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Old 14th July 2012, 09:08 AM   #31
Vostro is offline Vostro  South Africa
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Late Edit:
Quote:
Originally Posted by Vostro View Post
The simulation with the "darlington VAS" caused Q3 to saturate badly
only when amplifier is diven into clipping the output.
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Old 17th July 2012, 08:49 PM   #32
Vostro is offline Vostro  South Africa
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Been thinking about layout and was wondering if there would be any benefit
between these two layouts ?

thanks
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Old 17th July 2012, 09:19 PM   #33
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"The simulation with the "darlington VAS" caused Q3 to saturate badly"

Try using a 1N4148 from the base of Q21 to the collector of Q3.
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Old 23rd July 2012, 08:01 PM   #34
Vostro is offline Vostro  South Africa
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Thanks djk, I tried with a 1N4148 and big problem clipping nearly entire top half cycle,

Then I realise I didn't make it clear that supplies are over +/- 60Vdc, causing 1N4148 to break a sweat.
I replaced with uf4004 and perfect, thanks for the advice, solved the problem.
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Old 6th August 2012, 11:56 PM   #35
Vostro is offline Vostro  South Africa
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I think I'm done and ready to build if I get some free time,

I decided to use 3 pair output since it fits my heatsink

Ive not decided on which driver transistors to use yet.
Im using MJ21194/3 OPS since I have some.

I was wondering it it will hold up to 4ohm load (2 amps bridged)
from 35V-0-35V 500VA toroid.
It will go into BassBin with single 400W 12inch 8R Bass speaker.
Making a active Bass speaker for a friend of mines bass guitar.

Also if I use the heatsink in attach, what length heatsink would be good
per amplifier.

Also is V/I limiter only way of protecting against short speaker terminals,
I think I must include this .

And lastly What is max supply votage you would reccomend for 4R and 8R speakers.

Thanks so much,
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Old 7th August 2012, 02:16 PM   #36
amptech is offline amptech  Scotland
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Vostro, v/I limiter or multi slope is a standard way in many amplifier circuits as with out them more damage can and will happen if o/p stage takes a direct dead short.. the main point of these simple circuits is to remove the drive voltages to the o/p devices.. take a look in to amplifier 'cook' books such as G randy slone's high amp book he out lines such circuits.

your question regarding using your amp in four ohms bridged.. try it at 8 before pushing it down to 4 ohms...(some power amps use more o/p devices to aid current share at such low loads.

max supply rails for your amp could run up to 60 vdc/ 70vdc.. but a safe bet would be 50vdc. your get more power output at different dc rails and up grade your filter caps to say 10000uf to 20000uf at higher dc rated..

anyway put things together and let us see...
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Old 7th August 2012, 03:07 PM   #37
Vostro is offline Vostro  South Africa
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Thanks amptech, Ill see if I can get hold of the book you advice,
The bridge amp will be used on a 8R speaker only,
I meant to say that each amp would see a 8R load as 4R each when bridged.

Yeah cant wait to get it built.
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Old 7th August 2012, 04:20 PM   #38
amptech is offline amptech  Scotland
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@vostro, if you was to add v-limiter circuit a rethink of pcb..or use strip board and prototype in to the working amp pcb..
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Old 26th September 2012, 09:08 PM   #39
Vostro is offline Vostro  South Africa
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Im going to add this small VI Limit to my amp,
Hoping it will be OK, If I get time, Ill do some testing and tweek values if needed.

Regards
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Old 26th September 2012, 09:24 PM   #40
Vostro is offline Vostro  South Africa
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Ive Built up my next Amp, Running from 45V-0-45V AC, using 3x MJL21194/3 as outputs.


To test it, I played a 20Hz, 1kHz, 20kHz signal into 8R resistive load.

Clipping starts at 180W into 8R, if I change RC filter for IPS rails I guess I could get more, but Im fine with 180W into 8R.


But I have a question about the clipping behaviour

The trailing slope of the positive halfcycle at output is clipping weird.
At 1khz its noticeable and at 20khz its very visible.

Im not sure what causes this, Advice will really be appreciated.

Thanks,
Vostro

- The Miller Cap is 100pf, ive not lowered it to 47pf yet,
- The amp is connected as is, no added protection baords etc.
- Aprox currents are indicated.
- Heatsink is only for testing.
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