Correct.
Yup. Though, again, I would take issue with the claim that the ME550 is a very nasty load. It is very easy for any number of low impedance source devices.
Z/B
Good, bad, or indifferent, IHF "standards" define the norm for consumer audio electronics offered in the stream of commerce. A priori, the ME 550 is a nasty load, as it is incompatible with many fine, commercially available, pieces of equipment. A strong suspicion of ulterior motives attaches to equipment that locks the end user into a single manufacturer's line. The suspicion may be incorrect, but it IS present.
FWIW, some of the members that frequent this "board" regard the IHF 10 Kohm "standard" as being difficult. I believe in lowest common denominator and design line level driver circuitry that comports with the 10 Kohm rule. Plug and play is a good thing, even in non-commercial designs, like mine.
I don't regard tubed equipment as automatically being good. For instance, Audible Illusions (AI) preamps are regarded as "sounding good, but operate the 6922 tubes outside the documented safe area. As a consequence, tube life is compromised and many variants, both OS and current production, fail quickly. Such a product is (IMO) unacceptable and I will not recommend it. "It sounds better that way." RUBBISH! It doesn't sound, period, if the tubes fail. Product offered in the stream of commerce should be reliable.
Finally, your notion that SS is always better than tubes/valves is absolutely incorrect. When a SS voltage amplifying device whose open loop distortion comes close to matching that of the triode found in the 6SN7 is developed, it will be front page NY Times news. Plenty of other examples exit.
Good, bad, or indifferent, IHF "standards" define the norm for consumer audio electronics offered in the stream of commerce. A priori, the ME 550 is a nasty load, as it is incompatible with many fine, commercially available, pieces of equipment. A strong suspicion of ulterior motives attaches to equipment that locks the end user into a single manufacturer's line. The suspicion may be incorrect, but it IS present.
FWIW, some of the members that frequent this "board" regard the IHF 10 Kohm "standard" as being difficult. I believe in lowest common denominator and design line level driver circuitry that comports with the 10 Kohm rule. Plug and play is a good thing, even in non-commercial designs, like mine.
I don't regard tubed equipment as automatically being good. For instance, Audible Illusions (AI) preamps are regarded as "sounding good, but operate the 6922 tubes outside the documented safe area. As a consequence, tube life is compromised and many variants, both OS and current production, fail quickly. Such a product is (IMO) unacceptable and I will not recommend it. "It sounds better that way." RUBBISH! It doesn't sound, period, if the tubes fail. Product offered in the stream of commerce should be reliable.
Finally, your notion that SS is always better than tubes/valves is absolutely incorrect. When a SS voltage amplifying device whose open loop distortion comes close to matching that of the triode found in the 6SN7 is developed, it will be front page NY Times news. Plenty of other examples exit.
I accept that some arbitrary standards may suggest that a 10k input impedance is desirable. I also understand and have explained why the manufacturer has chosen to use a 1k input impedance. It was done so because it sounds better (DBT tested). I can also tell you that all the same manufacturer's models built prior to the ME550 possessed an input impedance of around 75k. The 1k was chosen based on a new (in 1984) theory that superior sound quality would result. It did. The manufacturer has attempted to obtain the same high quality sound, using a high input impedance, but has not been successful. I should also add that, as consequence of commercial demands, related to multi-channel surround sound systems (where preamps are severely compromised), that subsequent lower end models have been released with a 100k input impedance and capacitor coupled inputs. Higher end amps retain the low input impedance. All the high end preamps I've examined from manufacturers like Mark Levinson, Krell and others work fine.
Sure, but then we could discuss some of the pathologically difficult loudspeaker loads that have been released over the years. ME has always been up front with what is required to properly drive the ME550 and other models. The same cannot be said for many speaker manufacturers.
That's because I have never stated such a thing. Not once, not ever. Valved equipment may have many advantages over conventional, high global NFB SS equipment. In fact, I used to built and listen to valve equipment, before I acquired an ME (preamp). If I could not have an ME preamp, I might well seek out a nice valve preamp. I've used a Conrad Johnson Premier 16 in my system and found that it sounded very nice, as did Allen Wright's 12 valve preamp.
