Current Class A/B amps?

[alexclaber]

[quote name='PauBass' timestamp='1435649435' post='2810877']We always record rehearsals when we are writing new songs, the difference from when I was using my DB750 to the recordings with Class D amps, confirm it for me, there's something missing, and I'm not talking volume.[/quote]

I bet it's that same thing I referred to earlier, about many lightweight amps not being able to deliver full power for long enough. So you get the attack of the note at full loudness but you don't get the WEIGHT of the note because the amp has run out of power by the time that comes through. Do you want to borrow our prototype power stage and see how it compares to the DB750's using the DB750 preamp to drive it?

[Beer of the Bass]

I'd be curious about how well some of the Class-D power amps made for PA use compare to a typical small bass head in this respect. For example, the Crown XLS series are light and not too expensive. While one of these plus a 1U rack preamp would be bigger than a micro-head it might be a useful point in between micro and heavyweight.

[Passinwind]

[quote name='alexclaber' timestamp='1435674910' post='2811291']
I bet it's that same thing I referred to earlier, about many lightweight amps not being able to deliver full power for long enough. So you get the attack of the note at full loudness but you don't get the WEIGHT of the note because the amp has run out of power by the time that comes through. [/quote]

Much as with speaker cabs, amp designers walk a tightrope of compromises to meet particular market slots. The commonly used ICE 250ASX2 can make full rated power of 500 watts bridged (8 ohms) for about 50 seconds at room temperature, yet it can only make 180 watts continuously without eventually shutting down. That's with a sine wave though, and that's not our game here. Duty cycle of the bass signal and cooling management are key factors in real world performance, and those modules were just never made with bass instrument amplification in mind. Yet many people love these amps, partly because not all of us need or crave a lot of low end energy in the lowest audible octave or two. The newer ICE modules don't need a fan at all and are predicated on a much more reasonable 3:1 duty cycle rather than the 8:1 figure that is pretty standard in home hi-fi and general purpose sound reinforcement apps (ie non-subwoofer duty). Many of us who do crave more beef down low have resorted to using multiple kilowatt pro sound amps regardless of class of operation or topology of power supply, and that can still be a mixed bag IME. And then again, as with speakers, transient response matters a great deal, so much so that the front side of the note may be more important to many than the sustain/backside aspect. IOW, there's more than one way to run an amp out of gas.

Looking forward to seeing what you come up with Alex.

Edited June 30, 2015 by Passinwind

[grandad]

Apart from recently going with the PJB Flightcase + PB300, (SMPS, Class D & Neo's), I changed the foldback from 2 x 12" wedges to a Yamaha 600i system, (SMPS, Class D & Ferrite).

The complete PA weighs 56 lbs, that's 2 x 10" wedges + powered mixer. Though I don't put the bass through it, the bass response is very good with the speakers on the floor.

[quote name='PauBass' timestamp='1435649435' post='2810877']
I'm beginning to agree with all of you that say that Class D amps lack something. I hadn't noticed much with my function/wedding band but since we are back with our loud rock band I do have noticed.
As much as I like all the Class D amps I have tried, and the one I have at the moment , more an more I'm having the feeling that, specially in our loud rock band, my bass sounds thinner. Yes, there's plenty of volume but I'm finding there's a lack of heft, the note weight is not there and this shows clearly on the band mix, I have lost my place a bit no matter how loud I turn up.
We always record rehearsals when we are writing new songs, the difference from when I was using my DB750 to the recordings with Class D amps, confirm it for me, there's something missing, and I'm not talking volume.
[/quote]

I know what you mean when you say "there's something missing". I thought so to initially but I think it maybe that one's 'focus' is distracted away from the lower frequencies to all the harmonics which are now more prevalent. I can still get my 'old school' sound with some drastic eq-ing. Attack is there as is sustain. Definitely crisper, not a soft sound.

Edited June 30, 2015 by grandad

[fretmeister]

Strewth.

I was just curious about current Class A/B amps and what was good! Not really even planning on buying, just curious!

