Old School vs. New School Amplification

[agedhorse]

So a digital wireless is the exact same thing as a digital amp? I think not.

You are right, it's generally FAR worse representation due to carrier bandwidth limitations.

 

[iunno]

[rant on]IMO, there is so much bad and mis-information mixed in with all this crap (in this post and others like it) that it's doing a serious dis-service to most folks here.

First of all, class d PWM, and digital representation of a signal is sampled so fast (typically 500,000 times per second) that the representation is absolutely correct to within a few parts per million.

Secondly, who says a square wave is ugly? A square wave is just a series of sine waves!!!

Thirdly, just about EVERYTHING you listen to anywhere in the world is either created, recorded, processed, mixed, delivered, play back and/or amplified with DIGITAL technology. Reproducing bass with a class D amp is trivial compared with what the industry can do.

And for your comment about class A being pure sine wave in, pure sine wave out, that too is pure crap. It CAN be, just like class AB, G, H, and D, but most often class A as used in preamps (it's not used in musical instrument power amps) is intentionally designed to enhance the natural non-linearities and distortion... doing so in a hopefully pleasing way (for some). A quick glance at the transfer function curves of the commonly used topologies along with THD numbers make this totally obvious to those who understand the science.

This post is not addressing your comments but others too that misrepresent the facts, science and engineering behind amplification which seem to be perpetuated the most by those who understand it the least. The best end results of any amp design is achieved by those who understand the art, the science and the reliability metrics that the serious players are looking for. This can be achieved with tubes, solid stand, and a combination of the two, depending on the skill and motivation of the designer. [rant off]

A simpler, less modified signal path is going to be cleaner than a heavy modified one like in class D. Show me even one example of a Class D amp sounding better than a similar quality class A/B. Or, show me an example of a touring musician with a relatively clean tone who uses a class D.

There are Class A power amps, as I've said I've heard one.

Guitar vs Bass doesn't really matter, a Bass has plenty of overtones, you aren't only amplifying bass frequencies. I don't know why you would even suggest that something that can't reproduce treble frequencies properly is going to be the same or even superior to something that can.

If class D was as good, I'd be all over it, but I want the best tone possible, which just does not happen with Class D. I think people just want to believe their little tiny amps are the be all end all, with no sacrifices for all the weight lost whatsoever.

Here's a blind test between an A/B and a D from the same manufacturer. There's a pretty clear difference to me, it's not huge but it's certainly there.

 

[agedhorse]

I wish I could set up a blind test for you and a bunch of my gear. I bet you a penny you dont pick out all tube vs full solid state.


Additionally I am not saying SS or any particular topology is better than another. Just pointing out that when it comes to amps, there is no "best".

I'm in with this, it will be eye opening and ego deflating at the least

 

[JimmyM]

You are right, it's generally FAR worse representation due to carrier bandwidth limitations.

While I totally believe that, I'll tell you...I really like my digital wirelesses and dislike digital amps like Line 6 and TC and all that They're not even good ones...old X2 pedalboard wirelesses from 2008.

 

[agedhorse]

My Bad Cat Hot Cat 100R is 4XEL34's Class A Cathode Biased.
So is the Hot Cat 30.
Matchless Amps are built that way too.

Sir, may I suggest that you understand the topic you are discussing better than you do so that you bring some factual representation to your argument?

Your Bad Cat 30, and all of the AC-30 varients are not really class A, they appear to operate closer to class A for the first "few watts" but transition to class AB above this. If you were to analyze the quiscent dissipation curves, you would see that it is simply impossible to maintain class A operation for more than say 10-15% of their rated output, and some even less than that.

The AC-100's and their varients are NOT cathode biased, they are fixed bias with a little added sponge resistor in series with the transformer primary, so if you think these are good sounding because they are cathode biased, you are quiute mistaken

The major reason why the amp sounds and feels different than fixed bias is because there is a different local feedback mechanism present and this is happening at the lower frequencies where the cathode bypass cap is functionally in transition, along with any (typically low level) global feedback that may be present. The way the output stage is driven, and how the output transformer interacts with the cathode biasing network all combine to give the cathode biased amp it's somewhat characteristic sound and feel.

Unfortunately for everybody, the marketing folks have contributed greatly to the distortion of facts in their quest to sell their products. This, IMO, serves only to "un-educate" the customer rather than teach them meaningful information that would suit their desire to understand better.

Sorry for being the bearer of bad news, but IMO better this than the perpetuator of all these silly myths.

