Does anyone care to ask an amplifier designer a technical question? My door is open.

@khiak  Can changing the power cord to the amp changes the musicality of sound at the speakers.

Some think so.

@fleschler  ramtubes - So, you don't believe power cables make a difference other than connectors and isolation transformers are worthless? Is that correct?

Do I detect a little nudge there?  I think isolation transformers are great when needed. I like balanced power which also isolates. These things have a good chance of reducing noise if one has noise.

My stand on power cords is entierly 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. 

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.

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.

* Discussion on diode transients and measurement thereof here:  https://electronics.stackexchange.com/questions/323507/bridge-rectifier-4-diodes-vs-single-chip

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.

@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.

@oem  This thread is going way to fast for me.. Way back, power cables was mentioned.. For those that said that they don't make a difference, does speaker cables and interconnects make a difference ? I felt that if the latter two makes a difference then the power cables do to.. I swear when installed Audioquest's Hurricanes it improved the sound.. Maybe its just me thinking that ??.. I need one more to complete the full loom (4pcs).. I'll try 4 $100 cables after the complete loom and see..

We can slow down, no problem. 

Audio cables make a difference no doubt. However after $100 I think there is little to gain. Cables have measureable and predictable effects of capacitance, inductance etc. 

Just because they make a difference it does not follow that a power cord does. In power cables there is not much to measure and a lot of other wire to consider. 

@ffzz 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?

I think thats a little light on power. 8 feet is more than double a meter so 9db loss there but 3 gain for stereo so lets make it minus  6 dB on your sensitivity. You are going to get 87 db per watt. 10 watts will get you 97 and 20 watts will get you 100. If that is peak, not average then 30 watts is barely ok. If your room is absortive then more power is needed. 

100 db is a high level, have you checked with an SPL meter.  I listen no louder than 90 peak. A 30 watt amp is fine for me and most people but they dont listen at 100 dB

The class of amp will make no difference. 

In my experience, it is not a myth and it does incrementally improve the sound quality. My understanding of the technical reason is it reduces the negative affects of the crossover by (almost) directly connecting the amplifier to the drivers.

The best crossover is no crossover. When are we going to stop piddling around with tiny effects when we can bi amp and do someting that really makes a difference.

Many of these cables and little tweaky things cost more than a good electronic crossover and a second amp.

@tinear   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

I heard the amps were very light weight, had tiny transformers in those big cans. He has to be cutting corners somewhere at those prices. Check the weight of the 275. Wheres the measurement?

Roger

For a technical look at Bi-Wiring, please see  http://ielogical.com/Audio/CableSnakeOil.php/#BiWire Please note that these are Spice models and not actual system measurements.

He was doing fine till he got here on #1..   

  To go back to our marble and donut example, a higher frequency would be represented by inserting a marble faster in the tube, with a correspondingly fast-moving donut. So with a multi-frequency signal such as music, the higher frequencies entering the cable reach the other end earlier than the lower frequencies.

  Also as we saw, the “signal” moves down the wire’s outer circumference, and not in the wire. Therefore, the velocity of propagation of the signal (versus the velocity of the actual electrons) is determined by the dielectric or insulation material that the electromagnetic wave is predominantly traveling through. The slowing effect of the dielectric varies with frequency, throwing another variable into velocity of propagation—but giving us a way to play with it.

Do they higher frequencies get there sooner, i think not. The second part is skin effect which has pretty well been delt with as a no go in reasonablely small conductors. Dielectric on a 8 ohm cable is ludirus. Hes just measuring inductance for that time thing.

Whenever people start talking about time, they suck in the audiophiles and make big errors in logic.

Sorry I cant read anymore without ruining my day.

 In an electronic circuit, when current flows through a resistance, voltage is developed.

Most would say when a voltage is applied aross a resistance a current flows. An ampifier supplies a voltage and the current is determined by the load. Tere is no current till there is a load.

However in designing a preamp (the most difficult thing to get right) is that we drop voltages across resistors to get our operating points. Has anyone thought why preamps have so many more resistors than anything else?

But I am still thinking about voltages not so much currents till I get to the output stage of a power amp.

