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In Reply to: RE: Initial A/B test between PP and SE 6bq5 amps posted by hahax@verizon.net on June 23, 2017 at 19:30:38
"Intellectually it has always bothered me that single ended amps are asymmetrical, that is they crop the negative half of the wave form, compress it relative to the positive half. "
Tubes want to turn on more than they like to turn off.
DHTs less so.
What you describe is the behavior of a tube with plate curves that have narrow spacing of the grid lines to the right and wide spacing of the grid lines to the left of the idle point.
Take a look at the plate curves of a 300b above (or 2a3 or 45 or 845 or 211). You don't see this un-even spacing between the grid lines.
The plate curves in the post below are that of a triode wired KT88 where you will get the affect you describe.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
for whats its worth Säkuma has been recorded as saying that he likes the beauty in the treble of his 10y pp preamp and the power in the mid-range of his se amps. I believe he likes to mix both to achieve a balanced sound. maybe both se and pp fail and excel in different objectives.
I believe in ten years there will be chip amps that will be so good that they will render this hobby redundant though it may take some of us another twenty years to accept it.
It's not SE vs. PP that accounts for the affect you describe but the tubes themselves.PP just "hides" this affect to some extent.
If we use linear tubes, operated and loaded properly it's not a problem to start with.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/23/17
The problem is not the type of tube. It is single ended topology, the circuit itself so there is no way to get rid of it. I've checked with many designers and had it confirmed. Nelson Pass agrees, for instance and he is a fan of many things single ended amps do.
"The problem is not the type of tube. It is single ended topology, the circuit itself so there is no way to get rid of it. I've checked with many designers and had it confirmed."
Actually, the "problem" is not with the circuit topology or the tubes, it is that you are relying on your interpretation of what you think "many designers" are saying. If you try to understand the theory that Tre' is explaining, you can rely on your own sound judgement to make your own assessment.
I'm obviously not a designer but as previously mentioned would you consider Nelson Pass knowledgeable on the subject, especially since he is a fan of single ended amps? And he told me that they are asymmetrical amps. And other designers, one of whom designed a single ended amp, who have designed PP triode amps have told me the same.If I recall correctly the affect is into a real, world reactive load rather than a simple resistive test load.
And yes, I will admit to being a curmudgeon here.
Edits: 06/24/17
Please explain how a tube used in a PP circuit magically becomes linear when the tube itself is not?The output of a PP amp can be more linear than the output of a SE amp when using non-linear tubes but each tube remains non-linear.
Or, to turn it around the other way....
Please explain how a linear tube magically becomes non-linear when used single ended?
We have only been talking about the output stage of a system.
What about a preamp stage or the input stage of an amplifier.
If it is single ended, using extremely linear tubes like a 6sn7, does the output of a SE preamp magically become non-linear (asymmetrical)?
If you believe that then you need to show me.
Take a look at the plate curves of a 6sn7 above.
I've plotted a horizontal load line (CCS loading) at about 14ma, 200vdc plate.
Can you show how the output of the 6sn7 becomes asymmetrical just because the circuit that it's used in is SE.
In a PP or SE amplifier circuit any asymmetry in the output waveform has to start with asymmetry of the tubes used.
With PP most of the asymmetry of tube #1 is canceled by the asymmetry of tube #2 but that is not the same as saying that in the absences of a PP circuit the tube itself becomes anymore asymmetrical than it is to start with.
Here's what I'm trying to explain to you that I don't think you understand,
A SE circuit doesn't cause asymmetry, it just allows the asymmetry of the tube being used to show up at the output while a PP circuit hides that asymmetry.
So if you're going to use a SE circuit, you need to use very linear (symmetrical) tubes.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/25/17
Try drawing a 5k SE load on an HY51A's plate curves. Idle point at g=0V, 100 mA( around 590V at the plate ). Take a look at what +/-30V of grid voltage will do for you...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
That is what I got from my tests too. I compared three different SE amps; 813, 45 and 6bq5 with a test setup that allowed me to switch between two amps with the push of a button while both amps remained on. I could hear virtually no difference between any of the SE amps, but when I compared a PP 6bq5 amp to the 6bq5 SE there were audible differences. I believe they were due to the topology. I have also read several articles that report basically the same results.
