John Curl's Blowtorch preamplifier part II

[john curl]

It is just better to pay the price. You can't get quality for nothing, at least in my world view.

 

[mullardel34]

John,

Agreed; I've already placed my order for the genuine Toshiba parts. I was trying to identify some points where those who don't want to incur the additional expense could go...

 

[mullardel34]

JC-80 Build Sub-Thread

John,

Is there anything in the topology presented in the schematic that would disqualify this PC board from successfully implementing a useful JC-80? Does the eBay-sourced JC-80 PC board face any showstopper issues?

Thanks in advance!

 

[31697B]

take two jFETs of same type -- tie the drains together. tie the sources together. A dual gate jFET?
I saw this done somewhere, i think.

 

[fas42]

It is just better to pay the price. You can't get quality for nothing, at least in my world view.

In fact there are two ways: money, or much personal effort; and money effectively merely passes the baton to someone else to hopefully apply similarly focused, appropriate effort ...

Frank

 

[wayne]

The Toshibas have a slight sonic advantage over the IR parts especially in the midrange clarity. I wish it wasn't so but it is. If you want the best for audio use the Toshibas.

 

[john curl]

I don't know WHY they switched to those Toshibas, but I think it is not a risk that I would do to change them, just to save a few dollars. There must have been SOME REASON that they chose these parts over the IR's.

 

[john curl]

34, so far, so good!

 

[EUVL]

> Since the independent JFET's don't share a common substrate, there's no inherent thermal balance, but .....

This one is really an old story. Doesn't time fly ....... :

http://www.diyaudio.com/forums/solid-state/135154-next-best-thing-2sk389-2sj109.html
http://www.diyaudio.com/forums/group-buys/135359-toshiba-dual-jfet-heatsink.html


Patrick

 

[kamis]

I don't know WHY they switched to those Toshibas, but I think it is not a risk that I would do to change them, just to save a few dollars. There must have been SOME REASON that they chose these parts over the IR's.

What about Hitachi K216/J79 in the same position, similar to Vendetta second stage? Lower capacitance compared to IR Mosfets?

 

[jan.didden]

> Since the independent JFET's don't share a common substrate, there's no inherent thermal balance, but .....

This one is really an old story. Doesn't time fly ....... :

http://www.diyaudio.com/forums/solid-state/135154-next-best-thing-2sk389-2sj109.html
http://www.diyaudio.com/forums/group-buys/135359-toshiba-dual-jfet-heatsink.html

Patrick

I just discovered I still have NOS of the Siliconix U441 matched pairs.
Seems very well matched, although it is a two-chip design.
Anybody used these in input stages?

jan

 

[john curl]

The Hitachi device will NOT WORK in that location because the pin-out is different. IF you must substitute, just use the Fairchild IRF devices, like the others on the BOM.

 

[scott wurcer]

take two jFETs of same type -- tie the drains together. tie the sources together. A dual gate jFET?
I saw this done somewhere, i think.

A true dual gate FET has both gates modulating the same channel. There is often a front and back gate that can be tied together, or at times the back gate is tied off to the source or a carefully chosen potential. The top gate often has far less leakage and makes a useful electrometer (Ig < 20fA).

 

[john curl]

Yesterday, I got access to a new BLUE RAY player worth a good deal of money.
At least it will be an A rated product, in my favorite mags, like its predecessors from the same company. To evaluate its sonic quality level, I hooked it up to my STAX direct drive tube driven electrostatic headphones and a quality SACD recording. WOW! At least on first listen, I will know better with more sources and a longer evaluation period. That is when some 'nagging' signature might well appear.
I also evaluated its video performance in HD, and again: WOW! I didn't know what I was missing! However, normal DVD videos, were good but not that much better than any other player, AND the selection of Blue Ray videos are such 'crap' or so darn expensive, that they are almost impossible to collect, if you already have a previous collection of DVD's.
So much for the 'latest' digital technology.

 

[zinsula]

The Toshibas have a slight sonic advantage over the IR parts especially in the midrange clarity. I wish it wasn't so but it is. If you want the best for audio use the Toshibas.

I assume one reason could be the awkward behaviour of the IRF P Channel parts which was pointed out by Nelson Pass and Charles Hansen.

Uh, and i'm not going to ask how you did this listening evaluation...

 

[Joshua_G]

Yesterday, I got access to a new BLUE RAY player worth a good deal of money.
At least it will be an A rated product, in my favorite mags, like its predecessors from the same company. To evaluate its sonic quality level, I hooked it up to my STAX direct drive tube driven electrostatic headphones and a quality SACD recording. WOW! At least on first listen, I will know better with more sources and a longer evaluation period. That is when some 'nagging' signature might well appear.
I also evaluated its video performance in HD, and again: WOW! I didn't know what I was missing! However, normal DVD videos, were good but not that much better than any other player, AND the selection of Blue Ray videos are such 'crap' or so darn expensive, that they are almost impossible to collect, if you already have a previous collection of DVD's.
So much for the 'latest' digital technology.

Hi John,
Which player is it?

 

[31697B]

dual gate jFET -

A true dual gate FET has both gates modulating the same channel. There is often a front and back gate that can be tied together, or at times the back gate is tied off to the source or a carefully chosen potential. The top gate often has far less leakage and makes a useful electrometer (Ig < 20fA).

Could you then have a jFET with input and gnfb applied to same transistor via dual gates? Simplify circuitry some more while keeping performance.

 

[bcarso]

A true dual gate FET has both gates modulating the same channel. There is often a front and back gate that can be tied together, or at times the back gate is tied off to the source or a carefully chosen potential. The top gate often has far less leakage and makes a useful electrometer (Ig < 20fA).

See the four-terminal JFETs here: Ultra-Low Noise JFETs

 

[john curl]

The Fairchild IRF's P channel do NOT have the IR P channel problem That is why Fairchild was mentioned in the BOM.

 

[31697B]

Hi John,
Which player is it?

bet you a dollar it is an OPPO-95 modified.