A Su-Sy Ono?

[sbear]

Hi, Everyone. Since I can't afford to buy any more parts for my 100W Aleph-X project, I have been researching an Ono project to waste my spare time. And out of curiosity I put together a schematic for a SuSy Ono (which I thought the Xono was, but It seems its not). Since I will be using this pre balanced, my first thought upon looking at the ono schematic was that a seperate inverter circuit that copied the output and inverted it was rather cumbersome solution now that I have been privy to the secrets of "X". It seems SOOOOO Simple!!! So of course there has got to be a reason why it won't work. I would love to hear a little feedback on whether this circuit is do-able or not, and if any obvious changes need to be made if it is.

My own conclusions left me with a few questions I would like to discuss:

First, this design uses a RIAA filter for each side of the "X"ed preamp. Will this wreck havoc on the EQ curve, or not. My initial thought was that since both filters are in the feedback loop, the end result would be a average of the seperate filters. Is this a correct assumption? Or, more likely, would trying this be dangerous to my health?

Second, the "magic resistors" which help stabilize the absolute offset. (I labeled them R99 and R99x) Are they needed or not in a preamp circuit like this? I'm guessing yes, but I have a feeling I will have to change the resistor values.

Third, which goes along with the previous question, would I need to decrease the 100K output resistors to ground in order to help stabilize the absolute offset? I have a hunch that I won't need to, but then again. . .

Fourth, did I do the negative input on the diff pair to ground the right way in order to match impedence (i.e.-are R21a and 21b correct?)

So here it is. Let me know what you think.

[Nelson Pass]

No reason you couldn't do it, but I will point out that using
active balanced inputs on phono stages is very difficult. Usually
the common mode noise is so large that you find that it runs
quieter with one input grounded. This effect comes from the
fact that significant noise reduction is ordinarily achieved by
having one side of the cartridge's output grounded, which really
loads down any stray noise pickup. When we want to float the
output of a phono cartridge, the usual solution is to use a
transformer.

[sbear]

Nelson, thank you for the reply. But your responses raised a couple more questions! Well, first I guess I should explain my goals for this design. My goal is not necessarily to build a pre with a lower noise floor or lower distortion, the main goal is to come up with a more elegant way to get a balanced output from the Ono. The original design copied the positive output, then inversed it. This solution caused the negative output to go through 2 more gain stages than the positive output. After taking a look at Su-Sy circuits I saw the possibility of using a Su-Sy design on the Moving Magnet portion of the Ono (I have not changed the Moving Coil portion at all). The way I am seeing it, it is just like using a single ended input on an Aleph-X (using the positive input only and grounding the negative input) and getting a balanced output. This way I don't believe I am floating the cartridge outputs; one side is still grounded and the other goes to the positive input. Is this correct reasoning? or did I fall off into the deep end a while back?

I guess I should just build it and try it, but of course I don't have enough money to finish my first project yet. So who knows when it will happen.

My foremost concern is the dual RIAA filters, I have absolutely no idea if it would work OK, good, bad, or not at all. Any comments?

[GRollins]

A couple of quick thoughts:
1) Another possibility would be to build non-EQ "X" gain cells and sandwich the EQ between them as a passive filter.
2) If you use tight tolerance parts, the variation in EQ between the phases will be minimal. If you then run the phases though a differential, it will tend to iron out any differences between the phases.

Grey

[Onvinyl]

Hello all,
I just came over this older thread, and saw a topic mentioned that always struck me, the pro's and con's of balanced phono input stages, and the fact, that two godfathers of elegant audio engineering (Pass, Borbely) seem to favour asymmetrical input.
I have found the balanced option superior to asymmetrical input sonically whereever I could compare, be it diy or commercial. (Not that I'm that experienced) So, I'm driving my phono balanced.
But Nelson Pass wrote:

Usually
the common mode noise is so large that you find that it runs
quieter with one input grounded. This effect comes from the
fact that significant noise reduction is ordinarily achieved by
having one side of the cartridge's output grounded, which really
loads down any stray noise pickup. When we want to float the
output of a phono cartridge, the usual solution is to use a
transformer.

1. Common mode noise: If you're talking about the connection wire that takes on noise and RF, shouldn't twisted wire solve this? I have twisted copper wire and have no noise problem, judged by ear.

2. What help offers an input transformer in avoiding stray noise? I'm helpless

Which other malificious effects can we awaite with balanced phono input?
regards,
Rüdiger

[Nelson Pass]

Originally posted by Onvinyl
1. Common mode noise: If you're talking about the connection wire that takes on noise and RF, shouldn't twisted wire solve this? I have twisted copper wire and have no noise problem, judged by ear.

2. What help offers an input transformer in avoiding stray noise? I'm helpless

Common mode noise would be the noise picked up equally by
both strands of the twisted pair. If they are both terminated in
high impedance to ground, then quite a bit of noise gets
picked up, and the differential input of the active circuit may not
be that effective in eliminating it.

For example, if you want a balanced phono input loading the
cartridge at 47 KOhms, the you are probably looking at two
inputs, each loaded with 23.5 KOhms. The noise picked up by
leads loaded into this impedance can be substantial.

In an unbalanced circuit, one side is grounded (no noise there)
and the other is loaded by 47 Kohm in parallel with the source
impedance of the cartridge, which is generally quite low.

In both cases shielding is a very big help.

Transformers avoid this issue by magnetically isolating the
common mode noise out so that it never sees the circuit.

[Onvinyl]

Hi Nelson,
thanks a lot for the explanation!

If they are both terminated in
high impedance to ground, then quite a bit of noise gets
picked up,

I'm still confused: in my case it's a ccs'ed jfet differential with one 500R Resistor from gate to ground per fet. So, effectivly, the 'high' impedance does not lift the cart from ground, rather, seen from the differential input (providing hopefully high cmrr), the resistors 'shunt' the noise to ground. This works better with low resistor values Iguess, I for myself did not try the mentioned 47k.

Or am I completly off and mix everything up?

Rüdiger

--
beedfack aures cll

[Nelson Pass]

I think it's worth trying and see what you get. Honestly I've
never taken it seriously because the potential for issues, but
not having actually built one, I could be surprised. Here's your
chance to do some original work.

[Onvinyl]

Hi,

Here's your
chance to do some original work.

Well, this train has departed some time ago:


http://www.diyaudio.com/forums/showt...122#post378122
http://www.vacuumstate.com/images/RTP5_rev_1.GIF
http://www.klaus-boening.de/html/sch...tml#MKIIInew_B

I'm pretty sure there is a lot more to find.
If I'm not mistaken, at least some german phono designs use the obsolete SSM2017 (or so) as a first stage in an 'instrumental'/bal-to-unbal mode (of course the tonearm wiring has most likey to be changed for all these stages).
thanks a lot,
Rüdiger


--
beefdack plseh

[zinsula]

See also page 3+4: http://ayre.revealsystems.net/pdf/p5xom.pdf

and a review (in german though): http://www.stereoplay.de/sixcms/medi...tp0704Ayre.pdf

Sorry Mr. Pass

Ciao, Tino