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HELP! High gain, low noise fet advice needed!

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Lenin

Member
2002-02-15 1:42 am
London
I desperately need some recommendations for a high gain, low noise fet for a phono stage I'm pulling together.

Its made up of 2 linear gain stages, with passive eq. The gain stage topology is essentially a very simple triode type circuit. (Yep, you read that right). With just 1 device in each stage.

I'm trying to achieve extremely high MC gain (good enough for low o/p Ortofons, etc) and I'm just terrified about ensuring that in particular, the first stage is treated with the care it requires. (Hence my search for a high gain, low noise device).

I understand Toshiba fets have a decent sonic reputation . Any recommendations anyone? (Toshiba or anything else)

.:confused:
 
The 2SK170's are good for this application and should be readily available from MCM or Consolidated. Use 4 in parallel for lowest noise. Borbely might also have 2SK147 which are even better but $$$$.

It would probably be a good idea to cascode either of these FETs, especially if you use them in parallel.

Good luck

Phil
 

Werner

Member
2002-01-18 11:12 am
Belgium
Also look at the DIY Pass Pearl, which is a
two-stage cascoded 2SK170 phonostage, and
the Pacific from William Walther of Maison de ''Audiophile.

I myself started out with a Pacific-like circuit on the breadboard, and then added cascodes in both stages. These are FETs now, but I will try BJTs too. Once I also had paralleled input transistors, but I think the added complexity is not really worth it. YMMV as you desire larger gains. I only
manage about 44dB with 19V rails.

I have another breadboard with a single-stage
phonopre, comprising of an SRPP-like gain stage feeding a passive RIAA through a capacitor. The RIAA includes the 100k volume pot of the linestage.

Promising, but with given FETs it is not easy to get the SRPP thingy right.
 
Hi Michael

Harry's right on both about cost from MCM and not being able to specify grade. I asked MCM about this once and they said they were lucky to get the transistors let alone a specific grade. I get ten or so and if they are the grade I want, order more. Then I match and select them.

If you buy them, please post what grade you get. I need a bunch myself, plus the J74 complement.

Phil
 
thanks, i couldnt find the datasheet before hence why i asked the question :) what's the go with that? have toshiba stopped producing these parts? for that matter, toshiva seems to have removed most of the datasheets for the small signal fets we commonly use.... surely they have not all been discontinued

UPDATE

I just checked back @ the toshiba site http://www.semicon.toshiba.co.jp/eng/prd/mpsig/ft_mpsig.html and some of the datasheets are now present ... looks like they may have just been updating their site.... hopefully the rest of the datasheets will return soon...
 
the order results are in ........

PH104 said:
Hi Michael
....
If you buy them, please post what grade you get. I need a bunch myself, plus the J74 complement.
Phil


All:

My order came today. I ordered 20 each of:
2SK170, 2SJ74, 2SA970, 2SC2240

I got (drum roll please):
2SK170-BL
2SJ74-GR
2SA970-BL
2SC2240-GR

Note: I HAVE NOT checked all 20 pieces of each to see if any IDSS or HFE grade mixing occured. I will check later and let you know.

Certainly can't beat the price nor speed of delivery from MCM.
Thanks for the tip, Harry

mlloyd1
 
Sorry - Thanks Phil for the MCM tip.

Haven't started actually building the analyzer yet. Just going through my parts bin to see what I have and what I need. Also thinking about how I want to do the various range switching - relays versus multi-wafer rotaries kind-of-thing. Relays offer some benefits that could be useful. Also there were some updates that I want to look thorugh as well before I start.

I'll keep you guys posted as to progress.

Michael
 
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