Yes this Marantz 8B sounded more clear then McIntosh MC30. But despite Marantz bass wasn’t bad, MC30 bass was on the other league. It was also a big difference in complex music reproduction. 8B was good on very simple music but the sound became muddy and congested with bigger number of instruments and voices. On the other hand, the complex music wasn’t an issue for MC30.
@alexberger Sounds to me as if the modifications didn't have the desired effect. Feedback is a bit more complicated than it might look on a schematic. The Marantz 8B has a more sophisticated feedback design than most amps you see from that era; IMO/IME its unlikely that a technician 'adjusting' it would be successful in getting the amp to actually perform better.
@hilde45 Thanks!
|
Hi @atmasphere ,
Power supplies of all vintage tube amplifiers from 50-60x look so miserable with such small capacitors. It is especially true for stereo amplifiers when PS is used for both channels in parallel without any separation. I can say for sure such a PS will not work for a SET amplifier without feedback even if it is just 2 watt power.
How does it work in all these vintage amplifiers? Does feedback make them less sensitive to PS or the reason is the push-pull topology?
|
@alexberger Do some of these vintage amps use a choke in the power supply?
|
Hi @invalid ,
Yes most of vintage amplifiers use chokes in power supply.
But they use very small capacitors in B+.
The issue with small capacitors is not the 120Hz noise from AC , but voltage stability during playing of load and complex music.
|
Nice blog post on SETs recently, here.
A few excerpts. It’s not a long post and worth a read:
"The SET’s very existence calls into question fundamental beliefs and assumptions we routinely make about technical performance, sound quality, and the correlation between them. These amplifiers expose a crack in the edifice of audio engineering theory that is based on the conviction that an amplifier can be judged by its technical specifications or measured performance....
This paradox arises because the technical measurements that attempt to quantify amplifier sound are simply inadequate and incomplete....Predicting an amplifier’s sound quality or judging it to be good or bad based on existing criteria is like looking at a few still images from a movie and then attempting to discern from those static photos the movie’s plot, characterizations, dramatic arc, and meaning.
The SET exposes the fact that certain aspects of amplifier performance are not quantified by the traditional measurement arsenal....
Some will suggest that listeners are merely responding to the SET’s euphonic distortion—that the SET sounds good because of its distortion rather than despite it. There’s no question that the largely second-harmonic distortion component of an SET is much more sonically benign than the upper-order distortion components of Class AB solid-state amplifiers. But a first-rate SET amplifier’s magical qualities go far beyond this simplistic interpretation. The SET’s resolution of inner detail that, singularly, conjures up a strikingly vivid picture of the instrument creating the sound is certainly not merely a euphonic second-harmonic distortion artifact....
This essay is neither a renunciation of all amplifiers other than SETs nor an evangelical campaign for the world to embrace the single-ended-triode amplifier. SETs are limited in the loudspeakers they can drive, exhibit other practical drawbacks, and are certainly not for every listener...."
https://www.theabsolutesound.com/articles/the-single-ended-triode-paradox/
|
I've long agreed with Harley after having been through virtually all classes of amplifiers, both tube and SS. Virtually certain most of those amps measured better than the SET's I've owned, yet none provided the immediacy, the resolution, transparency, and the micro dynamics of my SET's.
I posit at least part of this quandary is a function of low parts count in SET. SET doesn't have to negotiate multiples of caps, resistors, transistors, what have you, and if point to point wired no circuit board. I can hear sound quality differences with a changing out a single resistor, cap or hook up wire, this goes to show how transparent these amps are. I used to have to change out multiples of these items in other amps to exact a change in sound quality. This suggests a signal passing through a less circuitous route is less changed/affected/contaminated, in other words more pure to the source.
|
Power supplies of all vintage tube amplifiers from 50-60x look so miserable with such small capacitors. It is especially true for stereo amplifiers when PS is used for both channels in parallel without any separation. I can say for sure such a PS will not work for a SET amplifier without feedback even if it is just 2 watt power.
