Voltage mode vs current mode phono stages


Can someone explain the differences in layman's terms and why is one better than the other? 

rsf507

It is very straightforward-

Moving Magnet cartridges produce high voltage, but low current.

Moving coil cartridges produce high current ( higher than MM's ) but very low voltage.

Moving coil step up transformers convert the high current/low voltage of a moving coil  to high voltage low current.

Alternately a better option for moving coil cartridges is to use a current gain input stage instead of a voltage gain input stage. This suits the MC better and in theory should have less loss because you are not converting current to voltage as a precursor to the amplification of the very small signal.

Just to embellish what Dover wrote, the upshot of his analysis is that for LOMC cartridges with very low internal resistance (10 ohms or less?), all other things being equal, a current drive phono stage makes a lot of sense (because the capacity to produce signal as current is inversely proportional to the internal resistance). But you will not want to use such a phono stage with MM or MI cartridges and even not so much with some LOMCs that have a relatively high internal resistance, e.g., >20 ohms, although that is far from a hard cut-off. From what I can tell, most current drive phono stages consist of an input stage that converts current to voltage. Downstream from the I/V converter is pretty much like any other high gain phono stage.

Ok thanks now please explain phono stages that are voltage mode and phono stages that are current mode?

See above. For current drive the phono stage input impedance needs to be as near zero as possible so as to “see” the cartridge as a current source. It also has be amplified by current and to put out amplified voltage in response to current. That’s why I called it an I/V converter. Ultimately the stage has to put out amplified voltage just like a conventional stage. It’s basically as simple as Ohm’s Law. Conversely a conventional voltage driven stage has to have an input impedance that is a multiple of the cartridge internal resistance, in order to amplify its output voltage.

Maybe some CH Precision owners could join in?

Their reference phono stage allows for both voltage or current gain situations by featuring an array inputs which are easily user optimized.

From the info I’ve gathered, the 10 ohm or lower LOMC Current Injection (transimpedance) theme as mentioned by @lewm seems to be their preferred method of playback.

LOMI pickups are now joining the current party! (pun intended)
 

 Not too sure how LOMI cartridges would work into a current driven phono, because of their high-ish inductance. Have you tried it? Or has anyone?

boothroyd, Apart from the fact that SoundSmith are the only company that currently market LOMI cartridges, what was your point?  Have you tried to drive a current mode phono stage with an SS LOMI?  Thanks.

I have two cartridges, Audio Tekne, 0.1mv, 2 ohms and ZYX Ultimate Omega, .23 mV, 4 ohms. Both are considered LOMC. I started with a current mode phono, Channel D Lino C 2.2. And then added a Sunvalley EQ-1616d tube phono paired with a Audio Tekne MC-4818 permalloy core SUT. I prefer the voltage mode combination in my system. It has a more dynamic, more transparent presentation, cymbals sound crystalline clear, spookily real. The soundstage width and depth are about the same with the Lino C. The tube/ voltage mode phono sounds more vivid, the SS current mode sounds more warm and relaxing. This is the most surprising and counterintuitive result having lived with both for a good 6 months.

 I don’t think that one technology is better than the other. If paired with the right cartridge, current mode phonos are plug n’ play, whereas voltage mode is an endless pursuit of SUT’s and loading. I have admittedly rather entry level stuff, so not the final word. 

Ledoux, First, thanks for being one of the first among us to make a direct comparison and to report on your result.  You wrote, "The tube/ voltage mode phono sounds more vivid, the SS current mode sounds more warm and relaxing."

It's a matter of semantics but the words "vivid" and "warm and relazing" convey (to me, anyway) very similar feelings about how the two stages sound side by side.  But perhaps you chose those adjectives to show how close they are.  Especially since you describe the voltage amplifier as also being more "dynamic"; to me that also goes with vivid.  I guess the main point is that you prefer the voltage mode phono stage, adjectives notwithstanding. On the Channel D Lino, did you choose a version that does RIAA in the digital domain, or is it all analog?  Both of your cartridges ought to be very good at producing current, based on dividing their output voltages by their respective internal resistances (V/R = I).

