sarees@watlion.UUCP (Steve Rees) (08/07/86)
Can anybody point me toward references (schematics, articles, etc) about GOOD quality, low- to medium-power Class-A or current-dumping amplifiers? The more specific the reference the better, but even general leads would help. Thanks, Steve Rees University of Waterloo
ins_adyc@jhunix.UUCP (Donald Y Chen) (08/13/86)
> Can anybody point me toward references (schematics, articles, etc) about > GOOD quality, low- to medium-power Class-A or current-dumping amplifiers? > > The more specific the reference the better, but even general leads would > help. > > Thanks, > > Steve Rees > University of Waterloo Steve, I can give some idea who makes these Amps. For a mere $8000+ Mark-Levinson makes the awesome 25W ML-2A. These are dual mono which is reflected in their high price. British Fidelity makes some amps. The top of the line is the 175wpc $3500 model supposely a bargain. I suggest you get two. In the current-dumping arena I only know the Quad 405 and its two successors. I don't know the price but it's less than $1000. I hope this information (limited) has been helpful.
abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ)) (08/15/86)
With reference the the original articles below, what is a "current-dumping" amplifier? > > Can anybody point me toward references (schematics, articles, etc) about > > GOOD quality, low- to medium-power Class-A or current-dumping amplifiers? > > > > The more specific the reference the better, but even general leads would > > help. > > > > Thanks, > > > > Steve Rees > > University of Waterloo > > Steve, > > I can give some idea who makes these Amps. For a mere $8000+ Mark-Levinson > makes the awesome 25W ML-2A. These are dual mono which is reflected in their > high price. British Fidelity makes some amps. The top of the line is the > 175wpc $3500 model supposely a bargain. I suggest you get two. > > In the current-dumping arena I only know the Quad 405 and its two > successors. I don't know the price but it's less than $1000. > > I hope this information (limited) has been helpful. *** REPLACE THIS LINE WITH YOUR MESSAGE ***
shop@uwmcsd1.UUCP (Thomas Krueger) (08/18/86)
> With reference the the original articles below, > what is a "current-dumping" amplifier? Assume you have a 100W (rms) amplifier. If it is 100V at 1A, this is not a current dumper. If it is 10V at 10A this amp would be a current dumper, useful for driving speakers with very low impedances. (An example is the Acoustats with the older matching transformers). - Tom -- Thomas Krueger ...ihnp4!uwmcsd1!shop or University of Wisconsin Milwaukee uwmcsd1!shop@rsch.wisc.EDU Computing Services Electronics Shop 3200 N. Cramer St. (414) 963-5172 Milwaukee Wi 53211
abeles@mhuxm.UUCP (J. Abeles (Bellcore, Murray Hill, NJ)) (08/20/86)
> > what is a "current-dumping" amplifier? > > Assume you have a 100W (rms) amplifier. If it is 100V at 1A, this is not a > current dumper. If it is 10V at 10A this amp would be a current dumper, > useful for driving speakers with very low impedances. (An example is the > Acoustats with the older matching transformers). > Am I correct, then, in concluding that the label "current-dumping" has nothing to do with the design of the amplifier (since merely putting a transformer on the output would change the effective output impedance from 100 ohms to 1 ohm, to use the above example)?
shop@uwmcsd1.UUCP (Thomas Krueger) (08/22/86)
> > > what is a "current-dumping" amplifier? > > > > Assume you have a 100W (rms) amplifier. If it is 100V at 1A, this is not a > > current dumper. If it is 10V at 10A this amp would be a current dumper, > > useful for driving speakers with very low impedances. (An example is the > > Acoustats with the older matching transformers). > > > Am I correct, then, in concluding that the label "current-dumping" has > nothing to do with the design of the amplifier (since merely putting > a transformer on the output would change the effective output impedance > from 100 ohms to 1 ohm, to use the above example)? Partially... in a solid-state amplifier, transformers are avoided because of the phase shifts and high frequency ringing involved are difficult to compensate for. Therefore, current dumping is not only a function of the output impedance but also of the power supply current capacity. If the power supply is capable of putting 2A into the load, no matter what, the voltage swing on the output would clip as drive to the output stage increased (along with the output stage melting down). If the amp is designed with high current output design with a low ouptut impedance (Accoustat amps come to mind) with a power supply stiff enough (like a lot of supply capacitance and a large power transformer) the amp will be able to 'dump' current without self destructing. As an aside, anyone ever think of desgning large complimentary solid state amplifiers with no power transformer for 120VAC? - Tom -- Thomas Krueger ...ihnp4!uwmcsd1!shop or University of Wisconsin Milwaukee shop@csd1.milw.wisc.edu Computing Services Electronics Shop 3200 N. Cramer St. (414) 963-5172 Milwaukee Wi 53211
ark@alice.UucP (Andrew Koenig) (08/23/86)
> Therefore, current dumping is not only a function of the > output impedance but also of the power supply current capacity. My understanding is that "current dumping" is a trademark of the Acoustical Manufacturing Company in Huntington, England, and refers to a particular circuit configuration they use in their power amplifiers (QUAD 403). The idea is that the output of the amplifier is the difference of the outputs of two separate parts. One, called the current dumper, has a lot of power capacity but only mediocre linearity. The difference between the output of the current dumper (divided by a constant) and the input is then amplified by a smaller amplifier on which considerable care is taken to minimize distortion. This is easier to do here because this amplifier is smaller. Its proponents claim that this is a way to get a lot of power with very low distortion and only a little more design effort than would be necessary for a much smaller amplifier. I am not qualified to evaluate this claim. > As an aside, anyone ever think of desgning large complimentary solid state > amplifiers with no power transformer for 120VAC? I think it would be an incredible safety hazard.
