few phono preamps with balanced inputs .. why?

[lfleib]

Hi Bo-bo,

The tone arm cables that I've taken apart or repaired, do not look like your "normal" coaxial interconnect. They look more like a microphone cable in stereo, with a fifth wire - the tonearm ground. Because of this configuration, it would be easy to connect them in a balanced mode, using the tonearm ground for both channels.

I am interested in the advantages and disadvantages of doing this. Unless your turntable sits in front or on top of a TV set, or some kind of electrically noisy environment, I think it is probably counterproductive. If you set out to design the worlds greatest phono stage, I think you would want the fewest parts of the highest quality.

Yes, I have a KILLER phono stage. It is an AHT - American Hybrid Technology prototype. The SN was higher than the test instruments available. The resistors are Vishay. The signature version had encapsulated Vishays - the same as in the Space Shuttle. Sonically, it disappears, it's like it's not there. I'm not worried about something being better, or looking to replace it. I just wanted to know how balanced lines apply to phono, and why people with home stereos are jumping on the bandwagon. I suspect that for the same money you could get a better sounding unbalanced unit.

[bo-bo]

Hello Lfleib,

I guess you are right. If you have the phono cord as a dual mike + a ground wire, you can go balanced. BUT, what's there to be gained? You have a hybrid stage, that is unbalanced. So, if you go balanced, you would need an input transformer OR an additional, non-inverting input on your stage. Either option would be costly. And it will make things worse: 3 dB extra input noise for a differential input (because we double the input noise resistance. Not 1 "resistor" to put the signal through, but 2). With a transformer it depends, but at least you add the ohmic (DC) resistance to the noise. Suppose primary were 3 ohms (high end!), that would add 1 dB to the ever present noise of the cartridges noise (at Rcart=12 Ohm, some 93nV over 40kHz of bandwidth). And we have to remember that we would be adding components to lose background hum and radio-noise that in most real world circumstances pose no problem for a single ended input. Lfleib, I am nearly certain that going balanced would NOT be worth it in your set-up. As in MOST turntable-phono set-ups. The transformer coupled input is the radiant exception, though!

In most SE phono set-ups, one better takes up something along the line of a direct uninterrupted wire all the way from cart to phono stage input. Get rid of as many as possible connectors (if there are superfluous connectors left of course). Substituting connectors with solder joints (e.g. at the tonearm base) could be a stepping stone. That's reversible by the way: If you don't like the change, you solder the connector back in. Or have it done by a technician with heat-proof fingers

cheers & enjoy your records,
Bo-Bo

[lfleib]

Hi,

I think that whether you have a high end set up or a table with a built in arm and cable, you can get great musical performance. Cable noise is not the major factor limiting Lp reproduction in most home set ups.

One thing I find interesting is the reported improvement in the overall sound when balanced units are used in balanced mode. Common mode noise rejection should not account for these improvements.

By the way, the AHT phono stage is solid state.

[tresaino]

Hi guys, two new important developments, for me at least:
(a) last friday got a response from the engineer who developed my new preamp
(b) yesterday, saturday, I picked up my new custom made 5 pin-XLR cable, that allows me to run balanced into the phono preamp. Will test today, sunday, and report first impressions.

While we wait for (b), let me start by reporting the few thoughts I got from the engineer, and also comment a few things written here over the last few days.

Some additional observations from the engineer of the preamp, I try to translate as good as I can:

- people in the professional world confirmed to him that a balanced generator does not need central tapping, because this is done correctly in the “differential receiver”, in our case in the phono preamplifier. For this to work, the generator (in our case the cartridge) should not have any connection to the ground of the arm or of the turntable. He noted that this was also said by some in this forum.

- he said that with a 5pin-XLR phono cable and the AM Audio phono preamp one can compare the sound in balanced and unbalanced modes by ear, as all one has to do is move the internal switches for both channels to “MC input balanced”.

- he asked me to report back to him my listening impressions, as he believes that it should sound better in balanced, even in an overall unbalanced system. Hey, will try today!

Now some other comments:

most Moving Coils have an output impedance that approaches zero, so in my book considering this as an “impedance-balanced line” doesn’t seem quite right, at least not without introducing a transformer or impedance matching head amp at the cartridge end.

if the output impedance of a cartridge is the same as its internal impedance, am not sure your first assumption is correct: many MCs have high internal impedances, for example Denon 103s have about 40 Ohm internal impedance, and top end Benz cartridges too, and many others too.

