Need to build JC 2 preamp

Hello Folks

I am prepare to build John Curl's JC2 preamp. However I am not electronic expert. I do not know the purpose of the 100R trim pot in the phono stage and the 500R trim pot in the ling stage. Does anyone can help to tell me the purpose & how to adjust these trim pots to get the best performance of this preamp circuit?

Thanks
 
HKC said:
Hello Folks

I am prepare to build John Curl's JC2 preamp. However I am not electronic expert. I do not know the purpose of the 100R trim pot in the phono stage and the 500R trim pot in the ling stage. Does anyone can help to tell me the purpose & how to adjust these trim pots to get the best performance of this preamp circuit?

Thanks
Does anybody have a schematic.
at least a clip of that part, where the trimpot is.

Thanks - will make it 10 times easier to give some advice to you

/halo - according to ElsoKwak halojoy is "A Fan of John Curl"
- well, not exactly
- halo is even more of "A Fan of Elso's Work on Digital Timing"
 
Remake of John Curls JC-2

Hi HKC,
Rather than trying to rebuild a JC-2 may I suggest to build something more "modern" like Sonny Andersons circuit. This easely surpasses the JC-2 in soundquality.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=1794&highlight=sonnya

Quite a few of the FETs and transistors for the JC-2 are no longer available. Also a monolitic dual sounds much better than a handmatched FET.
The 500 Ohm pot in the line amp sets the quiescent current of the inputstage and the 100 Ohm pot in the phono the offset.
Please note that the linemodules in real world have two pots. One is controlling the offset but not shown in the schematic.
I believe the schematic is a very crude and early one. I opened some defective modules with boiling antifreeze. (ates away the epoxy a bit) and found MPSU05 and MPSU56 outputtransistors in the modules, NOT FET's. (Also obsolete tranasistors) Also the line amp is slightly more complicated. And input FETs were 2N4392 and 2N5115 (metalcan).:cool:

halojoy, Thanks for the kind words. :blush: :blush: Did you receive my email regarding the Denesson JC-80 made by John Curl?;)
 
this is halo promoting halojoy

halojoy said:

Does anybody have a schematic.
at least a clip of that part, where the trimpot is.

Thanks - will make it 10 times easier to give some advice to you

/halo - according to ElsoKwak halojoy is "A Fan of John Curl"
- well, not exactly

HKC,
This is probably too much
A way to promote myself, but ....

This is a Thread I started at AudioAsylum:
http://db.audioasylum.com/cgi/m.pl?forum=tweaks&n=50004&highlight=elso+cartridge&r=&session=

I was "groman" there
Here, I get answers by Thorsten, Elso and John Curl
So I have actually dicussed with JC
not only in this thread - you know I started a lot over at AudioAsylum.
------------------------------

But :p I am more Happy with this Forum :p
It has more human qualities, than that doubious AA....

:p Regards to HKC & Elso

/halo - will have to check his emails
for another JC-construction
 
Re: Remake of John Curls JC-2

Elso Kwak said:
Hi HKC,
Rather than trying to rebuild a JC-2 may I suggest to build something more "modern" like Sonny Andersons circuit. This easely surpasses the JC-2 in soundquality.

http://www.diyaudio.com/forums/showthread.php?s=&threadid=1794&highlight=sonnya

Quite a few of the FETs and transistors for the JC-2 are no longer available. Also a monolitic dual sounds much better than a handmatched FET.

If anyone is interrested i am planning to upload a modified circuit with 2N5912 as input diff, BC550B/560B from 2N5401/5551 and J5XX or CRXXX current sources....
place C3 on a starground, which is missing of the old circuit which is really good... but ...

This should eliminate most of the trimmers.....

Should then be able to perform more than 100V/us, and have low distortion and be a "single" gain stage...

any comments?

Sonny
 
So will many other be -including halojoy

Come on, sonnya!
Start a Thread
Can become a lively thread.

--------------------------------
I am in thoughts of buying myself
100+100 2N5401/5551 for use in high voltage applications.
I use 550C/560C so far upto 45v
Thinking of buying
SC2240/SA970 to use for input devices, goes upto 120V
And some BC640/630 maybe

And MJE15030/31 for output/powerdriving.
With MJ15024/25 for high power.

I am quite limited to these choices, as we have almost
only one supplier in Sweden
www.elfa.se - without them, we were lost ...:bawling: :bawling:

/halo - likes to increase the voltage in designs
- get more Tube-like
 
Re: So will many other be -including halojoy

halojoy said:
/halo - likes to increase the voltage in designs
- get more Tube-like
Hi halojoy,
You raise a interesting point regarding the difference between tube and sold state circuits. Mr. Metaxas has some interesting thoughts about this:
http://www.metaxas.com/pages/masnewfiles/index.html
(Click on technology, then on voltage regulation) ;)
 
Thanks, I will see what he thinks.

I know I have been on that website once before.
Probably some year ago.
I recognize some of the names of the amplifiers.

Thius is some of what he, Kostas Metaxas AUS, has to say:
The most significant difference between VALVE and TRANSISTOR circuits is the amplifier/power supply regulator circuit interaction which is far more critical in Transistor circuits.