I have never and will never claim the following statements to be true:
Valves = bad, SS = good.
and:
SS = bad, Valves = good.
There are good and bad examples of both types of technology. The trick, as I'm sure you know, is to pick which is which.
We could enter a long discussion here, but that will get me into trouble, so I won't.
The 12AX7 has *NO* business in a linestage...LOL
I would go with a transformer OPT, likely the Peerless S-217-D. The amplification stage would probably tap the EL84 tube, rigged in triode and layed out as a LTP. SE input
P output. I would rig it parafeed with a cap between the CT, and take output from resistively bypassed CCS-es with mu-follower outputs. Output impedance would be dominated by the DCR of the secondary.
cheers,
Douglas
I would go with a transformer OPT, likely the Peerless S-217-D. The amplification stage would probably tap the EL84 tube, rigged in triode and layed out as a LTP. SE input
P output. I would rig it parafeed with a cap between the CT, and take output from resistively bypassed CCS-es with mu-follower outputs. Output impedance would be dominated by the DCR of the secondary. cheers,
Douglas
While it may be indulgent for some to speak in tech language and criticise my aspirations at my expense --- it has no value for me in laymans terms - nothing to date has made much sense to me in what has been discussed, except for the person suggesting the 'champ amp', however since this has an IC I feel it would be defeating the original intent and most likely compromise the valve natural sound...
I really just need -easy-to-understand- solutions rather than listening to dialogue I cannot fully understand --- and some criticism of my aspirations...
Can we please just limit the posts to what is of practical value in step by step explanations as I have requested time and time again --- thanks...
I really just need -easy-to-understand- solutions rather than listening to dialogue I cannot fully understand --- and some criticism of my aspirations...
Can we please just limit the posts to what is of practical value in step by step explanations as I have requested time and time again --- thanks...
T/S
This is a DIY "board". Some technical expertise is expected. Most of the members active on this "board" (including me) are hobbyists, not professional electronic engineers.
Properly functioning equipment (tubed or SS) is transparent. If euphony is what you seek, you are, despite of stating otherwise, in effects machine "territory". IMO/IME, tubes/valves are the "easy" way for a DIYer to achieve excellent results. The simplicity of tube/valve circuits allows for far fewer missteps. Certainly, excellent results can be achieved with SS. However, squeezing top notch performance out of SS is (I believe) something best left to professionals, like Nelson Pass and John Curl.
BTW, a SS CCS load for a cathode follower is not directly in the signal path. It just so happens that some SS parts make excellent "spear carriers" for tubes/valves. CCS loading a cathode follower yields BETTER results than a resistor.
I'm not criticizing your aspirations. Unfortunately, some of things you mentioned are ill suited to the task at hand. A buffered volume control capable of driving the ME power amp's very difficult I/P impedance is what you need. You definitely don't need line stage gain. Amplifying a signal and later attenuating it or vice versa worsens S/N performance. In tube/valve circuitry, cathode followers made from 6H30Π (6n30p) twin triode sections fulfill the situation's requirements.
This is a DIY "board". Some technical expertise is expected. Most of the members active on this "board" (including me) are hobbyists, not professional electronic engineers.
Properly functioning equipment (tubed or SS) is transparent. If euphony is what you seek, you are, despite of stating otherwise, in effects machine "territory". IMO/IME, tubes/valves are the "easy" way for a DIYer to achieve excellent results. The simplicity of tube/valve circuits allows for far fewer missteps. Certainly, excellent results can be achieved with SS. However, squeezing top notch performance out of SS is (I believe) something best left to professionals, like Nelson Pass and John Curl.
BTW, a SS CCS load for a cathode follower is not directly in the signal path. It just so happens that some SS parts make excellent "spear carriers" for tubes/valves. CCS loading a cathode follower yields BETTER results than a resistor.
