Sound Quality Vs. Measurements

[gk7]

Thank you.

 

[210]

Hallo Torsten!

Based on personal knowledge, experience and measurements
I can tell you the two golden rules of Sound Quality Vs. Measurements:

Rule1) A musical sounding amplifier just produces odd order harmonics when it starts to clip.

Rule2) A transparent sounding amplifier has low overshoot and settling time (tip: can be reached with fet-input).

Regards,

 

[210]

 

[tvrgeek]

All amplifiers sound the same!

There, now it's been said. Bookmark this post, folks, so you can quote it later as needed.

I have absolutely no question that amp-driver combinations sound different changing only the amp part of the system. None. Zero. I can clearly hear it, my wife extremely so. If you are so lucky not to hear a difference, you have an advantage over the rest of us as you have more beer money. Bookmark THAT.

Anyway, books came. Reading Self first. I am starting at the beginning, that is by understanding the numerous variations of the LTP. Sure is a lot of variations and that is not even looking at the connections for feedback. Searched the web and came across several discussions here. (Jan, you may remember some). Also went through all my old hobby DIY type magazines to read Nelson's, Jan's, and Erno's contributions among others. It is interesting to see how thinking has changed from the early 80's to now. Step two is to reverse engineer the samples I have and breadboard a few that look interesting with modern parts. Any advice in the modern part arena is gladly welcomed. I seem to remember some comments about basic differences in NPN vs PNP that could explain why one was selected over the other. Any feedback on that topic is also most welcome. ( I should use FETs anyway, right?)

Thinking more on measurement and perception. The issue could just as easily be a "good" amp actually degrading something that masks a driver problem as it could be a "bad" amp being basically correct allows a driver problem to persist. This leads to a logical question: If my speakers were good enough, would we still hear a difference in the amps? To throw a wrench in all that, cheap commodity amps universally sound pretty poor with my commodity speakers. Some mid range amps sound fine, some do not, Most really good amps sound fine, a very few do not. ( within the sample I have had the privilege to listen to in my home. Probably about 30 or so amps.) With this observation, the best of the best would universally sound "bad". Can't say that is so.

Digging out obsolete datasheets may be the biggest problem in reverse engineering my various schematics.

 

[revboden]

Of course it depends on how bad or good things are, but in general I'd say good speakers matter more than the amp.


edit: not saying that a good amp can't help a good speakers performance. (if they like each other)

 

[tvrgeek]

Absolutely, no question. Speakers are the biggest problem. The very best are pretty poor. But, the jest of this thread is how different amps sound on the same speakers. Speakers should cost several times what your amp does or you have not spent your money for the best bang for the buck. My two cents of course.

If you wonder, I am using first generation Paradigm Studio 20's with a modified Bheringer crossover to my own peerless based sealed subs. The 20's were great for the price and actually pretty good. My subs are very good. I also have several pairs I made, some old Kef Q1's and even an original pair of Faccets. Back to the books.

 

[tvrgeek]

Hmmm...
If my speaker has a zobel or sufficient compensation to present a resonantly well behaved load, does the amp still need the output zobel? This is one of the places I have considered that could be causing my "delay" symptom. Also, inside or outside the feedback loop is something else to think about. Always wanted to try 4 wire sense at the driver but that is a lot of additional parastatics to profile. Guess internal self powered has the advantage there.

 

[Wavebourn]

Of course it depends on how bad or good things are, but in general I'd say good speakers matter more than the amp.


edit: not saying that a good amp can't help a good speakers performance. (if they like each other)

I disagree. Good singers, musicians, composers matter more.

 

[tvrgeek]

I stand corrected. I guess I have to admit the recording engineer is the next most important link. Unfortunately, I can't do anything about either.

 

[john dozier]

If you think the 20s are good, try the Signature 1, v3. And yes you can do something about recording quality by supporting good engineers as listed in the credits. Regards

 

[210]

I think, amp-feetback (typically?) has the hardest job to do,
because it has to correct all the misbehaviour of the circuit.

 

[godfrey]

I tend to feel sorry for the input stage, because it gets blamed for everyone else's mistakes.

Internal mutterings of a feedback amp:
Feedback network: Oh look; the output stage is clipping. Let's go beat up the input stage again, that should fix it.
Input stage: sigh....
2'nd stage: O no! What they gonna do this time, switch me off or saturate me so bad it hurts?

Happy weekend, everyone!