As mentioned earlier, the devil is in the details. Some speaker crossovers are more complex in their action than a symmetric electronic one. My dbx223 sits in the cupboard because the dual 4th order did not sound as well as the 4th/2nd passive on the mains or the electronic 3rd / passive 1st for the sub

.

Digital may have promise, but at this stage, new hardware elicits no interest.

The RM-3 crossover I use is all discrete push pull followers in the high end, op amps in the low. DIgital crossovers are not recommended. Too may A/D and D/A coversions to be done well at a price. Then there is the code that runs them. 

Analong crossovers are available, why get a digital one?

Good drivers need no correction because they are good, look at the response curves. No one is going to convince me that a bunch of coils (some with iron) capacitors, lossy resistors is better than a direct connection to the drivers.

Audiophiles will spend copiouis dollars on cables that have minimal effects and ignore the real powerful effects because they are daunted by the thought of bi amping. Get some help, read some books, do something important.

Is there a bi-amping group somewhere on this forum? I'd rather go there and help them. Seems all I get here is disagreement.

HAPPY NEW  YEAR, Make a resolution to do something important to your system. At a minimum make a bi amp speaker, even a little one. Crossover kits are available for less than the price of a bi wire.

Roger,
           Thanks for this great thread! It is one of the best threads I have ever read on this website! Your time educating us non-technical prople is greatly appreciated. I still own the original Beveridge Model 2׳s and have a couple questions after reading your earlier comments about these speakers. You mentioned in an earlier post that the perfect room for these speakers is one that is 11’ W by 24’ long. You mentioned that they needed to be at least 6 feet from the rear wall facing each other. Then you commented on their amazing imaging saying that they should be 2 times 6ft or 12 feet area for imaging. Were you just saying that both speakers were 6 feet away from the rear wall or were you saying the speakers should be pulled 12 feet from the rear wall in this perfect room?

The speaker will be 6 feet from the rear wall. 12 feet is the depth of the image which is 6 ft to the wall and 6 more for the sound to return to the speaker. a 12 mSec delay feels like 12 feet.

Very nice speaker, hold on to it. I hope visitors appreciate it.

Lastly, i have stayed away from your RM-1 (and RM-2 Power supply) Beveridge preamp because I have been told that the preamp is very hard on tubes used in it. This seems very much counter to your later works. Is this true or myth about the RM-1/2? If so, is there a later fix for this issue or should I just buy a later preamp of yours. I have used many preamps with the Beveridge 2’s. Currently I am using an old PS Audio 4 preamp in the passive mode. I obviously am
a fan of your work!

The early runs of the preamp ran hot even though I ran the tubes at one half dissipation. I reduced it to 1/4 rated dissipation. We upgraded many but there are some high current ones out there.12 tubes makes some heat so it needs free air and not in a rack or stack. Many of them come to me with Ram tubes so I can tell last time we sold the customer tubes. Its typically 3 years. Now a tube can get noisy at any time and its a very low noise preamp so people use the MM input for cartridges  0,5 mV and up.. Therefore they would run the line higher and a noisy tube would be obvious.

Lets say this. For its 1978 vintage it something few can do. Its DC coupled, no output capacitor, many features for phono lovers. Try one out. Clean or better yet, replace the 12 pin connector from the power supply. 

If people want to know about RM-1s I will write up a white paper. If it was still in production I would be sending on to Stereophile for JA to bench text. There would be no drop off in the bottom or top end at any load, even a ohm. Output impedance is 100 ohms, very rare for tubes of the day.

I would say it rivals an SP10 in many ways and perhaps more reliable. 

More about Beveridge and the company on request. He was my mentor and very out of the box.

the velocity of propagation of the signal (versus the velocity of the actual electrons) is determined by the dielectric or insulation material that the electromagnetic wave is predominantly traveling through.

I would like to see some proof of this. 

@rollintubes  I am sold on tubes for analogue audio but am confused by all of the information on power. I see from many posts that tube power need not be very high or as high as the speaker manufacturer claims as a requirement, i.e. a 200 WPC SS amp is needed to drive a speaker with 85db sensitivity (the manufacturer requires a minimum of 75 WPC, but likes at least 100 WPC), yet I have used a tube power amp with 40 WPC on the speakers and it sounds terrific. I have read that it is in the output transformers and SS amps are generally direct coupled.
Will you please explain this phenomenon?