I'm not criticizing your aspirations. Unfortunately, some of things you mentioned are ill suited to the task at hand. A buffered volume control capable of driving the ME power amp's very difficult I/P impedance is what you need. You definitely don't need line stage gain. Amplifying a signal and later attenuating it or vice versa worsens S/N performance.
In tube/valve circuitry, cathode followers made from 6H30Π (6n30p) twin triode sections fulfill the situation's requirements.
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Hi Zaphod Beeblebrox,
I'm very, very familiar with those
I agree, this aspect of the amplifier design acts merely to lock customers into this particular manufacturer. It is very unlikely other preamplifier manufacturers will ever follow this example as the market is simply too small. But it is way off standard
The 1K input impedance will not sound any better than ones ranging from 10K to 100K. The test would only show that other commercial preamplifiers are unhappy driving a 1K load. The 1K amplifier input impedance would lower susceptibility to radiated noise of course. That shouldn't be a problem with good cables and a reasonable listening environment. So the 1K impedance test would heavily favour the matching preamp. It's also possible that the designer has trouble with designing higher output impedances. The output stage in this preamplifier would approximate a headphone amplifier output stage, assuming you are going for a 10R output impedance or lower.
-Chris
So it's a Stasis amplifier like the ones made by Nelson Pass and Nakamichi - right?
I'm very, very familiar with those
Actually, nothing could be further than the truth here. The most common input impedances range from a low of 10K (difficult load for a preamp) to 100K. 50K is a very common input resistance.
Ahhhh, no. It isn't if you expect to maintain the noise and distortion specs. Can it be done? Yes, but there is a cost penalty for that.
I agree, this aspect of the amplifier design acts merely to lock customers into this particular manufacturer. It is very unlikely other preamplifier manufacturers will ever follow this example as the market is simply too small. But it is way off standard
The 1K input impedance will not sound any better than ones ranging from 10K to 100K. The test would only show that other commercial preamplifiers are unhappy driving a 1K load. The 1K amplifier input impedance would lower susceptibility to radiated noise of course. That shouldn't be a problem with good cables and a reasonable listening environment. So the 1K impedance test would heavily favour the matching preamp. It's also possible that the designer has trouble with designing higher output impedances. The output stage in this preamplifier would approximate a headphone amplifier output stage, assuming you are going for a 10R output impedance or lower.
-Chris
Well, apart from some minor similarities, no.
Mea culpa. Sorry to mislead you. I should proof-read more carefully. The INVERTING input of most SS amps employ impedances or around 1,000 ~ 3,000 Ohms. The ME550 is no different in this respect. The designer theorised that a similar impedance on the non-inverting input of the diff amp made some sense (don't forget: ALL prior ME designs employed a more or less standard 75k Ohm input Z). Two, otherwise identical amps were constructed and DBT tests were conducted. The low impedance design was preferred by all listeners. The decision was made to build amplifiers with the 1,000 Ohm input Z.
The manufacturer is well aware that it is a non-standard input Z. Nonetheless, the sonic improvement is tangible. All other low input Z ME models can be easily modified to present a more reasonable 15k or 68k (selectable) input Z. Unfortunately, due to the unique topology of the ME550, this cannot be accomplished easily (but it can be done).
Have you done the tests? The manufacturer has. In fact, I was one of the test subjects and I can assure you that the difference, whilst not earth-shattering, is audible.
Well, no. I could list quite a number of commercial preamps that are quite comfortable with such a load impedance. OTOH, there are a large number that would not be happy with such a load. They should not be used and the manufacturer is quite clear in this.
Nope. It's just that the results are better when the impedances to earth from the inverting and non-inverting inputs of the diff amp are similar.
Yep.
Hi Zaphod Beeblebrox,
So, what differences did you notice between the two impedances?
-Chris
Try me. Your description shows zero differences.