Listen to TRE.Think of it this way-- a PP circuit is a processor-- it forces
reduction of signals and distortions found in the Common Mode--
including musical artifacts that are in the common mode (not all parts of music are). Since most of audio here in the States uses 60 HZ A.C. power,
PP and/or balanced circuitry is commonly used to PARTIALLY SHORT OUT
A.C. interference that is Common to both sides of a signal--
hence, the "Common Mode" moniker. Of course, some artifacts
of music are also found in the Common Mode, so they also get reduced/processed by a PP and/or balanced circuit.Single-Ended cannot do this. The only thing it can do is amplify
ALL of the signal, which includes both the negative and positive of it.That is why S.E. sounds more real. It hasn't been processed.
S.E., of course, is much more expensive and harder to build right.
If you don't do a lot of exotic engineering and spend some real
money on S.E., you will prefer the easy to get extra bandwidth and power
with PP-- and that is why most users have PP amplifiers.They're NOT getting ultimate musical expression with PP. What they
have is easy to get POWER and lots of EASY TO GET bandwidth.Since Common-Mode reduction is inherent to PP topology, low hum
levels and low distortion measurements are EASY TO GET-- allowing
MUCH cheaper parts and engineering costs and MORE power.S.E. has only one saving grace: it can actually reproduce music the
way it was recorded.No PP amp has ever done that-- or ever will.
-Dennis-
Edits: 06/24/17
"Of course, some artifacts of music are also found in the Common Mode, so they also get reduced/processed by a PP and/or balanced circuit."
Could you please define precisely what you are meaning when you use the term "common mode"? As normally understood, it refers to a signal that is common to both the inverting and the non-inverting inputs of a differential amplifier. From the context in which you are speaking, it appears you do not mean this. Therefore, a precise definition of what you intend to mean by "common mode" would perhaps be helpful.
Chris
Nothing wrong with your understanding as far as diff-amps go.
We're talking about the same thing. Common-Mode signals (common to both positive and negative going parts of a signal), can be found in many
places in a balanced or push/pull circuit.
When you holler at someone, or when a piano plays, there is only
a single-ended signal. Same as when your dog barks at you.
IF we record this with a single-ended microphone, then the signal is
still intact at that point-- it is still Single-Ended.
Now, let's record with a different microphone-- one that has two generator coils (balanced dynamic mike as an example). Then, let us connect a Center Point equidistant from the two windings-- between them.
Now, we can collect positive going at one coil's output, and at the same time, we can get the negative going sample at the other output.
We have a center-balanced circuit now. Anything that is contained in BOTH
outputs AT THE SAME TIME is cancelled by the Center Connection. We have installed processing-- we have installed CMR or Common-Mode-Reduction.
Why is it called CMR (CM Reduction) instead of CMO? (common mode obliteration!). That's because the generator has both resistance and back-EMF (electro-motive force)-- cancellation is not 100%-- Common Mode is reduced, not eliminated.
Another example would be a twin-generator mike where each coil had it's
own twin output leads, and were not Center-Connected.
Each coil could independently drive a S.E.-input amplifier-- the two amps
could be coupled into a single push/pull amp-- and presto! At that point we have once again installed CMR.
There are many points in a P/P amp where CMR can be installed-- an
example is on a tube's cathode. The cathode resistors for a two tube
gain stage could be tied into each other, after the cathode connections,
and then this common point can be returned to ground. CMR has once again been installed. You could do this with a double-winding transformer also.
Another example is G2 operation in a Tetrode, or in a Pentode P/P amp. Ideally, G2 gets its own separate power supply. One could run the B+2 to each G2 and have a little CMR there between the two amp stages-- that occurs in the common power supply.. OR-- one could give EACH G2 its own series resistor, connect the two resistor end points together in a Common hookup, then connect this to B+2. You have just improved CMR in the amp tremendously. It will sound faster, cleaner,
"hotter" and MUCH more "on-time"-- musical transient pace, rhythm, and timing....
Two power chokes can be installed as a CMR device. Even in my S.E. amps,
I am using a double-wound power choke. The two coils are operated counter to each other, but the choke's iron core is common to both windings.