It is my understanding that 200 watts per channel is a maximum to not blow up the speaker. That is a lot of power for a voice coil to absorb. Almost everyone has too big an amplifier in my opinion. I know this as I have measured power at listening levels in customers homes to be only a few watts. To say 200 watts is "needed to drive a 85 db speaker" means that the speaker will be putting out 105 db SPL. I listen at 85 db, anything higher is for short periods. Do you listen at 105 db?

Your 40 watt tube amp sounds terrific because thats all the power you need. Small amps generally sound better than big amps. In designing big amps, certain sins are committed. Small amps can be more responsive and delicate. 

I am currently designing several 30 watt/channel amps for those who agree with what I have said above.

@jyprez 

yes, I would be happy to pay for coursework on the subject. What do you offer?

Currrently basic amplifier design. Are you local to Richmond. CA 94806?

http://www.audiosystemsgroup.com/TransLines-LowFreq.pdf

The last paragraph of this 3 page paper dealing with transmission lines admits that we are not in transmission line territory at audio frequencies..    
Electrical Wavelength at Audio Frequencies can be computed from Fig 2. At 1/20 wavelength and below, transmission line effects are negligible, and the circuit can be analyzed using simple lumped circuit parameters. At 1/10 wavelength, transmission line effects are still quite small, and can generally be neglected. Fig 3 shows the characteristics of the RG59 cable of Fig 2. Typical balanced audio cables have similar properties, typically differing from Fig 1, 2, and 3 by no more than a factor of 2 in frequency. Thus, at audio frequencies, a cable less than 2,000 ft long is no Fig 3 Electrical Wavelength at Audio Frequencies more complicated than its series resistance and parallel capacitance. As the cable becomes longer, or as frequency increases, the cable will begin to behave as a transmission line.

michaellent

Why can’t people stay focused? Ramtubes started this discussion about amplifiers and it looks like it fell into the cable whole again!
Start your own thread about cables of any different kind and stay out of the ones that have nothing to do with it!

Thanks Michael. I appreciate your request for a return to amplifier discussions. 

ON TONE CONTROLS

The typical bass control has a hinge point at 1,000 cycles, much too high. In my system I use the Subwoofer level control (100 Hz and below) to set the bass to the right level without making vocals muddy like most tone controls do. Typical bass controls have lift the male vocal 3 dB to get 6 dB in the low bass. We dont want to hear that. 

My woofer level control is right next to my volume control on my crossover and I note I move it several dB depending on the recording, listening level and bass quality.

For treble, usually I want a cut for bright recordings, rarely would I want a boost. A cut control is much easier to make than a boost. Typical cut/boost controls have a hinge at 1,000 also which is too low.

Whoever chose 1 KHZ as the hinge point made a big mistake, and once  made was copied over and over. I would choose around 200 Hz for the bass and 4 Khz for the treble and leave 200-4,000 unmodified.

@c1ferrari    Re: Beveridge

Hi, Roger,
You'd worked on the Bev DD amps for my Model II's when you were situated in Santa Barbara. Unfortunately, Rick was unable to complete the restoration process and my panels require attention. Can you assist?
Thanks for the attention.

We havent done any panels for a long time. Chat with the other fellow on here who wants to stretch some mylar. We have the right Mylar as mentioned in my reply.

@michaellent

 I want to learn about amplifiers

Hi. What would you like about amplifiers? They are my favorite subject and life's work. Did you check out the YouTube videos and Burning Amp?

Realizing early on that the applications in the RCA and other manuals are just one of many possibilities I like to create new applications that are within the capabilities of the tube yet not in the book. Most USA manufacturers copy the same "typical" application from each other. European makers often have many more applications. I noted this in my BAmp talk.

The RM-10 is unique in that it gets over 40 watts (at the plates) with one pair of EL-84s. In the standard application EL-84s achieve 18 watts per pair. However that application is based on a low B+ which is desirable if one wants to make highly cost effective amplifiers. So most manufacturers use that application though many other applications could be created. Mine is at a very high B+ which I have found to be very reliable and gives longer tube life than some of the low B+ apps. 