Anyway I have been thinking, and I knew five balanced stages (by heart) when I saw your remark that no five had been mentioned yet. They are:Vacuum State Electronics RTP3, Einstein "the turntables choice (Bal option)", Borbely EB 804, EAR 834P and Manley Steelhead.

Hi bo-bo, the EAR 834P is definitely NOT balanced, it has neither balanced entries nor exits. The top model EAR 88PB is also not a fully balanced model, as it has only balanced outputs, but on balanced inputs. Not even sure about the Manley Steelhead. Anyway, I think we would all agree that there are at least 5 fully balanced models on this planet by now.

Hi, I have an unbalanced phono stage that I'm quite happy with. It has a SN ratio greater than 90db with MC or MM, and can drive a power amp with a passive line stage.

My new preamp does not reach a 90db S/N ratio, and I have some sympathy for bo-bo’s reaction. How where these apparent 90db measured anyway? My new phono preamp declares a S/N ratio for MCs of 80.5 dB (weighted A, on a 0.5 mV input, closed at 0 Ohms, with the gain set on maximum), and for MMs of 86 dB (weighted A, on a 5 mV input, closed at 600 Ohms). The devil is in the detail, isn’t it?

As Carl Sagan said: "If you REALLY want to make an apple pie from scratch, you must first create the universe".

He said a good way of saying profound things. Another one, that I think applies very much to turntable playback theory: "There are no penalties for breaking the laws of physics; the universe is just arranged in such a way that you cannot do it"

Steerpile, I remember having seen early 20th century black and white movies with pies trying to break the laws of physics for a while. But they were creamy, without apples, to increase the effects on people’s faces.
Hey, I will start reading Sagan.

[lfleib]

Hi tresaino,

Although the AHT is dead quiet, the piece you are currently using is probably quieter than the record. The AHT has frequency response from 1Hz to 60KHz, + or - 0.05dB. THD is 0.0015%. SN is 90dB (A-weighted @ 0.5mV) for MC, and 98dB for MM. Gain can be set as high as 66dB, or at 46dB. This is achieved with the best parts money can buy and military IC's.

The important thing is how it sounds. The AHT is amazing. Check out the Absolute Sound #104 and #106. It was, at the time, the only 5 star component for 3 or 4 years.

I'm reasonably sure, because of what others have reported, that the AM phono stage will sound much better in balanced mode. Rather than only comparing it to itself, compare it to others - balanced or unbalanced.

Here's a link for an AHT review. http://www.soundstage.com/revequip/frank02.htm

[ben556473]

I would very much like to see a picture of the inside of that unit. Would that be possible?

[tresaino]

I would very much like to see a picture of the inside of that unit. Would that be possible?

Yes that is possible! Sundays help, I prepared them this morning, see below.

Am about to report on first impressions, but first a few words on the setup: I spent the first half hour verifying the main variables: that the turntable was 100% level (I moved things around recently so had to do this), VTA optimized (arm parallel to surface record), azimuth, and VTF (set on 1.9 grams for a Benz LP). Ok, done.

An extra word on the cable: relatively long, 1.5 meters, it hangs down behind the electronics and does not get in contact with almost anything. Almost, because there is a - 90 angle - contact with the power cable running to the normal preamp, situated below the phono preamp (see picture). Also, I left an extra ground wire on the phono cable disconnected from the earth on the phono preamp (not sure this was necessary, but I wanted to be sure I wasn’t messing up things).

Take a look at the pictures below: the first one shows the phono preamp in "topless", the second one shows the details of one of the two phono channels, and the third one shows the “sw6” switch for MC unbalanced to MC balanced (note these are dual switches, for each channel, and gold plated, to ensure nothing goes wrong).







I first connected the cables and then left the internal switches for the MC input on “unbalanced” and listened, and then moved the internal switches to MC input “balanced” and listened again.

The sound? Clearly more transparent, liquid, and punchy and “direct” in “balanced”. I think it is about 15-20 % better in “balanced”. I went back and forward a couple of times and the impressions remained the same. Will have to confirm with a few audio buddies over the next few weeks, to ensure there’s no, or not too much, placebo effect.

Well, is it worth it? I conclude yes: getting rid of the coax and installing a balanced interconnect on a turntable gives advantages most of the time, even with a single ended phono input.