How does it work in all these vintage amplifiers? Does feedback make them less sensitive to PS or the reason is the push-pull topology?
@alexberger Feedback improves power supply rejection and crosstalk; ideally anything that isn't the signal. For example, in an LP mastering situation, the feedback winding on the cutter head is essential to allow channel separation. The stereo LP would not exist without it.
Such a power supply as you described above will work fine in any SET that is running class A1 on the power tube, since at any signal level current draw is constant; IOW from idle right to full power. Consequently this statement:
The issue with small capacitors is not the 120Hz noise from AC , but voltage stability during playing of load and complex music.
-is false.
Boosted capacitance does help with a stereo amp or even a mono amp if the amp is push pull and operating class A2 or any form of class AB (IOW where current draw varies with power), so as to reduce intermodulation.
In all cases, the proof of the pudding is to put an oscilloscope probe on the power supply rail and run the amp up to full power at a variety of frequencies to see what sort of noise is present in the power supply. Since the output circuit isn't linear, power supply noise can intermodulate with the audio signal in the output section.
@hilde45 The article you quoted was true back in the 1980s but is not true now. The real issue isn't that we can't measure it, its knowing what the measurements are telling us. That knowledge is in short supply! I've been explaining exactly why SETs sound the way they do. Again, in a nutshell: They shine when not presented with bass or asked to make much power. I've already explained why they sound good when they do so.
Harley's mistake was simply not asking amplifier designers why SETs sound the way they do. But if he had done so he might not have had an article to write  I was online pointing this out when this article originally published a few years back.
I posit at least part of this quandary is a function of low parts count in SET. SET doesn't have to negotiate multiples of caps, resistors, transistors, what have you, and if point to point wired no circuit board. I can hear sound quality differences with a changing out a single resistor, cap or hook up wire, this goes to show how transparent these amps are. I used to have to change out multiples of these items in other amps to exact a change in sound quality. This suggests a signal passing through a less circuitous route is less changed/affected/contaminated, in other words more pure to the source.
@sns This statement comes to a false conclusion. The reason you hear differences due to components is not because SETs are particularly transparent (due to their having the highest distortion of any kind of amp made, and because distortion tends to obscure detail, its arguable they are the least detailed amps made), its because they lack feedback.
Feedback helps the amp reject that which is not the signal. Artifacts from wire, resistors, capacitors and transformers are not the signal, as well as noise from poor grounding, layout problems, line Voltage and so on. So when there is no feedback, everything (and I mean everything) makes a difference.
The problem of course is whether or not the feedback is applied properly and we've all heard amps where it wasn't. I've no doubt that many might prefer an SET over such amps! But its usually not due to detail- its (IME, IMO) due to amps with poorly applied feedback not sounding particularly musical on account of harshness or the like.
|
Thanks @atmasphere
I would love to hear what Harley would say in response.
|
"@atmasphere Feedback helps the amp reject that which is not the signal. Artifacts from wire, resistors, capacitors and transformers are not the signal, as well as noise from poor grounding, layout problems, line Voltage and so on. "
Ralph can you explain in a bit more detailed manner [my own ignorance] how "feedback" sort of identifies, isolates, and/or removes these other things that are "not" the signal. A local 50-year tech now retired has debated this some about how some amp designers do and don't leverage feedback for the circuit, or in the right ways. He actually gets somewhat aggravated in conversation about this topic, lol.
|
@decooney asks a good question for @atmasphere
One thing which seems to hang on this answer is when and whether the general audiophile precept that "simpler is better" is true.
|
explain in a bit more detailed manner [my own ignorance] how "feedback" sort of identifies, isolates, and/or removes these other things that are "not" the signal.
@decooney The various influences described above (resistors, caps, transformers, tubes, et. al) are part of why the amp makes distortion.