Emission Labs, makers of large triodes like the 300B, lists many applications (operating points, load impedances, etc) for each of their tubes. I did some for Jac Music on the new 45B and confirmed them on the bench, not by simulation. See note below applications.

http://emissionlabs.com/datasheets/EML45B.htm

@radiointerference 

Hello Roger, thanks again for this opportunity seeing you worked for Harold Beveridge , I have two questions, 1). I have a pair of Beveridge 2SW's with a panel that has gone south. I am looking to make a jig to tension the mylar film. Can you shed some light on how to rebuild the panels, I have some background info on the mylar but would like to know the tension techniques to properly rebuild.

We stretched the mylar a bit beyond its elastic limit, so tight as you can get it. A silk screen stretcher works well or look on YouTube for other clever ideas. Weights will not do the job. We have the mylar in stock. It has to be coated both sides and heavy and well attached to the brass strip. There is significant current on the mylar. Nothing like the high resistance film of a Quad.

Question 2), I had purchased a set of Counterpoint SA-4's about 2 years ago needing repair/restoration. One was functional one was not but found one tube had vented, I think it was due to mishandling during transportation.

Can you give info on what to check for, and possible ECO's on this amp so I can proceed with a restoration for a set of Quad 63's I am planning to use them on.

I dont have any ECOs. I gave Counterpoint the design and Michael Elliott would be the one who changed things. Dont get his individial bias mod. Try to make the amps as original as possible. We have tubes for them. 

You need a schematic and some good diagnostic skills to get them going. 

Concerning tone controls, thank you,,, very good to know

It appears in design the good ideas are only done briefly by the few yet the bad ideas are done by the many and go on forever.

I think the choice of a single hinge point was the biggest mistake. Its actually easier to split them in two which I did in the C-4 preamp.

@bdp24   Roger, could it be the old 1kHz frequency was chosen in relation to the RIAA equalization curves?

That would have been a better choice resulting in 500 Hz for the low hinge and 2 Khz for the high. I would prefer a larger gap as stated earlier. The single point of 1 KHZ is trying to hit the middle numbers wise but not sound wise.

The RIAA points were chosen by the density of program material. BTW the RIAA curve we are familiar with that is 40 dB of EQ from top to bottom is not the RIAA curve. It is the RIAA plus MM/MC curve.

The RIAA playback curve for a semiconductor cartridge is only 12 dB from 500-2,000 Hz. Thus RIAA boosts the highs 12 db and cuts them 12 dB on playback... Does anyone find this interesting or alarming that we call the RIAA curve the big one and not make much mention that it is for velocity transducers only?

@atmasphere 

Does anyone find this interesting or alarming that we call the RIAA curve the big one and not make much mention that it is for velocity transducers only?

Ralph please explain your comment below.

No. Its well understood that is the case. There has been some controversy over other types of transducers as you point out, won't be properly equalized. IMO/IME the producers of such cartridges should offer their products with an equalizer to set things right.

Would readers care to comment that this is news that the RIAA curve is only 12 db not 40 db bottom to top.

Producers of amplitude cartridges do provide EQ, they have to in their box that powers the cartridge. Sao Win tried to EQ mechanically with little success. I built the equipment so he could measure his cartridges (which he did not before). Soon after he gave it all up from frustration of lack of uniformity. 
 
A year or two ago the Panasonic cartridge was reviewed with its"box" and there were great errors found in the resulting frequency response. The reviewer was a bit disappointed that these people could not get it right. 

Hey Roj, Its Verastarr Mikey..

Id like to know when we roll tubes and hear differences that are so different and unique even when its the same exact tube type, how and what exactly are we hearing ? Lets take 2 6sn7GT for instance, that for the purpose of this question have near identical electrical characteristics.
Thanks man !

First how many of the characteristice are near identical. Mu, Gm, Rp and bias point. These vary widely. With 6SN7s microphonics can play a large role.

I cannot comment on what you are hearing. If you want to be sure of what you are hearing it takes two identical circuits for the two tubes, an A/B switch, matched levels. We find with many listeners that the difference we hear rolling tubes are small enough to disappear. One cannot just swap a tube, we have found the sonic memory to be too small.

