High Current SS amps with input impedance = 200K

Mapman -- OK, I looked further and found the 45 amp peak current mentioned in this manual for the Ref1000M Version 1. It is not mentioned, though, in what I had been looking at, which was this manual for the Ref1000MkII.

In any event, I think that Guido's answer essentially settles the issue.

Best regards,
-- Al

al,

the 45 amp spec is published in the amp's user guide on the bel canto website.

Thank you Al, the figures of 40 to 45 Amps on peak current are inline with published specs for ICEpower 1000 ASP offerings from several other manufacturers. It is worth while pointing out that the 1000 ASP module is capable of yielding a more/less continuous output of 500W, hence the 30.1 Amps max continuous current you have calculated, while the peak current of 45A is sustained only in short bursts, hence the seemingly discrepant figures of peak current vs max power rating. Regards, G.

Guido -- While I certainly don't question your subjective comments, I don't think that the statement that 45 amps from a balanced amp output is roughly equivalent to 90 amps from unbalanced amp outputs is correct. If the spec is 45 amps (and btw I don't see that spec at the Bel Canto site), a maximum of 45 amps (plus whatever margin is built into the specification) would flow between the amp's red speaker terminal and black speaker terminal, regardless of whether both of those terminals are actively driven, or only one of them is actively driven.

The specs I do see are 500W into 8 ohms, 1000W into 4 ohms, and a rated minimum load of 2 ohms. If we assume that 2000W can be delivered into 2 ohms, that corresponds to a current of 31.6 amps.

Mapman -- Congratulations on the new amps! Enjoy!

Darkmobius -- As you realize, Class D technology is at the opposite end of the spectrum, relative to Class A, in terms of the amount of power that can be delivered relative to the amp's size, weight, and heat generation. Your characterization of them as "voltage amplifiers," though, is correct in the sense that they typically have extremely low output impedances (or, equivalently, very high damping factors). That allows them to deliver an output voltage which is directly proportional to input voltage regardless of load impedance, within the limits of their current capability (which in this case is very substantial).

Regards,
-- Al

Thanks Guido,

For some reason, whenever I read "high current" I always picture the pure Class A massive heatsink monsters from the late 80's/early 90's like the Class DR-3VHC, Levinson ML-2, Krell KSA-100, etc.

I guess that caused me to associate high current with high heat and huge size.

In the particular case of the Bel canto Ref 1000 Mk.2s, the 'moderate' peak current of 45 amps is deceptively low. . . As the 1000 Mk.2s have a balanced output with active positive and negative leads on the speaker terminals, the current is roughly equivalent to a 90 Amp peak for a more common non balance output design, where the active signal would be relegated to the positive terminal, while the negative is left to float. I have used the Bel canto babies on my big Vienna mahlers v1.5s, and the authority that they yield is something to be beheld.

Enjoy them, Mapman! G.

Dark,

Not sure about a clear answer to your question.

The BC ref1000 specs indicate Peak Output Current: 45 amperes.

I've seen higher and lower. I suspect the switching nature of the power supply optimizes application of delivered current perhaps in comparison to other types?

Mapman(or someone),

correct me if I'm wrong, but my perception has been that IcePower amps are not necessarily "high current" amps, being more of the voltage amplifier type.

Hello all.

Some closure on this for me finally. I ended up with a used pair of Bel Canto Ref1000 mkiis. They are up and running in my system. Very sweet indeed! I'll post some more impressions or whatever else might come up relating to these back in my system listing.

Thanks for all the feedback you all have provided to help me with this decision both here in this thread and elsewhere.

Mapman, IMO the BC 1000M (formerly 1000 Mk.2) are likely to occupy the current price/performance sweet spot of moderately priced 500W ICEPOWER gamut. While I have not been able to listen to W4S in the same system as BC, the general impression of me preferring BC significantly and easily over W4S has been very consistent during several RMAF visits. Of course, BC 1000M is quite more expensive than W4S as well. . . and to make things just a little more exciting, W4S is said to be introducing soon reference level amplifiers based on ICEpower, which I have not heard yet. G.

I've continued to research amp options for my system since my last postings here.

The bigger Class Ds that specifically address input impedance matching with tube pre-amps in general are still at the top of my list as a result of cost effectiveness, favorable reviews and commentary, specifications and small footprint and resulting impact on my current system layout and configuration.

The Bel CAnto ref 1000 mkiis (currently going for under $4000 used) would seem to be the holy grail in my case based on what I read and have gathered in lieu of hearing one.