I totally agree on your opinion that one technology is not necessarily superior to the other, given one uses either with an appropriate LOMC.  Current drive is just a la mode at this moment.  We also have LCR and LR types of RIAA correction that have drawn attention in the last 5-10 years.

@lewm I did not mean to confuse or sound noncommittal in my compare. Both are capable units, equally enjoyable. With the voltage combo on the first needle drop there was a definite sit up n’ listen - ‘wow’ moment. With the Lino C, it just sounded right from the get go. I think in Fremer’s review, he described the unit has having an orderly or no nonsense sound on the warm side. That is what I am hearing. SS sounding more warm than the tube unit, go figure. I do believe the real gem is the Audio Tekne SUT. It’s just that this Japanese brand flies way under the radar in the US.

I am not using the RIAA in the digital domain with the Lino C. One more word on this unit, there are several upgrade paths available from Rob that makes very appealing to own long term. 

The tube/ voltage mode phono sounds more vivid, the SS current mode sounds more warm and relaxing. This is the most surprising and counterintuitive result having lived with both for a good 6 months.

@ledoux1238 

This may due to the specific design of the Channel D Lino rather than the technology employed.

I currently use a current sensing MC step up feeding the phono input on a Marantz 7 tube pre. It is vastly more transparent than using SUT's in a direct comparison. The SUT's cannot match the transparency, low end extension and speed of the current sensing step up. I own and have tried most of the highly regarded SUT's such as Audio Note, Tim Da Pavaracini 's Head ( which he says is the best he has ever made ), Cotter and many others. They can't compete.

This combo has also seen off my old Jadis, Klyne System 7, Lamm and many other much vaunted phono/pres.

The Goldmund PH2 phono is another example that is shockingly dynamic and quick.

I think you highlighted the SUT issue accurately when you said 

whereas voltage mode is an endless pursuit of SUT’s and loading.

You can spend a fortune on decent SUT's, buy a new cartridge, and have to start the process again.

Better off with the best high gain ( non SUT ) phono you can afford.

 

@dover Are you referring to Van Den Hul The Grail MC stage in current mode? I think the base model sells in the eight thousand level. If so, you have answered the OP’s original query as to which mode is superior. Although I have a suspicion that a EMIA LCR phono stage with their silver SUT by Slagle / Jackson  might be the persuasive counter argument that might have eluded you from the voltage side.

 

I think this is like many other things in audio. An allegedly "better" technology does not mean the listener will prefer it sonically and, as with everything, you need to try and see. I recently had a current-mode phono preamp for audition, but I much preferred a similarly-priced voltage-mode preamp, which was slightly noisier, but much better to my ears. Understanding the technology is fine, but it always comes back to the same old story. No getting around it, IMO.

Dover did not mention what current driven device he is using, so far as I can see.  However, he did say he feeds its output to the phono section of a Marantz 7 preamplifier.  That suggests he is using one of the very few available outboard devices that do the current to voltage conversion ahead of any conventional MM phono stage.  I think Sutherland makes such a device and a few others.  I think that's a great idea, as it does not require or may not require a major purchase cost for a whole new phono stage.  I am using such a device that was custom made for me, not commercially available. I use it only with the Ortofon MC2000 cartridge.  Output goes to a modified Silvaweld SWH550 phono stage in MM mode.  I have two other voltage driven phono stages that both have enough intrinsic MC gain for any of my other MC cartridges.

I did some reading on the van den Hul Grail.  The basic unit seems to be SE only.  The SB version costs nearly twice as much and provides balanced circuitry and some other unique features.  Depending upon whose review you read, the RIAA correction is done using either only inductors and resistors (LR type) or using capacitors along with LR (LCR).  Then there are the SE and SE+ versions that cost 3X as much as the base and include upgraded power supplies. I am not sure whether the base model (~$9000) has the fancy RIAA circuit or not. Fremer compared the base and the SE versions to the CH Precision with X1 PS.

@lewm , I think Fremer sleeps with his CH Precision. Nice unit but way more stuff than I need. I prefer simple.

