In a 30 year old unit, hum is not surprising and it need not have anything to do with the subject. Your logic makes some sense regarding phono stage gain. Good point about phono gain at tape outputs being 46db. The fact remains that a SUT is not needed.
Added an SUT...not sure I understood this
I just added a Denon AU-320 step-up transformer in between my AT-OC9XML cart and my ARC SP-14 preamp. I am glad that the (relatively quiet) hum that had been present before is now gone...and I mean gone...since that was what motivated me to add an SUT.
However:
I sort of expected that I would also experience a noticeable increase in gain. Specifically, using the 40-ohm (10X) tap, I would have expected maybe a 6-8 dB increase in volume, and more with the 3 ohm tap. I am not hearing that, and in fact am getting the opposite effect. This means I actually have to peg the volume control if I want to achieve 95 dB levels at my listening position, something I rarely, but still occasionally, do.
Also, I removed the 22-ohm loading resistor upon connecting the SUT. I noticed previously that a 40-ohm loading still had the cart sounding pretty bright. But with no loading and using the 40-ohm tap, things sound natural. I sort of expected I was going to need to add a 40-ohm resistor (at the tonearm) to achieve the same loading.
All of this confuses me; I'm happy so far with the sound yet perplexed. Perhaps some good Samaritan here will be able to explain why I am hearing what I am hearing. in the meantime, I'm just going to enjoy my quieter background.
86 responses Add your response
Dear @atmasphere : " Failing filter caps have a way of eating power transformers in older gear and you really don't want that happening! "
Good to know that because this year I changed the filter caps in my 35 years old amplifiers. Every day is a learning day.
R. |
Dear @perkri : Please read this link about DC in the signal. Was instructive for me: https://www.diyaudio.com/community/threads/toroidal-transformer-noise.279794/
R.
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Just finished building a Hiraga Super 30 watt Class A amp 500VA transformer, followed by 192KuF of capacitance in the power supply Toroidal transformer hums on start up, had to instal a Hypex Soft Start board so as to manage the inrush of current on start up as the magnetic field stabilizes.Humming stops once warmed up. In an SUT, traditional transformers are used, and the discussion had to do with electrical hum, and not physical hum. The reason the hum goes away when the SUT is added is because the DC in the signal isn’t passing through the transformer. |
and
since the OP has solved his issue I have to ask if 100Ω is minimum and 20Ω means something is wrong, what would happen if he used the MCCI current injection stage that would provide a less than 3Ω load and liked the sound?
dave
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He hasn't solved his problem, although he now knows why the SUT did not work ( there was a 100ohm loading resistor already in the SP14 ), I believe the last post I saw was that he still had hum issues. He is not using a current injection stage. Apparently he is going back to loading at the tonearm 25ohms, which means that given there is already a 100ohm loading resistor in his SP14 that he is effectively loading his 12ohm cartridge at 20ohms. If you think this is a good idea - good luck to you. I really don't care what the OP does - but for those who are more open minded, I have set up plenty of OC9's over the years - in most instances where customers were using solid state phonos ( excluding current mode ) I found optimum loading usually around 400-470ohms. Do you not think the cartridge designer and manufacturer knows what they are doing when they recommend a minimum of 100ohms ?
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If I had to guess that spec is set to assure near maximum output of the cartridge. Changing the loading value makes subtle but easily audible changes for many. I know of several people who routinely load MC carts at 3-5X the internal impedance. They do this out of sonic preference and not out of ignorance or to thumb their noses at "accepted practice". I have yet to see a published minimum load that comes anywhere near the <3Ω of the MCCI which precludes their use in general if one were to adhere to the manufacturer's suggestion.
Odd... it seems to me that insisting one trust a published suggested load over their ears is just the opposite of open minded. I am not saying that the OP is correct in their 20Ω choice or exactly why that value was chosen. It may very well be that the 4dB reduction in cartridge output from that cartridge-load ratio may be partially responsible for some additional noise. The point I was / am trying to make is the disconnect between minimum recommended load and the use of a stage such as the MCCI. dave |
Yes - I have seen this phenomenon myself when I was a high end audio distributor in the 80's. Usually it is psychological, they like an effete sound or rolled off top end because their mother told them off too much when they were young.