The Wyred st-1000 ($2000 new, under that used) would appear to be the very close next best thing for significantly lower cost.

My impression is that the Wyreds and their ilk are driving down the resale value of the Bel Cantos and their historically pricier ilk (like SPectral and perhaps to a lesser extent Rowland).

Any comments on Wyred st-1000 versus BelCanto ref1000 mkii? I might be tempted to try the Bel Cantos at some point soon if further convinced that the sound differences justifies the cost premium?

Al,

THanks for the kind words and explanation. I will con't to experiment.

Yes, you can cross all the Ts and dot all the Is and there is still that mysterious place known as ..... The (audio) Twilight Zone....

Ominous music cue........

As we all know very well lots of things in audio are both unexplainable and unpredictable. Almarg (Answers)

Al, I said practically the same thing in the "This Makes No Sense" thread.

All things occurring with the performance of audio systems are not guaranteed to make sense. If everything made sense, man would this be simpler. Foster_9

So our thinking is practically the same on the subject.

Glai -- Wow! I looked at your system description, and I must say it is utterly magnificent. Congratulations!

As to why the Ref 3 did not give you the tight bass and the better transient response that the other two preamps do, I have no ideas to offer. What I can say is that I doubt it has anything to do with the somewhat higher output impedance of the Ref 3, considering that your interconnects are short, your power amp input impedance is reasonably high, and considering its outstanding reputation among many of our members, and the excellent reviews of it that I recall seeing.

Emerson -- Glad things seem to be shaping up. Again, there is no technical explanation that I can envision for the effects the Burson buffer stage seems to be having, and I doubt that it has any relation to the impedance issue this thread has focused on. As we all know very well lots of things in audio are both unexplainable and unpredictable.

Regards,
-- Al

Al, thanks for the feedback as usual. I have a bit to add on the Burson AB-160 buffer. It's been in my setup for 3 days with signal going through (72 hours). What they say about it is true. It will take a budget player and lift its performance. The Burson is not connected to any of my players; it's between my amp and preamp. I have 3 different players connected to my VTL preamp, a Raysonic CD128, a Jolida player and an Onkyo. The low fi Onkyo is playing like a more expensive player now. It surpasses the other 2 players in extension, dynamics, low end, openness, you name it. And it has some inexpensive Tributaries IC's connected to it. Budget stuff in all. For the past 2 years I've only been using the Onkyo player for sending signal to facilitate break in with new gear and new cables. This is my experience with the Burson Buffer in my system 3 days. As others have said, the Burson seems not to have as significant of an affect on the performance of better players. At this point, I would say it is a detriment to the other players I have. Listening to this budget player with the Burson in place has also revealed what my speakers are capable of in the lower bass region. I had not heard these speakers go as low before.

Al,

Thanks for responding. Th preamp in questions:

Einstein the tube, 100ohms
Allnic L400, 250ohms (supposely flat with transformer coupled design)
ARC Ref 3, 600ohms (1400ohms at 20Hz)

I use interconnects 1 meter in length Nordost and Stealth.

Many thanks for your insight

Glai, it's only possible to offer speculation in response to your question, without having more complete information on the particular designs (which may be unobtainable). But I wouldn't be surprised if a tube preamp with a nominal output impedance spec of 600 ohms were to rise to several thousand ohms at deep bass frequencies.

And the 600 ohm impedance itself could have consequences at high frequencies as well, if your interconnect cables were long and/or had high capacitance per unit length. That could very conceivably account for the degraded transient attack you mentioned, by rolling off the upper treble.

Also, perhaps in the case of the particular designs you were using, there was some degree of correlation between lower output impedance and better quality parts in the output stage. As well as the possibility that variables elsewhere in the designs, unrelated to the output stage and impedance matching effects, might have accounted for the differences in those particular cases.

Regards,
-- Al

I'm currently using a Burson AB-160 buffer between my McCormack DNA-500 amp and VTL preamp. I'm waiting for it and associated cables to break in and sonics to stabilize. I'll report back with developments after it gets some significant hours on it.

Emerson, as I recall it was not readily possible to determine the low frequency output impedance rise of your VTL 2.5. However, Stereophile has numbers on the 5.5, which it describes as being descended from the 2.5, and the two models have nominal output impedances which are very close to one another (195 and 200 ohms). For the 5.5 they measured 184 ohms at mid/hi frequencies, and 409 ohms at 20Hz, which is a very minimal rise that would have negligible frequency response impact into 10K.

