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Jack Read contact or Purity schematic

synaesthesia

synaesthesia

Apr 13, 2004
1,557
44
UK
#1
I've acquired a Read purity preamp, and it's in good condition except for the Balanced DI out. Something is wrong somewhere as the Balanced DI out is very noisy, very hissy and the bottom seems to have fallen out. The EQ seems to work but not in the same way as the line out, the tone is completely off, andthe EQ spectrum is much less.

The line out is OK, a bit hissy, but the tone is nice and thick and the EQ works.

Has anyone got a contact for Jack Read? I could also use a schematic and I can trouble shoot it or fix it with a schematic. The sticker over the chassis is still unbroken so the unit has never been opened.

Thanks in advance.
 
#7
I would like to thank synaesthesia for sending me a PM once he figured out his problem. I put in the new tube and all is fine. He is a class act and shows once again the great community that TalkBass is.

Wally
 
#8
Wally Malone said:
I would like to thank synaesthesia for sending me a PM once he figured out his problem. I put in the new tube and all is fine. He is a class act and shows once again the great community that TalkBass is.

Wally
Click to expand...

It would be nice if Synaesthesia would post the resolution to his problem so that the rest of us would know the fix if we ever hear of the problem again or have a friend who has the same trouble.

Paul
 
#9
Nothing special in the present fix, you just need to find a 12AU7 or ECC82 that will work nicely with the READ. The second tube is for the XLR out. It is a bit finicky and several 12AU7s I tried , it didn't like. I presently have a 12AU7 from GT that seems to work OK. It is less noisy now, but certainly not in the performance territory that my Demeter VTBP, or Alembic F-1X gives me in the studio.

Jack Read has gone silent, and is not returning emails or phone messages to date. He works for a big name audio company now, one that makes small speakers in arrays. I rather leave him in peace if he has no further pride in the product. I will be working on an internal modification to the Read purity, to tap the line out and use either a Jensen transformer to feed the XLR or make an active circuit. In truth, I will probably try both. Not a difficult mod, but I do not presently have space in my work/travel/music schedule to look into this until October.

I am not particularly impressed with the READ's tube driven DI and would be happy to dispense with it. The tone in the XLR output is not even close to the 1/4" line out. So if you have your stage sound EQ'ed, your XLR out to FOH is a different tone..... the line out is very fat and bassy at flat setting, and the XLR considerably brighter and thinner at the same EQ settings, or EQ bypassed settings. I like the line out tone better.

FWIW, a Jensen transformer works and works well, I don't need the hassle of finding a tube that behaves etc. The schematic is online at Jensen-transformer..... the transformer you need is the JT DB E. It is not rocket science to retrofit this into the Read preamp.
 
#11
Other than Wally, i have had 2 other emails/PMs about issues wth the Read purity. One says there were those that were handbuilt by Jack and those that were subcontracted to another manufacturer to put together.

If you search hard enough on the net, you will find Jack discussing diagnosing this noise problem, and it seemed to be a mystery even to him. One fix he offered was to shorten the length of one wire and turn the transformer 45 or 90 degrees and the noise went away.

But at this time, I am more interested in jensen type fix. For those who want to get into it here is the link:

Invalid Link Removed

you want APP# AS008.

FWIW, the better tube driven DIs cost a lot, such as the Demeter ones and the A Designs Reddi Tube DI. I can't see how the READ would have an equivalent tube DI for the price it sold. FWIW, It's a great preamp, gets great tones, has the most useable deep and bright switches (others bring out the tubby bass and the slashyour throat highs). I like it a lot, but I am certainly not using the XLR out until I modify it.
 
#14
Just wanted to report that all went well on the gig and I they did use the DI. In fact the soundman gave me compliments on my sound in general. The Read was powered with a Stewart 2.1 played bridged through an Accugroove Tri210 and Accugroove Tri112. I played my F Bass BN5.

Wally
 
#15
Glad it worked out Wally.

News update: Jack Read is back on the scene and has replied to my email. So we are emailing and trying to find a solution to the XLR discrepancy. Apparently he has fitted a different coupling cap to some units to increase the low end of the XLR out. I'll report if there is anymore info to share. Have asked him audaciously what he thought of the Jensen fix.
 
#16
This is from Jack Read, proceed with caution if you know what you are doing, if you do't take it to a qualified engineer:

" I think a Jensen DI fix would be perfect, but I would suggest building it as an external box that splits the line-out signal. I would strongly recommend this approach, as the voltages present inside the Purity are very high (over 300 volts) and potentially lethal.

Here are some examples of circuits that I think would work:

Invalid Link Removed

Invalid Link Removed This is another possibility that could be built as a small outboard box.
Invalid Link Removed Here’s another; instead of a guitar input you would have the Purity signal as your input.

One of the difficult features to implement in the Purity was a DI level control that would not have any effect on the line-out signal. I wanted to keep it a pure tube circuit without adding too much to the cost of the preamp. Without the level control circuit in place the DI and line-out would have identical signals.

This is, essentially, how the Purity works:

All of the gain and EQ are handled by the 12AX7. The output of the 12AX7 is sent directly to the inputs of the 12AU7, where it gets split in two. The 12AU7 is set up as a cathode follower. The signal tapped from one cathode is the line-out; the signal tapped from the other cathode goes to the DI circuit. The DI circuit uses a large capacitor (100 uF on later models) to isolate the DI level control from the rest of the circuitry. Earlier versions may have had a smaller cap, 10 uF or 25 uF. The most current circuit was recognizable by the long, black 100 uF electrolytic cap.

Again, I strongly recommend NOT opening the preamp, as the voltages present inside the Purity are very high (over 300 volts) and potentially lethal. If you could make the modifications as an external box that would be much safer."

I have decided on the Jensen fix as it will immediately give me some equity between the XLR out and the 1/4" out. But I will be trying the Capacitor modification as well. Personally I'd install my Jensen inside, but if you don't know what you are doing don't attempt this, go see a qualified Engineer or electrician.
 
#18
synaesthesia said:
This is from Jack Read, proceed with caution if you know what you are doing, if you do't take it to a qualified engineer:

" I think a Jensen DI fix would be perfect, but I would suggest building it as an external box that splits the line-out signal. I would strongly recommend this approach, as the voltages present inside the Purity are very high (over 300 volts) and potentially lethal.

Here are some examples of circuits that I think would work:

Invalid Link Removed
Click to expand...

That's a standard DI circuit, no need to build it yourself unless you feel like it. Radial makes a nice version using that very transformer. The Radial version is a bit more like this though:

Invalid Link Removed
 
#19
The Radial is cheaper I think than DIYing an external box. I am looking though to retrofit the Jensen within the 1U chassis as a permanent fix. But if you want an external box, yes it would work out about $20 - 30USD less on parts, not factoring your labour & time for DIY.

BTW, the difference between the 100uf Capacitor and the ones with the lower values (10 - 25uf), if you want to keep using the tube driven DI, is that it allows more lows to pass through.
 

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