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Old 13th February 2011, 06:02 PM   #481
osscar is offline osscar  Latvia
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Hi,

Nice and massive Monster !
What are your thoughts about monster sound?
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Old 15th February 2011, 03:18 AM   #482
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Quote:
Originally Posted by triode_al View Post
Well, I have a batch of original Toshiba 2SJ55 and 2SK175 - how would that do? Absolute thermal stability and a veritable hot - hot monstre. What do you think?
albert
Sounds good albert do you have alot of them ? I might be interested

-Dan
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Old 15th February 2011, 09:21 AM   #483
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Hi Dan,
I have some ten pairs, so I can even successfully match them. They are refurbished, outside is rusted to a little extent. But hey, they are the most searched for components . . .
I bought them in Guangzhou when I worked there a couple of years back. Always on the lookout.
k175 j55.jpg

How about a 20W or 30W Hiraga Le Classe A with these components, of course the output configuration remains the same (with the 2SA634/1k8 and its base resistor of 0,47 ohm. Just add a stopper resistor. It's just not noir et vert anymore .
albert
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Old 16th February 2011, 03:18 AM   #484
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It would be interesting to listen to what is the spec in these ?
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Old 16th February 2011, 08:43 AM   #485
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Default spec sheet

Hi Dan,
Here are the specsheets for these output transistors. (from AmpsLab site)
2sj55.pdf
The J55 can be seen as a beefed up version of the J50, used by Hiraga. From 7 Amp max to 8 Amp and from 160V to 180V rating. From 100Watt to 125Watt. Indeed, the case is heavier.
2sk175.pdf
The K175 can be seen to be a heftier K135 (higher voltage rating) used in many amplifiers. It can thus also be used as a replacement for the Nemesis one-transistor amplifier.
see the comparison thermal plot of 2SJ49/50 where you see the 75 degrees transfer plot is below that of 25 degrees:
2sj49_2.gif

The "most important" advantages from a construction point are:
  • the thermal resistance is negative, so with rising power the device shuts downs.
  • the output source is on the case so the two cases need not be isolates towards each other
  • the sound is superb

It can imho be used in a darlingnot such as the Monstre and the 20/30Watt, and in the case of the Monstre schema the collector of the driver transistors need a load resistor that is aptly chosen, I think in the same configuration as the 20W. (In his article, Hiraga says the two output stages have the 'same' configuration).

I have made an output stage based on these with a tube driver and the sound was warm and referenced to the driverstage (I used tubes like ECC35).
The drawback is that the mid-bass seems to have a kind of extra mellowness depending on the source resistor if I am right.

Note my Le Monstre has this extremely short rise-time of about half a ns as specified and the -3db is around 500 kHz... (closed loop) I expect that a large gate capacitor of a Mosfet takes long to charge, and thus will have different behavior in the stage. While upping the driver current has it's limits too. In this aspect the 20W configuration is at an advantage, as it already can be fitted with large drivers.

What would you suggest?

Many have used Mosfets in this output stage, ZenMod being one of the promotors I saw.

albert
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Old 18th February 2011, 03:14 AM   #486
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Hi Al,

I think you could probably transplant the out put pair for these mosfet and change the resistors like you suggest however bias would need some attention and also a couple of other resistor values

The benefit would be if you started with just a resistive 8 ohn load for testing and say 9-12V split rail you could probably sort these issues out on the test bench before hitting the amp with a larger supply (that is what i did with the monstre and le class A recently)

I personally opted for 2SC5200/2SA1943 in Le Class A however a Vfet monstre could be something really special - if you can you should try it!

-Dan
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Old 27th March 2011, 02:59 PM   #487
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Quote:
Originally Posted by danieljw View Post
Sounds good albert do you have alot of them ? I might be interested
-Dan
Daniel, I tried to PM you but you have PM's off. So here in 'broadcast':
I suggest a swap: for the 2SJ55 and 2SK175 Toshiba FETS I posted about.

I plan to make a matching set-up.

Then you could get two matched pairs from me, and you
  • send me a fitted PCB (for example Le Classe A - such as sold by dieroehre on ebay if that is good quality)
  • with equally matched input pairs and drivers - you do the hard work there (I haven't seen a seller yet with Le Classe A PCB's fitted and stocked but Le Monstre has a good supplier on ebay)
  • A collector resistor from the driver to the opposite rail of approx 6.8k would be needed as the Fets can't source a current on the gate.
  • I like the BD140 /BD139 for driver because these are so very linear. You saw how that Lineup uses them in the Le Monstre
  • - without the outputs of course and without the output resistors. [I plan to use 1ohm2 output resistors; Hiraga advises 1 ohm for the output pairs with fets in this Le Classe A article]

How's that for a deal (it's a steal, I know ).

I do understand that with a FET output, the Le Monstre configuration would be interesting too, if run at minimum 20 V and 1,5A.

albert :-)

(It would be nice if this were theoretically spiced before building.)
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Old 28th March 2011, 06:27 AM   #488
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Hi Albert,

Sorry I will check my PM and see what is wrong with it.
I only just saw this message !!!!!!

Just before we go done this path I better check out the datasheets of these parts closely, but your idea sounds good so far

Did you link/post the datasheets I remember seeing them breifly.

-Dan
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Old 28th March 2011, 07:17 AM   #489
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Quote:
Originally Posted by triode_al View Post
I like the BD140 /BD139 for driver because these are so very linear. You saw how that Lineup uses them in the Le Monstre[/I]
Hey, al.
Actually BD139/140 seems not be the top choice.
I changed to another pair of TO-126.
2SC2911/2SA1209

And they lowered THD considerably compared to BD139/140.
It should be same for Hiraga 20 Watt
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Old 28th March 2011, 02:15 PM   #490
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Daniel,
The types I have are higher power and higher voltage than the traditional 2SJ50/2SK135.

- of course I do think a collaborative development path would be good; why not create a new PCB (that even could be made with 'military style' fully riveted component holes). At least my bad habit is to change what is working good.

Let's source the crowd.

Since ages, discrete input transistors are used in Le Classe A. But why not use dual transistors. Like MAT01 (NPN)/, MAT02 (also NPN, Hfe 650) and Mat03 (PNP, hfe 150). This type of devices might be interesting, as they have advantages over separate, discrete transistors in the input stage:
Quote:
A fundamental requirement for accurate current mirrors and active load stages is matched transistor components. Due to the excellent VBE matching (the voltage difference between VBEs required to equalize collector current) and gain matching, the MAT03 can be used to implement a variety of standard current mirrors that can source current into a load such as an amplifier stage. mat03 datasheet
And this will apply to the input stage of the Le Classe A too, even though the transistors are differently configured.
Too bad: The MAT02 AND MAT03 CAN NOT BE MATCHED - different Hfe.

Other newer types are the LS310(NPN) and LS350(PNP) Series Monolithic Dual Transistors can be matched because of similar Hfe 150.

When re-designing a PCB, the various footprints of such devices and various discrete components could be catered for.

Good idea?

albert
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