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.
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.
Attachments
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.
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.
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?
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?
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
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
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:
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
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:
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
Onvinyl said: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.
Hi Nelson,
thanks a lot for the explanation!
Or am I completly off and mix everything up?
Rüdiger
--
beedfack aures cll
thanks a lot for the explanation!
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
Hi,
Well, this train has departed some time ago:
http://www.diyaudio.com/forums/showthread.php?postid=378122#post378122
http://www.vacuumstate.com/images/RTP5_rev_1.GIF
http://www.klaus-boening.de/html/schematics.html#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
Well, this train has departed some time ago:
http://www.diyaudio.com/forums/showthread.php?postid=378122#post378122
http://www.vacuumstate.com/images/RTP5_rev_1.GIF
http://www.klaus-boening.de/html/schematics.html#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
See also page 3+4: http://ayre.revealsystems.net/pdf/p5xom.pdf
and a review (in german though): http://www.stereoplay.de/sixcms/media.php/188/stp0704Ayre.pdf
Sorry Mr. Pass
Ciao, Tino
and a review (in german though): http://www.stereoplay.de/sixcms/media.php/188/stp0704Ayre.pdf
Sorry Mr. Pass
Ciao, Tino
NP: 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.
Should one of the cartridge outputs be grounded at the tonearm?
I am experiencing a lot of hum with standard single ended preamp.
Tom
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.
Should one of the cartridge outputs be grounded at the tonearm?
I am experiencing a lot of hum with standard single ended preamp.
Tom
Update:
I have not located all my notes, but I did run across something that indicated that I had the headamp section (I tend to use moving coil cartridges) right at the turntable, possibly even inside it. This was a year or two ago, so I don't remember off the top of my head. The signal from the headamp then went out a cable to the "normal" phono stage with the usual 40dB or so of gain and the RIAA EQ.
Once the signal has been through the headamp, it's not as prone to mischief--not immune, mind you, just a comparative improvement. Setting aside the effects of the RIAA, 40dB translates as a voltage amplification of 100x. That's a lot of amplification, and any uncancelled hum or noise will get pretty obnoxious. However, it's still better than applying 60 or 80dB (1000x to 10,000x) of gain to the same amount of hum/noise.
Quoting from memory, I think the headamp was giving about 28dB gain.
Shielding is of paramount importance. Period. Don't depend on CMRR to bail you out of noise pickup problems. Also critical is the power supply. Anything nasty on the rail will, to a greater or lesser extent, show up in the output. Differentials can cancel common mode noise fairly well, but follower outputs or common Source/Emitter/Cathode gain stages are sitting ducks.
In my case, I have an old Goldmund Studio turntable. It's a totally enclosed design, with enough room inside to park a car. It's been a while since I looked, but I believe that the interior is coated with graphite paint as shielding. Open chassis designs are not going to give you the option to shield the circuitry that way. Yes, there are uncoated plastic and wood chassis designs out there that don't shield the signal and supposedly they work just fine. I dunno, call me superstitious, but I'd prefer to have at least some aluminum paint or copper foil or something to keep the evil demons at bay. And that's saying something, because there's so little RF where I live that I can usually get away with murder. Not on this.
Grey
I have not located all my notes, but I did run across something that indicated that I had the headamp section (I tend to use moving coil cartridges) right at the turntable, possibly even inside it. This was a year or two ago, so I don't remember off the top of my head. The signal from the headamp then went out a cable to the "normal" phono stage with the usual 40dB or so of gain and the RIAA EQ.
Once the signal has been through the headamp, it's not as prone to mischief--not immune, mind you, just a comparative improvement. Setting aside the effects of the RIAA, 40dB translates as a voltage amplification of 100x. That's a lot of amplification, and any uncancelled hum or noise will get pretty obnoxious. However, it's still better than applying 60 or 80dB (1000x to 10,000x) of gain to the same amount of hum/noise.
Quoting from memory, I think the headamp was giving about 28dB gain.
Shielding is of paramount importance. Period. Don't depend on CMRR to bail you out of noise pickup problems. Also critical is the power supply. Anything nasty on the rail will, to a greater or lesser extent, show up in the output. Differentials can cancel common mode noise fairly well, but follower outputs or common Source/Emitter/Cathode gain stages are sitting ducks.
In my case, I have an old Goldmund Studio turntable. It's a totally enclosed design, with enough room inside to park a car. It's been a while since I looked, but I believe that the interior is coated with graphite paint as shielding. Open chassis designs are not going to give you the option to shield the circuitry that way. Yes, there are uncoated plastic and wood chassis designs out there that don't shield the signal and supposedly they work just fine. I dunno, call me superstitious, but I'd prefer to have at least some aluminum paint or copper foil or something to keep the evil demons at bay. And that's saying something, because there's so little RF where I live that I can usually get away with murder. Not on this.
Grey
tmblack said:
The standard has been one side grounded at the preamp, and
the whole thing enclosed in a shield grounded at the preamp.
If you are experiencing a lot of hum, then something is responding
to a magnetic field - if you can get rid of the magnetic field or
shield against it, then the noise will tend to go away. The other
possibility is a ground loop, and you can track that down, too.
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