Does anyone care to ask an amplifier designer a technical question? My door is open.
I closed the cable and fuse thread because the trolls were making a mess of things. I hope they dont find me here.
I design Tube and Solid State power amps and preamps for Music Reference. I have a degree in Electrical Engineering, have trained my ears keenly to hear frequency response differences, distortion and pretty good at guessing SPL. Ive spent 40 years doing that as a tech, store owner, and designer. . Perhaps someone would like to ask a question about how one designs a successfull amplifier? What determines damping factor and what damping factor does besides damping the woofer. There is an entirely different, I feel better way to look at damping and call it Regulation , which is 1/damping.
I like to tell true stories of my experience with others in this industry.
I have started a school which you can visit at http://berkeleyhifischool.com/ There you can see some of my presentations.
On YouTube go to the Music Reference channel to see how to design and build your own tube linestage. The series has over 200,000 views. You have to hit the video tab to see all.
I am not here to advertise for MR. Soon I will be making and posting more videos on YouTube. I don’t make any money off the videos, I just want to share knowledge and I hope others will share knowledge. Asking a good question is actually a display of your knowledge because you know enough to formulate a decent question.
Starting in January I plan to make these videos and post them on the HiFi school site and hosted on a new YouTube channel belonging to the school.
Years and years ago I re-tubed my ARC SP-10 with your RAM tubes and the phono stage quieted down mighty well. And then a year or so later I heard your RM200 amp at a dealer in Phoenix and that was a very nice sound as well. Thirty years later, I have a question that I imagine you or some of the other techie gurus might be able to answer.
I swap between amps with some that only have single-ended inputs and others with only balanced inputs and others with both. My preamp has outputs for both. I recently acquired a very nice 4m balanced IC. For the cases when I want to use the single-ended input only amp, the CAT JL-3 monos, I will need to use an XLR to RCA adapter into the amp. The adapter I bought has the neg line tied to ground. But this results in the preamp's neg output line being shorted to ground which does not seem to be a good thing. Would it make more sense to put a 10k, 50k, 100k, etc., resistor inside the adapter from the the neg pin to ground to more accurately simulate what the cable would otherwise see as the amp's input impedance?
I swap between amps with some that only have single-ended inputs and
others with only balanced inputs and others with both. My preamp has
outputs for both. I recently acquired a very nice 4m balanced IC. For
the cases when I want to use the single-ended input only amp, the CAT
JL-3 monos, I will need to use an XLR to RCA adapter into the amp. The
adapter I bought has the neg line tied to ground. But this results in
the preamp's neg output line being shorted to ground which does not seem
to be a good thing.
Its probably not- check with the manufacturer of the preamp. If the output is transformer coupled, then this is required. So it really depends on the preamp!
But if I were you, I would simply use the RCA output if using an amplifier with a single-ended input. There is no advantage of using the really nice balanced cable if you are going single-ended- the single-ended requirement actually results in the **entire** connection being single-ended so the cable is not operating as designed and intended.
ramtubes you stated " My stand on power cords is entirely intellectual from an amplifier designer and transformer makers point of view. I know what is inside a transformer and how it works. When you know about transformers, house wiring etc. we can further discuss this interesting topic."
Caelin Gabriel of Shunyata Research Inc. knows much more than I do and he is an electrical engineer with a high pedigree in the audio industry. Whether his cables and noise suppression equipment are correct or not, I don’t know. However here are three of his quotes concerning power cables and sonic degredation due to faulty power supplies in equipment.
" Misconception #3: There is up to a hundred feet of wire in the walls, so the last 6 feet of power cord can’t possibly make any difference.
Answer: “The power cord is not the last 6 feet, it is the first 6 feet from the perspective of the component. As stated in #1 the local current and electromagnetic effects directly affect the sonic performance of the component.”
So, he feels that the upstream house wiring all the way the transmission towers are not as relevant as the Power Cables leading to the equipment.