[Guest bassman7755]

[quote name='fretmeister' timestamp='1435695458' post='2811626']
Strewth.

I was just curious about current Class A/B amps and what was good! Not really even planning on buying, just curious!
[/quote]

We basschatters never let the topic get in the way of a good argument.

[Chienmortbb]

Well the 220 Watt Ashdown Rootmaster is an AB but the higher powered unit is Class D.

Both AlexClaber and Passinwind are right. It is all about the power supply and whether the amp/power supply are designed for pro use. The ICEPower module used in the TH500 is really designed for home hifi/home cinema use and is not really suited for use as a bass amp. The one used by Pasdinwind in his latest modular amp is a whole different beast, That said a lot of people love the TH500 so what do I know. A lot of class A/B amps and Class D use chip amps designed for the consumer market and suffer from marketing hype. Power output quoted at 10% distortion,

A good Class D or Class AB or Class G or H will sound good if the content is good. And remember that most valve amps of any power is Class AB although it is usually called push pull.

Now I am fascinated by Barefaced bringing out an amp. Do you have any more info Alex?

Edited August 27 by Chienmortbb

[Dad3353]

[quote name='Chienmortbb' timestamp='1435703955' post='2811755']...
Now I am fascinated by Barefaced brining pit an amp. Do you have any more info Alex?
[/quote]

Don't press the point, it'll only rub salt in his wounds.

[PauBass]

[quote name='alexclaber' timestamp='1435674910' post='2811291']
I bet it's that same thing I referred to earlier, about many lightweight amps not being able to deliver full power for long enough. So you get the attack of the note at full loudness but you don't get the WEIGHT of the note because the amp has run out of power by the time that comes through. Do you want to borrow our prototype power stage and see how it compares to the DB750's using the DB750 preamp to drive it?
[/quote]

I'd love to Alex!....I'll get in touch by PM asap.

[quote name='grandad' timestamp='1435690812' post='2811549']

I know what you mean when you say "there's something missing". I thought so to initially but I think it maybe that one's 'focus' is distracted away from the lower frequencies to all the harmonics which are now more prevalent. I can still get my 'old school' sound with some drastic eq-ing. Attack is there as is sustain. Definitely crisper, not a soft sound.
[/quote]

Yes, I can also get the tone out of the amps I have owned/tried, as I said lots of volume, they are incredible powerful for such small amps, but once on the mix is when I find the lack of note weight, not just me, my band mates also thought so.

[quote name='Chienmortbb' timestamp='1435703955' post='2811755']
Well the 220 Watt Ashdown Rootmaster is an AB but the higher powered unit is Class D.

Both AlexClaber and Passinwind are right. It is all about the power supply and whether the amp/power supply are designed for pro use. The ICEPower module used in the TH500 is really designed for home hifi/home cinema use and is not really suited for use as a bass amp. The one used by Pasdinwind in his latest modular amp is a whole different beast, That said a lot of people love the TH500 so what do I know. A lot of class A/B amps and Class D use chip amps designed for the consumer market and suffer from marketing hype. Power output quoted at 10% distortion,

A good Class D or Class AB or Class G or H will sound good if the content is good. And remember that most valve amps of any power is Class AB although it is usually called push pull.

Now I am fascinated by Barefaced brining pit an amp. Do you have any more info Alex?
[/quote]

So, it's seems there's more to it than psychology then.

[Chienmortbb]

Yes much more than psychology. Unfortunately almost all manufacturers inflate the output specs. One well known brand has used the same power supply/amp module in a number of models and had quoted 350W 420W and 640W.

On the datasheet it shows 350W at 1% distortion. 420 peak at 10% distortion and goodness knows where the 640W came from.

[wateroftyne]

I'm keen to see what Alex comes up with, too. He seems to have a pretty good understanding of what I've been hearing whenever I've played through micros...

[gorandelac]

9 years later... so what is good class AB amp today?

[BassAdder60]

Ashdown ABM600 or 750 

[bremen]

Is Alex still here?

