a major issue for me, I strive to throw up a virtual depth in the sound field. I think it was related to the choice of the voltage amplifier. But, as with so many aspects of this art, I do not have a proof for this. But I can say that the depth of image is magnificent with the NAKSA.

Cheers,

Hugh
Hi Hugh,

In your Naksa 70, 80, 100, do you use lateral fets or bipolar?

Thanks
Do
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Old 15th November 2013, 10:32 PM   #1142
AKSA is offline AKSA  Australia
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Hi Do,

I can see your interest is piqued...... I am sorry I speak with riddles!

No, either! The N70 uses a npn and pmos pair, the N100 two npn and a very large single pmos, and the N80 uses an IRFP240/9240 pair only.

You didn't expect this, did you?

Cheers,

Hugh
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Old 16th November 2013, 03:33 AM   #1143
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Yes, I am actually very curious. This all seems very interesting to me.

I will send you a pm to discuss further about your products.

Thanks
Do
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PREAMPs : AMB α10 + JC-80 clone | Balanced DCB1 | LDR3x | AMPs: AMB β24 | Aleph 5 | VSSA | ML-2 | Fetzilla | Telos 390 Clone | My_Ref FE
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Old 22nd November 2013, 08:15 AM   #1144
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Default Heat sinks at high bias

Quote:
Originally Posted by mikelm View Post
l would settle for +/- 36V @ 0.75A - with my amp and to my ears this combination sounded better
(been offline for too long!)

For that bias, what rating of heat sinks would be needed?

Cheers
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Old 22nd November 2013, 08:22 AM   #1145
AKSA is offline AKSA  Australia
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This is a total dissipation of 72 x 0.75 = 54 watts per channel. (NOTE MY CORRECTION, HELL, CAN'T DO MATHS!!)

Therefore, each heatsink, one for channel, must move 54 watts which at 0.4C/w is an increase of (73 x 0.4) = 22C over ambient.

If you listen in a room at 25C, which is pretty warm in fact, this means a 0.4C/watt heatsink, which is about 10" long and 3" tall, will run at 47C.

This is just hot enough to leave your finger on it for about 20 seconds. At 65C you can touch the heatsink for no more than 2 seconds. So 47C is acceptable.

OTOH, if it is 35C in the room on a hot day with no AC, turn off the FetZilla. You don't want to fry you FetZilla since the junction is at least 25C ABOVE the heatsink temperature..........

Cheers,

Hugh
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Last edited by AKSA; 22nd November 2013 at 09:28 AM.
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Old 22nd November 2013, 08:44 AM   #1146
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Fried Fetzilla would not smell as nice as fried prawns I'm thinking !! Definitely to be avoided.
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Old 22nd November 2013, 08:59 AM   #1147
mikelm is offline mikelm  England
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Quote:
Originally Posted by otto88 View Post
For that bias, what rating of heat sinks would be needed?
Yes, agree completely with Hugh about heatsink. mine are .42 degrees / watt
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Old 22nd November 2013, 09:45 AM   #1148
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Quote:
Originally Posted by AKSA View Post
I always had one comment about the FetZilla - that is lacks depth of image. This is a major issue for me, I strive to throw up a virtual depth in the sound field. I think it was related to the choice of the voltage amplifier. But, as with so many aspects of this art, I do not have a proof for this. But I can say that the depth of image is magnificent with the NAKSA
I have been playing around with this "fetzilla" design on & off for about three years now and I am very pleased with how it has turned out. My version is DC linked with a servo & composite o/p pairs plus some more subtle mods. I have not heard either Hugh's version or his Naksa ( which I'm sure must be very good ) but I am not aware of any shortcomings in the imaging or depth of field department with my fetzilla design as it stands. Recordings made with some space like some old Ella big band songs or Ry Cooder's world music collaborations are reproduced quite holographically.

The subtle mods I refer to have been mostly searching out and eliminating any elements of the circuit that have ANY tendency towards resonance. These circuit elements that have a tendency to "ring" at a particular frequency are excited by a broadband music signal ( but probably not by a 1khz test tone ) and really mess up the sound, including imaging, in a big way. Other resonances can be excited by the action of the power supply.

My personal, but objectively unproven, view is that any reasonable topology can be made to "work" very well and play very nice sounding music if the time is taken to fully optimize each approach. My Fetzilla optimization took me 3 years so far and I'm sure there is still room for improvement.

I think there will always be some difference in "sound" between different well implemented topologies but I also think these differences will be small and probably be a matter of personal preference. Certainly every finished design should be able to reproduced Good Dynamics, Natural Musical Tonality and Spacial Coherence.

mike

Last edited by mikelm; 22nd November 2013 at 09:48 AM.
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Old 22nd November 2013, 10:31 AM   #1149
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Or to put it another way . . .

The fact that Hugh designed his Fetzilla remotely from start to finish, having not ever listened to it but using only the subjective feedback from Greg, and that so many think so highly of this design is a testament to his great knowledge & experience. I know he was never intending it to be a "top of the line" design.

All I'm saying is that with some extra attention on this design there is more potential there which I think, among other things, can meet Hugh's "depth of field" criteria and make it a "high end" contender

Last edited by mikelm; 22nd November 2013 at 10:33 AM.
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Old 22nd November 2013, 04:01 PM   #1150
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Quote:
Originally Posted by AKSA View Post
This is a total dissipation of 72 x 0.75 = 54 watts per channel. (NOTE MY CORRECTION, HELL, CAN'T DO MATHS!!)

Therefore, each heatsink, one for channel, must move 54 watts which at 0.4C/w is an increase of (73 x 0.4) = 22C over ambient.

If you listen in a room at 25C, which is pretty warm in fact, this means a 0.4C/watt heatsink, which is about 10" long and 3" tall, will run at 47C.

This is just hot enough to leave your finger on it for about 20 seconds. At 65C you can touch the heatsink for no more than 2 seconds. So 47C is acceptable.

OTOH, if it is 35C in the room on a hot day with no AC, turn off the FetZilla. You don't want to fry you FetZilla since the junction is at least 25C ABOVE the heatsink temperature..........

Cheers,

Hugh
Thanks Hugh!
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