This is what the engineer behind the AM Audio told me, and based on listening impressions so far I can agree wholeheartedly: a balanced input for MCs is already worth it in an unbalanced system. This is big news for me! Next steps will be a balanced preamp, and then perhaps balanced amps. But that will take some time, am not in a hurry .. also not moneywise, ahem, if you know what I mean.

leib"]I'm reasonably sure, because of what others have reported, that the AM phono stage will sound much better in balanced mode.

Absolutely correct!

Rather than only comparing it to itself, compare it to others - balanced or unbalanced.

No adverstisement intended but, frankly, I think I stop here. I tried and owned several phono stages over the last years, including top Clearaudio and EAR models. This one gives me a 10 year warranty, factory serviced. That should do it for a while.

Would I move back to unbalanced? No way!

[ben556473]

Thanks for the pictures and report. I think your phonostage has more components in it than my turntable, phonostage, amplifier and speakers combined.
Are the two 'cans' to the right your stepup transformers? Are you operating in fully balanced from the cartridge to them or single ended to the transformers then balanced into the phonostage.
Either way it all looks very complicated and far above my head,I'm sure it sounds sublime. Your phonostage has two power supplies each of which are more capable than my amplifiers! Very impressive kit indeed. Thanks for showing and glad to hear it's given an improvement.

[tresaino]

Are the two 'cans' to the right your stepup transformers? Are you operating in fully balanced from the cartridge to them or single ended to the transformers then balanced into the phonostage.

Yes, Stevens & Billingtons assembled by Bent Audio. I have not used them yet with the new preamp, as the Benz LP (40 Ohm internal impedance) is not a good match for step-ups loaded into 47kOhm. I can actually change the MM load to 56kOhm, but why bother if the Benz works so well on the MC entry? I keep the Bent step-ups for low-output low-impedance carts (currently on repair), so have not tried the fully balanced road yet.

Either way it all looks very complicated and far above my head,I'm sure it sounds sublime. Your phonostage has two power supplies each of which are more capable than my amplifiers! Very impressive kit indeed. Thanks for showing and glad to hear it's given an improvement.

You're welcome. If you click on the company's website you'll see pics of the interiors of all their preamps and amps (although not in such detail).

BTW, this is also way above my head. I still fail to understand why "balanced in" sounds better also in an overall unbalanced system. I'm sure that once we'll read Steerpike's summary in the making it will start coming through.

[bo-bo]

Hi all,

I'll share with you what I understand of the differences between balanced and unbalanced. Quite certain that won't be the definitive word, but maybe it can help a little.

BTW, this is also way above my head. I still fail to understand why "balanced in" sounds better also in an overall unbalanced system. I'm sure that once we'll read Steerpike's summary in the making it will start coming through. Wink Very Happy

A balanced line is quite simply the most 'neutral' way to transport a signal. So, even going to a "plain" single ended phono input, it pays of to treat the minute MC signal the very best way you can. Especially noisewise the very first step in the amplification chain is crucial. And because of the enormous amplification involved (approx. 80 dB at mains frequency), the difference between very good and excellent can be heard easily

One thing I find interesting is the reported improvement in the overall sound when balanced units are used in balanced mode. Common mode noise rejection should not account for these improvements.

and indeed it doesn't. There are two major factors that contribute to the superior perceived quality. The phono amp must already have a differential input, otherwise one could not go from unbal to bal by the flick of a switch. That also means that noisewise, there won't be much difference in perceived noise levels (mentioned common mode noise will be lower, but in good designs this is unlikely to differ much). However, if you switch to balanced mode the input level will be split between + and - inputs. This gives two big advantages:
1) The 6dB lower (halved voltage) input level massively reduces very first stage distortion. and 2) The same 6 dB are now available for extra headroom, potentially giving more power and dynamics to the music.

regards, and enjoy the music
Bobo

[blakep]

"1) The 6dB lower (halved voltage) input level massively reduces very first stage distortion. and 2) The same 6 dB are now available for extra headroom, potentially giving more power and dynamics to the music."

Thanks Bobo for that incredibly succinct technical explanation aligned with the sonic benefits. While I have absolutely no technical understanding on this (and who knows, someone may well come forth to argue or dispute the technical merits -I have followed these threads before!), your description (in so few words!!!) of its sonic merits is deadly accurate, at least in terms of what I have heard using a balanced phono pre through to a balanced integrated. Deadly quiet, less distortion, improved dynamics!

Well put!!

