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Old 6th February 2013, 08:13 PM   #81
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100 % right . I will have a drink on Thursday with John . I think Carlsbor was his favourite fairground amp . He has repaired everything I have ever named , uses Turbo Sound himself . As you say about makes and quality .

HH proves that something that others would dismiss have successful commersial lives . When I see amps that are 70% protection systems I despair . It is possible to build things that are simple and work .

Last edited by nigel pearson; 6th February 2013 at 08:17 PM.
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Old 29th March 2013, 07:33 PM   #82
Aniket is offline Aniket  India
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Default 980W@2R 0.169%THD@20kHz

Quote:
Originally Posted by vedmitraa View Post
Here is a circuit of 2n3773 8 pairs,70-0-70 volt d.c. 42 volt output at 0.497% distortion power output 887 watts into 2 ohm
With just 24mA bias per device, and 9.3nV DC offset. 980W@2R ultra low THD of 0.169% @ 20kHz, with 5 pairs MJL21193/4. THD could be further reduced using more output pairs.
Just simulated my design, wonder it would perform like this in real.

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File Type: jpg 980W_2.jpg (292.3 KB, 402 views)
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Old 29th March 2013, 08:09 PM   #83
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I think you could build it with a pair of devices and try 8R . How is it at 100 W 8 R ?

24 ma should be excellent as bias .

I often still use TO3 devices . I have no problem using flying wires to the PCB . That way adding a few is not difficult .

I have even run transistors in buckets of water . It sometimes works well enough until the water contaminates . 1 bucket per device . I think I have gone to 70V before now ?

My dream is to put some TO3's with their heads in a water pipe . It should work reasonably well . Not perfect as the die is on the connection side . A pump will be needed . Isolated TO3P even better . 90% could be in the water .
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Old 29th March 2013, 09:10 PM   #84
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by Aniket View Post
Just simulated my design, wonder it would perform like this in real.
Why, of course not.
There's a ton of important parameters that simulation is not considering which will affect end results big way.
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Old 29th March 2013, 09:14 PM   #85
AndrewT is offline AndrewT  Scotland
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Aniket,
ask the simulator what current is passing R3 and R4?
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Old 30th March 2013, 04:03 AM   #86
Aniket is offline Aniket  India
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1.079 and 1.08 mA through R3 and R4 respectively. Images attached.

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Aniket
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File Type: jpg 980W_2.jpg (464.7 KB, 289 views)
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Old 30th March 2013, 09:00 AM   #87
AndrewT is offline AndrewT  Scotland
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1.079 and 1.08 equals 2.159mA through Q3 collector. Add on ~1% of this for base current and you should have ~2.18mA through R6, giving Vr6=479.6mVdc.
Is that what is being modeled?
You MUST check this when you build !!!!!!!!!!!!!!!!
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Old 30th March 2013, 10:46 AM   #88
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It is a very brave design . I know of a commersial design that uses 0R47 as emitter resistors , the designer feels it gives reliability ( I have no idea if true , seems logical ) . He also insists only Motorola devices to be trustworthy . His belief is they survive double the current of competitors . His preference is for devices that offer 4 MHz . Again as they seem to be tougher and sound nicer ! No simulator knows that . Worth a thought ?

Even if you had no proper heat-sink you could run it for a few seconds with two output devices into an 8 ohm load . 2 x 50 watt car bulbs in series taken to 20 V rms would be a start ( careful they will get very hot , 4 = full load ) . If the amp doesn't die quickly you head for the sky . I feel a bit jealous of you , I am useless with simulators and yes I never read instruction manuals . Nelson Pass said the same . Hey what does he know ?
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Old 30th March 2013, 12:42 PM   #89
dvv is offline dvv  Serbia
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Actually, emitter resistors could be taken as a form of local feedback, so increasing their value will be good if they should run into a very difficult load.

As ever, there is a price to pay. Increasing their value can (but not necessarily) increase distortion and reduce bias to ridiculously low values. Off hand, the bias spread they are supposed to perform would be 30-40 mA per trannie, which is low.

Actually, Nigel, I've seen as much as 0.68 Ohms in commercial designs, Krell once did all of 1 Ohm, and the LAS I introduced in the other thread uses 1.5 Ohms, 17W emitter resistors, but admittedly, that's a rather exotic design.

The higher the value of the emitter resistor, and if the requirements stay the same, the higher power dissipation will be needed, although this also depends on what is expeczed of the amp regarding low impedances.

The point being that these resistors have much to do with thermal stability of the amp its so called "bias spread" under higher power dissipations.

In purely audio terms, the lower the value, the smaller their influence on the sound and the greater the transistors' ability to push out more current.

With all respect, Andrew, I would suggest you look over, preferably read in detail, Bob Cordell's manual on designing power amp. It's like 600 pages and is by far the most complete "manual" I have ever seen, compared to which Douglas Self is a baby in nappies.

You will find in it literally ALL of the procedures you need to follow, plus the math.
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Last edited by Mooly; 12th May 2013 at 11:26 AM. Reason: Email removed re copyright issues
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Old 30th March 2013, 12:47 PM   #90
AndrewT is offline AndrewT  Scotland
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dvv,
what problem have you seen, that I have overlooked in my advice?
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