To illustrate this phenomenon using the the most basic amplifier gain stage, let us assume that our input signal is a 1.0 Volt peak to peak, 1 kHz sine wave and the amplifier stage has a gain of 10 so that the output voltage is 10 Volts peak to peak. For simplicity, resistor R is the load resistor which dictates the overall gain.
If this was a VALVE amplifier, the high voltages which are typical in valve circuits (from 200-400 Volts DC) would result in a valve of around 50,000 to 100,000 Ohms for resistor R.

The equivalent transistor amplifier using much lower voltages (from 12-15 Volts) would have a substantially lower value of R between 200 Ohms-100 Ohms. Therefore the power supply used in the transistor amplifier is virtually directly linked to the transistor amplifier circuit compared to the isolation of over 50,000 Ohms in the Valve circuit.
 
Re: Need to build JC2 preamp

HKC said:
Hello Elso & Halojoy

Thank you for the information for JC2. The Sonny Andersons circuit also interested me. I will make a decision to choose one among the two circuits.
Thanks again for all the inform.

You could easily replace the J113 in the inputpair with 2sk389 if you want to.

For Halojoy ::)

I will make a version for you with 2sc2240 and 2sa970. i believe you will order BL parts? am i right?

Elso ::magnify:

Should i make it a stereo board, smd or leaded resistors?

By the way this circuit could very very easy be enhanced to be an power amp. :cool:
 
Re: Re: Need to build JC2 preamp

sonnya said:


You could easily replace the J113 in the inputpair with 2sk389 if you want to.

For Halojoy ::)

I will make a version for you with 2sc2240 and 2sa970. i believe you will order BL parts? am i right?

Elso ::magnify:

Should i make it a stereo board, smd or leaded resistors?

By the way this circuit could very very easy be enhanced to be an power amp. :cool:
Hi Sonny,
I don't like SMD. I did some experiments to convert my line amp to a poweramp. It worked till white smoke rose....:bawling: Powersupplyissues are even more important so it seems...
But I can make PCB's myself. I am just interested to see the schematic. Maybe I can learn something or I did overlook a circuitdetail in mines.;)
 
Hello Elso

I read your post in the Audioaslyum before I posted this thread regarding the JC2 preamp. I am not familiar with electronic theory I would like to learn more about this circuit:
1. Does the circuit posted on the marklev.com is a workable circuit that I can knock off without any problem since you said the circuit is a very crude & early one.
2. Where should I take the measurement to read the quiescent current in the input stage?
3. How much quiescent current should I get by adjusting the 500R pot in the iput stage?

To Sonnya

I downloaded the pcb-top file but there is no image in it. Please advice what should I do.

Thanks again for everything.
 
Thanks, sonnya

For Halojoy :

I will make a version for you with 2sc2240 and 2sa970. i believe you will order BL parts? am i right?
www.elfa.se
Here is what Smallsignal Bipolar I can buy:
http://www.elfa.se/elfa-bin/lt.pl?sort=&pics=&213467&214943&2009911
-------------------

Here is what Small MOS & JFET I can select:
http://www.elfa.se/elfa/produkter/se/20/2009926.htm
-------------------------------------------------------------------

Has anybody some experience about using
the MOSFETs in DIL: IRFD120/IRFD9120
I see Pass have tried them.
But they have 360-390pF - That is much for a 1.3Watt device

caplocks say (in Thread about the very good MJE15030/31 transistors)
that MJE15030 have only 50-100pF
and that is a 50Watt 8Ampere !!!! TO220 Device

40 parallelled of IRFD120 would make 52 Watts
and something like 14.000pF !!!!!!!!
-----------------------------------------------------
Bad examples? Well I have read some bad maths & limping thinking
by people, trying to force Devices they do not like,
to seem bad...

I can say that BD139 have bad data for input pair in a RIAA amp,
and that it has poor performance at 10 Watt operation.
Does this say anything about the quality of BD139
No, because that is not what it is suited for.
To be a Input pair in very small signal applications.
Or to operate at 10 Watts
------------------------------------------------

/halojoy - hopefully doing some better math, next time :D :D :D
 
I built this circuit using GR (Idss: 2.6-6.5) grade 2sk389/j109s and ZTX450/550s, but forgot about the need to change the drain resistors. Can someone please tell me what value drain resistors I should use instead of the original 100ohm ones? Thanks in advance.

As for Fred's suggestion to cascade the J-FETs, my layout is kind of small, so I'd really like to get this circuit working with just the resistor change.
 

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Folks, the JC-2 is not an EASY design to make. Many of the original parts are obsolete. The circuit topologies are still viable, and almost typical, today. Thirty years ago, this was an advanced design. Elso has not been productive in improving this design, and while I respect his opinion, I find errors in his estimate of the sound quality potential of this design. Done right, it can still keep up with most anything today. There are some oversights, however, that we made in 1973-74, that need to be fixed. We attempted an upgrade to existing units in an article a few years ago in 'Positive Feedback' written by Chuck Hollander. It might be useful to find this article on the internet.