I will be able to address this better in a while as I ordered a Channel D Seta L Plus which can be run either way. I plan to run it in current mode because of the theoretical advantage, the most important one is less interference with tracking. Every generator is also a motor. With less impedance this effect is more limited. 

@ledoux1238 , I think what you are hearing is a frequency response shift. Whether or not one is more or less accurate than the other is up for grabs. If I have two systems and turn the upper midrange and treble just 2 dB on one of them everyone listening will prefer the brighter unit even though it is "less accurate." In my own system I intentionally boost the bass because I feel it gives you more of the experience of a live performance even though it is "less accurate." This is why everyone has the right to listen to whatever they like. Unfortunately, that might make someone else cringe. My point is what a system sounds like is an extremely fast moving target. Interpreting what other people say is virtually impossible. There are characteristics which are more definable like those of the image. 

whereas voltage mode is an endless pursuit of SUT’s and loading. I have admittedly rather entry level stuff, so not the final word. 

@ledoux1238 If you have the right voltage mode phono section, its also plug and play- no SUT and no worries about loading.

@lewm 

Have you tried to drive a current mode phono stage with an SS LOMI?

While I have not, Peter explained to me that he is quite impressed with the results as long as suitable phono cables are utilized - something which I’ve often tried to emphasize. 

"Suitable" = very low capacitance, I assume. My question was more about the effect of MI inductance on cartridge output impedance as frequency increases and how that affects the efficiency of current drive.  It would be of interest to know which of the many "transimpedance" phono stages PL uses.  Because my own investigation indicates they vary quite a bit in input impedance, some not so close to zero as one might like.

@atmasphere Of course, Ralph, you are right. A built-in phono, well chosen, is also a simplicity. I come from that tradition: Audible Illusions, CAT, MFA Luminescence. My current situation of line + phono stage is really to explore the possibilities of the medium, it's a learning experience for me, not a search for a particular sound.

 

@mijostyn Isn't the difference between a 'warm' and 'lean' sounding system a shift in frequency responses?  Or are you saying that the shift in frequency response is really a shift away from neutral / natural sound? I thought that's what difference devices do, ameliorate or exacerbate sound through the manipulation of frequency responses. Sorry, I get a bit hung up on terminology.

Please provide reporting of the Seta L+ somewhere in this forum. It would provide important data point, especially coming from you. BTW, in my communication with Rob at Channel D, he found a way to squeeze a '1/4 Seta L20' into a Lino C ( with a modified chassis). Yes, fitting a quarter of his TOTL phono into a Lino C! 

 

@dover Would you confirm if my guess on the Vd Hul Grail is correct? Like Lew, I did a bit more research on it, and it seems a very accomplished unit. Fremer compared it favorably with the CH Precision. Would be interested in hearing more from you on the Grail. Thanks!

 

 

 

 

 

 

 

 

 

 

@dover Would you confirm if my guess on the Vd Hul Grail is correct? Like Lew, I did a bit more research on it, and it seems a very accomplished unit. 

@ledoux1238 

No it is as @lewm  stated - I have a bespoke moving coil step up using current mode/current sensing - the output is connected to the Marantz 7 phono (stage )  input.

It is not available commercially.

 

@lewm

"Suitable" = very low capacitance, I assume. 

Please excuse my ignorance and technical understanding, but I have a strong opinion that the + & - cartridge signal paths should be as similar as possible. Such a belief shuns any use of coaxial cable - yes, inductance not good.

On transimpedance phono inputs featuring RCA style inputs, such an assumption isn’t so intuitive. Knowledge of SME’s use of twisted pair phono cable construction sheds light perfectly on this scenario as each + & - path of their RCA outputs feature identical runs all the way back to the cartridge pins exhibiting perfectly balanced cartridge signals without XLR outputs. Continuing on that theme, SME only accesses the optional signal shield via a “drain” wire which exits the rear of the output RCA connector for optional noise control if needed - just tie it with chassis ground.

As far as keeping capacitance low, as long as each + & - cartridge signal path is again equal, I cannot see where that would hurt - Mogami W2549 works exceptionally well and is a well known low capacitance conductor.