While still not true, I'll grant you that the inverting input is often lower impedance than the non-inverting (or signal input) inputs. It's that standards thing, you know? If people don't stick to them, then standards don't mean anything anymore and it turns back into the ugly old days when everything goes. The end losers are the consumers in that silly situation. However, there are ways that can satisfy both requirements. There are commercial examples out there.
Yes, but not blind. I took it down to 50R. Can you see why that figure was used?
So, what differences did you notice between the two impedances?
No, you can list a bunch of preamps that would drive that amplifier. It doesn't mean they were happy with that load. All it means is that they made noise that sounded okay.
So, there is a caution on the outside of the box to warn potential buyers of the low input impedance? This "feature" is so far from expected standards that I think it would be only fair to make it more than obvious. Otherwise, it's like a trap for some people. You can't assure that every salesman will disclose this situation to every customer. In fact, I'll bet it is something the manufacturer would rather not talk too much about. Not before the sale anyway.
-Chris
The only schematic I can locate is that for the Nakamichi PA4/7. I assume they are similar to the Stasis designs. The Naka uses a Sziklai pair type of output. The ME does not. The Sziklai pair was tried by the designer back in the mid-1970s, but was found wanting, so he went in a different direction. Rather than coupling the driver transistor via the collector to the base of the ouputs, he uses the emitter.
Huh? "Still not true"? Then you say:
"I'll grant you that the inverting input is often lower impedance than the non-inverting (or signal input) inputs."
I believe that is exactly what I said.
Standards that may imposed from an 'authority' may impair the ability of a designer to build the best product available. We have seen it many times over the years. In the US automobile industry, standards were imposed which actually impaired safety and performance. Things like headlights that turn with steering (which my present car has and it is brilliant) were made illegal in the US. Standards made, without regard to potential performance gains are hardly worth adhering to.
RF work, presumably. My last oscilloscope (A Tek 7854) employed a 50 Ohm input on one channel for very high frequency work.
Bass response sounds more 'secure', imaging appears to be more accurate. So-called 'micro-dynamics' appear to be a little better.
Well, given the fact that I have tried a number of different preamps, I can assure you that not only do they sound excellent with the low input impedance, the results are slightly worse, when the high input impedance option is selected (not the ME550, I might add).
In the same way that Infinity never placed a caution on the outside of the box for any of their speakers (like the one below), or any electrostatic speaker manufacturer doesn't warn their customers, no. That said, dealers of the product are well aware of the issue and make consumers aware.
That is a good point, but, ultimately, a waste of time, as the ME550 has been obsolete for around 20 years. ALL other ME models either employ a system to raise the input impedance, or are inherently high input impedance. Only the ME550 (and it's predecessor, the ME55) cannot easily cope with such a change.
Incorrect. The manufacturer is VERY upfront with the specifics regarding his product. As am I (as someone who sells it). ME amps are very different to all other SS amps. As such, they do not necessarily suit every listener.
I recall, once, delivering one of the larger models to a well-heeled listener, for evaluation back in the early 1980s). He owned a pair of B&W 801 speakers, in a superbly damped listening room. His amp was a Carver 1.5T. I knew the amp well and knew it's limitations. Even better, his reference recording was a fine copy of a live Frank Sinatra LP. I knew I had a sure sale. He 'phoned me the next day ad asked me to collect the amp. I was stunned. I asked what he didn't like about the amp. His words:
"I hate it. It's as though the musicians are right there in the room with me."
Taught me a valuable lesson. Some listeners are uncomfortable when presented with too much reality.
T/S
This is a DIY "board". Some technical expertise is expected. Most of the members active on this "board" (including me) are hobbyists, not professional electronic engineers.
Properly functioning equipment (tubed or SS) is transparent. If euphony is what you seek, you are, despite of stating otherwise, in effects machine "territory". IMO/IME, tubes/valves are the "easy" way for a DIYer to achieve excellent results. The simplicity of tube/valve circuits allows for far fewer missteps. Certainly, excellent results can be achieved with SS. However, squeezing top notch performance out of SS is (I believe) something best left to professionals, like Nelson Pass and John Curl.