Even though this choke is in series with a single-ended D.C. power
system, Common-Mode-Reduction has been successfully applied to
quieting the power supply. Pioneer, as an example, likes to use
CMR chokes on the A.C. line input to some of their high-end Blu-Ray
players. CMR power conditioning......
There are many more ways to understand the Common-Mode that I
can't think of at the moment, but rest assured, studying this area is
a big deal.
In GENERAL-- the more places and ways you can find to install
CMR in any push/pull amp or in any balanced circuitry of any kind--
the better it will sound. The results of applying CMR are large.
In GENERAL-- any attempt, whether on purpose, or accidentally--
to install any form of CMR to a Single-Ended signal will seriously
degrade it, unless you are just trying to strip the A.C. line hum & noises from the signal. This is a compromise that you have to
think about for quite a while before you get all that you can get
performance wise-- musically. Overdo filtering of any kind here-- and your S.E. amp has just become "ordinary" sounding...
In GENERAL-- one has to decide whether to honor music as #1, or
whether theory is all there is. Of course, one has to look at BOTH.
BUT-- that isn't the question. What combination of all of these ideas, and more, is going to really "kick-butt" and put the musicians in
your listening room-- fully intact, not just impressively for some kinds of music.
"It's A Long, Long Way to Tucumcari".
-Dennis-
Let's just stick to the original statement
"Think of it this way-- a PP circuit is a processor-- it forces reduction of signals and distortions found in the Common Mode--including musical artifacts that are in the common mode (not all parts of music are),"
since I don't think any of the further complications of microphones with two coils, etc., added anything particularly useful.
You appear to be saying that if you just take a perfectly standard unbalanced audio signal, e.g. from a CD player or a record player, then some of the musical content is in "common mode" and some is not. Sticking just with this case, can you give a definition of what you mean when you say the signal is composed of part that is in common mode and part that is not?
It doesn't seem to me that there is any notion of part of a musical signal coming out of a standard unbalanced source (one "live" wire and one ground wire) having any "common mode" part. It is just a signal on a single wire.
Therefore I ask again, for this simple situation, if you can define what you mean by the "common mode" part of that musical signal.
Chris
and your skill at using terms and phrasing to bash All But Yours, is without Peer.
It is, as a technical description( as it is presented ), a complete load of misinformation. Cattle exhaust, male, solid form.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
"Now, let's record with a different microphone-- one that has two generator coils"
There is only one coil in a microphone.
Each end of that one coil (one piece of wire) is connected to the primary of a transformer in the mic body.
The secondary of that transformer is connected to the primary of the input transformer of the mic pre through a 2 conductor, shielded cable. Only the shield is grounded.
Neither end of the secondary of the mic transformer or the primary of the preamp input transformer is connected to ground.
The only thing that gets rejected by CMR is the hum and noise picked up in the cabling between the two units, not any of the audio signal.
None of the audio signal produced by the microphone coil moving in a magnetic field is rejected by the CMR of the balanced connection between the secondary of the mic transformer and the primary of the mic pre input transformer.
You do not seem to have an understanding of what CMR is or how it works.
You really need to forget what you think you know about this subject and read a book.
Good grief Dennis!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
What it means is he is a SE amp salesman, and this 'loss of music' is one of the boogie men he chooses to blame PP for having...;)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
It sounds like you think he DOES understand this stuff and is just playing games?I'm not convinced he understands much at all so (in my mind) he is sincere but terribly misguided, but I could be wrong.
You may be right, he could just be jiving everyone.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/27/17
You are reading things into my post that are not there. I did not say the pp amp sounded better than the se amps, only that it sounded different. I have been building and listening to SE amps exclusively for 15 years now, so you are preaching to the choir. My post simply says that I did not hear differences due to the tube type in the se amps, but I did hear a difference between the pp and the se amp. In other words the tube type does not matter, it is whether it is a pp or an se amp that matters.
Edits: 06/24/17 06/24/17 06/24/17
Everything, of course, matters.
If all the S.E. samples sound like S.E., then I agree with you.
If they all sound the SAME-- then your system isn't transparent
enough to show you the enormous differences in tubes...
Anyhow, I wish all of you well. One could talk this thing
forever and get nowhere, or one could learn from it.
Prosper and do well! -Dennis-
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