walter
Well-known member
If these are truly a cheap, and not about good, near impossible to repair device, they may end up in some Behringer equipment, and I will get ahold of 'em, if I haven't already. btw, I get the E-spam from Hearst.
Class D audio amp
- Thread starter walter
- Start date
Help Support GroupDIY Audio Forum:
mhelin
Well-known member
[quote author="Svart"]I saw those some time ago but they are difficult to get here in the states, at least I can't find anyone who has them to sell. I'd like to see if they use off the shelf ICs or custom programming.
[/quote]
They use single IC opamp (pre stage) but otherwise discreter circuit (the UcD modulator is on it's own circuit board). I think they published some kind of schematics (without component values) of the internals of it, some folks at diyaudio.com actually have re-engineered that stage.
[/quote]
They use single IC opamp (pre stage) but otherwise discreter circuit (the UcD modulator is on it's own circuit board). I think they published some kind of schematics (without component values) of the internals of it, some folks at diyaudio.com actually have re-engineered that stage.
Mlewis
Well-known member
[quote author="bobkatz"]
I'll let you know how they sound compared to my $6000 Class A Pass X250!
[/quote]
if they really can compare sonically with some of Nelson's amps (even if they're not quite as good) then they seem like an absolute bargain. Especially since the amp can be run as a stereo amp with the ability to upgrade later simply by buying another one and running them in parallel as pair of monoblocks. The list price is a full $2000 dollars cheaper than the X250 and thats if you buy two and wire them as monoblocks.
The cost of buying one L-301 and a pair of L-505s doesnt seem too shocking compared to it's competition in that performance range.
is there any chance you'll be listening to the amp wired as a single stereo amp rather than the parallel monoblocks?
i look foreward to hearing what you think of them.
I'll let you know how they sound compared to my $6000 Class A Pass X250!
[/quote]
if they really can compare sonically with some of Nelson's amps (even if they're not quite as good) then they seem like an absolute bargain. Especially since the amp can be run as a stereo amp with the ability to upgrade later simply by buying another one and running them in parallel as pair of monoblocks. The list price is a full $2000 dollars cheaper than the X250 and thats if you buy two and wire them as monoblocks.
The cost of buying one L-301 and a pair of L-505s doesnt seem too shocking compared to it's competition in that performance range.
is there any chance you'll be listening to the amp wired as a single stereo amp rather than the parallel monoblocks?
i look foreward to hearing what you think of them.
bcarso
Well-known member
[quote author="bobkatz"][quote author="SSLtech"]Yup. It's like switch-mode, usually PWM.
Been used in bass amplifiers for a good while, generally considered down-market, got a reputation for unreliability and generally being near-impossible to repair.
It's all about cheap, not about good.
Keith[/quote]
Not necessarily, Keith. These amps have come a LONG way in their development. You would not believe their tonality, with the proper board layout (critical) and good power supply design, not necessarily a switcher, either. Sonically, the Bel Canto EVO is very nice. I've just received a pair of Class D Lipinski amps and I'm wiring up my speaker cable as they are "power biamped" in each channel. I'll let you know how they sound compared to my $6000 Class A Pass X250!
Bruno Petsys knows where all the class D bodies are buried and he makes excellent-sounding Class D amps.[/quote]
Putzeys is the man. The only other person in switchmode I have such high regard for is the considerably older Gerald Stanley, the genius behind Crown for many years. Unfortunately the Crown patents, which Gerald continues to generate, are locked up and vigorously policed by Harman International. From what I can see, with the exception of one partially-prior-art workaround that is clumsy and that I'm keeping to myself for the moment, only they can take advantage of the elimination of shoot-through currents in the output stages, a serious drawback of all other approaches.
It is sad in a way, because in the right hands the Stanley balanced current amp could probably be made to sound as good as anything. In the meantime we have Bruno's very satisfying approach of involving the output filter intimately in the PWM, rather than dealing with it as a necessary add-on evil. Since overall feedback is being applied intrinsically, the vagaries of non-zero-deadtime in the output switches can at least be alleviated.
Putzeys' explanation of how bogus and mislabeled the "pure digital" amps are is a glorious thing. But oh how the two-drink minimum types (i.e., Marketing) love them.