They also have numbers on a couple of other VTL models, the 6.5 (150 ohms at 20 Hz for the unbalanced outputs) and 7.5 (69 ohms at 20 Hz for the unbalanced outputs).

So it would seem that VTL's design approaches reflect sensitivity to this issue.

Regards,
-- Al

I think there is more than just a calculated drop of output in the bass frequencies. 0.4db would be difficult to hear especially at 20Hz.

My SS amps have input imped of 67K ohms. I have used a few tube preamp that has specified output imped of 100ohm to 600ohm (may be higher in the bass freq.) Subjectively, there is tighter coupling betw the pre with the lowerest output imped and the amp. I hear better transient attack in the mids and tighter bass. In some ways, it is similar to changing the load imped on cartridges.

I suspect that there is also interaction in the time domain and/or dampening.

I am pretty confuse myself. Any help is appreciated.

Foster,

Yes, it will be interesting what that device might do in your case. On paper, the VTL and McCormack appear to be a pretty good match. The DNA 500 is the only other (non Class D) 500w/ch amp that I have considered to-date.

I'm currently using a Burson AB-160 buffer between my McCormack DNA-500 amp and VTL preamp. I'm waiting for it and associated cables to break in and sonics to stabilize. I'll report back with developments after it gets some significant hours on it.

I once thought I was in love with ARC D400, at least on specs. . . until I heard it. . . and my ears started to 'bleed'. Am I ever glad I did not buy it without auditioning!G.

Interesting reading. Several of us made this mistake when starting. This is an excellent lessons learned for new audiophiles. Why don't A'gon create a lessons learned folder entitled "Audiophile 101". I learnt the expensive way.

Here are the leading contenders for the position of amp in my main system:

1) Wyred 4 Sound st-1000 or sx1000, best value, 500w/ch Class D offers potentiall best overall dynamics in my price range, 60K ohm input impedance, reported best of class results by OHM guru and fellow agoner Mamboni

2) Musical Fidelity A308CR, similar to what I have, 31K ohm input impedance, 250w/ch local seller, can audition in my system, 60+ amps current deliver (total for both channels I'm assuming

3) Musical FIdelity A5CR, similar to A5CR but significantly higher current delvery based on user guide specs, none available currently but I am not in a rush and could wait.

Is anyone familiar with A308CR versus A5CR that can offer insight on what all is different?

4) Larger ARC SS amp, D400 or 300.2, 150Kohm input impedance, 200 w/ch or so , I would have few reservations trying out other ARC gear that can fit in nicely with my pre-amp and the OHM 5s.

All thoughts welcome!

THanks

Hi Bob, Please consider my posts in this context - I was not trying to do anything more than provide a 'simple' answer to the OP's question without getting technical nor doing his research for him. That is a methodology I have used professionally as well as in these forums. In retrospect I probably didn't do it well here. It didn't work out well did it! :-)

As Al pointed out Stereophile had reviews which specifically addressed this particular unit, information that was available to all who cared to read it. I knew about them as well and had read them when they were published. In the future I will try to emulate Al more and simply refer folks to the source and avoid adding an interpertation and describe how it would actually effect his situation (unless he were to ask of course). That will be more helpful to the poster's understanding, perhaps stimulate his curiosity and encourge further research into the issue, but as importantly, avoid potential unpleasantry between the responding posters.

Hope you guys all have a nice day...............

Newbee (& Bob), thanks very much for the kind comments; much appreciated. I've learned a good deal since I've been here from your posts, too, as well as those of all of the other regulars who've participated in this thread.

My statement of "less than 0.4db" loss at 20Hz with a 10K load was a quick rough swag, and the actual number is probably close to 0.1db (and almost certainly less than 0.2db). The exact calculation is a little complex, because the preamp's output impedance is partly capacitive and partly resistive, and resistive and capacitive impedances don't sum linearly.

But with the numbers being that small at 20Hz, and undoubtedly totally negligible at say 30Hz and above, there's no need to be more precise. 0.1db is the commonly accepted rule-of-thumb for conservative level-matching, but that figures to be driven mainly by mid-range frequencies, where the ear is vastly more sensitive.

Thanks very much again for the nice words.

Best regards,
-- Al

Almarg sez "Amen from me too, of course"

To the profusion of Amens I would add that Almarg should get a few hozzanah's and more than one Amen for fleshing out the actual detail and providing a concise answer to the OP's concerns regarding the use of the SP16 with SS amps and not joining the crowd wandering thru the desert firing at phantom snakes from the hip.