phil@saber.UUCP (Phil Gustafson) (08/23/86)
> > As an aside, anyone ever think of desgning large complimentary solid state > amplifiers with no power transformer for 120VAC? > > Thomas Krueger ...ihnp4!uwmcsd1!shop or Yes. They usually stop thinking about it when they consider that the speaker wires for such an amplifier would pose a lethal shock hazard. phil -- --------------------------------------------------------- All opinions except attributed quotations are mine alone. Satirical comments may not be specifically identified as such. -- Phil Gustafson Voice: (408)435-8600 Saber Technology Corp. 2381 Bering Drive Mail: decwrl!sun!saber!phil San Jose, CA 95131 idi!saber!phil
GOT@PSUVMA.BITNET (08/24/86)
> >As an aside, anyone ever think of desgning large complimentary solid state >amplifiers with no power transformer for 120VAC? Yes, I even think there may be a few being marketed. Its really not a great idea though, because you get no isolation from the power lines. All the noise, spikes, and dropouts will come right through, unless you use a hefty isolation transformer. ------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Sunil Gupta | Bitnet: got@psuecl P enn | got@psuelc2 S tate | U niversity | UUCP : ihnp4!psuvax1![psuecl, psuecl2]!got E ngineering | : ihnp4!psuvax1!psuvma.bitnet!got C omputer | L ab | ARPA : got%psuecl.bitnet@wiscvm.arpa "I dares ya to step across this line! _______" - Bugs ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
kchen@imagen.UUCP (Kok Chen) (08/26/86)
>> ark@alice writes: > > My understanding is that "current dumping" is a trademark of the > ... amplifiers (QUAD 403). > Right on! This is the first proper description of "current dumping (TM)" that has appeared so far. In fact, what <ark> has described is the way Quad does FEED-FORWARD. The error signal from the cheapo high-current section is fed to a lower power section to cancel at the speakers (instead of feeding the error signal BACK to the input of the high-current amplifier). I, for one, would be interested in hearing more on feed-forward power amp topologies. One idea that I kicked around has been to difference the main and feed- forward paths by feeding the output of the main driver to one speaker wire, and the output of the error-signal amplifier to the second speaker wire (like a diff amp). Two possible flaws in this: 1) won't work with electrostatics that require single ended inputs, and 2) the finiteness of the first driver's output impedance will introduce some positive feedback to the second driver. Another idea: the feed-forward signal (the input to the second amp) can come from an auxiliary cable that goes straight to the speaker terminals (like in remote-sensing power supplies), instead of to the output of the first driver. I haven't tried out any of these ideas yet, except on paper (I do have a spare DH-120 that I don't mind modifying and blowing up, though, if I ever find time :-). Anyone see major flaws in the logic? Kok Chen Imagen Corporation (we don't manufacture amplifiers; in fact, we don't even do anything remotely analog!)
dh@vax135.UUCP (David N. Horn) (08/29/86)
As far as I recall, the "Current Dumping Amplifier" was a name given to an interesting design of amplifier introduced by Quad (name of a Hi Fi manufacturer in England headed by Peter Walker) about ten years ago. It had two amplifiers for each channel, one high power but slow amplifier to do most of the work, and one low power but fast. A comparator sensed the difference between the input signal and the output divided by the gain (i.e. the distortion), and the fast amplifier made up the difference. The technique was also known as "feed-forward". A number of articles on current dumping were published in "Wireless World". By the way, Peter Walker has a very good reputation for producing top quality products way ahead of their time. Dave Horn, AT&T Bell Labs, Holmdel, vax135!dh
newton2@topaz.berkeley.edu (08/29/86)
I will endorse Dave Horn's comment that Peter Walker of the Acoustic Manufact- uring Co. (Quad) has an excellent reputation (is his name Walker? All I remember is the company). During a period of more-than-usually obsequious sycophancy, I asked Ray Dolby if there was anyone in the audio world whose commercial style he admired in the same way that I found *his* approach admirable. Without hesitation he mentioned Peter Walker[?] (we had already agreed on Henry Kloss), but couldn't seem to think of anyone else (like Ike when asked to list a single achievement of Richard Nixon as Veep, I'm sure if I'd given him a week he'd have thought of one.) As to why I found (still find) Ray Dolby a bird so rare in the commercial audio aviary, if you have to ask... ...I guess I'll have to expatiate, later. Doug Maisel (415) 848-5247 56 Panoramic Way Berkeley, CA 94704
szepesi@fluke.UUCP (Les Szepesi) (08/29/86)
> [...] > One idea that I kicked around has been to difference the main and feed- > forward paths by feeding the output of the main driver to one speaker wire, > and the output of the error-signal amplifier to the second speaker wire (like > a diff amp). [...] > > > Kok Chen > Imagen Corporation (we don't manufacture amplifiers; in fact, we don't > even do anything remotely analog!) The biggest problem I see with this is that all the current coming from the output of the "main driver" must also pass throught the output of the "error- signal amplifier". (KCL) This now implies an error amplifier with very good linearity, THD, etc that also can source and sink large currents. The whole point of the original topology was "To build a low power, quality amp is cheaper and easier than to build a high power, quality amp." Les Szepesi -- Les Szepesi decvax\ John Fluke Mfg Co. ihnp4 >!uw-beaver\ PO Box C9090 MS 274G allegra >!fluke!szepesi Everett, WA 98206 USA ucbvax >!lbl-csam / (206) 356-6362 hplabs/