BTW, a SS CCS load for a cathode follower is not directly in the signal path. It just so happens that some SS parts make excellent "spear carriers" for tubes/valves. CCS loading a cathode follower yields BETTER results than a resistor.
I'm not criticizing your aspirations. Unfortunately, some of things you mentioned are ill suited to the task at hand. A buffered volume control capable of driving the ME power amp's very difficult I/P impedance is what you need. You definitely don't need line stage gain. Amplifying a signal and later attenuating it or vice versa worsens S/N performance.
Tech talk is fine and interesting Eli, when at some point it translates into practical step by step solutions for what I started this thread for. So far - I have been trying to work out how to practically apply some comments into my project, however the comments have been too general and vague in terms of a clear step by step pathway.
Are you suggesting that using 'the champ' will only reduce Z value without being in the sonic pathway, and as a result would not affect sound quality??
Looking at the online comments and Utube videos from those who made this preamp - all are very pleased with the results. The ones who were critical of the design, never made one nor heard one ... Practical application and the end-result wins hands down over theorising with no real practical outcome ... IMO.
Some have made further mods, such as using 12AT7's and other tubes...changing a few values here and there, but overall - all that make this preamp end up quite happy with the outcome ...
Are you suggesting swapping a couple of 12AX7's with 6N30P's ??
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The ME550 will drive both speakers with ease and without nasty current limiting effects.
Infinity Kappa 9 impedance curve:
Or the Acoustat Spectra Something-or-other:
Infinity Kappa 9 impedance curve:
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Or the Acoustat Spectra Something-or-other:
An externally hosted image should be here but it was not working when we last tested it.
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The 'Guanzo' valve buffer preamp I was using is also considered a good headphone amp...
Here it is encased and rebranded, but comments are generally good...
Amazon.com: SainSmart Assembled 6N3 Hifi Buffer Audio Tube Headphone Amplifier Pre-amp Kit with Transformer: Home Audio & Theater
6N3 Hifi Buffer Audio Tube Headphone Amplifier Pre-amp Kit – SainSmart.com
It sounds great with a NAD amp, phenomenal with Rotel 990BX, OK but mediocre with the ME550 amp...in comparison
I got 4 of them...they were $AU45-50 on ebay...
Not sure what the Z output is on them...however if they are anything to go by, the JP200 should sound pretty good...
This is one that I modified and encased - removed the pot; resoldered entire circuit board with Mundorf silver solder; hard-wired leads (silver-plated balanced mic cable - shielding grounded) with RCA's only on one end - to be used in this instance as a valve buffer ---
--- makes a big difference when put between pre-amp/amp on NADT773
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Too bad you're so far away T-S, I have a buffer pre that runs a 5687 cathode follower to a bi-filar Permalloy cored OPT. Its output z is OTO 100R.
Even tubes benefit from a low input impedance. Last time I played with this, in combination with the 5687 amp, I believe I quit at 4k7 Ohms. That pre couldn't have cared less and the system sounded better than it did with a 10k Ohm grid circuit...
The circuit I proposed using an S217D OPT would be even lower...and is not quite what I would call difficult...as long as you can source the 217's( and they are not so bad to get new production of ).
cheers,
Douglas
Even tubes benefit from a low input impedance. Last time I played with this, in combination with the 5687 amp, I believe I quit at 4k7 Ohms. That pre couldn't have cared less and the system sounded better than it did with a 10k Ohm grid circuit...
The circuit I proposed using an S217D OPT would be even lower...and is not quite what I would call difficult...as long as you can source the 217's( and they are not so bad to get new production of ).
cheers,
Douglas
Too bad you're so far away T-S, I have a buffer pre that runs a 5687 cathode follower to a bi-filar Permalloy cored OPT. Its output z is OTO 100R.
Even tubes benefit from a low input impedance. Last time I played with this, in combination with the 5687 amp, I believe I quit at 4k7 Ohms. That pre couldn't have cared less and the system sounded better than it did with a 10k Ohm grid circuit...
