HELP! High gain, low noise fet advice needed!

[Lenin]

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)

.

 

[PH104]

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

 

[arnach]

Hmm

The Aleph Ono uses four matched 2SK170s in the first part of MC input stage. You can get these from Borbeley for $2/ea, and matching will add 50% to each or total value, you'll have to check.

-- Aaron

 

[Werner]

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.

 

[HarryHaller]

2SK170

Much cheaper at MCM. The 2SK147 is not made any more. I think it wold only have a real noise advantage for MC phono stages. The 2SK170 is very quite and great for everything else. Cascodes are a great idea. Use the 2SK170 at between 8 and 15 vots drain to source voltage for low device capacitance and low noise.

H.H.

http://www.mcmelectronics.com/Search/search4-frame.jhtml?_DARGS=/common/prodsearchform.jhtml

 

[mlloyd1]

what IDSS does MCM give you these days?

Harry (and others who may have bought from MCM recently):

What IDSS grade (G, BL, V, ??) do you get from MCM?
I'm thinking about ordering some if they have the higher grades.

Thanks!
Michael

 

[HarryHaller]

Fet

I don't know if you can specify in your order. I think I usually wind
up with blues or greens which work fine. Violets are real hard to find.

H.H.

 

[PH104]

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

 

[HarryHaller]

JFETs from Borbely

The prices for the jfets are in euro dollars. The bias groups for
the K170 and J74 are green and blue. He has the K147s listed but they are EXPENSIVE!

H.H.

 

[mlloyd1]

re: MCM's JFETs ...

Phil, Harry:

Thanks. I'll order some and report on what I get. Who knows, maybe I''ll get some V

mlloyd1

who is still upset because he can't find his stash of 2SK146 and 2SJ73 duals that he got from Borbely Audio years ago

 

[jam]

Lenin

I do not think you will will get enough gain out of a two stage phono stage for a low output Ortofon. Noise will be a big issue. It will probably be ok with a high output MC.

Jam

P.S. Wayne at Pass Labs might be able to help. I suspect you will need a three stage circuit.

 

[AudioFreak]

Could someone please explain what is the difference between the different IDSS Grades.

 

[mlloyd1]

Japanese JFET IDSS grades answer

AudioFreak,

From the 2SK170 data sheet:

GR (Green) 2.6-6.5mA

BL (Blue) 6-12mA

V (Violet) 10-20mA

View the data sheet at a number of places; this is one that I like.

mlloyd1

 

[AudioFreak]

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...

 

[mlloyd1]

the order results are in ........

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

 

[HarryHaller]

Data sheets

Data sheets at:

http://site.pcmagazine.com.tw/audio/parts/parts.htm

H.H.

 

[PH104]

Hey Michael

thanks for posting the IDSS grades.

Looks like another order to them is on the way.

Oh - by the way - although Harry's a good guy, I first mentioned MCM.

Phil

PS - How's the THD analyzer coming?

 

[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