@lewm 

My question was more about the effect of MI inductance on cartridge output impedance as frequency increases and how that affects the efficiency of current drive.

Seems like a question for PL. I would pose a similar inquiry for J Carr to the evolution of the Lambda Series of Atlas & Etna as their current delivery seems to be much improved over previous versions. I suspect lower inductance generators.

@ledoux1238 , Yes, I will report on what I think in my system. That is a lot of stuff to cram into a Lino C! I was going to get a Lino C but it turns out the Seta L plus is a better unit even though it is less versatile. 

Most of the differences we hear are in amplitude variation across the frequency band, bright, dark, warm, vivid are all caused by frequency variation to which we are quite sensitive. These variations can be caused by intension, our systems, resonances anywhere and acoustics and are way more prevalent than other errors such as distortion and group delays. 

 Isn't the difference between a 'warm' and 'lean' sounding system a shift in frequency responses? 

@ledoux1238 IME on a system level that is often caused by distortion. The ear assigns a tonality to all forms of distortion. Lower orders (2nd- 4th) add warmth and they can mask the presence of the higher orders. If the higher orders are not masked, even in tiny amounts they cause harshness and brightness. The ear is keenly sensitive to them as it uses them to sense sound pressure.

For example in a phono section to know whether its a frequency response error causing the tonality or distortion, you have to measure the phono section with an inverse RIAA network to see how accurate it is. If its has flat response but sounds bright, distortion is likely the cause.

Boothroyd, LOMC cartridges, like the Lyra cartridges you mention, will have inductance in the low micro-Henry range.  The low output MI cartridges made and marketed by SS have an inductance in the low milli-Henry range.  In other words, the inductance of their LOMI cartridges is about 1000X higher than that of a Lyra or other typical LOMC.  (This is no attempt to critique the SS cartridges; I actually prefer MI cartridges over most other types, and I am grateful to SS for carrying the MI banner.) The point is that level of inductance might affect the cartridge's capacity to produce signal as current, especially at high frequencies. Thus I am curious about what happens when you mate a Sussuro, for example, with a current driven phono stage.

@lewm Since the cartridge functions as the input resistor to the opamp, the impedance of the cartridge affects the gain of the circuit (as you probably know, the gain of an opamp will be the ratio between the feedback resistor and the input resistor). This suggests that as the impedance of the cartridge goes up, the gain of the circuit goes down, which is probably good since the output of the cartridge will be higher.

I've not messed with this circuit to any great degree, so I don't know what constraints might exist, but I'm sure there are limitations- there always are. I just thought I'd point this first bit out.

Hi Ralph, You wrote, "This suggests that as the impedance of the cartridge goes up, the gain of the circuit goes down, which is probably good since the output of the cartridge will be higher."  The linear relationship between voltage output and stylus velocity (higher at higher frequencies) is accounted for by the RIAA correction.  Would you want the cartridge to alter that relationship by virtue of an upgoing internal impedance? Also, the paradigm for current drive is you want the cartridge to have a very low internal resistance/impedance to begin with, which makes it a decent current generator.  Obviously, I am parroting ideas that are in the air without much depth of knowledge. But this question points out how consumers are a bit confused by "current drive" or a term like "transimpedance".  I think there are an array of products that each may do it differently enough to defy generalization.

Boothroyd,

I found this in the Sussuro cartridge owners manual:

"Please also note that some designs of “current amplifier” preamp circuits will not allow loading in the range required, causing the Sussurro MK II ES to sound very dull – caused by improper loading, resulting in loss of high frequencies."

What I could not find was a spec for the inductance of the Sussuro, but if memory serves it is about 50 mH.  This would give an impedance of 314 ohms at 1000Hz.  Let's say it's only 10mH; then divide 314 by 5.  Still high for a typical current driven phono.  Add the impedance due to inductance to the coil resistance of only 10 ohms.  I emphasize again that I love MI cartridges as a rule.  This is more about the usefulness of most current driven phonos stages.

lewm,

I would reach out to PL for clarification. FWIW, he was using a Loco with one of his LOMI pickups when he indicated the results were very encouraging as long as proper cables were used.