Misconception #4: There is a tremendous amount of electrical interference and EMI coming from outside the home that we need to protect our equipment from. This implies that we need some sort of power conditioner or filter to protect the equipment.
Answer: “Most of the EMI that affects the audio quality of a system is generated by the audio components themselves. Electromagnetic waves that traveling through space dissipate in power at the square of the distance from the source. Further, very high frequencies that propagate through the power circuit do not survive for long. Power lines present a high impedance to MHz and GHz signals due to the relatively high inductance of power lines.
"A primary source of audible sonic degradation is caused by the power supplies in our audio/video components. Most components use FWBR (full wave bridge rectifier) power supplies that generate an incredible amount of transient noise when the rectifiers switch off. The design of a power cable can significantly affect the reactance of these signals within the power supply. The power cable is effectively part of the primary winding of the power transformer. The transition between the various metals used in a power cable and its connectors can cause electromagnetic reflections and diode-like rectification of the noise impulses as they propagate away from the power supply. If the power cable presents a high impedance to these signals they will be reflected back into the power supply where they will intermodulate, thus increasing the high frequency noise levels of the component. Most power supply filters are ineffective at blocking very high frequency noise components and much of it is passed through to the DC rails. The sonic effects of this include: high background noise levels, blurred or slurred transients and a general lack of clarity and purity of the sound or visual image.”
Here he is stating that the equipment power supply creates the sonic degradation.
Misconception #5: There is some sort of conspiracy among audio designers that keeps them from producing a "proper" power supply that is not affect by power cable quality.
Answer: “This concept is like saying that if a speaker where properly designed, you wouldn’t need to use a good quality speaker cable. PowerSnakes have been tested with the most modest of mid-fi equipment and the most exotic state of the art components. We have yet to find a component that cannot be improved by replacing the power cord.
"As long as power supply design is based upon FWBRs or switching supplies, the power cord will always be significant.”
Basically, he is stating that power supply design generally is at fault resulting in power cords making a significant difference.
Are your RM series amps and pre-amps designed to prevent all of these problems? Are most equipment designers not designing their equipment correctly? You would know as I don’t.
Okay, does atmasphere believe that power cables can make huge differences in an amplifier’s sonic performance and why?
I’m not picking a fight, I just don’t understand the rationale behind what is so obvious to many audiophiles and my personal experiences with testing cables on high end equipment (limited to about 2 dozen systems). Is it because our equipment is all faulty due to poor design or poor implementation?
Is Caelin Gabriel wrong to suggest that the first 2 meters of wire connecting the equipment is the most important compared to the upstream wiring?
Does most of the EMI come from the equipment and not from in the air contamination?
These are relevant questions, especially for me, a non-engineer. Only one of my friends is a manufacturer, the others are famous mastering engineers so most of my friends are non-technically knowledgeable audiophiles.
No, Mr. Gabriel is not completely wrong and makes some good points. Yes, your points are reasonable. Perhaps this is just not the place to go there. I may disagree with the OPs opinions on cords and caps etc...but he started this thread for a different reason in general and I respect that. I also appreciate his desire to answer questions and share knowledge. It’s OK to have different experiences and opinions and let them rest for the greater good of the thread.
Thank you for the responses above. The preamp is Aria WV5, the last design by Michael Elliot of Counterpoint 10 years ago. The last thing I want to do is to put anything else in the line such as a transformer.
My experience has been that the most sensitive cable in the system is the IC from line stage and amp, where I was using ARC, BAT, Aesthetix, Counterpoint, Wolcott and CAT. Just putting some cheap 4-5m RCA IC here is going to destroy much of what my system can achieve with a good IC here. And so why not just use one leg of the XLR cable when I have a single-ended amp? I just thought it might be a good idea to not just float the negative line.
Prof uses the measurement canard which is as old as it gets and is well proven to be ineffective when it comes to human hearing at it's limits - which is the subject at hand.
Interestingly enough, his entire job rides on doing things that are either unmeasurable or so close to being unmeasurable that it is not worth bothering to try.
