FS: Classe Audio 70 power amp

[jandl100]

Excellent Canadian audiophile power amp.

240V UK voltage.

75wpc into 8 ohms, doubles to 150wpc into 4 ohms ... Sturdy power supply!

A really subtle powerhouse. Loads of grip, but very musical too. :)

RCA & XLR inputs.

PWO & Excellent condition - a few light marks, but nothing much.

£325 UK del.
May consider swaps or px.

One hell of a lot of amp for the money, imho! :^

Original box, packing and manual.

http://i262.photobucket.com/albums/ii114/jandl100/Classe70f.jpg

http://i262.photobucket.com/albums/ii114/jandl100/Classe70r.jpg

[Reid Malenfant]

£325 UK del.

One hell of a lot of amp for the money, imho! :^

Original box, packing and manual.

I'd definately agree with that :) Still loving my Classe DR5 Pre amp as i type. If that power amp is anything like this then it's as you say, "One hell of a lot of amp for the money" ;)

Hope you find a buyer chap, superb VFM with all the original boxes etc :smoking:

[jandl100]

Hope you find a buyer chap, superb VFM with all the original boxes etc :smoking:

Yup, thanks for that.

A great amp, and will drive most speakers on the planet, I think. A real high current powerhouse.

Not just original box etc, also the original Classe plastic bag that the amp is wrapped in inside the box! :)

.... perhaps you'd like it for your hot weather amp, Mark. ;)

[Ali Tait]

Is that biased in class A at all Jerry? Those look like hefty heatsinks on the back.

[jandl100]

Is that biased in class A at all Jerry? Those look like hefty heatsinks on the back.

I don't think so.

To quote from the advertising blurb sheet (Also included in the sale! ... wottabargin. ;)) ... " heat sinks ... efficiently maintain lower output transistor case temperatures, allowing ultra high current and voltage with a reduced number of devices, resulting in faster and truly transparent response as well as total freedom of dynamic contrasts."

Cor. Sounds good, dunnit! :eek:

[Ali Tait]

It does!

[jandl100]

Go on, Ali ... ya know ya wonnit for yer stats :eek:

[Ali Tait]

I've spent enough this month! Anyway,Nick is currently building the direct coupled amps to drive the stats.

[Effem]

Classe amps are a lot better sounding than they look and my Model 10 is no exception.

Someone should grab this beauty, because at the price it definately won't disappoint.

Good luck with the sale Jerry.

[serendipitydawg]

Hello Jerry

Definitely interested in this amp.

I've sent you a PM

[jandl100]

Hello Jerry

Definitely interested in this amp.

I've sent you a PM

Thanks Matthew

PM replied to.

Looks like this may be sold. :)

[jandl100]

SOLD stp :)

Do, please, post a write-up of your system once this beastie arrives, Matthew. I'm sure many folks here would be interested! :)

[Glen B]

Is that biased in class A at all Jerry? Those look like hefty heatsinks on the back.

I don't think so.

To quote from the advertising blurb sheet (Also included in the sale! ... wottabargin. ;)) ... " heat sinks ... efficiently maintain lower output transistor case temperatures, allowing ultra high current and voltage with a reduced number of devices, resulting in faster and truly transparent response as well as total freedom of dynamic contrasts."

Cor. Sounds good, dunnit! :eek:

All class AB amps run in class A up to a point determined by the level of standing bias/quiescent current, after which they run in class B. The class A output of the Classé Model 70 is approximately 0.19W or 190mW into an 8 ohm load.

This is calculated using Ohms Law formula V/R=I, where V is the bias voltage, R is the emitter resistance, and I is the bias current, and formula I x I x R=W, where I is the bias current, and R is the load resistance.

The total bias on the Model 70 output stage is 42mV, and value of output transistor emitter resistor is 0.27 ohm. Therefore bias current is 42/0.27=155.5mA and class A output is 155.6 x 155.6 x 8 = 0.19W.

[Ali Tait]

Ok thanks,yes am aware of that, what I meant was,is there any significant class A output,which appeared to be the case given the large heat sinks.

[Glen B]

IMO, the Model 70 heatsinks are not that large, certainly not enough to support any significant class A output. The larger models with side heatsinks offer more class A output, up to 6-8 watts before running in class B. BTW, the only Classé models to ever run in full class A are the DR-3 (25W) and DR-3VHC (40W).

DR-3:
http://img.villagephotos.com/p/2003-5/191557/DR-3.JPG

[StanleyB]

Anyone got a Pioneer M-25 that they are not using? That one has a good implementation of class A and B.

[Ali Tait]

IMO, the Model 70 heatsinks are not that large, certainly not enough to support any significant class A output. The larger models with side heatsinks offer more class A output, up to 6-8 watts before running in class B. BTW, the only Classé models to ever run in full class A are the DR-3 (25W) and DR-3VHC (40W).

DR-3:
http://img.villagephotos.com/p/2003-5/191557/DR-3.JPG

Prefer valve amps myself.