Feedback works by taking a small amount of the output Voltage and applying it to an earlier part of the circuit where it is out of phase with the audio signal. When the two are mixed, a corrected signal is generated which has the corrections needed to make the amp put out an undistorted signal.
In theory.
In practice feedback can generate distortion of its own. This is especially true if the feedback is mixed with the audio in a non-linear way, such as inside a vacuum tube or transistor. This is very common; in addition to harmonics the non-linearity of the feedback node can generate intermodulations as well.
Your tech friend is right. Too many designers just use a resistor and call it good. If a lot of feedback is used, this can lead to instability. The amount of feedback used and where its applied makes a difference too. If you want to do it right, this complicates the successful amplifier design in a lot of ways since the math for a second or 3rd order feedback loop isn't trivial.
|
One thing which seems to hang on this answer is when and whether the general audiophile precept that "simpler is better" is true.
@hilde45 I think it was Einstein who pointed out that a thing can be too simple to do its job well. I prefer simplicity myself and like to keep things simple if I can. But while a thing might appear simple, from just viewing it you may not see how much is really going on.
For example to get a 300b to sound right it has to be biased properly. That requires one to generate a load line so that you can see if the output transformer used is going to load it correctly, in addition to the operating Voltages. You can't see that just by looking at it.
A self oscillating class D amp can be a fairly simple circuit too. Looking at one, you can't see that the math behind it is pretty complex.
Of course, a lot hangs on what is meant by 'simple'...
|
|
@atmasphere
I think it was Einstein who pointed out that a thing can be too simple to do its job well.
Everything should be made as simple as possible, but not simpler.
-Albert Einstein
|
@mclinnguy Thanks!
So what is actually simpler? Many say SETs are. But they have problems that are very difficult to solve like the elliptical load line I've mentioned several times. I think they are just too simple.
In a conventional push pull tube amp the problem of core saturation in the output transformer is solved (so no elliptical load lines). This allows the the transformer to have much higher inductance at low frequencies and generally lower distortion at any frequency.
If the PP output circuit is biased class A1, it induces no more noise in the power supply than an SET. If the circuit is fully differential then the zero feedback distortion signature can be just as pleasing if not more so then that of an SET.
What I'm getting at is there is a thing I like to call 'elegance'; a simple solution to a difficult problem.
The original Ultra Linear concept was elegant. It was so popular that many sought to get around the patent by simply moving the UL tap to a slightly different spot, sacrificing some linearity to avoid paying a patent royalty. This was so prevalent that most UL transformers made today still do not conform to the UL patent, despite it being long expired. That's why some people like UL designs and others don't- they are not all equal. But the original idea worked quite well and displayed that quality of elegance.
In case those reading these words aren't familiar with the concept, UL operation allows a pentode power tube, either single-ended or push-pull, to have the linearity of a triode combined with 90% of the power of a pentode while being much easier to drive than a power triode. Anyone doubting this probably should read the original patent issued to Acrosound in the 1950s (David Hafler, one of the inventors, left Acrosound for Dynaco; knew how to break the patent and did; the UL patent was never licensed to Dynaco).
|
Again, in a nutshell: They shine when not presented with bass or asked to make much power. I've already explained why they sound good when they do so.
@atmasphere Ralph, I'd like to test that with the implementation of my SETS (I've got the low power part covered with high efficiency speakers and modest listening levels). So I figure I need to split the audio signal before it gets to the SET and create one for the SET and one for my powered subwoofers. The first being treated with a high pass filter and the latter a low pass filter. It so happens I own a MiniDSP 2x4HD which I think can do the job. The only limitation is that I need to then use the internal Dac of the of the MiniDSP and it is not my preferred Dac. Are there alternative approaches that won't cost too much? My music server is a Mac mini running Roon. Roon can do DSP but as far as I know I can only treat one signal stream at a time and there is no way to split the original signal in two and get two outputs from the computer. Any ideas would be appreciated.