Hoisted by his own petard. (modern translation: he blew himself up)
Interestingly enough, his entire job rides on doing things that are either unmeasurable or so close to being unmeasurable that it is not worth bothering to try.
Not true. It is relatively trivial to measure the diode switching noise*. IF that noise is reflected through the transformer, increased by the transformer** and ameliorated by the power cable, then the results should be eminently measurable.
first the swapped polarity from amp to speaker does no harm and most will not hear any difference as long as the swap is the same on both sides. All you have done is invert absolute phase which has been a point of contention for many years.
As to one speaker not playing. probably just a loose wire.
No damage will occurr
For the phase hawks out there. The battery test is valid and is the standard. Though easy it is not entirely correct and JBL tested for in, + not out. Below resonance a cone speaker flips its polarity. So in the normal condition above resonance the cone is moving in for +.
Just something to throw at someone who thinks they know everything about speakers.
@jafox Thank you for the responses above. The preamp is Aria WV5, the last design by Michael Elliot of Counterpoint 10 years ago. The last thing I want to do is to put anything else in the line such as a transformer.
My experience has been that the most sensitive cable in the system is the IC from line stage and amp, where I was using ARC, BAT, Aesthetix, Counterpoint, Wolcott and CAT. Just putting some cheap 4-5m RCA IC here is going to destroy much of what my system can achieve with a good IC here. And so why not just use one leg of the XLR cable when I have a single-ended amp? I just thought it might be a good idea to not just float the negative line
.
What to do with the negative? There are two answers and it depends on the driving end (preamp). You are correct in your earlier post to float the negative, no resistor needed, as long as your preamp is balanced via electronic buffers. We dont want to short those.
The other case (not yours I suspect) is where the preamp has a output transformer where both leads are floating. Then you must connect the signal negative to ground or no sound.
daveyf: first the swapped polarity from amp to speaker does no harm and most will not hear any difference as long as the swap is the same on both sides. All you have done is invert absolute phase which has been a point of contention for many years.
As to one speaker not playing. probably just a loose wire.
Roger, see my lengthy response to Davey dated 12-22-2018, as well as Davey’s original statement of the question on the previous day. I believe that he did not simply invert absolute phase, but instead he caused the high and low frequency sections of the speaker to be driven with opposite polarities. On the speaker that was producing sound, that is. That would of course have adverse sonic consequences, while not causing any damage.
On the speaker that was not producing sound a loose connection is one possibility, but another possibility (which I cited in my post) is that he was applying the + output of the amp to both the + and - terminals of one section of that speaker, and the - output of the amp to both the + and - terminals of the other section of that speaker. Which of course would result in no sound (and no damage), since no voltage difference would be present between the + and - terminals of each section of the speaker.
@Jafox, to add to the responses Roger and Ralph have provided to your question, fyi I believe that as a special order item Cardas can supply XLR-female to RCA-male adapters that leave pin 3 unconnected, rather than shorting it to ground (pin 1) as is done by most such adapters.
preamp is balanced via electronic buffers. We don’t want to short those.
Depends on the circuit design. A lot of pro gear has IC balanced outputs that can short either leg to Gnd and the output acts single ended, driving no current into the shorted leg.
However, as Roger said, if you don’t know the output is single ended capable, only use one leg.
AND if using balance lines, only connect the screen at the driven end. A shield grounded only at the receiver forms pair of low-pass filters for common-mode noise
Ralph, couldn't he use a Jensen transformer to make he XLR to RCA change? Would it still offer the proper grounding?
Yes.
Okay, does atmasphere believe that power cables can make huge differences in an amplifier’s sonic performance and why?
I don't use the word 'believe' because I made the measurements which showed that the power cord **without question** can affect the amplifier's performance. The measurement is easy- the voltage drop from one end of the power cord to the other. Its not rocket science and its not mumbo jumbo woo. Anyone with a 3 1/2 digit DVM can do it. After you know what the voltage drop across the cord is, then measure the resulting differences in the amplifier: output power, distortion and output impedance. You will find that they all change. So by this simple means you have a tool to correlate with what you hear. So in a nutshell, I don't believe it, I **know** it.
