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DIY Jadis preamp

209.112.136.234
Posted on August 6, 2009 at 22:54:09
DAVID
Audiophile

Posts: 763
Joined: September 26, 1999
 Anyone have any experience w/ this DIY preamp kit? If so, how did it sound? Is this a good company to work w/? Never done a kit before, except in electronics school some 25 years ago. Thanks.

 

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RE: DIY Jadis preamp, posted on August 7, 2009 at 06:20:30
Norbert2nd
Audiophile

Posts: 6
Location: Frankfurt a. M.
Joined: May 9, 2006
 Hi David,

I have successfully built a complete JP-200 "deluxe" kit (with some alterations, see below). Analogmetric as a company are easy to deal with but delivery is not exactly the fastest. They respond quick to emails.

If you are a beginner as a kit builder I have to warn you about lack of building support. The information on the analogmetric web site and forum is very basic and all you get. There is no overall wiring diagram or step by step instructions to lead you. So you have to know what goes where.

I have no idea if that preamp is even close to the original Jadis JP-200. I guess not because the original is a 4-chassis design including phono preamp stages.
The sound of this line stage is very much depending on the tubes you use. If you put in Mullards you get that typical (brown) Mullard sound which is not my cup of tea.

With the right tubes you can build a very transparent and detailled preamp featuring a huge soundstage. Before I have used a Silk-based TVC from DIYHifiSupply which tends more to the lean side. Compared to the TVC the JP-200 clone has more timbre, body and weight. Amount of detail is on the same (high) level.
Over the years I have come to the conclusion that a preamp is really a necessary component in a decent sounding system. Not to add voltage gain but to add those properties mentioned above. For me it is a deliberate departure from a "neutral" amplifier system. But sins of omission are not tolerated!

The rest of my system is a slightly moddified SlimDevices Transporter as source and Hypex-based Class-D poweramp feeding my Tannoy IIILZ Monitor Mk II speakers.

I have made the following alterations to the kit:

Power supply:

- Use the optionally available 10H choke
- Use 6x4 as rectifier tube (7-pin socket is not included!)
- Replace C1 and C3 with a single Mundorf tube cap of 10uF, 1000V
- Replace C7 with a TAD Oil Cap of 0,25uF, 600V

Amplifier board:

- Replace all resistors with Takman REY 0,5W metall film types
- Change R7A and B to 1kOhm
- Change R10A and B to 1,5 kOhm
- Change R14A and B to 100 Ohm
- Add C9A an B (which are not supplied with the kit) two TAD Oil Caps 0,25 uF / 600 V
- Replace C1A and B with Ampohm Aluminium Foil, Paper in Oil Cap 0,047 uF / 630 V
- Replace C2A and B with Ampohm Aluminium Foil, Paper in Oil Cap 0,1 uF / 630 V
- Replace C5A and B with Ampohm Aluminium Foil, Paper in Oil Cap 1,0 uF / 630 V (depending on the imput inpedance of your poweramp you might need a bigger value)
- Replace C4A and B with silver mica 8 pF / 500 V and place a silver mica 22 pF / 500 V capacitor between grid and cathode of T1A and B to fight self oscillation
- Use ECC81 / 12 AT7 for the cathode follower position (T3A and B) to lower output impedance

Lowering gain from 20 to 12dB:

- Change R5A and B to 33 kOhm
- Change R3A and B to 1 kOhm

General:

Be warned about the input selector and output delay protection kit which are included in the "deluxe" version of the kit: Both have ground planes which are connected to the local power supply ground. There is no dedicated signal ground plane! If you use the Analogmetric tube tube power supply there is only one low voltage supply you can use to feed both modules which is the unregulated part of the heater supply. Bad thing is that the heaters are connected to pin 4 and 5 of the ECC83s and pin 9 is grounded. As a result the ground plane of both modules is at -6,3V to ground! This converts ground planes to perfect anntenas.

- Add two ceramic 10 nF / 500 V capacitors to HF-wise shunt the "ground planes" of the input and output modules to signal ground
- The delivered Shuguang 12AX7B are not too bad for chinese tubes but I would recommend to find out which NOS tubes you like

Best regards,

Norbert

 

Wow..., posted on August 7, 2009 at 09:15:50
DAVID
Audiophile

Posts: 763
Joined: September 26, 1999
 ..thanks for the informed reply. Makes me realize how long I've been out of the bit and pieces of electronics. I may search around for an easier first.

I do have one question, when you write "0,25 uF" do you mean a standard 25 microfarad cap or is that a way of writing pico farad? Not recognizing the use of commas. Thanks again for your reply.

 

RE: Wow..., posted on August 7, 2009 at 09:29:08
Norbert2nd
Audiophile

Posts: 6
Location: Frankfurt a. M.
Joined: May 9, 2006
 ... sorry, I mean 0.25 uF or 250 nF. In Germany we use the comma as "point" and the point es thousand separator, e. g. 1.000,45.

 

RE: DIY Jadis preamp, posted on August 7, 2009 at 14:02:04
xaudiomanx
Audiophile

Posts: 3647
Joined: August 16, 2004
 Hi David,

If it is the same board as on DIY Gene then I highly reommend it. That company does a nice job in copying circuits for very little money. The tech support is not one of the Asian strong points. Most of those companies are just parts sellers but they do a great job.

As in the other responder stated, the parts choice isn't of the best but at what level will you hear it? Until you familiarize yourself with the sonics of different parts I would go with the generic parts sold with the kit and make changes later, a little at a time.

As for support? I can only assume that you will get help from the people here. These guys are amongst the best around and are very supportive of each other, even though they don't always agree on issues.

I do have to say that WIMA caps aren't my first choice but they are good.

DIY Gene also sells a regulated power supply kit for the JP-200.

Hope this helps!
Paul

 

RE: DIY Jadis preamp, posted on August 7, 2009 at 15:13:58
becketma@yahoo.com
Audiophile

Posts: 1352
Location: Sunny Tucson AZ
Joined: May 21, 2007
 I've run across this site:
http://glass-ware.stores.yahoo.net/aiallinoneki.html
It does come with instructions.
Best from Tucson
Bob
"He (R.M. Nixon) was a foul caricature of himself, a man with no soul, no inner convictions, with the integrity of a hyena, and the style of a poison toad." H. S. Thompson

 

A point to point JP-200, posted on August 7, 2009 at 21:52:46
jantle2


 
Browsing on the web I found this - its not in English but the schematics and photos are universal.

Nice work, but putting a replica Jadis into a replica AR chasis is interesting.

 

OK..., posted on August 7, 2009 at 23:56:19
DAVID
Audiophile

Posts: 763
Joined: September 26, 1999
 ...what would you guys think is the most important as far as sonic quality goes. Changing the signal resistors to Vishay or metal film or the caps or both? My money will be limited and will have to wait till Alaska's Permanent Fund this October.

 

RE: DIY Jadis preamp, posted on February 22, 2010 at 22:46:51
chungtat


 
Hi Norbert,

What is the B+ you are using?

 

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