If you read my earlier posts correctly I suggested he should try the higher loads. The OP has chosen not to try higher loads. The only reason I took the time to write my post with regards to published specifications and recommended load was to inform the thousands of readers of these forums whom do not post, but might rely on what they read in the thread.
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apologies to all for veering off topic here.... I have yet to se actual measured frequency sweeps from a MC cartridge that show the ""rolled off" top end you suggest above. Can you point me to some?
I have the same belief.... kinda... I was just trying to point out to the 'thousands of readers of this thread' that the whole concept of "current injection" flies 100% in the face of blind adherence to the manufacturers minimum load spec. ie...I see the natural conclusion of your logic to be: if 100Ω is the minimum <3Ω cannot sound good so it need not be tried. dave |
Once again, please read my posts more thoroughly - here is what I posted initially
The SP14 does not use current injection mode. Your insistence on bringing into the discussion another variable ( current mode ) that is irrelevant to the OP's issues only serves to add more confusion to an already confused OP. |
the last post in this thread from the OP is below:
to which you responded with the text quoted in my first post here where you insisted there must be something wrong with his system. I applaud and support the OP's POV that what sounds best is best. I brought current injection into the topic because it is a perfect example on how an amplification method that many find appealing provides a load that is in stark contrast with what any cartridge manufacturer suggests as optimal. I for one would like to see more discussion about how to reconcile this discrepancy. dave
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Dear @dover : He already did it in this thread and in the cartridge loading one too. I can't understand why came here again with the same topic but is up to him:
R. |
They know that the designer of the phono preamp may not have taken the RFI generated by the cartridge and tonearm cable into account. The 100 Ohm resistor detunes the resonance that they create and so prevents RFI from messing with the preamp.
The maximum output of the cartridge will be with little or no load. 47K is the industry standard in this regard and qualifies in this regard. |
the industry standard of 47kΩ was adopted from the MM cartridge world and applied to the MC realm because is first and foremost "does no harm".... until you throw a SUT into the mix that is. Once a SUT is added the load the cartridge can see can get vanishingly low to the point where you actually start losing gain as you increase turns ratio. My best guess is that the min load value specified for a cartridge is a value that still assures nearly full specified cartridge output and has little or nothing to do with the sonic behavior of the cartridge. What I want to know is why the minimum load value that has to be strictly adhered to in the case of a traditional phono stage can be completely ignored in the specific case of the MCCI with a published input impedance of <3Ω. This is completely ON topic since it relates directly to the OP's insistance that a 20Ω load sounds best on his AT-OC9XML. dave
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Obviously you haven't got a clue so I'll explain it to you - actually here's a quote from JCarr
In other words comparing the resistive load in a current mode mc input to the the resistive load in a voltage gain mc input is like comparing apples and oranges. If you cant understand what JCarr wrote, and don't understand the difference between voltage and current then I cant help you any further. |
JCarr makes the exact point I am ultimately trying to get to when he says the below.
I don't necessarily agree with his use of the term "forced" but that is for another day. He attributes "part of the reason" for the difference in sound to the load the cartridge sees and I fully agree with that thought. Since this branch of the topic is about the load the cartridge sees and not how that load is obtained, discussing the difference between current and voltage amps is not at issue. It just so happens that a current amp gives an extreme example of "non-traditional" loading. A cartridge is a two terminal device that sees a two terminal load downstream. It doesn't know or care what form of amplification that load takes, it just does what the load tells it to do. dave
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Yes, JCarr sort of contradicts himself a bit and ends up being half right. The reason a cartridge sounds different under a heavy load is because the low load impedance suppresses output voltage. But a preamp that is uninterested in output voltage would not be affected by this phenomenon. In the case of the IV preamp, the low input impedance (not quite the same as load impedance) results in high current flow through the preamp. It does for the IV preamp what a high load & input impedance does for a traditional preamp--maximizes the electrical signal that the preamp is using. Changes in sonic character between the two approaches may be based on inherent differences in the architectures, or based on differences between the way the cartridge's--let's call it "frequency response"--as expressed by its current output varies from its "frequency response" as expressed by its voltage output, but those changes cannot be attributable to the effect of loading on voltage output since the IV preamp effectively ignores that effect. |
so add more gain. I'm not trying to be cheeky here but this becomes a problem related to what happens downstream of the cartridge and not with the load the cartridge sees. If you load a cartridge severely and do not have a capable low noise good sounding stage after it things will indeed go south.... this is not a problem with the cartridge load per se but with the behavior of what follows.
how can the two be separated form each other? from the cartridge POV, how can 3Ω be different than 3Ω? I am speaking primarily about the effects of the load on the electromechanical behavior of the cartridge and what impact that may have on the sound.