@lewm , I already have the program so, yes I plan on trying it. But, I am ordering the RIAA board as back up. I should be able to do it with the equipment I have now as long as I do not get into a jitter war. Channel D recommends a combination ADC/DAC using the same clock. Their favorite is the Lynx HiLo. Nice unit but I would rather not have to buy one. I'm pretty sure digital correction will sound fine. The question is how much more of a pita is it going to be playing records that way vs the old fashioned way. You know I will be happy to forward my opinion.

Peter Ledermann related to me directly that his MI cartridges will not work well with a current mode phono stage. The high frequencies will be rolled off. He did not give me the reason why but I am sure it has something to do with inductance and impedance.

I don’t understand. If you order the Channel D with digital RIAA, then you have to supply your own outboard AD/DA converter? Or does the Seta output a digital signal that the user has to convert back to analog, or what?

Yes, the Grail is a very under-exposed amp.  I have had the SE for two years having auditioned it at home for three months against two other similarly priced units (COVID prevented the dealer taking it back).

There are three Grails.  SE is the middle one, perhaps a bit more towards the flagship than the base.  It can run single ended or balanced.  I run balanced from cartridge to power amp.

Grail has a good claim to be in the best sounding group of phono amps.  It manages to combine a near clinical accuracy with a musical presentation, which is rare in phono amps; one usually has to favour one or the other - as others have stated, warm or lean.

I won't be replacing it.

@clearthinker 

Supposedly, one purported advantage of the current based phono stages is that you don't need any loading.  Some literature on the Grail SE indicates that you have options for MC loading from 40-400 ohms; however, other discussion about the same phono stage says that you don't need to adjust loading, as it's done automatically through the circuit.  Which is correct? 
Thanks. 

@drbond 

Firstly my Grail is the SB, not SE, sorry.  I have had it about two years.

The model range is Grail, entry.  SB, separate power supply on umbilical, but same amplification circuitry.  SE, separate supply for each channel.  SE+, some selected components.  SB and SE can be run balanced or single-ended but input and output must be the same mode.  One might have presumed the SE is single-ended and SB balanced.  Not so.

The reading of the literature you mention is a mis-reading.  In the vdH specs it is stated that the current operation provides automatic matching for cartridges in the 40-400 ohms.  On the SE and SB there is the additional possibility of changing the capacitance by hard-wiring capacitors into the back of an XLR socket.  vdH suggests this might be done in the case of moving magnet cartridges but doesn't see the need on moving coils.

I have listened to a wide range of top-end MC cartridges on the SB and it works well with all of them.  It is priced at c.£14k in the UK, but I believe cheaper in the US.  In my estimation it is at least a match for amps selling at double that.  For instance I tried the Boulder and found that to be dry and over-clinical, analytic rather than musical compared with the SB.  I found it noticeably better than the AR Ref 3 and lesser ARs.

Here is the vdH website on their phono stages:

https://www.vandenhul.com/product-category/electronics/

The way I read it, the SB offers balanced operation; the base model may only offer XLR inputs into an SE circuit. I don't know. The language is only a little less vague and confusing than what you find on the Channel D website. Clearthinker, I think you made the most cost-effective choice among the many Grail iterations, but it occurs to me that their statement about auto matching for cartridges in the 40-400 ohm range might mean that if the cartridge has an internal Z of 4 to 40 ohms, which covers just about all low output LOMC types, then the current drive stage will accommodate it.  It's a bit confusing and suggests that voltage drive is an option.  I cannot blame drbond for being confused. But you own one, so let us know.  Most reviewers don't have a clue.

@clearthinker If the Grail was ‘under-exposed’,  it certainly has caught my attention with the discussion here. 

What are some of the higher internal impedance LOMC you have tried? Presumably it was the Boulder 1008 that you made the compare to?

Yes it was the Boulder 1008.  I really didn't like it.  It sounded very 'transistory'.  I didn't move on to the 2008 mainly because of the price, but I felt it likely there would be a house sound that doesn't suit me.

