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Class D Amps - Anyone else having second thoughts?

#122
Something I learned really well working on high speed microprocessors - at the end of the day, it's all an analog circuit.
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Yep. At one company I worked for, we had to be real careful in the narrow time slot occupied by ECL RAMs' transitions from 0 to 1 and back again. And not only that, we also had to define a 1's precise voltage. This was in a multi-board processor's L2 cache. Those chips were finger-fryers. Games with etch lengths/delays for timing to hit things just right, adding inductance or de-spiking with particular etch shapes... ugh.
 
#123
craig.p said:
Yep. At one company I worked for, we had to be real careful in the narrow time slot occupied by ECL RAMs' transitions from 0 to 1 and back again. And not only that, we also had to define a 1's precise voltage. This was in a multi-board processor's L2 cache. Those chips were finger-fryers. Games with etch lengths/delays for timing to hit things just right, adding inductance or de-spiking with particular etch shapes... ugh.
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I was working on some very interesting Low Voltage Swing circuitry (Invalid Link Removed) that was exceedingly analog in nature.

Never mind what even a "digital" clock waveform looks like at 6+ GHz. Let's just say that laser voltage probing shows the squarewaves to be more like very noisy triangle waves... and you start having to worry about whether your rise/fall times are so large with respect to the clock period that your signal is never transitioning.
 
#124
aborgman said:
I was working on some very interesting Low Voltage Swing circuitry (Invalid Link Removed) that was exceedingly analog in nature.

Never mind what even a "digital" clock waveform looks like at 6+ GHz. Let's just say that laser voltage probing shows the squarewaves to be more like very noisy triangle waves... and you start having to worry about whether your rise/fall times are so large with respect to the clock period that your signal is never transitioning.
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Makes audio design look downright relaxing ;)
 
#126
agedhorse said:
We do... but not in the bass market. We have 3 tube amps in our guitar line for years that have been successful and also very reliable. In fact, we probably have as much or more experience with all tube platforms than most other manufacturers since we do both guitar and bass amps.

One problem (from a manufacturer's perspective) with an all tube bass amp is that they end up being large, very heavy and expensive if you want to sell a reliable product.

The other problem is the marketplace tends to be very focused on a specific platform such as the SVT. If it's not an SVT they are not interested. That's a tough nut to crack. Look at the variety of manufacturers who have introduced an all tube amp only to discontinue it within a short time frame.

The players have for the most part spoken, They are interested in compact, high performance and lightweight. That is why the industry is headed that way.
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I agree to a point... The people who want an SVT are 80% rock / metal / hardcore players. The All Tube releases from Sadowsky, Eden etc have all been positioned as the tube amp for the connoisseur... mostly on account of the incorrect assumption that the connoisseur will pay the accompanying price tag. This is a mistake. Position the amp from a correct marketing standpoint and it will sell accordingly. Try to sell an SVT wrapped up and packaged as an Epifani.... dont be surprised it doesnt sell. SVT buyers dont buy Tecamp.

BigOldHarry said:
That all rings perfectly true -

My only concern about the current crop of class D amps is the frequency of failure (perceived or otherwise). I've read too many threads about frustration with GK and Carvin class D amps - and the one class D amp I have direct exposure to crapped out within 2 weeks. That said, I've played *many* at stores that gave me serious GAS (GB & EA leap to mind) - - and I have not read too many complaints about either company's class D amps... Perhaps what I've been seeing is that the low-end builders (GK / Carvin) are making all the class D amps look bad...?
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Many manufacturers use OEM class-D SMPS output modules made from companies like HYPEX and Bang & Olufsen. I can tell you one thing for certain... you will have a very hard time making a B&O module crap out.... and I have been steadily beating the ever living shnot out of my Carvin DCM 1000L for months with zero problems....
 
#127
maybe not tecamp but they'll buy a small amp as a backup. they probably won't be as ridiculously cheap as me and buy a used crate power block and a vt :bassist: but they'll buy one.

btw, the power block is surprisingly good if all you need is a handful of watts. have to defeat the preamp and it's never 100% clean, but it's close enough for gigs. and it's class d...used it on 4 or 5 gigs recently and it's worked just fine every time. must be a good 6-7 years old.
 
#128
pablomigraine said:
you will have a very hard time making a B&O module crap out.... and I have been steadily beating the ever living shnot out of my Carvin DCM 1000L for months with zero problems....
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The DCM 1000L uses a B&O part? I did not know this.
 
#131
craig.p said:
Well, as long as we're talking about this type of technology, take a look at Invalid Link Removed of implementing an ICEpower500. Pay special attention to the first interior shot -- at how the power supply absolutely dwarfs the B&O. :eek:
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And look at how the small-ish gauge DC supply leads negate much of the effect and supposed benefit of such a stout power supply.

The audiophile market (I have designed several products for this market many years ago) is full of "looks makes good sound" marketing and while it looks impressive, the benefits of CMRR are inconsequential when it comes to a typical class D power stage.

The amp will only draw current based on the load and signal level. An overbuilt power supply can not alter ohm's law.
 
#132
burnunit said:
No second thoughts at all, but...I don't use effects, I like transparency and want to hear the bass rather than the amp, so maybe my tonal goals are somewhat different from yours.
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good luck with that one. nearly all the pres that people think are "transparent" have a voicing that is anything but, and having a "transparent" cab is impossible.
 
#133
agedhorse said:
The DCM 1000L uses a B&O part? I did not know this.
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No no, I was making and example of TWO manufacturers who've gotten it right from a "seat of the pants" standpoint IMHO. The Carvins use a proprietary circuit, and a fairly well sorted one from where I sit. Lots of copper, thick leads, extra thick PCB, good quality resistors and caps etc. Their fan still sucks tho. I can "feel" a slight difference between the light and my regular DCM, but it feels like the well is nearly as deep so to speak.... no lag in speaker creasing thumb-thump triplets.
 
#134
And look at how the small-ish gauge DC supply leads negate much of the effect and supposed benefit of such a stout power supply.
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Yes, that is interesting. Someone somewhere decided running mass copper all the way out to the B&O didn't accomplish anything. Maybe that short run didn't matter all that much.

the benefits of CMRR are inconsequential when it comes to a typical class D power stage.
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Of course I'm just guessing here, but the focus may have been more on low PS impedance in general, in order to improve "sock" down at the low end. It's interesting that the article says HH believes in stiff regulation, and yet the B&O appears to be feeding directly off a very "soft" power supply, at least if my old eyes are reading the wiring correctly -- the antithesis of stiff regulation. Or maybe this power supply is in two stages: stage 1 being highly-regulated, feeding a stage 2 (that being the capacitor bank) for transient ability. I did that once on an old Hafler power amp, just for grins. But I had to watch how fast I put those big electrolytics in-circuit at power-up. The guy who stole it is probably still trying to figure it out.

The amp will only draw current based on the load and signal level. An overbuilt power supply can not alter ohm's law.
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Right, but also this: an amp will draw only the current it can get its hands on at a particular instant in time. Thus the capacitor bank, for the momentary demands, to preclude current starvation on the peaks. Now the question is whether [DEL]current[/DEL] VA storage like this actually has audible/tactile benefit during loud bass transients. I'd love to take a thin-sounding or dead-sounding lightweight and replace its power supply with a huge toroid and an army of electrolytics, just to see if its impact at the bottom end would improve.
 

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