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Old 10th November 2009, 07:28 PM   #41
Did it Himself
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I would imagine that 2 amps built the same drift similar amounts so the cap isn't needed.

But I do agree Mooly that for the "gains" bridging is not worth the extra hassle for this guy.
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Old 10th November 2009, 10:12 PM   #42
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don't mean to butt in here rather rudely, but I think Mooly and another user did explain why: becuase of instability with the midpoint voltage, and the need for a phase inverter (mind you a transistor with taps on emitter and collectro would work fine I suppose).
But mainly for this reason, which is my own:
This is a circuit that was designed decades ago, when bridging wasn't even a word in audio. It would be counter-intuitive to apply modern-day techniques to an old design which will only show more its shortcomings in bridged mode. It will not retain its essence. At least that's what I think. I have an amplifier that is a copy of an EICO Cortina 3070, just like the schematic (very close) and can tell you that the midpoint voltage is not only subject to instability, but has the "thump" when you turn it on...

If you want more power, why not then take another design, like the more common PNP-NPN push pull circuits?

Or simply raise the supply voltage...
Quote:
Originally Posted by richie00boy View Post
Why do you say the circuit is unsuitable for bridge?
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Old 11th November 2009, 07:54 AM   #43
Pigy is offline Pigy  Serbia
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Quote:
but has the "thump" when you turn it on...
This problem exists with today's modern amplifier also.

This problem is solved using individual components.
I want to say that there are seeds that will solve it

I know that will need me to phase inverter for bridge amplifier.

I send you a scheme very simple inverter.

Edit my sheme with the differential pair of transistors requires a good knowledge constructors.I do not have to.

If I had the offset of the 2-3V, I know that it is more complex and spam.
Then I have a big problem to make the bridge amplifier
I hope so that I don't have that big ofset.

I think that dissipation of offset voltage to be spend on emiters resistors on output transistors?Am I right?

Can you tell me whether this amplifier can really give 25W?

The voltage of 30V, I think I can not get 25W?
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Old 11th November 2009, 08:14 AM   #44
Mooly is offline Mooly  United Kingdom
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Hi Pigy,
30 Volts supply will give you around 26 volts peak to peak across the load (transistor losses and all) which is around 10 watts rms into 8 ohm and 20 watts into 4 ohm
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Old 11th November 2009, 12:07 PM   #45
Pigy is offline Pigy  Serbia
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Quote:
Originally Posted by Pigy View Post
This problem exists with today's modern amplifier also.

This problem is solved using individual components.
I want to say that there are seeds that will solve it

I know that will need me to phase inverter for bridge amplifier.

I send you a scheme very simple inverter.

Edit my sheme with the differential pair of transistors requires a good knowledge constructors.I do not have to.

If I had the offset of the 2-3V, I know that it is more complex and spam.
Then I have a big problem to make the bridge amplifier
I hope so that I don't have that big ofset.

I think that dissipation of offset voltage to be spend on emiters resistors on output transistors?Am I right?

Can you tell me whether this amplifier can really give 25W?

The voltage of 30V, I think I can not get 25W?
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File Type: gif OkretacFazeZaMost.gif (13.1 KB, 195 views)
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Old 11th November 2009, 12:47 PM   #46
Mooly is offline Mooly  United Kingdom
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Hi Pigy,
I think you have to decide what you want to do

I still say the design is not suited to bridge operation for all the reasons outlined.

If you go ahead anyway then the IC phase splitter is best (you need a split supply) and you must AC couple the speaker.
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Old 11th November 2009, 01:11 PM   #47
lohk is offline lohk  Europe
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Quote:
Originally Posted by tiefbassuebertr View Post
Some years ago I find on the web a German diy project, that have the same topology. Unfortunately this article is deleted. Because I have store this websites, I have make a pdf file (see botton). The same author has descript a possible of a bridged version about this topology - but unfortunately this article I haven't. Both article was release in the no longer available German diy magazine "ELRAD" (not "elector") between 1985 and 1990 - as I know.
You can ask Mr. Gerhard Haas about this article, title "Brücken-Teufel" (bridge devil) - Go to the weblink
EXPERIENCE electronics - Contact
to send an e-mail about this -
because about EXPERIENCE electronics - HiFi-Amplifiers 'Classic'-Series
this information presently not available

Many thanks for mentioning these amps and for the links - I have made one of these "black devils" way back in 1986, I think, but it had such a good sound that some studio people never gave it back to me. Why did that design not create more attention? Even in those days simple design with output caps were somehow suspect...
Gerhard Haas published another article with some modifications to the original circuit, do you have this informations? (I have only the orginal ELRAD mags with the basic article. - ELRAD was btw also the first magazine which published John Lindsey Hood in german)
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Old 11th November 2009, 01:13 PM   #48
wg_ski is offline wg_ski  United States
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The simple way to phase invert - works on most feedback amplifiers. For this circuit, this is all the trouble I would go to. It takes just one more component.
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Old 11th November 2009, 02:03 PM   #49
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I would not use that method on this amp as the different gains and feedback resistors will cause different offsets.

There is a balanced line output project on my website which would be exactly what you need to produce identical but phase reversed signals that will happily drive the amp.
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Old 11th November 2009, 03:04 PM   #50
wg_ski is offline wg_ski  United States
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Quote:
Originally Posted by richie00boy View Post
I would not use that method on this amp as the different gains and feedback resistors will cause different offsets.

R5 is capacitively coupled, the DC gain is 1. How bad could it be with just a little resistor selection? 50 mV?
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