Is there possibly a way to split the output from a Dac and then apply the high and low bandpass filters using some combinations of resistors and capacitors as done in a speaker crossover?
|
@bruce19 You could install a coupling capacitor between the source (perhaps a preamp) and the SET, with a value calculated to have a -3dB point at the desired crossover frequency.
Frequency in Hz = 1,000,000/Capacitance in uF times Resistance on Ohm time 2Pi (Usually when this formula is used the one million is a 1, but the capacitance is in Farads, which is too large to be easy to use. So I do the formula this way so I get practical audio values)
So if you wanted 60Hz as the crossover frequency and the input impedance of your amp is 100KOhms, then the capacitor would be about 0.027uf (that yields a 59Hz -3dB point).
This cap can be tiny since it does not need to handle much Voltage. So you might be able to install it inside an RCA connector of the interconnect cable.
|
@bruce19
If you already own the 2x4, there's no harm experimenting with an active crossover setup like you described, which sounds like it would work fine. If you're pleased with the proof of concept, then you can consider the DAC question. Just my 2¢! 🙂
|
That is great, thank you! I needed that specificity of detail in your example to get it. I'm looking forward to giving this a try. Probably as good a jump in performance as a $1,000 cable :-)
|
@atmasphere
PS to the previous reply. Does the type pf cap matter? Film or ceramic? I don't think electrolytics come in that small a rating.
|
@bruce19 There's a kind of ceramic cap called an 'NP0' (for Negative Positive Zero) which can sound surprisingly good. They are available with leads and in the value you need, are about the size of a small bead. By ceramic cap standards they are expensive, costing a few dollars each. You might look into them; we've compared them to a number of high end coupling caps and heard no difference. I don't think they are available in values above about 0.1uf. But they are available in Voltages as high as 630V. You only need 50v though so the part will be tiny. Here's a link from DigiKey:
https://www.digikey.com/en/products/detail/murata-electronics/RDE5C1H273J2M1H03A/10703951
|
@atmasphere
Thanks again! You mention using them as coupling caps. I'm curious might they also work well as coupling caps in my Elekit TU-8900 kit or other sets with 0.1 uF coupling caps with say the 0.1 uF and 1kvdc rating? I built it with the stock coupling caps figuring I might try the expensive type later, but at $4 apiece these are a much cheaper experiment than Audio Note copper or silver caps.
|
I hooked up my Dynaco ST-35 to my speakers and did some listening.
97 db speakers -- JBL 16inch woofer and Beyma AMT tweeter.
HEARING:
Very strong grip on bass. Amazingly good.
Mid range less warm, intimate than I expected.
Highs pretty clear, though perhaps some slight roll off.
Overall, there is a slight lack of finesse, smoothness in the mids and highs that I am looking for in a lower-powered amp.
I think I'm not hearing this amp at its potential and it may be due to the tubes it came with:
Sovtek 6BQ5 power tubes (4)
Sylvania nos 12DW7 pre-amp tubes (2)
If anyone has suggestions for good alternate tubes for this amp, I'm all ears.
|
@hilde45 I'd go with a set of JJ EL84s before Sovteks or for that matter any Russian made version.
Have the tubes been tested? If any are bad all bets are off.
If you have level controls on your speakers it might be a good idea to run pink noise through the system and using a spectrum analyzer app on your phone, adjust the controls slightly for best results. This amp has a lower output impedance than any tube amp (such as an SET) that runs no feedback so if your controls (if you have them) were optimized for an SET they won't be right for this amp.
Your amp in the photo looks fairly new. Apparently there's a resistor option on this amp; do you know which kind your amp uses? It looks like they might be the carbon film resistors. IME the metal films sound better.
If the amp has been sitting unused for a while or is brand new, it may need some break-in time.
I doubt its actually rolled off- this amp has full power bandwidth well past 50KHz.
|
Thanks @atmasphere. I need to check into those things and I have a friend/tech who can help.
|
