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Old 9th May 2007, 04:59 PM   #11
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Default hmm...

Tino,

The 'missing' systems (pwm, oscillators etc) you describe would not be found in a class H amp. The amp is not switching in the class D sense of the word, but rather uses a 'semi-'conventional class AB output stage, whose voltage rails are switched to provide a higher level of output voltage when the input signal demands it. In this way the output can run more class A from the lower voltage rails, switching to something closer to class B for higher output power. If you are interested I suggest you read Doug Self's book, it has a section describing this class of amp, and IIRC his 'sample' is rated at >50w.

It may seem to you that 14kg is heavy for an amp, in reality it's about half the weight it should be for this power rating, hence the need for class H to enable smaller heatsinks.

While age allows you to judge some things about equipment and people, attempting to use it as a foil in a technical discussion tells us more about you and your age than anything else. Typically those wishing to be regarded as adults don't argue that way, not that an argument was even necessary in this case.

HTH

Stuart
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Old 9th May 2007, 05:02 PM   #12
tino96 is offline tino96  Italy
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Quote:
Originally posted by Nigel Goodwin
I've got a paper manual, it's a SERIOUSLY complicated design, the actual output devices are KAB01's, which includes four power transistors, two run off +/-35V, and two off +/-64V - they are fed in turn by two driver IC's, TA2030. The TA2030's are fed from what looks almost like a complete amplifier in itself (with 18 transistors), except the emitter resistors are 150 ohm, and outputs are taken off both emitters.

It's got a pretty nice spec though!

Hi Nigel, right, the first two run off +/-35V and are the few watts in pure A class, and two off +/-64V for good peak power...
the KAB01's powerpacks provide to 120+120 W per channel 8 ohm load..
Pleas, can you scan for me your manual?
Many thanks in advance
Regards
tino96
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Old 9th May 2007, 05:34 PM   #13
K-amps is offline K-amps  United States
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Quote:
Originally posted by tino96
I have the amplifier... i'm not wrong...

this ampli is 25 years old....

how old are U?

p.s.

weight..... 13.9kg

do U've never seen a 100+100 w H-class amplifier??
Stuart: Not quite sure he will get the help he needs if he keeps his fingers in his ears...


TINO: I do have the SM and the manuals for the 990 somewhere. Hope Nigel scans it for you, I do not have the inclination. Good luck.

Some info on the DLD Kenwoods (Translated)

I have owned all of the amps in the link above except the 990. I sold all but the KA-3300D. Which was a second generation to the KA-1100D/ EX. The 3300 is 170wpc/8 ohms @1kHz and weighs 18+kg and is class-H. Uses the same TA-2030... infact I have some TA-2030's lying around.... too bad they will remain un-used...
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Old 9th May 2007, 05:44 PM   #14
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Tino,

I have the KA990SD Service manual in PDF format. Not sure if there's any resemblance to the KA990EX, but if you're interested, contact me trough the mail-option of the forum.
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Old 9th May 2007, 05:53 PM   #15
K-amps is offline K-amps  United States
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The power amp sections should be the same. SD is US version, EX is Euro. EX might have additional Digital pre-amp section but that does not matter for what Tino wants.
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Old 9th May 2007, 08:17 PM   #16
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Quote:
Originally posted by tino96
I have the amplifier... i'm not wrong...

this ampli is 25 years old....
Actually 19 years old, the manual is dated 1988, but I would agree it's NOT class H.

It's more like Class G, a linear amplifier that increases it's efficiency somewhat by using a lower supply voltage for lower output powers.
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Old 9th May 2007, 08:36 PM   #17
K-amps is offline K-amps  United States
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Yes it is a 1988 model. I have always wondered if they are class-H or G.

In the purist sense the Kenwoods are a perhaps class of their own. They are essentially 2 OP stages paralelled with both having fixed PSU rails.

At a given time either the lower half is conducting the signal or as it approaches threshold, the TA-2030 switches the signal to the hi-volt devices. The 2030 acts like a dual driver stage.

At no point is the rail switched (therefore not a pure class-G) nor continuously modified (as in class-H) but the drivers feed the signal to one of the 2 sets of outputs depending on the amplitude of the signal.

Technically at lower power both sets are active with the hivolt stage getting only a fraction of the current and the low-volt device getting the brunt of it, but after a threshold, the entire signal is handled by the hi-volt devices.

So the hi volt stage is never completely switched off onlty at a predetermined threshold, they take on all the current from the drivers.

It's a toss what you want to call it but I think it's a class on it's own.
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Old 9th May 2007, 08:38 PM   #18
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Default hairs to be split...

...I'm not sure what the 'official' definition of class G vs class H is (perhaps wikipedia has an entry, would that be official?), but I think the key thing is that for either the voltage rails for the output transistors change, in 2 or more steps. The rest of the amp is not unlike a traditional class AB amp...

IIRC Doug Self suggests calling his (class G?) 2 step design class AC (or BC), since the outer transistors are not on all the time (class C), the inner transistors will be on some (B) or all (A) of the time.

Stuart

Edit: k-amps description makes it sound more like G than H, but perhaps it does deserve another descriptive class. Though AFAIK no-one has done it since...too complex for the results perhaps?
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Old 9th May 2007, 08:40 PM   #19
K-amps is offline K-amps  United States
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True...

The Kenwood might be closer to the Doherty amplifier of the early 30's.

This is what I found on the Wiki...

A hybrid configuration that is receiving new attention is the Doherty amplifier consisting of a class B main stage in parallel with a class C auxiliary (or "peaking") stage....

However in the Kenwood, the Peaking OP devices are ON all the time.

Infact I removed the low volt devices completely as an experiment and the amp kept on playing as if nothing happened. (it did run hotter) but clear as Paris Hilton's driving record.

I surmised that the TA-2030 shifted the current to drive the higher volt devices with no Low volt devices left to drive... if the hi volt devices were class-C, I would not have heard clear distortionless sound... the 2030 is a smartly designed switcher...

Kenwood could have made it a better sounding amp had they had a beefier driver after the 2030... IMHO. Feeding OP devices via 150 ohm and then 20 ohm resistoers is not exactly high current in a BJT OP stage...
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Old 9th May 2007, 09:19 PM   #20
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Quote:
Originally posted by K-amps
Kenwood could have made it a better sounding amp had they had a beefier driver after the 2030... IMHO. Feeding OP devices via 150 ohm and then 20 ohm resistoers is not exactly high current in a BJT OP stage...
It's already got a pretty impressive spec though, if I remember correctly from the quick glance earlier, something like 120W RMS per channel to 8 ohms at 0.004% distortion.
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