questions about quasi complementary audio output stages

What are the drawbacks with quasi complementary audio output stages, like, say, this one:

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Do they give more distortion than the usual Sziklai output stages?

I understand that 40 years ago good PNP transistors didn't exist, but why are quasi complementary output stages not seen so often in designs nowadays?

Michael

Reply to
Michael
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It uses 2N3055s? ;-)

Probably not - if you note the connection from the junction of the bottom of R12 and the collector of Q6 back to the junction of the top of VR1 and the bottom of C4, the gain is "strapped", linearizing out all the foibles of crossover distortion and what-not.

Just follow the money. ;-)

Cheers! Rich

Reply to
Rich Grise

"Rich Grise"

** Sziklai output stages are not the most common seen in audio amps.
** Absolute horse shit.

The technique is called " bootstrapping " and simply has no effect on crossover distortion.

... Phil

Reply to
Phil Allison

ke,

Sure they're not the most up-to-date, but what's wrong with those? :- D

M
Reply to
Michael

This quasi complementary Darlington arrangement seems to operate without the need for a center-tapped secondary transformer. What are the audio ramifications of not using a center-tapped secondary?

M
Reply to
Michael

You hae to use a great big huge capacitor to keep the DC off the speaker.

Hope This Helps! Rich

Reply to
Rich Grise

Well, other than having a beta of five, they're just fine. In fact, I once had a job in a Rat Shack repair department, and when we'd get an amp or receiver with blown output TO3s, we'd just routinely slap a couple of 3055s in there.

And you don't need that quasi-circuit since they invented the MG2955. ;-)

Cheers! Rich

Reply to
Rich Grise

OOps: MJ2955.

Reply to
Rich Grise

"Rich Grise"

** More absolute bollocks !!!!

Go look up a data sheet sometime - f*****ad.

..... Phil

Reply to
Phil Allison

Where did you think I found the data?

Phil, go take your meds and don't act like a nincompoop.

Trust me - people will like you better.

Good Luck! Rich

Reply to
Rich Grise

And you get great big thumps in the speaker when the thing charges the cap to ~1/2 VCC unless you put a relay or switch in.

I had an old heathkit that used that output stage (more or less). It had an annoying hiss that would eventually die out. Some time later I added a switch and relay so it would default to no speakers when turned on (to prevent my girlfriend from waking me when she powered it up) that got rid of the hissing too. Changing the output cap finally cured it - the hiss would be gone before I could troubleshoot it.

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The ones I saw had a split power supply so there was very little DC offset. I built some and repaired a lot of others.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

I think mine was the AR15 and I think the AR1500 was the first split supply receiver with DC coupled output stage.

I had a part time job repairing consumer electronics and kept a big bipolar cap on my test speaker to avoid blowing it whilst troubleshooting. That and a variac to raise the voltage slowly, saved a lot of grief.

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I had two sets of three 24 Ohm 300W non-inductive resistors in parallel for an eight ohm loads, with small speakers and dropping resistors so I could test amps at or near full power without breaking the windows. It was very handy for testing guitar amps for rock bands.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

Me too. I had three 2 ohm 75 watt resistors bolted to a chunk of aluminum, and switches so I could short the series cap and/or switch in the dummy load resistors.

Them were the good old days...

Now days they use a lot of modules. I fixed an old (late 80's) X brand receiver for a friend recently with four high power Darlington output modules. If I didn't find the silly (discontinued) things on a surplus web site ($15 ea), it probably would be too expensive to fix. I doubt one could make a living fixing what they turn out today (if it ever breaks)

I keep my homebrew discrete mosfet alive and it is damn near indestructible. I had several hot strikes from the Tesla coil hit the speakers and the only damage was a 100K 1/4W resistor opened that was supposed to provide a ground reference to the input of the output stages. I think the TC did it...

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I've seen a 4' Tesla Coil make a football player scream like a little girl, so what chance did that tiny resistor have? ;-)

Another handy item was a good 4" speaker mounted in an old Alliance U100 rotor control case with a line transformer, a couple switches and a pair of banana jacks. The front of the case had a piece of perforated metal between the speaker and the case. It let the sound out, but protected the cone. The bottom metal plate was installed with contact cement so it didn't rattle.

One switch selected either 25V / 4 Ohm or 70V / 8 Ohm and the other selected high or low impedance. It was quite handy looking for the right pair of wires on school intercoms, paging systems and other speaker systems.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.
Reply to
Michael A. Terrell

.

Homebrew discrete mosfet? 2sk1058?

Reply to
Michael

20 years old I'd have to look up a schematic.. Some complimentary Hitachi parts for the bass amplifiers and ordinary bipolar for the treble amps. I got a pair of surplus Crown amps (500 watts into 8 ohms and 1,000 into 2-5 ohms) intending to tri-amp but never got around to it. Too many interesting things to do and never enough time.

The Crown amps were a steal for ~$150 each - never used and intended to go into an MRI for hospitals as "gradient" drive amplifiers, but they are stock Crown audio amps, weighing in at >100 lbs each. No meters on the front.

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