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Old 10th June 2009, 10:20 AM   #11
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Quote:
Originally posted by Magura
That's the right spirit...love you attitude!
Magura
I see your point quite well. I did make a year ago a 50W version of Zen9 as stereo power amp. My god, sometimes I had to ask somebody to help me in moving it from listening place to working bench. It weight is close to 40 kg. You can see this monster in the enclosed picture.
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Old 11th June 2009, 09:35 AM   #12
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Below is a picture with measured output characteristics of LD1010DA transistor (i.e. dependences of drain current Id vs drain-to-source voltage Vds at various fixed gate-to-source voltages Vgs). It illustrates nicely the triode-like features of the device ingeniously apply in real schematics by Nelson Pass. The transistor was mounted on a heat sink during measurements. I hope this picture could be useful for DIYers who build Zen9 or F3.
I also have attached typical output characteristics of a pentode-like MOSFET (2SK1058) and of V-FET (or SIT) transistor TKS45F323. The last is really behave as a solid state tube. I would be very grateful if somebody knows where or from whom these TKS45F323 could be available.
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Old 11th June 2009, 11:26 AM   #13
flg is offline flg  United States
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Great work Vladimirk
Now I need some time to digest...
I'm not familiar with the TKS45F323 or SIT? You don't mean SiC do you? I go search...
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Old 11th June 2009, 01:36 PM   #14
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Quote:
Originally posted by flg
Great work Vladimirk
Now I need some time to digest...
I'm not familiar with the TKS45F323 or SIT? You don't mean SiC do you? I go search...
Vertical FETs or, in other words, Static Induction Transistors were discussed many times at this Forum, but the type indicated above is the best for audio among them.
Not the same, but similar transistors were used in the legendary Yamaha-B1 ana Yamaha-B2 amps.
Obtaining the TKS45F323 transistors would give big inspiration for every DIYer for a next project.
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Old 11th June 2009, 02:37 PM   #15
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I have several of the Yamaha B-2's that I want to simplify
(zenify). Plan on using several stereo units and parallel the
2 channels per unit for more drive current for my Acoustat 2+2's.
(have 2 pairs of 2+2's and a pair of Model 2's.
Perhaps based on a Zen V5 (comp pairs). I guess the
2SK76 / 2SJ26 are depletion mode devices though
so designin new driver stage seems biggest hurdle.
On all but one unit that was modded to bypass the speaker
relay switches and input switch they are all noisy and
intermittent which is why I don't mind redesigning.
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Old 12th June 2009, 04:09 AM   #16
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Quote:
Originally posted by coloradosound
I have several of the Yamaha B-2's that I want to simplify
(zenify). Plan on using several stereo units and parallel the
2 channels per unit for more drive current for my Acoustat 2+2's.
(have 2 pairs of 2+2's and a pair of Model 2's.
Perhaps based on a Zen V5 (comp pairs). I guess the
2SK76 / 2SJ26 are depletion mode devices though
so designin new driver stage seems biggest hurdle.
On all but one unit that was modded to bypass the speaker
relay switches and input switch they are all noisy and
intermittent which is why I don't mind redesigning.
Sure your intentions are absolutely correct. You first of all could think about removing or replacing old connectors and relays and even volume control. Speaking about the TKS45F323 transistors I have in mind a tube-spirit schematics with output transformer. But it will be off-topic to go into more detail here.
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Old 12th June 2009, 07:31 AM   #17
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Speaking about the Damping Factor of power amp (this parameter is not so good with Zen or FirstWatt F amps) one should also remember about speaker cable. I’d like to show interesting measurements done with top-quality speaker cable STEREOVOX LSP-600c. Variations with frequency of absolute value of the cable impedance Z and of active component of this impedance are shown in the picture below. Next picture illustrates measurement setup used for these measurements.
One can see, that very well sounding cable measures terribly bad, its Z rises to several Ohms at 10-20 kHz ! It measures worse than a piece of cheap speaker wire. This story resembles situation with THD parameter.
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File Type: jpg Измерения stereovox_resize.jpg (44.8 KB, 1425 views)
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Old 12th June 2009, 07:33 AM   #18
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The second picture
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File Type: jpg Измерения stereovox_1.jpg (90.4 KB, 1411 views)
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Old 13th June 2009, 07:28 AM   #19
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In the picture below I show the results of measurements
1) of Gain variation with Frequency (Pass Band measurements) and
2) of 10kHz Square Wave Response
for the Zen9 4,8A and Zen4 2,8A monoblocks. Load is 5,1 Ohm resistive.
Zen4 is approximately 10 times faster than Zen9 and indicates some problem with periodic set-up process, possibly its NFB compensation capacitor should be checked.
But what I would like to stress, listening of both amps (by me and several friends) do not reveal differences in highs reproduction, they are very subtle (if any), nobody can give preference to definite device. The bass and mids are better a little bit with Zen9.
At the same time, we immediately feel difference with highs, if we connect cheap speaker cable or replace output capacitor C1 (the replacement does not affect measurements).
The question is, again, to which level measurements are important and have sense ?
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File Type: jpg measurements zen9 & zen4_resize.jpg (80.6 KB, 1277 views)
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Old 13th June 2009, 08:01 PM   #20
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I know it would be a whole different thread, Vlad, except
I have tried to get other threads going with about same
response and it is VFET. I could bypass all the switches/
controls, but am still left with 6 amps that could do nothing
more than drive 8 ohm loads! These Acoustats go down
to 1-2 ohms at some of the lower freqs! I thinks that if
I could use single driver boards to run all devices in parallel
it would do what I want much better and maybe going
all out and coscoding the outputs with some large MOSFET'S
ot BJT's and maybe even regulating the output stage as well!
I have tons of high uF caps and trannies around of much more
substantial capability than what Yamaha had that it may be
possible. (Like a complimentary Z v9)!
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