 

In another thread in this forum,celebrating the Gallien Krueger class AB amps,  someone linked to an interview with Bob Gallien. He says he designed the power supplies to be "not too stiff", ie with small reservoir caps so the amp was deliberately designed to behave as Alex says here. I find that a bit odd.

 

Sure enough, the schematic shows half as much capacitance as I'd usually expect to see.

 

These are great sounding, sought-after amps, no-one complains of them lacking weight/heft/loudness.

 

 

 

On 30/06/2015 at 15:35, alexclaber said:

I bet it's that same thing I referred to earlier, about many lightweight amps not being able to deliver full power for long enough. So you get the attack of the note at full loudness but you don't get the WEIGHT of the note because the amp has run out of power by the time that comes through. 

 

 

 

[gorandelac]

I mean I'm in for Class AB amps, wanna try without Class D... been there too long, so checking what are the options today.... Don't want all tubes amp.... almost bought Merlin, but it went away... damn

[Chienmortbb]

22 hours ago, bremen said:

Is Alex still here?

 

In another thread in this forum,celebrating the Gallien Krueger class AB amps,  someone linked to an interview with Bob Gallien. He says he designed the power supplies to be "not too stiff", ie with small reservoir caps so the amp was deliberately designed to behave as Alex says here. I find that a bit odd.

 

Sure enough, the schematic shows half as much capacitance as I'd usually expect to see.

 

These are great sounding, sought-after amps, no-one complains of them lacking weight/heft/loudness.

 

 

 

 

Reducing the smoothing caps will mean that the power supply rails sag or drop earlier. In valve  amps sag is often considered pat of the Tube amp sound.

Of course large smoothing caps are expensive so I suspect that was also part of the reason for going with a lowish capacitance.

 

[gorandelac]

Just found it and it's coming

 

 

[bremen]

On 27/08/2024 at 13:39, Chienmortbb said:

Reducing the smoothing caps will mean that the power supply rails sag or drop earlier. In valve  amps sag is often considered pat of the Tube amp sound.

Of course large smoothing caps are expensive so I suspect that was also part of the reason for going with a lowish capacitance.

 

All true.

 

My point, though, is that Bob Gallien says it was a deliberate decision to use a mere 2000uF reservoir caps in order to get a particular sound, and users of his amps enjoy their 'heft'.

 

So maybe, counter-intuitively; a stiff, conservatively rated power supply doesn't equate to a 'beefy/hefty' sound as conventional wisdom has it, but some sag is what's called for. In which case one of the possible reasons for some class D amps not sounding so great is that the switching power supplies in them are too good, too well regulated, not saggy enough.

 

As Deaddog remarks, valve amps sag and valve amps have heft. I wonder how much the HT rail on an SVT drops at full power.

 

I'm going to hook an olde fashioned unregulated linear power supply up to my classD amp, bypassing the smps, and see what happens. I suspect confirmation bias might win, though, so don't believe a word I say.

[agedhorse]

8 hours ago, bremen said:

All true.

 

My point, though, is that Bob Gallien says it was a deliberate decision to use a mere 2000uF reservoir caps in order to get a particular sound, and users of his amps enjoy their 'heft'.

 

So maybe, counter-intuitively; a stiff, conservatively rated power supply doesn't equate to a 'beefy/hefty' sound as conventional wisdom has it, but some sag is what's called for. In which case one of the possible reasons for some class D amps not sounding so great is that the switching power supplies in them are too good, too well regulated, not saggy enough.

 

As Deaddog remarks, valve amps sag and valve amps have heft. I wonder how much the HT rail on an SVT drops at full power.

 

I'm going to hook an olde fashioned unregulated linear power supply up to my classD amp, bypassing the smps, and see what happens. I suspect confirmation bias might win, though, so don't believe a word I say.

This kind of goes against all the mythical BS about an amp needing a big transformer and filter caps to sound “hefty”. 
 

There’s an awful lot of attributing cause and effect in the fade of multiple examples contrary to the premise.