Sure the IV preamp can ignore that its low input Z effectively reduces the output voltage to 0. My question is how can the cartridge ignore that it is seeing a load that is possible a fraction of its internal impedance? Lets get back to the simple question I asked.... If going well below a cartridge manufacturers load is not recommended, how can we reconcile the use of transimpedance amplification or in your case a load that is 1.7X the cartridge internal impedance? It is my belief that when specified by the cartridge manufacturer the load value range would relate to the behavior of their cartridge and not in response to the unknown capabilities of what follows. In any case... Like you I feel that number is only a suggestion and people should feel free to use whatever load sounds best to them. dave
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This is a second take on woofhaven’s post, nothing to do with what Intactaudio posted above, or only tangentially. Woof, you seem to ignore the fact that none of the available current driven phono stages actually presents a "perfect" zero impedance load to the cartridge. Each of the different units has a finite input impedance that is above zero and usually less than 10 ohms. Case in point is my BMC MCCI that I bought recently to experiment with current drive in my home system. (Otherwise, I would have to depend upon others’ opinions, which I don’t find helpful to do.) The MCCI has an input Z stated by the maker to be <3 ohms. I guess that’s why Intactaudio uses that value in his thinking process. In other words, none of these devices is "perfect" when it comes to current drive, because they really cannot be perfect; zero ohms is a short circuit to ground. My experience with two or three very good LOMC cartridges driving the MCCI is that you cannot predict in advance what you’re going to get out of the phono stage in terms of either gain or tonal balance. I’ve had to think of the cartridge and the MCCI as a single device where a major determinant of the output SQ and db is taking place at the interface between the cartridge and the MCCI I/V stage. The cartridge internal impedance, its voltage output (because that affects current output), and probably its inductance along with the ~3ohm input Z and the current amplifying devices of the MCCi would seem to be the important variables. So, there’s no free lunch, and there is nothing inherently superior about current drive vs voltage drive, at least so far in my experience. This is not to say that the results cannot be superb. |
Most SUTs are meant to drive a 47,000 Ohm load since they are also built to work with a specific cartridge. Generic SUTs (like Jensens) might also be built to drive 47K although with some additional loading to allow it to express the turns ratio correctly with different cartridges (which have different source impedances). Some Jensen transformers are meant to drive lower impedances but IIRC that's still about 6.8KOhms.
A transimpedance input is a special beast. It requires an opamp and when you set up an opamp circuit with feedback, you get something called a 'virtual ground' where the input signal meets the feedback signal. Its not actually ground ('virtual' means 'almost or nearly as described, but not completely or according to strict definition.'). This is why "virtually 100%" is not in fact 100%... Anyway, in a transimpedance amp the cartridge is substituted for the input resistor. The significance here is that if the virtual ground were actually ground, the signal going thru the input resistor (or coming from the cartridge) would be snubbed at the virtual ground- the signal would stop dead. But it doesn't! The lesson here is that virtual ground isn't in fact ground. Thus while its impedance might appear to be quite low, it does not function as if its impedance is actually that low. IOW it does not have all the qualities of an actual ground! Its confusing yes, but in actuality the cartridge isn't driving an impedance that is at or near ground (which would be 0 Ohms or very nearly that). Its actually driving something quite a lot higher. The gain of an opamp circuit is defined by the input resistor vs the feedback resistor. For example if the input is 100 Ohms and the feedback is 1000 Ohms, the gain will be 10. Since the cartridge is a variable source impedance from cartridge to cartridge, the gain of the circuit will vary from cartridge to cartridge too- more gain with a lower source impedance, less gain with a higher source impedance. This means the output will not vary that much as you change out the cartridge, but it also means that the circuit inherently has limits (due to the amount of feedback applied) and won't work with every cartridge. |