Been used in bass amplifiers for a good while, generally considered down-market, got a reputation for unreliability and generally being near-impossible to repair.
It's all about cheap, not about good.
Keith[/quote]
Not necessarily, Keith. These amps have come a LONG way in their development. You would not believe their tonality, with the proper board layout (critical) and good power supply design, not necessarily a switcher, either. Sonically, the Bel Canto EVO is very nice. I've just received a pair of Class D Lipinski amps and I'm wiring up my speaker cable as they are "power biamped" in each channel. I'll let you know how they sound compared to my $6000 Class A Pass X250!
Bruno Petsys knows where all the class D bodies are buried and he makes excellent-sounding Class D amps.[/quote]
Putzeys is the man. The only other person in switchmode I have such high regard for is the considerably older Gerald Stanley, the genius behind Crown for many years. Unfortunately the Crown patents, which Gerald continues to generate, are locked up and vigorously policed by Harman International. From what I can see, with the exception of one partially-prior-art workaround that is clumsy and that I'm keeping to myself for the moment, only they can take advantage of the elimination of shoot-through currents in the output stages, a serious drawback of all other approaches.
It is sad in a way, because in the right hands the Stanley balanced current amp could probably be made to sound as good as anything. In the meantime we have Bruno's very satisfying approach of involving the output filter intimately in the PWM, rather than dealing with it as a necessary add-on evil. Since overall feedback is being applied intrinsically, the vagaries of non-zero-deadtime in the output switches can at least be alleviated.
Putzeys' explanation of how bogus and mislabeled the "pure digital" amps are is a glorious thing. But oh how the two-drink minimum types (i.e., Marketing) love them.
Mlewis said:
I finished terminating my custom cables after about 10 hours of work (why 10 hours to terminate speaker cables? See my post under "locking banana plug".)
Anyway, I finished the terminations at 4 PM today and I set up the Lipinski amps, which had been warming up for 48 hours in another room (with no I/O). But these Class D amps may not need any real warmup and they never get warm to the touch. Each amp has a balanced and unbalanced input, a bridge or "biamp" mode switch, and a high gain/low gain switch.
I tested the unbalanced input but my power amps are on a different AC home run than the monitor controller so there was a tiny bit of hum. The balanced input had no hum at all.
I matched gain to the Pass amp with a 1 kHz tone to less than 0.1 dB with my Cranesong inline attenuators (these are Switchcraft A3FM XLR to XLR adapters with a hole drilled in the side to access a balanced T pad whose secondary has a variable trimpot in it, very clever). I use these to set up K-system gain from my Avocet.
The mode to use according to Andrew Lipinski is the biamp mode. He says don't even bother with the bridged mode unless you want to create a high powered mono amp for sound reinforcement purposes. I guess he feels the bridged mode has too high distortion, I don't know for sure.
In biamp mode this is essentially two amplifiers in a single chassis with a mono input. With a little work he could add a switch to make it into a budget stereo amp. You really have to have bi-wirable loudspeakers to take advantage of this amp, at least if you are to believe what Lipinski has to say about not using the bridged mode.
I spent 4 hours with a pair this evening and I'm keeping them in my system for the rest of the week. I felt absolutely no urge to send them packing or to switch back to the Pass, which is sitting idle underneath! And that says a lot. Midrange is pure and transparent. There is absolutely no grain, none of that "Bryston sound" that sends me packing" (if you haven't guessed, I'm not impressed by Brystons). These Lipinski amps have more in common with tubes or Class A Pass amps than typical class A/B solid state.
Bottom end is minutely less extended and less "robust" than the Pass, but you can't pick up the Pass without a forklift, and I can hold one Lipinski amp in each hand, so give them a break!
So if the Lipinskis had been available at the time I bought the Pass, I probably would have skipped the Pass, that's how good the Lipinskis are. The bottom end issue is definitely a nitpick. The price/performance ratio is awesome. Highly recommended.
Nitpicks are very small, so I won't bother in this post. It's two thumbs up, next best thing to a Pass X250 at 1/4 the price, if I recall correctly.