[lfleib]

Hi Bobo,

Finally, I'm getting an explanation. Thank you.

I understand the bit about the extra headroom, but how does 1/2 the voltage massively reduce first stage distortion? I would think that a higher voltage signal would have less noise and distortion, as long as the electronics can handle it. Also, wouldn't the duplication of parts on the differential input add to the imperfections?

[Steerpike_jhb]

as long as the electronics can handle it.

Only 6dB of headroom is not very comforting. A level shift of 6dB should under no circumstances result in massive distortion. (that makes it sound like the effect of a A/D converter).

You'll find a variation of level of more than 6dB among different brands of LP, so I don't agree that this minor reduction in nominal level accounts for any obvious change in sound.

[bo-bo]

...how does 1/2 the voltage massively reduce first stage distortion? I would think that a higher voltage signal would have less noise and distortion, as long as the electronics can handle it. Also, wouldn't the duplication of parts on the differential input add to the imperfections?

Hi lfleib,

ha, this can be confusing indeed. But actually you subconsciously (?) seem to know the answer already: " as long as the electronics can handle it." Let me explain. The phono stage is actually some sort of small amplifier made up of a couple of amplification stages (1 single stage is doable, but not often seen). Now as the incoming signal is getting bigger and bigger, this small amp, and especially its first stage is put to the test: It must deliver or the signal will get distorted. Now you have to realise the input is before any RIAA correction has taken place. So, at high frequencies the input level may be quite high. For example a signal +10 dB above nominal level at 15 kHz transduced by a 0.4 mV nominal cartridge would give an input voltage of 9.1 mV. And the poor first stage MUST give it a near LINEAR amplification of say 100 times (bringing the output of this stage up to 910 mV). It is thinkable that the frail, optimised for low-noise, first stage can not follow the "steepness" of the signal at this "high" a level: the signal's slew rate, especially at high frequencies, may have become too high. A balanced input, with a halved signal (the other half on the mirror input circuit) thus helps prevent slew rate limited distortion.
With respect to intermodulation distortion a lowered signal level works even better. If there are several loud frequencies present simultaneously in a signal (as often found in music), non linearities of the amp give rise to a series of tonally additive and subtractive by-products. Most of the time this type of distortion (intermodulation) is more severe (!!) and more unpleasant (because not related to the music) than the often measured steady state harmonic distortion. As said, a 6 dB lower signal level reduces this type of distortion massively (perhaps 30 dB or so) so that this distortion level may well sink below the noise-floor. One could imagine that Single Ended a specific intermodulation product would be at -50 dB level (output), so audible, and in balanced mode drowned in the noise at -80 dB (both levels unweighted). Here you might say that the mentioned imagined example of a SE stage could not handle the high multitone signal without keeping the byproducts below detectability.

The additional components necessary to make an input differential do actually NOT make the characteristics of the amp worse. OK, noise will be 3 dB higher. However, linearity of the input stage will improve notably. The reason is that the errors of either input partly cancel each other. The improved linearity gives rise to a substantially lower distortion in a differential pair input compared to a single ended input (...with equal degeneration and bias of the active input elements. Don't worry if you don't understand this addition )

Now on to steerpike, to whom I apparently did not transmit my message in noise free mode.

Only 6dB of headroom is not very comforting. A level shift of 6dB should under no circumstances result in massive distortion. (that makes it sound like the effect of a A/D converter).

You'll find a variation of level of more than 6dB among different brands of LP, so I don't agree that this minor reduction in nominal level accounts for any obvious change in sound.

You are right, 6 dB of headroom is 'nothing.' But that is not what is meant here. It's 6 additional dB's on top of what the phono stage could handle used in unbalanced mode. For that reason I called these decibells "extra." So imagine the phono preamp has 15 dB headroom in unbalanced mode (nearly adequate), in balanced mode this would improve to 21 dB (still not great, but quite acceptable). In other words the maximum INPUT level that the phone stage can handle with acceptably low distortion doubles. And that can make a lot of difference, especially with solid state electronics! With transistors 6 dB difference in max level can kill the music. You may compare it to hard clipping, or you can think of highs becoming screechy (yuck...!!). If you can postpone that happening by an input loudness-factor of two, that is very welcome! To put things into perspective it would be the same as a phono input of 0.4 mV nominal sensitivity going into overload at 2.25 mV or at 4.5 mV. No kidding steerpike, this is a significant enlargement of the "safety-zone."

Greetings,
Bobo