The circuit I proposed using an S217D OPT would be even lower...and is not quite what I would call difficult...as long as you can source the 217's( and they are not so bad to get new production of ).
cheers,
Douglas
Now I remember what these are. I got 4 Beyer Dynamic 250/50-47ohm transformers with the intent on making a MC circuit to add-onto a Cornet valve phonostage I am yet to build.
Hmmm, so you are saying that the specs for the Peerless S-217-D (almost impossible to find) is what would be required for this activity??
Some recommend the Sowter 9530 as a replacement for the Peerless, but there must be others with same/better specs for this project...
Hi Zaphod Beeblebrox,
Just because a standard is not convenient doesn't mean it's wrong. Especially when so many other designers successfully abide by the rules and create outstanding products. It's a cop out to claim that standards make it impossible to design a product to do a common job. The masses have shown that to be false.
Right now the best sounding amplifier I have heard is a rebuilt Marantz 500, or maybe a Bryston 4B cubed (which I am told sounds close to the 500 done my way).
What do you currently use as your preferred amplifier at home?
-Chris
Okay, I have a good mental picture of it then.
A little loosely interpreted. You said
Which is very specific.
Like them or not, standards protect the consumer and the manufacturer as well. They allow equipment to be manufactured that will play nice with equipment from other manufacturers. There have always been people who wouldn't play by the rules, like your speaker examples a post down from this one. Wilson is another infamous example and he even admitted he made a mistake. A real designer / engineer would have caught this before it made it out into the wild.
Just because a standard is not convenient doesn't mean it's wrong. Especially when so many other designers successfully abide by the rules and create outstanding products. It's a cop out to claim that standards make it impossible to design a product to do a common job. The masses have shown that to be false.
Close, lab work in general. That is a standard that can be used to work to. Given that 1K was great, 50R should be that much better, you think? My own experience in labs has illustrated how good those connections are, and the triax connectors that use a ground and guard to protect a signal. If consumer (or pro) audi used that, reproduction of audio works would be amazingly good. Just think, an audio component built like test equipment with two shields. They would be massive and run cool. Perfect for people who like that sort of thing. Circuits on removable cards for quick troubleshooting and upgrades! What a world this could be. However, only a few could afford such a thing. But, the signal to noise level alone would impress, no doubt.
Okay, so not well defined except for better. How were the levels matched between those two amplifiers? For certain, you would have a small level change between those two amplifiers.
Having done some measurements myself along this topic, I can tell you with absolute certainty that the preamplifiers performed slightly worse at the lower impedance level of 1K. I feel expectation bias had a great deal to do with the impressions this experiment left on the crowd. The same thing holds true with power amplifiers. The lower the impedance load, the less well the amplifier will perform. It's just the way things work, the physics of the situation. No point in arguing that concept as it has been found true every time someone performs an experiment properly with equipment that can measure the difference. Four guys in a living room won't cut it.
Okay, I'll take that as a no. Just because one manufacturer is irresponsible doesn't give license for anyone else to do the same type of thing. Infinity was very irresponsible, and they should have foot the bill for all the equipment that was damaged trying to drive those at reasonable levels. They knew in the early concept stage that this design would be responsible for a lot of failed equipment. It's too bad no government was mandated to enforce departure of a reasonable standard load. A bad product is a bad product. People who profit from pushing bad products are committing a crime as far as I'm concerned. I feel the same about amplifiers that destroy loads because there is no mechanism to disconnect during a failure event.
I wasn't aware of that. I'm glad it isn't in current or recent production.
No warning label on the box? They weren't very upfront in that case. Can you guarantee every sale that was made had full disclosure? If you weren't present at each demonstration, I don't see how you could be. No warning on the box means things were not upfront. Just so you can see I'm not playing favorites, I feel that those terrible speakers should also have had a warning on the box stating they had a lower than standard impedance.
