Yeah, sometimes the balanced impedance is given as the sum of the legs, and sometimes as per leg, which is a source of confusion.
A few dB down at 20 Hz is not something I'd *aim* for, but it doesn't really effect the audible result. The Bryston still has that solid bass foundation that these amps are known for even when fed by the 3iX.
I'm currently using my 3iX with the Rogue M-180 monoblocks, with excellent results. These have a balanced input impedance that sums to about 75k Ohm (the specs on the Rogue website are either for an earlier iteration or wrong. See JA's measurements of the M-180s.) |
Zd543,
You may be right. And here is another simplistic answer that I received:
The A21 gain is 6dB higher when the balanced connection is used. The output of your Promentheus is also 2x, or 6dB higher than unbalanced. Each "leg" or "phase" of the XLR is the same voltage as the RCA and two legs is 2x more which = 6dB. The same thing occurs at the XLR inputs of the A 21. |
Regarding BAT's statement as quoted in Dave's post: It is also important to understand the role of the output coupling capacitor, present at the output of BAT preamplifiers. It is the size of this capacitor that will dictate the minimum power amplifier input impedance, not the output resistance of the preamp. That is absolutely true. It should be noted, though, that he refers to output resistance, not output impedance. The effects of the output coupling capacitor will be reflected in output impedance, which is what John Atkinson measures. "Is the requirement for minimum input resistance dictated by the output resistance of your preamps?"
No. However, this is a popular misconception. It is common to apply some old rules-of -thumb to things like preamplifier to power amplifier interfaces and state that there should be some magic ratio between the output resistance of the preamp and the input resistance of its load. People commonly mention numbers in the 10:1 or 20:1 area, some as high as 100:1. Unfortunately, there is no truth to such claims. As many of us know, one can perfectly transmit a signal in a system where the load impedance is equal or even lower than the source impedance (witness any cable TV system). The key factor is how much the output impedance VARIES as a function of frequency. A purely resistive output impedance will not vary at all. An output coupling capacitor will cause the output impedance to rise at low frequencies, to a degree that may or may not be significant in relation to the load impedance. The 10:1 rule of thumb guideline is, IMO, properly stated as follows: The input impedance of the amp should IDEALLY be at least ten times greater than the output impedance of the preamp, at the frequency for which the output impedance of the preamp is highest. The frequency for which the output impedance of the preamp is highest will usually be 20 Hz in the case of a preamp having an output coupling capacitor, such as most tube preamps. That goal will assure that there is not an impedance compatibility issue. If that goal is not met, the results may or may not be ok, depending on the specific numbers that are involved, and especially on how much the preamp output impedance VARIES as a function of frequency. IMO, based on JA's measurements the 10K minimum load recommendation for this preamp is marginal at best, and I would not assemble a system that way. Dave, I believe that the 10K/leg input impedance of the Bryston amp you referred to would be 20K as JA and others generally define it (the sum of the two legs), and even that resulted in a few db of rolloff at 20 Hz, as you indicated. Regards, -- Al |
Milpai,
I took a quick look at the specs on the A21 and found this: Input impedance: 33 k Ω unbalanced; 66 k Ω balanced. Even though your CD player is single ended, you can sometimes get away with running a SE component into a balanced component; without having to switch the balanced unit over to SE mode. I've tried it myself and it doesnÂ’t always work, but when it does, it usually sounds much better. Honestly, I'm not sure why. The only technical reason that I can come up with for the better SQ is that when running in balanced mode, the impedance goes up. With the A21 in balanced mode the impedance is 66k at opposed to 33k for SE. The higher impedance should be an easier load for whatever component is upstream; in your case, that would be the SA8260. Keep in mind, though, thatÂ’s just by best guess and could very well be wrong. |
Here's what BAT has to say on this issue:
"Is the requirement for minimum input resistance dictated by the output resistance of your preamps?
No. However, this is a popular misconception. It is common to apply some old rules-of -thumb to things like preamplifier to power amplifier interfaces and state that there should be some magic ratio between the output resistance of the preamp and the input resistance of its load. People commonly mention numbers in the 10:1 or 20:1 area, some as high as 100:1. Unfortunately, there is no truth to such claims. As many of us know, one can perfectly transmit a signal in a system where the load impedance is equal or even lower than the source impedance (witness any cable TV system). The unusual design of Balanced Audio Technology's preamplifiers allows their gain stages to drive loads with resistance much below what their specified output resistance ratings would imply. For example, the VK-50SE preamplifier can supply a load with 65mA peak current - an amount well beyond that of the great majority of preamplifiers on the market today. However, it is also important to understand the role of the output coupling capacitor, present at the output of BAT preamplifiers. It is the size of this capacitor that will dictate the minimum power amplifier input impedance, not the output resistance of the preamp."
Having owned a 3ix for several years, I've been down this road (even owned a BAT 250SE SS amp for a while.)
If you like the 3ix, I would not limit the amp search to those with 100k Ohm or above input impedance.
Atkinson measures the frequency response with a 600 Ohm load and 100k Ohm load, which is very unhelpful as no consumer amps are anywhere near a 600 Ohm load and most are below 100k Ohm. A 10k Ohm load would have shown the response to be down a few dB at the frequency extremes.
BAT's stated spec of 10k Ohm is a sensible minimum bound for the amp's input impedence. 66k Ohm is no problem for it at all. |
Zd542,
My passive unit is a dual mono TVC that is completely balanced. My source is a Marantz SA8260 SACD player with RCA outs. The CDP outputs 2.2V whereas the A21 has a sensitivity of 1V for full output. Even with the RCAs in place from TVC to A21, the volts were 2.2 as it is now. I do not understand how the XLR affected the performance. So I assume that the A21 is optimized for XLR connection.