Hi Ralph, please put your statement above into perspective for us non electrical savvy persons. Would a "normal" power cord supplied with a piece of gear have enough excess power passing capacity so that any drop in voltage due to the cord, is from one satisfactory voltage to a lesser, yet still satisfactory voltage to power the unit? Or are you saying that the power cords supplied with a piece of gear could be starving the unit for power and maximum performance?
Would a "normal" power cord supplied with a piece of gear have enough
excess power passing capacity so that any drop in voltage due to the
cord, is from one satisfactory voltage to a lesser, yet still
satisfactory voltage to power the unit? Or are you saying that the
power cords supplied with a piece of gear could be starving the unit for
power and maximum performance?
Much is depends on the equipment used, so the answer as a generalization is 'both' although I'm uncomfortable with the phrase 'excess power passing capacity'. Power cords like anything else are subject to Ohm's Law.
—-“Prof uses the measurement canard which is as old as it gets and is well proven to be ineffective when it comes to human hearing at it's limits - which is the subject at hand.”
Ah that’s right. Human hearing is more sensitive than our measuring instruments. Wait...what did we need those instruments for again? Oh yes, to extend our detection capabilities beyond the limitations of our senses. Heard any 26k sounds recently Teo? That’s ok - instruments can easily detect things you can’t hear.
Of course instruments can’t detect things you imagine. They really suck at that, admittedly.
— “Interestingly enough, his entire job rides on doing things that are either unmeasurable or so close to being unmeasurable that it is not worth bothering to try. “
Wha?? I work in film post production sound. What I’m doing is being measured all day long. I want to reduce a sound or boost it, or eq, it’s all measurable and measured!
—“Hoisted by his own petard. (modern translation: he blew himself up)”
You have no idea what you are talking about. I suggest stepping away from the bong before posting :-)
Thank you Roger and AL. Fortunately, the adapters I bought have 2 small screws to allow the case to be opened. I can cut the wire soldered from the negative to ground. I will give this a try.
"I don't use the word 'believe' because I made the measurements which showed that the power cord **without question** can affect the amplifier's performance. The measurement is easy- the voltage drop from one end of the power cord to the other. Its not rocket science and its not mumbo jumbo woo. Anyone with a 3 1/2 digit DVM can do it. After you know what the voltage drop across the cord is, then measure the resulting differences in the amplifier: output power, distortion and output impedance. You will find that they all change. So by this simple means you have a tool to correlate with what you hear. So in a nutshell, I don't believe it, I **know** it."
Ralph, thanks for providing this insight. I have been accustomed to thinking about power supply to amplifiers primarily as avoiding reduced current supply, not avoiding voltage drop. I had not really considered voltage drop before. I was especially intrigued by your statement regarding measurability of differenced in distortion as a consequence of voltage drop. My power usually measures around 120-123V from the duplex, in other words, it is a bit on the high side. I run my system through a PS Audio P-10 with the voltage set at 117 V (tube life!) , but my M-60s are supplied straight from the wall. They are not happy running through the P-10! From the point of view of distortion from the M-60's as a function of voltage, would you expect a measurable difference in distortion over the range of 115-125 Volts?
Not much meat or it sounds. I didnt read the whole thimg. In my RM-5 preamp I found the coupling of the power transformer to make a great difference. A well coupled primary has less noise, however a loosely coupled primary was worse. Takes some digging to see this.
I felt it best to use the Grid to take the pulses. What a cord might do I, dont think much.
I would like to see some scope photos of these diodes compared to others all the way down to the slow 1N4000 series.
my M-60s are supplied straight from the wall. They are not happy
running through the P-10! From the point of view of distortion from the
M-60's as a function of voltage, would you expect a measurable
difference in distortion over the range of 115-125 Volts?
You would certainly be able to measure a difference, not just distortion but also power.