You should see what I can do with an M-1.5t these days. I have a series of modifications that transform this model into something very nice to listen to. Even I was surprised at how well it turned out.
What preamp was he using? That would seem to be extremely important in this specific example. I will agree that the original M-1.5t sounds pretty ragged compared to many other power amplifiers.
Maybe the reality that was too much was the price tag? That tends to make things all too real! I have zero idea how expensive these amps were compared to the average price in that power range (which I also don't know).
Right now the best sounding amplifier I have heard is a rebuilt Marantz 500, or maybe a Bryston 4B cubed (which I am told sounds close to the 500 done my way).
What do you currently use as your preferred amplifier at home?
-Chris
OK. I should have a rough schematic somewhere. I'll send it to you if I find it.
Wilson failed to fix problems with the Watts, even up to version 6, AFAIK. And that was clearly a design fault. Different situation to the ME550. No secret was ever made about it's input impedance. It is clearly stated in the advertising material and the owner's manual. If a Wilson Watt purchaser avoided reading a Stereophile review, he/she would never know. Until their amplifier failed, of course.
I never said it was impossible. I just said that performance will be compromised somewhat, if a high input impedance was chosen.
Like I said: The theory was that the input impedance should closely match the impedance on the other side of the differential amp. If that diff amp is operated on the inverting input at 50 Ohms, then yes, the non-inverting input should be operated likewise. It's not the impedance, per se, but the impedance RELATIVE to the non-inverting input to the diff amp.
That said, Krell make (of did make) low impedance inputs for some of their products. The CAST system, I believe. It was touted to have several advantages over standard Voltage source ones and would, I presume, require a very, very low impedance load at the amplifier input.
I love the old Tek stuff (and HP, Gen Rad, etc). Built to standards domestic audio can only dream of. I miss my 7854, but I needed the real estate for one of those digi-scopes. Astonishing power and convenience and crap build quality, at a very low price. I keep my 2232 handy for those times when only analogue will do.
Levels were matched by the manufacturer. The ME preamp exhibits an open loop, DC coupled output impedance of 2 Ohms. I doubt any human ear could detect any level change.
Entirely possible. I, perhaps, should have run impedance measurements to verify. I did, once, try one of those Musical Fidelity valve 'buffers'. Although their output impedance is claimed to be quite low, THD, when driving a 1k load is very high indeed (ca. 10%). There are limits to what NFB can manage. MF were pushing those limits.
I certainly will not argue with expectation bias. I've fought against it for decades. It's why I fully support DBTs wherever possible.
Agreed. I will also agree that, perhaps, the manufacturer could have made things a little clearer. Hey, it was the 80s. Everything was fast and loose.
Agreed. That's a whole nuther can o' worms. I can tell you stories. And, since you mentioned it, the Marantz 500 protection relay is utterly useless in the even that an output stage goes DC into a loudspeaker. Same deal with the Model 240/250/250M/1200/1200b amps. I replaced dozens of the things, with welded contacts in my time at Marantz. There are much better ways to protect speakers.
Of course not.
I would be very surprised. That amp (along all the Carver 'Magnetic Field' amps had several fatal flaws.
No idea. And it didn't matter. I loaned him a much older amp than the ME550. It's input impedance was 75k.
I would not be that polite.
Nup. The guy was well-heeled. A property developer, living in one of Sydney's most prestigious suburbs. On today's prices, his home would have been worth a minimum of AUS$10 million. Probably more. I can usually spot those guys who pretend to be wealthy. This guy had none of those attributes.
Roughly half the price of a Krell KSA100 back in the day, but with superior performance. A little less than a Krell KSA50, but much higher performance (not, solely my opinion - DBT proved it, with disinterested listeners) So, pretty decent value.
I use various ME models, of course. A late model ME preamp, coupled, usually, to an ME550-II, or an ME150, or if I feel adventurous, an ME1500.
