[undertow]

I have found what I believe the superior output capacitor combo for the money in this unit.
- Output Capacitors better than paying for the DUELUNDS I had in here, and smaller combo than the Clarity MR's  which worked are a combination of 1.8 uF Clarity ESA, bypassed by a Mundorf Silver/oil .22 uF. I can suggest these values as you will get a bigger soundstage and deeper bass it seems using this 2.0 uF plus total value over the original 1.0 uF used by Jolida. The nice thing about the cap combo here is its under 100 bucks.

[undertow]

2012 update.
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Input Stage-

All capacitors replaced, using Nichicon Audio grade electrolytics, Wima film, and Evox Film caps, as well as taking out the generic ceramic caps replacing with Silver mica's.

-Caddok resistors for Cartridge load resistors, and for Gain resistors replacing the generic input dip switch selection board. For MM carts. of 4.0 mV and above HIGHLY suggest bringing down the input resistor which is a 1000 ohm to  maybe a 2000 or even 4000 ohm resistor. Its fine for some  MC- carts even to use the 1000 ohm in there, but some of these higher ortofon carts. put out and seem to maybe even overload the input stage on some high output recorded albums.

-Op Amps
As for oscillation issues there are none with AD797 from analog devices which are used in the top grade MBL equipment. Or from Burr Brown op637 even the op627 types seem fine. The 847KN DO NOT WORK.

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-Output Stage
After re-testing Duelund caps, and Clarity MR... The Clarity MR for the price in the 1 uF size is unbeatable. Now I like the ESA claritys bypassed by Mundorf Silver Oil as well saving space about the same price as the Clarity MR's.


I Removed the output board connected to the RCA's with the little generic Potentiometers on it and run straight cables to the outputs due to using the 12AU7's they are only 30% of the gain and I don't need the LOW output RCA's. 

_______________________________________ _____________

- Power Supply

All caps replaced - Nichicon, and Black gates, all bypassed by Solen 1 uF film caps.

Schotky hi speed rectifiers replaced all Diodes 1 amp versions.

Ceramic main fuse at the IEC vs. Glass.

_______________________________________ _____________

- MM carts
I found for really High output MM that I needed 12AU7 tubes to drop the gain, 12AX7's were pretty inflexible for volume control. 

-MC Carts.

You can use 12AX7's for MC carts. maybe some will be fine with 12AU7's if its enough gain.

_______________________________________ _______________

 I used the 33 gauge Cardas Tonearm wire for inputs, and outputs on the INPUT board to the tube stage.

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[bigdirty]

Undertow,

 Thanks for the update. This thread has been a great help and inspiration.

Looking at the partial schematic, R6 looks like a good spot for a higher quality resistor. your thoughts on this?

Underwood hifi, on their level 3 mod, upgrade the Single-Phase Bridge Rectifier (vishay DF04) on the phono board. I think this is where they use Telefunken SF4007 ultra-fast soft-recovery diodes. any plans on doing the same for your unit?

thanks again, your JD9 is always fun to see.

[jlafrenz]

For the LT1028 I see CN8, CS8 and ACN. Which is the proper op amp?

[bigdirty]

For the LT1028 I see CN8, CS8 and ACN. Which is the proper op amp?

I used "LT1028ACN8" in the sockets closest to the input in my unit.

[Syrah]

Hi Undertow and others.  I'm loving my modded JD9!  I'm using it with a Shelter 501.  At first I was not a fan.  Then I bought a Bob's Devices step up.  That changed everything.  Plugged into the JD9, it is great.

Now I'm thinking of trying out some 12au7s since the step up adds so much gain.  I have Brimar CV4004s in it now, which sounded the best of the odds and ends of 12ax7s I had lying around.

Any tips on best 12au7s to try?  My preference would be to roll a few new production tubes before venturing into NOS, unless there are some NOS out there that must be tried.

Also, if I drop the gain with 12au7, am I then better off using the High Output?  Which gain settings have the best technical performance?

Thanks!

[richandy]

Undertow:

Which of the AD797 should be purchased?

[richandy]

Undertow:

Which of the AD797 should be purchased?

Never mind. The AD797 is too noisy in the input slots. The sound seems rather thin when 4 are used with 2 OPA637. The best sound to me at least is using 6 OPA637, with mundorf 1.5 silver oil. The sound is more fluid and the bass is much more pronounce.

[Syrah]

Back to an old topic.  I'm now thinking of trying out these new Burson modules to replace the op amps. 

http://www.partsconnexion.com/opamp_burson.html

Chris is also selling extension cords, so they should fit - may on their sides.

Any thoughts as to whether this would be a good or bad idea?

[Syrah]

Old thread, but by way of update I now have the Linear Technologies LT1028 in the right input slots, Burson V5i in the middle slots, and Burson V5 in the output.

Wow!

The real kicker was the V5 in the outputs.  I needed the extensions, and some patience to get them to fit (on their sides).  But wow did that pay off.

Highly recommended set up.

[CxTurbo]

Sorry to bring back such an old thread. It has been the inspiration to modify my JD9 II.

In the Underwood modifications they are listing Riken Ohm resistors in the signal path, are these just the loading and gain resistors on the switch board? I noticed also a cheesy resitor and ceramic caps on the MC Low out put RCA's thinking this could also be a spot.

Any help would be wondrous.

-James

[Ixnay]

  Yes, I know. This a an old, but mighty thread. My question would be about RFI as in radio station interference. Has anyone dealt what that as an issue? Would like to get it taken care of. Also, there seems to be no tube schematic for this JD9. Go figure.
  FWIW, this has been a great topic and a lot of good ideas.