Yes, I love the TVC. The only negative against the TVC is - it does not have a remote...but who cares?
The XLR from TVC to the Parasound A21 made the biggest difference in my system. I should have done it on day 1 when I got the A21...but who knew. |
I've been torn about getting a preamp at all since the NAD works quite well as preamp (as it was designed to do). Just saw that stereophile just did a review of my DAC and gave what seemed quite favorable review - for whatever that's worth. I don't put too much value on reviews anyway.
My concern is am I adding less transparency and purity by adding another component in the chain. However my hope is the "tube" opens doors to the music for my Thiels as many claim it do for mixing the tube pre with SS amp. Fingers X'd. I've wanted to add a BAT for a while but they were out of my price range, and though I really didn't need it the price was right and I grabbed it. Worse thing that could happen is I end up with a nice piece of equipment. |
No problem Zd542, I took you're comments as good advice, if I was unclear that was my fault. It may end up that the Parasound isn't the best match in the world, but if it sounds even a little better then what I have now I'll be extremely happy since I'm pretty happy with what I have now. If for whatever reason it doesn't I'll begin looking for a used SS BAT amps in the future. I'd love to go tubes, but my pockets aren't deep enough for high power tube amps - even used. |
Milpai,
Is your passive unit balanced? Also, what do you have going into it for a source? I don't mean to pry but I'm a big fan of passive preamps. Not that many people see the value in using them so its always good to get opinions from other users.
To the OP, I posted a reply after reading your reply to mine. That was about 4-5 hours ago. I hope it turns up. I just wanted to clarify that I think you made a very good decision to go with the BAT. I list a few reasons why. |
I do use the XLR inputs, that was one of the reasons the BAT made my short list. I run xlr from the DAC as well. And I agree with you on the difference between the balanced vs. unbalanced. |
I have no experience with impedance matching. But from a very recent experience, if you buy the A21, try to make use of the XLR instead of RCA. It made a HUGE difference, with my passive preamp. Good luck. |
I didn't mean to sound harsh or anything, but if you read your origional post, it does seem like you are a bit unsure as to your decision. That's why I thought you were guessing. Also, BAT and Parasound are very different sounding products, in general. That threw me off as well.
The upside to this is that you shouldn't have any trouble at all getting the amp and the preamp to work together from a technical standpoint. As far as sound quality goes, you'll probably be very happy, as well. I've always felt that the preamp is the most overlooked component in most peoples systems. If you don't get it right its just one problem after another. In your case, the BAT will probably be the strongest component in the system. That's a very good thing. Everything should get better: imaging, resolution, transparency, dynamics should all be enhanced from what they now are. I think you will be surprised at just how big the difference will be. |
ZD542, my only option is to try gear since there are no stores near me nor anyone else with the type of gear I would like to hear that could let me borrow it. But what i have found years ago, even if I could hear the equipment in a store, if it wasn't my same system in the store, not to mention the same room it always sounded way different anyway. The only component I've ever been reasonably able to audition in a store and get a similar sound at home with is speakers. I didn't decide on BAT by chance, I did research on equipment that worked well with my particular gear and budget. I already own the amp, so that's a fixed variable. Trust me if I could hear all the gear before I purchase I would, even considering the issues with store auditions, but that is not my reality. |
I've used my 3ix with a Bryston 3B-SST, which has an input impedance of 10k/leg balanced. It is a few dB down at 20 Hz (measured with a voltmeter at the amp outputs), but nothing disastrous. The Parasound should be fine. |
This is the problem you have when you take a chance and just guess on a new component. Preamps are way too important to not get right. Given that, you probably will get lucky. BAT is very well made and should work with a large variety of products. The only advice I can give beyond that, is that if you are not happy, you will not make the situation any better with cables. You may think you will, and when you ask, you will get an endless list of recommendations on what cable you should buy to fix the problem. In the end, though, it just wont work.
Also, it is not clear if you already have the Parasound amp or just plan to buy one. If you don't already have an amp, I would strongly urge you to consider a BAT amp to match the preamp. Doing so can eliminate a lot of problems. |
Yes i did read the stereophile article and did read his concerns.
On the other hand the Thiels only go down to 32 hz so .2'at 20 hz seems ssomewhat irrelevant. I use Purist audio cables which have low capacitance and are only 14' in length anyway.
I went to BAT's website and they say minimum input amp impedance on the amp should be 10k, though I'm sure that is just a guideline.
I guess I'll know for sure once I get it in and hook it up. |
It sounds like you've already read John Atkinson's measurements of the preamp in Stereophile, in which he says that the balanced output impedance "ranged from a very high 14k ohms at 20Hz to 1850 ohms in the midband and above." It can be calculated that into 66K that will result in a rolloff at 20 Hz in the rough vicinity of 0.2 db, along with some extremely small effects on phase. Both of those effects figure to be imperceptible, and to be swamped by room effects and probably also by the deep bass rolloff of the speaker. As I have no experience with the preamp, though, I can't comment on its bass performance apart from the impedance matching issue. Also, given the relatively high output impedance at high frequencies, if the interconnect cable length is particularly long (say 15 feet or more) I would make a point of using low capacitance cables. Otherwise a very slight but possibly audible rolloff of the upper treble could result. Regards, -- Al |
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With an output of 1K on the BAT preamp you will be fine. I used a BAT VK-31se with the Parasound JC-1s and Thiel CS7.2s and got good sound. |
Not sure why I keep double posting when I ask a question from my I pad. Sorry |