I did a strict A/B for 50 people in the SFAS. They looked at me and said. Hey these all sound the same, where are the differences.

Given that they want differences, we are repeating the test this saturday and will not A/B. It takes away all their fun when thinigs sound the same Sorry, but good equipment sounds good.

Because I test a lot of tubes, use them in off book applications I get to see some real measurable differences but then the tubes are actually different on the test gear too. A curve tracer will tell you a lot. 

The question I have is why do you want these differences?

If you could design your own preamp wouldnt that be more rewarding than swapping parts?

@atmasphere 

Try telling the manufacturers of cutter electronics that.

How about telling us about the cutting process? The range of constant velocity cutting and range of constant amplitude cutting. 

I was not discussing cutting, but you appear to have something to say. I simply wanted to inform the readers here that the RIAA curve they generally see is not the RIAA curve but the RIAA plus EQ for velocity cartridges. From what I read the Amplitude cartridge people still have not caught on..

@ atmasphere

So what is the cutting curve? Can you show us please?

 @atmasphere 
Ralph, How about a curve. People here cant understand what you said, can anyone?

Can you ever give a simple answer?

From 500 Hz to 2000 Hz the response on the record is lifted at a rate of 6 dB/octave for two octaves. Thats 12 db total. Is this your understanding?

Ralph

Thanks for the link. It is clear to me that above and below 1 KHZ there is 6 dB of EQ on either side of the red line, making a total of 12 dB as stated before.

To be clear I am not talking about what is fed to the velocity sensitive cutting head but what is actually in the groove and what one must compensate for with a constant amplitude cartridge. It is interesting to note that in the better RCA consoles of the 1950s RCA actually applied this 12 dB shelf to their crystal (amplititude sensitive) cartridges. I dont know anyone else who did. 

The time constants are indeed 2 octaves apart at a rate of 6 dB/octave. Of course the corners are rounded but the eventual preemphasis is 12 dB starting at 500 Hz. 

See figure 2...  https://www.stereophile.com/features/cut_and_thrust_riaa_lp_equalization/index.html

This is also interesting. https://en.wikipedia.org/wiki/RIAA_equalization

Since the readers here dont seem too interested, I am going to sit this one out. 

@atmasphere To the third, a correct answer requires a correct question- the **response** is not raised; the **pre-emphasis** is, and by about 5 db (so the simple answer is thus 'no'). Remember that the curve is just that and is the amalgam of three timing constants. The range of frequencies to which you refer is the area where the response is relatively flat compared to the rest of the curve. It isn't flat because of the ordinates of the timing constants. So its a gentle curve in that range, and the **pre-emphasis** is 'lifted' by about 5 db over that range, not 12.

 
There are plenty of images on the web. Fig. 2 of the article at the link below is pretty good- you can see the 5 db or so rise in the pre-emphasis in the range of frequencies about which you asked:

We are talking about just two time constants that are at 500 HZ and 2200 Hz. Surely you know that time constants or frequency corners are defined points where the response is 3 db up or down. Since these are first order they eventually (within the audio range) come to be 6 dB. Thus 6 db rise for the first pole and 6 db loss for the second. 6+6 = 12 dB.

This is also confirmed by graph you presented from Stereophile. 

I am simply trying to tell readers that the high end of a disc is cut 12 dB higher above 2200 Hz. Also that the RIAA playback curve they are accustomed to seeing is for a magnetic (velocity) cartridge and the one for a displacement (strain gague) would be only 12 dB top to bottom as apposed to 40 dB.

How can you disagree?

I forgot the great Leak and Quad amps, low powered but wonderful

.

They are indeed. The Leak is a rather standard circuit as I recall. However the QUAD 2 has a very interesting circuit. Unique, thoughtful.

I sell more of my 35 watt than my 100 watt amplifier. I also get calls for the little EM7 2.5 watt single ended. How can some do with so little power and others "think" they need all those watts? Truth is nobody measures and the majority guessing are way off.

These older amps may be low powered in todays numbers but adequate for listening with reasonable speakers. I saw a 190# SS amp for sale here for $40,000. Now who needs that.

can you find the thread. I had no luck.