It seems that conditioners like the P10 are not happy with higher constant loads on them- they work fine with higher power solid state amps that have otherwise low quiescent current draw, but tube amps with larger draws (for filament circuits, perhaps also class A) seem to cause them trouble. For that reason we usually recommend running the amps straight out of the wall. If you want a really nice conditioner, a company called Elgar used to make some that are quite impressive.
A couple tech questions for Roger. Others please chime in too.
Is it possible to estimate how much amp power will be enough (i.e. never clipping) simply based on speaker specs (assuming they are correct), and listening habit/situation (i.e. distance from speakers, loudness)?
Yes it is. See two of my posts ealier in this thread, dated 11-26-2018 and 11-27-2018, which appear on pages 5 and 6 of the thread if you have it sorted with the oldest posts first.
I am getting some ground loop noise from my Classé 5300 amp. I read that a Ebtech Hum X will eliminate this. However, the box says do not use on any amps that draw more than 6 volts. I am not sure how many volts my amp draws. Does anyone know if I can use this with my Classé?
Yes. I used a cheater plug and the hum in the speakers went away. I know it isn’t safe that way and was hoping the hum x product would work. It actually did work but evidently the Classé has too much power for it.
I am getting some ground loop noise from my Classé 5300 amp.
I wired studios with 1000's of interconnections. We never used cheater plugs. E V E R !! Solve the problem, don't bandaid it. Sometimes it involved fixing the gear's internal wiring.
Are you using balanced or unbalanced inputs? If balanced, remove the screen connection on the amp end. In a balanced system, the screen should be lifted on all the driven ends.
Get some shorting plug and start with just the amp connected to the speakers. Add in each component back from the amp. When the hum starts, solve the problem there and continue.
In your case, both your VAC and Pass amps are capable of producing 32w I presume. What gave XA25 an edge over the VAC amp with your speakers? Does XA25 have less distortion due to its class A operation in the first 25 watt?
My former VAC Renaissance 70/70 MkIII amp is a class A amp employing four 300B power tubes per channel, in a push-pull parallel configuration, and is rated at 70 watts per channel. It is a 100+ pound beast, which I believe consumes something like 700 watts of AC at all times, converting most of that power into heat that is injected into the room.
The Pass XA25, as you realize, is rated at 25 watts into 8 ohms and 50 watts into 4 ohms, operating in class A, and it is specified as consuming 240 watts of AC. John Atkinson’s measurements that were provided in conjunction with Stereophile’s review, though, indicated that it is capable of providing 80 and 130 watts into those impedances, respectively. He stated that some of that disparity is due to the fact that Pass bases its power ratings for the amp on much lower distortion percentages than JA uses, and presumably a lot of that disparity reflects the XA25 transitioning to class AB when outputting more than a certain amount of power.
As I mentioned in my earlier posts that you saw my speakers are nominally 6 ohms, and have an unusually flat impedance curve as well as relatively high sensitivity, which makes them very versatile with respect to amplifier selection. Since like most solid state amps the XA25 is designed to provide an essentially constant output voltage into varying load impedances, for a given input voltage, (as long as the amp is operated within the limits of its maximum voltage, current, power, and thermal capabilities), even if we assume the very conservative 25 and 50 watt numbers it can be calculated that it is capable of providing at least 33.3 watts into 6 ohms.
I wouldn’t say that the XA25 has "an edge over the VAC amp." They are both wonderful amps, in their own ways, and some non-sonic reasons factored into my decision to change. See the comment I left two days ago near the end of the following thread, as well as a subsequent comment by member "1markr":
A question on another topic. My Marantz SA-11S2 has an Spdif through rca. I would like to add a BNC connection to go to my dac. Can I just install the BNC and jumper over with 75 ohm coax inside the player?
Thanks again for your thorough explanation. As a big fan of SET amps, I am delighted to hear your experience of XA25. Should I ever endeavor into the ss world, it seems that XA25 would be the natural candidate to try out.
@flashbazbo, the caveats that occur to me regarding adding a BNC output to your player are:
1) Be sure to select a 75 ohm BNC connector, rather than a 50 ohm BNC connector.