Ralph... we have been over this. I made a point above to never mention ground and simply referred to the cartridge as a two terminal device feeding a two terminal load. If the goal of that load is to maximize current draw then by necessity it must be low in value. Since both Ohm and Kirchoff must be obeyed.... all of the current leaving one terminal of the two terminal cartridge must traverse the load and return to the other terminal. The application of Ohm to this situation clearly defines all of the parameters at hand. dave |
You are correct in your conclusion, but IMO asking the wrong question. Rather than looking at it from the cartridge's perspective, consider the pre-amp's perspective. The pre-amp is the device that will be passing along a signal to the next component in the system. Both IV and traditional preamps "see" the entire "electromechanical behavior of the cartridge" but neither pays attention to the full set of that behavior. One type of circuit pays attention primarily to the current, and the other, voltage. Thus the two methods can look at a cartridge behaving in very different ways but end up paying attention to--and passing along--signals that are similar in character; i.e., if the cartridge's current under heavy load is similar in character to its voltage under a light load, expect an IV preamp to pick up a similar signal from the cartridge through its low impedance input terminals as a traditional preamp would through its high impedance (and lightly loaded) input terminals. |
I am the only one here asking the relevant question in this situation. This all goes back directly to the insistence that something was broken in your system if your cartridge sounds better with a 20Ω load. The only question I asked (and has yet to be answered) is how does one account for the use of a load well outside a manufacturers recommendation (ie a current amplifier as an extreme example) and still adhere to the wishes of the manufacturer? In your particular case I trust your assessment that the sound is good and suspect that anyone that insists otherwise based on a published spec is in error. Who knows I may be he only one with this belief.... it wouldn't be the first time. I did not drag this off topic into how current amps differ from voltage amps, others took it there. I really think this is a simple question that apparently nobody seems to have a good answer to. dave
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@intactaudio I misunderstood the intention behind your post then. Unfortunately, the question you have asked has a rather uninteresting answer. Everyone on this thread has been assuming I determined that the best sounding load for my cart was a large deviation from spec, apparently because one participant loudly and repeatedly felt the need to insist I did not know how to read the instructions that came with my cartridge. I have attempted to clear up that confusion by asserting that my cart in fact has a 20 ohm spec, but apparently I don't know whatever secret handshake a person needs to know in order to be taken at one's word on these forums. But none of that changes the fact that I am loading my cartridge at spec, which might render your question moot. I do agree with you, though, that if I achieved better sound at a different load than that recommended, I would use what sounds best.
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Looks like you've got the wrong cartridge. You claimed to have an ATOC9XML Paoerwork here
Note the recommended minimum load is 100ohms as I posted. The paperwork you have posted appears to be from the ATOC9ML/II which is a different cartridge. However the 20 ohm recommended minimum loading referred to is the minimum recommended loading when using a step up transformer. The recommended loading for a head amp is 100 ohms. See see up instructions #6. Here is the paperwork for the ATOC9ML/II
In your case your SP14 has a FET based front end, not a step up transformer, and the recommended minimum load is 100ohms.
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This is where you go wrong. Loading down a MC produces more current and less voltage. ( explained by Carr above ). Therefore whether the mc phono input is voltage mode ( as in SP14 ) or current mode is vitally important because in voltage mode loading down the MC reduces voltage going into the voltage based phono and reduces overall gain. With a current mode phono, loading down increases current and hence increases overall gain. I cannot fathom how you cant see the difference between increasing gain and reducing gain.