The only thing left is nit picks so I want to save them for a review I hope to write for P.A.R. Magazine.
Svart
Well-known member
Take it from the man himself! Class D is no longer the red-headed stepchild it once was.
Samuel Groner
Well-known member
A bit OT, but anybody knows how much class A these things really are? 1200 W in pure class A looks rather unrealistic.
Samuel
Mlewis
Well-known member
[quote author="bobkatz"]
Nitpicks are very small, so I won't bother in this post. It's two thumbs up, next best thing to a Pass X250 at 1/4 the price, if I recall correctly.
[/quote]
...My poor little credit card, he's come over all frightened. Cheers for the review Bob, it's very much appreciated.
Nitpicks are very small, so I won't bother in this post. It's two thumbs up, next best thing to a Pass X250 at 1/4 the price, if I recall correctly.
[/quote]
...My poor little credit card, he's come over all frightened. Cheers for the review Bob, it's very much appreciated.
Mlewis
Well-known member
[quote author="Samuel Groner"]
A bit OT, but anybody knows how much class A these things really are? 1200 W in pure class A looks rather unrealistic.
Samuel[/quote]
if you fancy sifting through countless pages, there's a thread at DIY Audio about X series supersymetry amps started by somebody who reverse engineered one. Nelson's quite free with the info he lets DIYers have in that thread.
http://www.diyaudio.com/forums/showthread.php?s=2f338ed0a638e8000ad6bfa34be3fca9&threadid=99
it doesn't say to what level the amp remains class A but the user manual does have plenty of good info.
A bit OT, but anybody knows how much class A these things really are? 1200 W in pure class A looks rather unrealistic.
Samuel[/quote]
if you fancy sifting through countless pages, there's a thread at DIY Audio about X series supersymetry amps started by somebody who reverse engineered one. Nelson's quite free with the info he lets DIYers have in that thread.
http://www.diyaudio.com/forums/showthread.php?s=2f338ed0a638e8000ad6bfa34be3fca9&threadid=99
it doesn't say to what level the amp remains class A but the user manual does have plenty of good info.
chrissugar
Well-known member
Many thanks for the review Bob.
:thumb: :thumb: :thumb:
chrissugar
:thumb: :thumb: :thumb:
chrissugar
Mlewis
Well-known member
Found it...
He's referring to the X1000 amp here not the X250 but you get the idea:
He's referring to the X1000 amp here not the X250 but you get the idea:
bcarso
Well-known member
quote:
..."Bottom end is minutely less extended and less "robust" than the Pass, but you can't pick up the Pass without a forklift, and I can hold one Lipinski amp in each hand, so give them a break!..."
And I'll bet with maybe just a scosch heftier power supply you wouldn't even have that minor quibble.
Thanks so much for sharing the evaluation Bob!
..."Bottom end is minutely less extended and less "robust" than the Pass, but you can't pick up the Pass without a forklift, and I can hold one Lipinski amp in each hand, so give them a break!..."
And I'll bet with maybe just a scosch heftier power supply you wouldn't even have that minor quibble.
Thanks so much for sharing the evaluation Bob!
bcarso
Well-known member
[quote author="Gus"]I have a question about power supplies for a class D. Is a switching amp "hard" on the power supply caps and sensitive to the ESR DF inductance etc?[/quote]
Short answer: And How.
The typical switcher has currents at the switching frequency flowing in the output filter all the time, and these plus any bits of onset-of-crossconduction and body diode reverse recovery charge are flowing therefore as well in the filter caps of the supply.
Ideally one would take the switching currents and signal currents into account if a regulated supply were used, and some do this in a feedforward fashion. There's probably a minefield here with respect to patents so for commercial use one must proceed with great caution. But most that use the topologies that are amenable to global feedback around the switcher use unregulated supplies*. If they are standard mains-frequency iron and copper you still have to be concerned about the impedance and behavior of the output caps etc.
If you use switchmode supplies then you have the problems of IM from the switcher supply and switchamp, especially if both are variable frequency. And then another problem arises: with reactive loads and a low-dissipation system, you can pump energy back into the rails and unless the supply has someplace to put it (like into the great big bulk caps on the unregulated mains supply) the rail voltage rises to potentially destructive levels**. Bridge mode operation helps here but requires twice as many big pieces of silicon and output filter.