 

[tvrgeek]

the 20's were really good for the price. Most of their line is. Really good value. There is a big step up available and they must be 15 years old. Drivers have gotten better. The S2 drivers look really impressive on the slick sheet. Maybe worth a hear. There are no pure beryllium domes available for DIY. I know I am getting somewhere when I build speakers that are in all ways better. Close last time, but no there yet. My last crossover put my Dayton/Vifa pair somewhere between my Q1'a and the 20's. My cabinets are better, crossovers better, but I need a big step in the driver department which means bucks.

Back to amps. Smaller amps tend to sound better to me that big ones, in the range I can even dream of. Thinking why. Less gain and what that means to the linear range of the devices ? Gain of 25 not 35 for example.

 

[abraxalito]

Back to amps. Smaller amps tend to sound better to me that big ones, in the range I can even dream of. Thinking why.

Here's a hypothesis for that. Small amp means small transformer, less capacitance to mains. So lower magnitude of common-mode RF currents flowing around the big loop between amp and pre (if its a poweramp) or amp and source (if its integrated).

 

[Pano]

Large amps have too many parts. The sounds get lost and confused along the way.

 

[ThorstenL]

Hi,

Here's a hypothesis for that. Small amp means small transformer, less capacitance to mains. So lower magnitude of common-mode RF currents flowing around the big loop between amp and pre (if its a poweramp) or amp and source (if its integrated).

We can easily lay this one to rest.

Only amplifiers of incompetent design will use generic mains transformers that allow large leakage from the mains (common-mode or differential-mode).

It is quite trivial to specify suitable means to minimise this for any kind of transformer size. It is both common and law in medical device designs so it is really nothing out of the ordinary or esotheric...

Ciao T

 

[ThorstenL]

Hi,

Back to amps. Smaller amps tend to sound better to me that big ones, in the range I can even dream of. Thinking why. Less gain and what that means to the linear range of the devices ? Gain of 25 not 35 for example.

I take it here you mean "lower power" when you write "small"?

I know this chap, his 2W SE Tube Amp has a DF (Dunker Factor) or 25 and is the size of a large side-table, it is most emphatically not a "small amp".

If for low power, there are several mechanisms we may include.

A lower power amplifier requires lower voltage supply rails. Until rather recent times generally, the higher the rated breakdown voltage of a transistor the poorer it's linearity (Beta, Gm), the lower it's Ft, higher parasitic capcitances and so on.

Equally, when using a single output pair a lower power amplifier can use transistors with lower rated collector current and power, again, this generally meant the ability to use parts with more favourable parameters for audio use.

Paralleling output devices can introduce it's own difficulties and so amplifiers with single output devices MAY be preferable to having to parallel devices, but this case is much less clear-cut.

There are of course exceptions to every rule and we nowadays get quite good highish voltage transistors etc. even compared to 10-15 Years ago, so most of these rules can now be thrown out of the window now and you can always make a high power amp by bridging two lower power ones, with some added potential benefits (which are not always realised of course).

Ciao T

 

[abraxalito]

Only amplifiers of incompetent design will use generic mains transformers that allow large leakage from the mains (common-mode or differential-mode).

I did say RF, explicitly. And RF is not going to fall in the category 'large'. Differential mode leakage is inevitable if you want to, you know, draw power from the mains.

It is quite trivial to specify suitable means to minimise this for any kind of transformer size. It is both common and law in medical device designs so it is really nothing out of the ordinary or esotheric...

Medical safety has spec for RF leakage currents? If so, do you have a link, I'd like to follow up.

 

[a.wayne]

Here's a hypothesis for that. Small amp means small transformer, less capacitance to mains. So lower magnitude of common-mode RF currents flowing around the big loop between amp and pre (if its a poweramp) or amp and source (if its integrated).

If so, wouldn't 2 smaller( or multiples) transformers be better than one big one ...?

Hi,



We can easily lay this one to rest.

Only amplifiers of incompetent design will use generic mains transformers that allow large leakage from the mains (common-mode or differential-mode).

It is quite trivial to specify suitable means to minimise this for any kind of transformer size. It is both common and law in medical device designs so it is really nothing out of the ordinary or esotheric...

Ciao T

Whats considered "generic" ....?

 

[abraxalito]

If so, wouldn't 2 smaller( or multiples) transformers be better than one big one ...?

I've made a few measurements and using two smaller transformers in parallel gave higher capacitance to mains than a single larger one within a particular construction style. I hesitate to generalize to between all transformer styles - R and EI core types offer less capacitance overall than toroids.