 

[agedhorse]

A simpler, less modified signal path is going to be cleaner than a heavy modified one like in class D. Show me even one example of a Class D amp sounding better than a similar quality class A/B. Or, show me an example of a touring musician with a relatively clean tone who uses a class D.

There are Class A power amps, as I've said I've heard one.

Guitar vs Bass doesn't really matter, a Bass has plenty of overtones, you aren't only amplifying bass frequencies. I don't know why you would even suggest that something that can't reproduce treble frequencies properly is going to be the same or even superior to something that can.

If class D was as good, I'd be all over it, but I want the best tone possible, which just does not happen with Class D. I think people just want to believe their little tiny amps are the be all end all, with no sacrifices for all the weight lost whatsoever.

Here's a blind test between an A/B and a D from the same manufacturer. There's a pretty clear difference to me, it's not huge but it's certainly there.

1. The signal is not heavily modified, I have never implied this and if you understood the math you would see that it can be LESS modified than many class A circuits that you hold in such high esteem.

2. Yes, there ARE class A amps. There has not been and of these comments that relate to any of the real class A amps. REAL class A amps are uncommon, especially above say 10-20 watts.

3. I never said ANYTHING about amplifying bass FREQUENCIES, I said bass which includes all of the associated harmonics. The harmonics ratios are such that it taxes the high frequency portion of any amp less than the lower frequency portion.

4. You are stating that class D amps cannot reproduct treble frequencies properly as a fact. I am now asking you to PROVE this, and it would be helpful to show the math because the math AND the measurements show otherwise.

 

[ordinarySUPERLOW4]

what is the sample rate if the class D is so digital? (newb to class D)

 

[FFTT]

As far as bass amps for recording mic'd up, sometimes its about what you hear or don't hear between notes, between phrases and as the note rings out or as it begins.
Does the amp have fan(s) or other sources of self noise like hiss?
Is the sound dry, processed, cool, warm, and how does it sit in the mix?

Is the sound versatile or more specialized, same with the instrument.

Regardless of what type of rig you put together, the goal is to best suite your own application or several applications and hopefully to spend wisely.

There is a lot of really cheap junk out there, so how do you know what good design is without looking beyond the price tag.

I chose my Reeves for purdy much the same reason as I chose my '99 Tacoma 4X4 SR5 V-6, because it will climb a mountain and last damn near forever with reasonable care. 285K and counting.
I can afford to buy nice amps because I don't have a car payment to deal with, so over the long haul I've benefitted in the total cost of ownership.

I'm not going to tell you that you are just spoiled because you have $30K into a Harley or a Speedboat, or some other prized possession.

There will always be strong opinions when ever you discuss new products and compare them to legacy benchmarks.

Those benchmarks have become reference points because they are time tested and well proven.

 

[agedhorse]

what is the sample rate if the class D is so digital? (noob to class D)

Good question. A PWM sample or time slice is made at a rate of ~300,000-500,000 times per second with the most common high performance class D amps used in this industry. This PWM pulse train (which is an amplitude to time duration transformation) can be re-integrated back to the original signal (within a few parts per million) because it's just a different way to represent the same signal, there is no data compression or loss involved, it's not digital because there is no data, no words, no bits, no memory, etc.

 

[ordinarySUPERLOW4]

300,000-500,000 times per second

To me, this is a perfectly suitable rate to be used in professional bass guitar applications. certainly inaudible. even faster than 96K so it dont matter in recording resolution much.

 

[agedhorse]

Excuse me FFTT, I specifically and clearly referenced ALL AC30 varients (there are probably 25 or more by 25 or more different companies, including one that I designed), it was YOU who specifically mentioned YOUR Bad Cat, and I was referring back to YOUR quote for clarity out of respect to others who are following this thread. I said nothing and implied nothing about any other brand regarding anything to do with tone, quality, size of company or country of orgin, or anything else. For you to imply that I did is disrespectful to me and everybody else here who is acting responsibly and IMO you have crossed the line with your comments.

I politely and respectfully suggested that you understand this topic better because your lack of factuality is confusing and misleading to others here who are trying to learn and understand. Your comments to me and ANY of the companies that I may happen to work for were totally uncalled for and I keep any potential commercial vested interest out of these discussions.

 

[agedhorse]

To me, this is a perfectly suitable rate to be used in professional bass guitar applications. certainly inaudible. even faster than 96K so it dont matter in recording resolution much.

This is not quite an exact comparison because the 96kHz sampling rate number numerical data points rather than the number of time duration slices (or samples). The reconstruction of the two representations is done differently though there are some similarities. I wanted to comment so that this comparison was not misleading, specifically because they do share some similarities as well.

