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Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Mon Apr 15, 2019 7:31 am
by mediatechnology
I meant to ask as I got in some 2068DD in readiness before you finally decided on the 5532. I assume the differences are small enough as to be not a worry in use?
I really don't know the answer to that but I suspect it may depend on the gain.
The compensation allows for either the NJM2068 or the 5532 and for the 5532 it can be relaxed a bit.
My recollection was that at maximum gain there wasn't any difference.

The NJM2068's niche is MM preamps and JRC's "secret sauce" seems to be having the right combination of noise voltage and current that gives it a slight edge, with my Stanton, over any other bipolar or FET op amp.
If the NJM2068 has an advantage in the MC preamp it will be at lower gains.

Now that I have a board I'd like to compare the OPA1612 (on an adapter) to the 5532 and 2068.
At low gains I bet the OPA1612 wins slightly over the 5532.
An NJM2114 is also worth looking at though they are EOL.

I'm shopping for a DL-103 right now.
I need to test it with a cart before I let this go out.

Also getting an extra ADC headshell.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Mon Apr 15, 2019 10:17 pm
by KMN
Of course, my eyes are terrible but it is hard for me to see exactly how you dealt with the transistor thermal coupling problem. Are they face to face..bonded somehow? Do you have any close up shots of that?

I was thinking maybe if you planned to insert the TO92's 90 degree bent, the flat faces could all be thermally tied via board copper....maybe a mounting hole could be used to apply down force via flat washer or something along those lines.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 16, 2019 3:52 am
by billshurv
That was mentioned as not fitted yet. Experiments to follow I believe.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 16, 2019 5:00 am
by mediatechnology
They are back-to-back and will be epoxied together.

The small metal "hats" I made from 3AG fuse ends I found worked pretty good.
I like wearing tin foil hats myself and the transistors seem to like it too.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Mon Apr 22, 2019 8:11 pm
by mediatechnology
A not so off topic question...

The DL-103 I need for the preamp test does best in high mass arms.
I have a low mass ADC LMF-2 arm.
The LMF-2 has 6 grams effective mass.
These two are not an ideal pair.

The DL-103 has 8.5 g mass and dynamic compliance (@ 100 Hz) of 5*10^-6 cm/dyne.
Based on the spreadsheet here the Fo calculates to be 18.7 Hz.
If I add a 3 gram shim that lowers to 17 Hz.
To get to 14 Hz I have to add 10 grams.

Suggestions? Lead cartridge body?
I don't have the complete counterbalance weights for the LMF-2 either.

An AT-F3/III with only a single 3 gram shim in that same arm has an Fo of 14 Hz.

Considering the low mass arm would the AT-F3, which has similar impedance and output as the DL-103, be a better cart to live with?

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 23, 2019 4:32 am
by billshurv
The DL-103 is an oddity. It shouldn't need a particularly high mass and yet people keep putting them in very heavy arms. There are some CNC machined metal bodies such as the paradox pulse around which have a good following, but still unconvinced.

Part of the confusion is that the japanese don't publish the useful compliance (10Hz). compliance measured at 100Hz is actually a measure of the VTF required to meet the tracking spec and nothing to do with resonant frequency.

The bigger problem with the 103 is it does put a lot of energy into the arm. http://korfaudio.com/blog26 for measurements.

I have a similar issue with my SME 3009 S3 arm which I bought for MM testing but want to try on MC. I have an AT0C9 for it but desperately trying to resist a NOS signet MK111E which is a 5g MC from the late 70s. Low mass high compliance MCs are rare now other than Van Den Hul and they cost too much!

AT-F3 is a good cart but will likely be outclassed by your stantons!

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 23, 2019 7:07 am
by mediatechnology
I had looked at "The Cap" https://www.denonaluminumbody.com/ which has 3.5 g of mass and doesn't require the DL-103's outer shell to be removed. The pulse looks like it has pockets for pellets to add additional weight which is cool but removing the cart motor from the Denon body is not something I want to undertake.

With 3.5 g I might be able to get there if I have the right counter-balance weight.
As it is now with the Stanton I have plenty of range left.

Edit:

1) Found this calculator: https://www.vinylengine.com/cartridge_r ... luator.php
2) This post showing an estimate of "13" (lateral) compliance at 10 Hz for a DL-103. https://www.vinylengine.com/turntable_f ... hp?t=35434 and this one about 12: https://www.vinylengine.com/turntable_f ... hp?t=78463

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 23, 2019 7:35 am
by billshurv
so with arm that's 14.5g, add bolts will be 15, which gives you a horizontal resonance around 12Hz. Sounds perfect without any additional mass.

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Tue Apr 23, 2019 8:52 am
by mediatechnology
That's what I was thinking...
Why not just try the DL-103 in the ADC arm and see what happens.
Having useful 10 Hz figures helps.

I can go ahead and test it with the ZTX851 preamp and add "The Cap" if I need to lower Fo.
With comparative 10 Hz compliance around "10-13" the resulting Fo looks to be more in the ball park.

I think I said the Stanton is around 5 g so all things otherwise being equal I think I should be able to counter-balance the added 3-3.5 g of the DL-103.

I looked at a Stanton chart and most of the Disco carts ran "10-13" where the Hi Fi carts ranged between "18-30" for the "Stereo Standard" and "Collectors" series. So "10-13" at 10 Hz for the DL-103 doesn't seem out of line.

At a minimum I'll know what it sounds like sitting on the arm rest. :lol:

Re: A Low Noise Balanced Input Moving Coil Preamp Using the ZTX851

Posted: Wed Apr 24, 2019 4:40 pm
by mediatechnology
While I await the cart's arrival I installed the moving coil preamp into the moving magnet preamp's enclosure.

Image
ZTX851 balanced moving coil phono preamp mounted in the enclosure.

Its a perfect tight fit except for the height of the Wima caps.
I'm lacking about 0.1" clearance.
If I were to use this box long term I think I'd mount the Wima caps on the underside or switch to the lower profile polyester.
If I decide to make another box and return this one to the MM preamp I'd lower the 9 pin D connectors about 0.2"

It measures just as quiet at the end of 50' of cable as it does on the bench.
Using the 10Ω terminator as the source resistance and with a 68 dB overall gain (flat) the NF is 1.5 dB.