BTW: The ME150 was the first amplifier to entice me away from listening to my Marantz Model 500. The ME150 had the balls of the 500, but with significantly better bass and a cleaner high end. All quite surprising, given the ME150 is *only* 180 Watts @ 8 Ohms (and 340 @ 4 Ohms, 600 @ 2 Ohms, 1kW @ 1 Ohm, et al.) The power transformer is rated for 5.5kW at 4% regulation. It LOVES tough loads. Wilson WATTs are no problem.
Hi Zaphod Beeblebrox,
I think we are in agreement on most things then.
One thing I noticed about the Marantz 500 was that most were not set up properly. When I rebuild one today, I use modern outputs that are matched very closely as well as matching all the diff pairs. I have my own series of updates as you might expect, but setting up the DC offset really makes a big difference. There are three offset adjustments per channel.
Most Marantz amplifiers and receivers will weld the relay contacts closed depending on the fault. They did use an SOA type approximation for current limiting that was very effective at preserving the music, but the relays didn't stand a chance. These relays are the same ones used by several manufacturers and are generally reasonably good at interrupting current. You could always glue some magnets to the sides of the relays near the contacts. This would help blow out an arc. Something Marantz needed.
I've been busy redesigning Marantz amplifiers (mostly) and Counterpoint products. The Counterpoint just to make them reliable, and improve performance. The Marantz just to squeeze that extra bit of performance out. The Marantz 500 is the runaway star over everything else I've done. It's very gratifying when you see performance like this. Hopefully you still have your 500. If you do, let me know. A little effort on your part will produce one heck of a nice amplifier. You may find yourself going back to the Marantz in that case. You wouldn't be the first to fall in love with the old boat anchor again.
The 500 typically measured 330 watts into 8 ohms. It is an animal for sure. Well worth a rebuild if you ask me.
-Chris
I think we are in agreement on most things then.
One thing I noticed about the Marantz 500 was that most were not set up properly. When I rebuild one today, I use modern outputs that are matched very closely as well as matching all the diff pairs. I have my own series of updates as you might expect, but setting up the DC offset really makes a big difference. There are three offset adjustments per channel.
Most Marantz amplifiers and receivers will weld the relay contacts closed depending on the fault. They did use an SOA type approximation for current limiting that was very effective at preserving the music, but the relays didn't stand a chance. These relays are the same ones used by several manufacturers and are generally reasonably good at interrupting current. You could always glue some magnets to the sides of the relays near the contacts. This would help blow out an arc. Something Marantz needed.
I've been busy redesigning Marantz amplifiers (mostly) and Counterpoint products. The Counterpoint just to make them reliable, and improve performance. The Marantz just to squeeze that extra bit of performance out. The Marantz 500 is the runaway star over everything else I've done. It's very gratifying when you see performance like this. Hopefully you still have your 500. If you do, let me know. A little effort on your part will produce one heck of a nice amplifier. You may find yourself going back to the Marantz in that case. You wouldn't be the first to fall in love with the old boat anchor again.
The 500 typically measured 330 watts into 8 ohms. It is an animal for sure. Well worth a rebuild if you ask me.
-Chris
Yup. I used to allocate 12 hours to repair and properly setup a Model 500 (don't forget: I had access to all the original Marantz spares and serviced the amp by the book, which included matched devices where required). Although only three were ever imported into Australia, two were unleashed onto the public. When they started failing, the bean counters held the last one in the warehouse. I repaired each of the ones in the market half a dozen times, until Superscope advised replacing the Motorola outputs with 2SD600/2SB555 (I think) replacements. The result was quite a reliable amp. I purchased the last one for not too much money (one month's mortgage payments in 1978).
Yep, but still not a reliable solution, IMO.
I'm pretty certain I used to measure 320 Watts @ 8 Ohms, but hey, it's splitting hairs. As for falling in love with it again, I doubt it. I will certainly admit that, back in the late 1970s, nothing on the market could touch the old 500. ME power amps, however, are very different to any SS amp you've ever seen/heard. I'm certainly interested in knowing can be done to the 500, as I need to rebuild mine sometime.
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