[Reid Malenfant]

The total bias on the Model 70 output stage is 42mV, and value of output transistor emitter resistor is 0.27 ohm. Therefore bias current is 42/0.27=155.5mA and class A output is 155.6 x 155.6 x 8 = 0.19W.
If you have the correct emitter resistance & voltage accross it then you have made a slight error ;) The amplifier must be push pull so it'll actually still be in class A up to 0.387W RMS into an 8 ohm load.

You need to double the standing current before one transistor switches off & at that point it'll be going into class B ;)

[Glen B]

The standing current was doubled, i.e, 21mV x 2=42mV.

[Reid Malenfant]

Ok, lets assume a 0.1556Amp standing current on a push pull output stage :)

Peak current before either of the positive or negative rail output transistors will be double this, above this one half will be cutoff ;)

Just say we have 0.3112Amp peak before one half of the output stage actually turns off we can get the peak voltage, 0.3112 (Amps) x 8 ohm resistance = 2.4896V according to ohms law... That's the peak voltage & current though, not the RMS voltage or current. 2.4896V peak is 1.7606V RMS (peak voltage divided by 1.414), square that & divide by the load resistance :) You get 0.387Watts RMS

[Glen B]

Reid,
FYI, I shot your theory by audio engineer Ralph Karsten, manufacturer of Atmasphere products on another forum. He said, without knowing more about the amp, the numbers seemed close, but in the example, the base current has been ignored. Another knowledgeable poster said: (1) He did not understand where you're getting the double current from ? (2) He thought that when the whole 0.1556A of bias current flows thru the speaker then the other transistor has to be off (Il=Ip-In). (3) You cannot calculate RMS because you don't know the shape (1.41x relationship applies only to sinewave). I don't intend to beat this topic to death, just thought I would mention the interesting responses I received.

Glen

Atma-Sphere Music Systems: http://www.atma-sphere.com/

[Reid Malenfant]

Reid,
FYI, I shot your theory by audio engineer Ralph Karsten, manufacturer of Atmasphere products on another forum. He said, without knowing more about the amp, the numbers seemed close, but in the example, the base current has been ignored. Another knowledgeable poster said: (1) He did not understand where you're getting the double current from ? (2) He thought that when the whole 0.1556A of bias current flows thru the speaker then the other transistor has to be off (Il=Ip-In). (3) You cannot calculate RMS because you don't know the shape (1.41x relationship applies only to sinewave). I don't intend to beat this topic to death, just thought I would mention the interesting responses I received.

Glen
Hi Glen, i think you'll find that any power measurements on amplifiers that actually mean anything are always W RMS & obviously using a sign wave :eyebrows:

Ok, yes i was ignoring transistor base current but in all honesty the beta of an output transistor at those sorts of currents (0.1556 - 0.3112A) & at normal frequencies (not supersonic) will likely be in the order of about 50 so perhaps a total of 3.112mA of the total is base current. however this doesn't change the fact that the very same is also flowing out the "emitter" & as a consequence can still be driving the load ;)

If this knowledgeable person can't understand how the current doubles then i'm afraid to say he needs to do some reading :scratch: The quiescent current is determined by the voltage accross the bases of the output transistors & this is set by the VBE of the transistor (usually a transistor) used to stabilise the thermal feedback. With a fixed voltage accross (though it does alter slightly & gradually to keep thermal equilibrium via the VBE transistor) the output transistors bases you get your 42mV accross each resistor. Now as one transistor turns on more to swing voltage & current to the load the other is gradually turning off. It will only turn off when the upper transistor is conducting nearly 0.3112A

As i say, if he can't see this then his knowledge needs improving :rolleyes:

I'm not going to beat it to death as you put it either, there is no way of getting away from the truth though :cool:

All the best :wave:

E2A:- I suggest you get your knowledgeable person to read "Self On Audio" by Douglas Self ;)

[Glen B]

Good explanation. I see how current doubles. Thanks.

[MrAcoustat]

IMO, the Model 70 heatsinks are not that large, certainly not enough to support any significant class A output. The larger models with side heatsinks offer more class A output, up to 6-8 watts before running in class B. BTW, the only Classé models to ever run in full class A are the DR-3 (25W) and DR-3VHC (40W).

DR-3:
http://img.villagephotos.com/p/2003-5/191557/DR-3.JPG

http://i814.photobucket.com/albums/zz61/MrAcoustat/ClasseDR3-VHC06.jpg

http://i814.photobucket.com/albums/zz61/MrAcoustat/ClasseDR3-VHC01.jpg

http://i814.photobucket.com/albums/zz61/MrAcoustat/ClasseDR3-VHC05.jpg

[Glen B]

Nice pictures of the DR3-VHC. BTW, a couple of months ago, I found out from the Classé factory that their CA-300 and CA-400 models have adaptive bias, and deliver approximately 60 and 80 watts class A respectively (20% of rated output). I did not ask about other models, however, their circuitry is similar, so I'm taking it for granted that they operate in similar fashion. I have noted similar levels of class A output reported in magazine reviews of other models, like the CAM-350 and Omega.

[hornucopia]

Anyone got a Pioneer M-25 that they are not using? That one has a good implementation of class A and B.
As has my Hafler DH200, where the bias is set for a few watts of Class A. The Firstwatt principle?