*the sensitivity to the supplies is one of the great downfalls of the open-loop so-called "pure digital" approaches. Most of the "digital" stuff now being touted sneaks in ways of compensating for the supplies, but none particularly elegantly imo.
**It is possible to make a switchmode regulator that sinks and sources current and returns it to the raw input, so that's one way to deal with the pumping effect.
Short answer: And How.
The typical switcher has currents at the switching frequency flowing in the output filter all the time, and these plus any bits of onset-of-crossconduction and body diode reverse recovery charge are flowing therefore as well in the filter caps of the supply.
Ideally one would take the switching currents and signal currents into account if a regulated supply were used, and some do this in a feedforward fashion. There's probably a minefield here with respect to patents so for commercial use one must proceed with great caution. But most that use the topologies that are amenable to global feedback around the switcher use unregulated supplies*. If they are standard mains-frequency iron and copper you still have to be concerned about the impedance and behavior of the output caps etc.
If you use switchmode supplies then you have the problems of IM from the switcher supply and switchamp, especially if both are variable frequency. And then another problem arises: with reactive loads and a low-dissipation system, you can pump energy back into the rails and unless the supply has someplace to put it (like into the great big bulk caps on the unregulated mains supply) the rail voltage rises to potentially destructive levels**. Bridge mode operation helps here but requires twice as many big pieces of silicon and output filter.
*the sensitivity to the supplies is one of the great downfalls of the open-loop so-called "pure digital" approaches. Most of the "digital" stuff now being touted sneaks in ways of compensating for the supplies, but none particularly elegantly imo.
**It is possible to make a switchmode regulator that sinks and sources current and returns it to the raw input, so that's one way to deal with the pumping effect.
Svart
Well-known member
Brad always has great in-depth answers. I'll put it a little more simply for those who might not be familiar..
Think of a switching power supply, if you have ever worked repairing these you would know that there are a few parts that are prone to failure but one part that WILL fail.
#1. The bulk cap
Yep the large value cap after the filter/rectification circuit and before the FET/chopper circuit.
It's pretty much the same thing in a Class D supply but include rail bounce too which seems to be a huge problem when it's overlooked in amp design.
And as Brad says, in a full bridge setup this is somewhat less of a problem.
In motor control we can add flywheel diodes and other devices that recirculate energy away from the rails but when driving a speaker that could lead to disaster.
And personally I have not seen a great degree of difference between low ESR and "normal" caps in the bulk cap situation. This is not a place for hard filtering of AC noise but rather of maintaining a bulk capacitance for instantanious current draw. It's assumed that the proper noise filtering had taken place before this stage and that the raw DC is more or less clean. You are also going to get a fair chunk of noise from the action of the MOSFET, it's flywheel diode and the trafo too.
Thanks The reason I asked is because I have noted over the years when fixing switching power supplies sometimes you need to get the same cap brand and part number.
It seems you can't just drop in a cap that looks on paper to be OK ESR ripple current DF etc.... and expect the circuit to work correctly sometimes.
I believe I have read the newer switcher chips allow more variation in parts.
Now what is strange the smaller switchers I have worked on the output caps fail more often than the AC side one(s)
It seems you can't just drop in a cap that looks on paper to be OK ESR ripple current DF etc.... and expect the circuit to work correctly sometimes.
I believe I have read the newer switcher chips allow more variation in parts.
Now what is strange the smaller switchers I have worked on the output caps fail more often than the AC side one(s)
Svart
Well-known member
A lot of companies know that the bulk cap HAS to be of a certain quality or the unit won't last a month. The output caps are then targeted in the cost cutting. They tend to use cheap, low temp, high ESR jellybean caps. Since these PSUs tend to be stuck in cramped, inadequately cooled cases they overheat and stress out the caps.
Yeesh, it just makes me realize how many poor powersupplies are used everyday. it gives switchers a bad name..
:shock:
Yeesh, it just makes me realize how many poor powersupplies are used everyday. it gives switchers a bad name..
:shock:
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