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I thought it was ok to mention current driven phono stages after the OP himself mentioned it. what we found was that the SP14 had a 100 ohm resistance across its phono inputs. That coupled with a 1:10 SUT resulted in the cartridge seeing a 1 (one) ohm load. Which is clearly a bad thing and explains the bad SQ. Per Dover’s point about the two different AT cartridges, I’ve never understood why the minimum load can be acceptably different for the same cartridge with vs without a SUT in the circuit. (Maybe not applicable here if indeed we’re talking about two different cartridges.) But you see this among those who use for example the DL103. |
again... not the topic at hand. The cartridge doesn't magically see a sut and say 20Ω is fine and scoff at that same 20Ω if it is a load resistor to ground before a Jfet. I concur with lew and it makes no sense to me how a loading a cartridge can have different "ideal" values for different amplification types. I think much of the confusion here stems from AT expecting you to pair their cartridge with their SUT. The AT1000T has a 20Ω input setting that claims a 26dB gain and specifies a 47kΩ termination. Simple math tells us that 26dB = 1:20 which reflects back 117Ω to the input labeled 20Ω. In this convoluted case 20Ω really does = ~100Ω! Assuming there are not other loads or networks inside the AT1000T to truly provide a 20Ω load, this small part of the discussion now makes sense. This labeling system is typical to the Japanese SUT's and the Denon that started this whole thread uses a similar input labelling method. Essentially the inputs are labeled with the approximate impedance of the cartridge they expect you to feed it with with no hard and fast rules as to how those numbers were devised. Now back to the OP and his finding that a 20Ω actual load sounds best. Sure he possibly got to that value by following a bunch of conflicting / confusing data but ultimately that is where he stayed. dave |
Dear @woofhaven1992 ; This was my very first post in your thread:
And this your answer to that:
" Yes I have been using the SP14 with no SUT for some time, and the sound is great except for a touch of hum just at the level of the noise floor. I decided to fiddle with this SUT as a way of addressing that problem, which otherwise has been persistent despite lots of attempts to address it, including having ARC work on the pre-amp twice. You are correct that through the SUT I lose some resolution, although I was blaming that on the crappy built-in output cable. I figured I could find a way to replace that but maybe I should, as you say, forget it. "
You answer should been the end to your thread. Don't you think?
R. |
Wrong. That is not what @lewm said. He said -
Lewm was comparing active mc amplification vs SUT's. You really do need to read posts more carefully, unless you are deliberately misinterpreting posts. It is clear from your conclusion that you do not understand how current mode and voltage mode gain stages work, and I would suggest if you are genuinely interested then you should do some study - there are plenty of high schools that run after school programmes that are excellent.
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This splinter of the OP's tree is in reference to the load a cartridge sees and in particular any variance from the cartridge manufacturers suggestions.
No.... Lew was wondering in what world 20Ω = 100Ω. How can 20Ω be unacceptable from an active stage but perfectly OK from a SUT? I entered my guess at an explanation that the 20Ω value is not an actual load value but the recommended input to use of the AT1000T. This input happens to load the cartridge at just over the 100Ω manufacture spec. Simply put a somewhat confusing manufacturers data sheet reconciles the difference and keeps the manufacturers suggestion consistent.
Other than the load value presented to the cartridge, how a gain stage operates has zero bearing on the topic of cartridge loading. My only reference to current amplification used a specific model (MCCI) since it has a published input impedance number of <3Ω. To be clear... it is the 3Ω that is the issue here NOT that it is a current amp. From the most basic perspective I want to know from you how a <3Ω load can be used with a cartridge that has a 100Ω minimum recommended load and possibly sound good? I can't be the only person who sees this disconnect. Since you seem unwilling or unable to answer that simple question, let me frame the same situation differently: Can we agree that the OP's cart into a 1:20 will see just over a 100Ω load and present approximately 8mV to the input of a "generic" gain stage? Now lets change that 1:20 to a 1:50 and then place an 11Ω resistor across the primary to add an additional load to the cartridge directly. The voltage output of this combo will be the same 8mV into the same "generic" gain stage. Now the load the cartridge sees will be 7Ω which is well below what you would deem acceptable. Both the measured and the subjective sonic results of the above experiment surprised me and really got me thinking about what loading a cartridge really does. It also makes me wonder what the manufacturers published values are based on. dave
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@dover Feel free to dunk, it's apparently important to you. Yes, you are right that I initially indicated the incorrect sub-species of the OC9. You remain incorrect, however, about the correct loading with the SP14, which contains neither a head-amp or an SUT built in. |
Wrong. The SP14 has a FET based input at the front end of the phono stage., Its same principle as a head amp. Correct loading is 100ohms minimum as per the manual. I don't have an issue if you prefer 25ohms, thats your ears. I post so that others reading can get the best out of their cartridge using the minimum loading as recommended by the manufacturer. My own experience with setting up many OC9's of various types in multiple systems is that around 400ohms is optimum and it is clear that you have no interest in even trying alternative loading. |