2) Looking at rear panel photos of the player, as might be expected it appears that the ground shell of the RCA jack is isolated from the metal panel. So you would want to select a BNC connector that is similarly isolated. Such connectors are readily available, but many BNCs are designed such that their ground shell is connected to chassis.
3) Waveform quality might benefit, at least slightly, if you were to disconnect the internal connection to the RCA jack and connect it directly to the BNC, rather than jumpering between the two connectors. You would not want to use both connectors simultaneously anyway, as significant impedance mismatches would result if 75 ohm loads were applied to both outputs. And if a need ever arose to connect an RCA plug to that output, BNC-to-RCA adapters are readily available.
What Al said- The issue here is something called 'characteristic impedance'. The BNCs are designed for cables with a characteristic impedance of either 50 or 75 ohms. Without getting into the designer's head, it uncertain what CI the RCA connection is actually working with, since RCAs have no termination standard and are used with all sorts of impedances. Hence Al's comment about waveform quality; reflections of the signal (noise) may be the result.
could you explain what shorting plugs are?
@bwguy They are connectors that have all their connections shorted together. Installed at the input of an amp or preamp, in this way one can be sure that no noise is present at the input of that piece.
@ieales
Depends on the circuit design. A lot of pro gear has IC balanced outputs that can short either leg to Gnd and the output acts single ended, driving no current into the shorted leg
.
iesles Please elaborate. I don't how the shorted lead drives no current?
AND if using balance lines, only connect the screen at the driven end. A shield grounded only at the receiver forms pair of low-pass filters for common-mode noise.
I would think the screen should be conneted at both ends and the negative leg to the RCA body.
@ffzz4 A couple tech questions for Roger. Others please chime in too.
Is it possible to estimate how much amp power will be enough (i.e. never clipping) simply based on speaker specs (assuming they are correct), and listening habit/situation (i.e. distance from speakers, loudness)?
If so, how?
Its rather easy. Imagine you listen at your speaker's real 1 watt sensitivity (2.83 volts for 8 ) ohms. If the speakers are relatively close and you sit at one meter and the sensitivity is 90dB and you listen at 93 then you are hearing 1 watt. The 3 dB extra is because you have two speakers. Lets say the room absorbs 3 dB and let your listening level be 90.
As you move away for every doubling of distance you loose 6 db from a point source, 3 dB from a line source and O dB from a large planar. Anyone please correct me on that. I am doing it from memory.
If you want to listen at 100 dB rather than 90 you need 10 dB more power which is 10 watts. 110 dB 10 times more at 100 watts. 120 db takes 1000 watts. It gets out of hand in a hurry.
If you want to throw out your numbers i will work it out step by step. Most people with 100 watts only need 20 or less. But we all like $100 better than $20 and its rare to see a 90 watt amplifier isnt it.
David Manly always rated his 80 watt amps at 100 watts for just that reason.
My speakers are 93db sensitive (1w/1m) with 8 ohm impedance (7ohm min).
With a listening distance of 8 feet, it seems 15w will be more than enough to produce 100db or so loudness that Symphonic music peaks into from time to time.
Assuming 100db is my max need, will there be any advantage of using, say, a 30w amp rather than a 15w amp? What if the amp is class AB rather than A?
Please elaborate. I don't how the shorted lead drives no current?
A cross-coupled opamp circuit wherein shorting one of the leads to 0V removes its drive. It was very common in the 70's & 80's. Later Analog Devices created monolithic driver with similar functionality and much better performance due to tighter on chip resistors and thermal tracking than discrete parts. Sorry I don't have examples or numbers.
I would think the screen should be connected at both ends and the negative leg to the RCA body.
I was speaking of Balanced like XLR. Single end Dual wires inside a screen should have the screen connected to the body at the driving end only and the -ve lead connected at both ends.
Richard... I am enjoying the heck out of this forum and am learning quite a lot. I am interested in your thoughts and insight into Bob Carver’s latest tube amps
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