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Old 9th July 2010, 07:53 PM   #41
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As soon as Mr Fang gets back from holidays, I will put my order in.
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Old 27th August 2010, 05:26 PM   #42
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Prakit,
there is a way how to further optimize this circuit in order to use it as a preamp.
The thing is that feedback resistor are heavily loading the output which is not a problem when driving speakers and using 3 pairs of MOSFETs in output, but for just one pair it's not optimal. In order to raise the value of feedback resistors we have to raise the value of input JFET's source resistors and the only way to do it (and keep the high Id through JFETs) is to introduce appropriate DC bias to JFET's sources. That's what R28 and R29 are for. C4 and C3 are shunting JFET's sources to ground, AC-wise.
R34 and R16 ratio (as well as R35 and R17) is responsible for the ammount of closed loop gain. R23 and R27 are setting the current through output MOSFETs (300mA or higher) and DC offset (the same way as in original F5).
Should be easy to try, and it should sound better. I'd like to hear your impressions...
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Old 28th August 2010, 09:21 AM   #43
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I forgot to mention something about the preamp in post #42
Using higher value source resistors for input JFETs lowers the OLG, but it's not very important since we need lower CLG in the preamp anyway. I suppose the most will need the gain of about 2V/V so feedback resistors can have lower value than 1k (470R will result in gain about 2.2V/V and it's still high enough resistance that won't overload the preamp).
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Old 30th August 2010, 12:02 AM   #44
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[QUOTE=thanh1973;2209552]Well IRF9610 is used in the front end of Aleph 3/30 etc, so they can't be too bad.
But I take your point, the toshiba devices are much more linear according to the data sheets.
Maybe I should also try the toshibas in the front end of my Aleph 30.

/QUOTE]

I bought some of these from Z to test out in similiar setup with Mini-A. Looking for tips assuming they won't drop right in.

Also plan to build this Mini F5 gig with 1 or 2 outputs and see how they do with a pair of lowthers, running off a 12V tranny.

Thanks for sharing.
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Old 30th August 2010, 08:55 AM   #45
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Mini-A will benefit from using k2013 as output devices (2 pairs per channell, 500mA per MOSFET, +/-15V supply). Use j74 as input LTP and your Lowthers will love it
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Old 30th August 2010, 10:32 AM   #46
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Juma-
Thanks for the response. I was thinking the 2sk313's as input and CS, and the IRFP240 as CCS and SemiSouth R100 as output. Replacing with one pair of sj74's won't do the heat, but the TO-220's do. I have this running now with the IRFP9610s. Here is a pic. Sorry it is hard to look at. More sorry this is off topic, but I find these Toshiba buggers exciting.
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Old 30th August 2010, 11:23 AM   #47
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If we are talking +/-15V supply optimal version is the one mentioned in post #45. Basically, it's Mini-Aleph-J with k2013 in output section.
j313 as input LTP won't do well with Id=10mA (maybe marginally better than IRF9610, but I doubt it).
IRFP240 and R100 in output will give sub-optimal results with such a low PS voltage.
I see that you are all excited about trying all the new devices at once but don't force it, let the fever cools off
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Old 1st September 2010, 04:25 PM   #48
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Juma, does this 3 pair of outputs F-5 have more gain than the standard F-5?
Is there a thread where all this is laid out? I suppose there are a few other changs besides just adding more mosfets?

russellc
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Old 1st September 2010, 08:24 PM   #49
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Quote:
Originally Posted by Russellc View Post
Juma,
1. does this 3 pair of outputs F-5 have more gain than the standard F-5?
2. Is there a thread where all this is laid out?
3. I suppose there are a few other changs besides just adding more mosfets?

russellc
1. 3 pair of what outputs ?
2. What's "all this" ?
3. What's your goal when you ask for "other changes" ?

Please, try to phrase your questions clearly, refer to post numbers and schematics, be precise - I don't know what you think, just what you write...
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Old 1st September 2010, 09:07 PM   #50
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Quote:
Originally Posted by juma View Post
I got interested in Toshiba's 2SK2013/2SJ313 MOSFETs last year when estman, a forum friend, sent me generously a set of dozen j313s. They impressed me with their superior linearity of transfer characteristics but not until recently (when I got the N-channel complements - k2013) I could not try them in classical push-pull circuit.
Using them in F5 (3 pairs per channel at +/-20V, 400ma per MOSFET for total bias of 1.2A per channel) transformed it into amp that leaves no wishes open.

Schematics and pics are here:
Novi amp sa 2SK2013/2SJ313 - DIYAudio.rs
This is the post I referred to. You said "Using them in F-5 ( 3 pairs per channel...) transforms it into amp that leaves no wishes open."

"All this" refers to the forgoing amp that "leaves no wishes open"


"Other changes" in regards to the F-5 and your adding of the output devices.

Clear enough?

Russellc

Last edited by Russellc; 1st September 2010 at 09:09 PM.
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