Almarg, you are a model for folks who want to help others asking questions here. You have intelligence, knowledge, and a generous interest in helping others that makes you stand out high above the crowd. The folks here are in good hands when you have the opportunity to join in threads.

You are an AGon treasure. !!!!!!

Thanks everyone for sharing your expertise and attention on this. Much appreciated. Impedance matching is one of those things that I know makes senes to look at for optimal "synergy" between components, but I learned a lot regarding the details of what might go right or wrong here.

Just because the IC connectors are physically standardized to connect things doesn't mean any two things all do it together equally well electronically for sure!

Amen from me too, of course.

I found the review very quickly because I was too dumb to think of looking in the component category listings. It is in the Power Amp category, because it was reviewed in conjunction with an ARC VS110 power amp. I just entered "Audio Research SP16" into their search function.

Best regards,
-- Al

How about a few Hallelujahs?

Very nice to see a good discussion showing a sensible approach...of course, many audiophiles will continue to blame their interconnects and keep spending when their problem is simply a matter of a poor impedance match and choice of components...around here cables and interconnects often get blamed for what are really equipment design/selection issues.

Several newer class D amps have imput impedances in the 40K Ohms, including my JRDG 312. . . but the highest may be the Bel canto Ref 1000 Mk.2. It has raised its input impedance to 200K Ohms from the previous version, which was a respectable 20K Ohms already. R1000 Mk.2 handle my 6Ohms wabbly load Mahlers without any difficulties. Guido

New Krell EVO amps do have input impedance of 200 Kohm on balanced inputs. So if that is what you are looking for ...

Al,
c
Thanks for the details.

I can say with confidence that the sp16 sounds very balanced, natural and lively with the MF a3CR I'm using (31K input impedance spec).

There is a larger (>200 w/ch)MF A308CR amp up for sale by a local Agoner. I think the impedance specs are the same as the A3CR but need to confirm. Since I like the current sound an would be happy with more of it, that might be something for me to consider again now that I have a handle on the impedance issues.

Here are Stereophile's output impedance measurements for the SP16L line-stage preamp, for which the ARC specs are identical to what Mapman quoted:

http://www.stereophile.com/tubepoweramps/901/index6.html

The measurements indicate 262 ohms at mid and hi frequencies, and 549 ohms at 20Hz.

Into a 600 ohm load (sic), they measured a loss at 20Hz of only 2.5db (see Figure 1). By my calculations, into a 10K load the 549 ohm output impedance would result in a loss at 20Hz of less than 0.4db.

So the output circuit, and particularly the output coupling capacitor, of the SP16 appears to be designed more conservatively than in the case of most tube preamps. And the recommendation of a 20K minimum load appears to be conservative as well.

Regards,
-- Al

Mapman, Note that I deleted the post you are responding to. Sorry about that. I was really responding to Tvads observations and was not at all pleased about what I was saying especially as it applied to you. I had already communicated all I could really offer to you in previous posts. And I saw no reason to continue the correspondence with Tvad although he is so serious I must admit that I do, sometimes, enjoy rocking his boat. He is a good guy and means well.

But, FWIW, if you can accept the accuracy of ARC's recomendations about amp matching with that pre amp, restricting your search for an amp based upon a desire for higher input impedence will not add to the performance of the amp/pre-amp combo. If the car takes regular gas and the tank is full, that is as good as it gets.

Hope you find the right amp for your Ohms.

"I don't know why Mapman is reluctant to consider ARC recommendations "

Newbee, what gave you that idea?

I'm not. I would assume ARC to be a most reliable source for recommendations regarding their equipment given their considerable history, experience and reputation, and the fact that their unit has been a home run to-date in my system.

Tvad has been around with a lot of different equipment I believe and has a good attention to sound quality and technical details so I do not discount his observations in this area either.

I agree with your point about validity of apples and apples comparisons between amps based solely on input impedance differences as well, but I do not doubt that higher amp input impedances relative to pre-amp output impedance is one (of several) technically sound measurements that one can attempt to optimize along with but not at the expense of others necessarily as well.

This is primarily for the OHM 5s which have a somewhat difficult load, are only 87db efficient and the more juice, the merrier.

Power requirement: 250w/ch minimum doubling into 4, high current.

I'd like to stay under $2500 if possible for now.

Also, logistically, I would prefer to stay away from large heavy, hot running monster amps if possible. I know that limits my options....

Tvad,

Any SS Amp recommendations given all this?