 

[Bob Lee (QSC)]

If class D amps really sounded as good as others, you would see guitarists using them as well.

Quilter Labs amps are quickly gaining in popularity.

 

[agedhorse]

An AC30 type amp IS cathode biased, as is a cathode biased HC amp such as the BC-30 which according to the schematics in public domain is a classic implimentation of the cathode bias topology. I do not see any indication that this is the case on the 100 watt amp however and the Vox AC-100 is not cathode biased. It should be noted that these topologies and their AC designations came originally from Vox, the AC-30 is cathode biased and the AC-100 is adjustable fixed bias. This is fact.

Class A power amps are entirely different from having class A preamps.

From all of the schematics viewable in the public domain, the AC-100 varients are not cathode biased. This is fact based on the definition of cathode bias topology, not an opinion. I don't know what the companies are claiming, you are the one who made the statement. If it's wrong, it's wrong. If you don't recognize that it's wrong, or you do not understand what cathode bias topology is, don't defend something you don't know.

I did not challenge your integrity, I challenged your factually inaccurate posts and information.

 

[Bob Lee (QSC)]

control of the speaker cone.

Are you really saying that control of the speaker cone is a bad thing? That is what tube amps are weakest at.

 

[Bob Lee (QSC)]

Class A outputs signal that is the most true to the analog input, that's all there is to it.

Not necessarily. I've built a number of fuzzboxes that were all class A.

 

[agedhorse]

Quilter Labs amps are quickly gaining in popularity.

Agreed, I recently provided PA for a tour date that brought a few "works in progress" chassis and amps out on the road. Can't remember if it was Hot Tuna, Robert Randolph, Ani DiFranco or the Outlaws (unfortunately, shows kind of run together with a busy schedule), but I remember thinking how funny it was that Pat went full circle from guitar amps to pro audiio and back to guitar. I also remember thinking there was nothing at all to dislike about the sound the artist was getting. I'm now thinking it was Robert Randolph's Family Band but not positive.

 

[agedhorse]

Not necessarily. I've built a number of fuzzboxes that were all class A.

I've also built some pretty impressive class A based oscillators, a few not on purpose either

 

[FFTT]

A Vox AC100 was not class A cathode biased, but the Bad Cat Hot Cat 100R is cathode biased with a class A front end.

I use the AC100 as a reference to the amp's tonal character in the clean channel as configured with Fane drivers.

An AC30 type amp IS cathode biased, as is a cathode biased HC amp such as the BC-30 which according to the schematics in public domain is a classic implimentation of the cathode bias topology. I do not see any indication that this is the case on the 100 watt amp however and the Vox AC-100 is not cathode biased. It should be noted that these topologies and their AC designations came originally from Vox, the AC-30 is cathode biased and the AC-100 is adjustable fixed bias. This is fact.

Class A power amps are entirely different from having class A preamps.

From all of the schematics viewable in the public domain, the AC-100 varients are not cathode biased. This is fact based on the definition of cathode bias topology, not an opinion. I don't know what the companies are claiming, you are the one who made the statement. If it's wrong, it's wrong. If you don't recognize that it's wrong, or you do not understand what cathode bias topology is, don't defend something you don't know.

I did not challenge your integrity, I challenged your factually inaccurate posts and information.

 

[Bob Lee (QSC)]

Agreed, I recently provided PA for a tour date that brought a few "works in progress" chassis and amps out on the road. Can't remember if it was Hot Tuna, Robert Randolph, Ani DiFranco or the Outlaws (unfortunately, shows kind of run together with a busy schedule), but I remember thinking how funny it was that Pat went full circle from guitar amps to pro audiio and back to guitar. I also remember thinking there was nothing at all to dislike about the sound the artist was getting. I'm now thinking it was Robert Randolph's Family Band but not positive.

Pat always maintained an interest in guitar amps, and even before he semi-retired from QSC he was toying around with some guitar amp designs. He did a limited run of amps, called the Quilter Slantmaster 50, to celebrate QSC's 40 years (I bought one of them). And then when he did semi-retire, he started Quilter Labs, designing guitar amps with a lot more knowledge and experience and resources than he had in 1968. And he's really having a blast at it, as the YouTube videos will show. I enjoy dropping by over there now and then and seeing what's going on.

I believe Robert Randolph is using one of the QL Steelaire amps. Allan Holdsworth, Pokey LaFarge, and a whole bunch of others are playing QL, too. It's the end of the day and I'm too tired to remember more.