I have Ortofons A90, Anna, Verismo; van den Huls Grasshoppers II and IV and Colibri.  Also Audio Technica ART1000, another sleeper, uses entirely difference suspension engineering.  These are all low impedence, between 3 - 7 ohms, the ART1000 is only 3 ohm, save the Colibri XGP which is 36 ohm.  I do not hear any artifacts that distinguish that but overall these vdHs have fallen behind a little.  The ART and the Verismo are the best I have.  Anna has a high mass that unfortunately doesn't suit my ultra low mass parallel tracking arm, so I use it in my second system where the amplification is vintage.

Clearthinker, that’s an impressive list of cartridges. Your colibri with 36 ohm internal resistance probably has a healthy voltage output. Do you run it into the Grail in current mode or voltage mode or does the Grail even offer that choice via separate pairs of inputs? Thx.

@lewm 

I am curious about what happens when you mate a Sussuro, for example, with a current driven phono stage.

This post from a recent Little Loco thread may shed some light:

I ended up with a Soundsmith Sussurro cartridge, but the Low Z (Low impedance) version. I would suggest if you were to buy one make sure Peter Lederman knows it's for a transimpedance stage.

The long version is that I contacted Peter and he contacted Ron Sutherland and compared notes. Peter built a low impedance version of the Sussurro and sent to me. I didn't like it, thought it was rolled off up top a bit. Peter offered to refund my money but I told him I would prefer he try to resolve and asked him if he would be willing to put in the time to do that. He agreed and I ended up sending the cartridge and the Little Loco to him to work with. The results are as you would expect if one of the most knowledgeable and talented guys in the cartridge/phono industry had your gear on his bench...an excellent match, I'm loving what I am hearing. 

My comparison is the Audiotechnica ART-9 which sounds pretty darn good but not nearly as good as the Low Z Sussurro, and my digital: Innuos Zen MKIII and Bricasti M1 SE MDX (who names these things?!) DAC. 

I actually picked the cartridge and Little Loco up at his shop because I was in the area visiting family. Peter took me on a tour, we listened to music, talked about dogs...he's a great guy, I'm really thankful for the entire experience (and for sure I'm glad he was willing to take the time to make the cartridge sound so good).

Hi Ralph, You wrote, "This suggests that as the impedance of the cartridge goes up, the gain of the circuit goes down, which is probably good since the output of the cartridge will be higher."  The linear relationship between voltage output and stylus velocity (higher at higher frequencies) is accounted for by the RIAA correction.  Would you want the cartridge to alter that relationship by virtue of an upgoing internal impedance?

@lewm I don't think I would employ any EQ on the transimpedance input (meaning the opamp). I would leave that for later in the circuit, such as a passive EQ network at the output of the opamp. In this case the constant velocity aspect of the cartridge really has nothing to do with it.

@lewm , IMHO the Grails are horrendously over priced. Looking at the internals the construction quality is not up to modern standards. As an example the boards are through hole not surface mount which is considered to be better. 

The Seta L Plus has significantly better construction, a better power supply and comes in at $10K. It's only down sides are it is not very versatile having only one input and switching between current and voltage mode requires going into the unit and removing or replacing a jumper. You would have no problem with that and I greatly prefer the simplicity.

Without ever having heard or even seen any current drive phono stage, my current favorite just based on tech and reviews and cost, plus balanced operation, would be BMC MCCI.

I suppose some aspects of SMD construction are beneficial, especially in a device centered around an op amp, but not all, and not when repair is needed.

I suppose some aspects of SMD construction are beneficial, especially in a device centered around an op amp, but not all, and not when repair is needed.

This is very true - the proper equipment required to work on SMD boards is around $100k. Most tech's can't afford this investment, and if a manufacturer using SMD technology goes bust - then your precious unit, when it develops a problem will be toast. Even with most manufacturers that use SMD technology, if there is a fault - the "repair" is a new board.

Personally I would never buy a piece of audio kit using SMD technology - seen too many disasters. If you do buy an SMD based unit you have to assume it will need replacing within 5 years.