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Old 28th April 2007, 11:45 AM   #1051
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Hi Carlos,

I was just looking through the "substitute transistor" list and was wondering about the input transistors. With the standard rail voltage of plus and minus 35 volts, which transistors are suitable.

Is Vceo > rail voltage the criteria?

Does your simulation show the actual voltage across c and e of Q1 and Q2?

Thanks
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Old 28th April 2007, 12:08 PM   #1052
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Default Emitters are near zero volt...and colector is -36 Vdc

Yes...Vce bigger than the rail will be enougth...better beeing twice the rail...to enter linear region.

So.... the transistor will hold a rail voltage, not from rail to rail.
Vce max beeing under that voltage will work fine there... the one that hold all voltage swing is the voltage amplifier.

The current swing in those input ones is very small..and voltage is also very small there.... as a consequence, power is small too.

The rail voltage more half the voltage swing (1.2 volts) will fit... (read Eva)

I think that all transistor suggested will work fine, and many of those were tested in my prototype....no problems Greg.

Selecting transistors that can hold twice the voltage you will have in your circuit, probably will fit, as the linear region use to be not so far away related half of max Vce.

Gain is very important for those ones...but even beeing this way..i could have very good results replacing 400 of gain to 120 of gain... even the colector load did not need adjustment.

Have you found something strange?.... go ahead....

Read Eva.... "Eva es la mejor"

http://www.diyaudio.com/forums/showt...931#post539931

regards,

Carlos
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Old 28th April 2007, 12:24 PM   #1053
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Default Re: Emitters are near zero volt...and colector is -36 Vdc

Quote:
Originally posted by destroyer X
Have you found something strange?.... go ahead....
Thanks Carlos,

No I haven't found anything. I was just looking at the wide range of Vceo in the substitute list and noting the lead orientation. Some will fit the same way as the 2N5401, some rotated and other will need 2 of their leads twisted.

regards
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Old 28th April 2007, 01:36 PM   #1054
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Default re. more power

Hi carlos,
I think I have the point then, I will use bi-amp in this instance. I have 2 (max 300W) woofers in a cabinet then, I will use one amp for each woofer. That make 4 100w rated amp. 2 smaller amp for the (max 120W) mids and (max55w)tweeters.

But can I press more on your X design. Increase a little bit more. I'm thinking of reduce the overall gain in exchange some more base current for the output, sure a buffer preamp is needed. If you can show me the way.

regard,
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Old 28th April 2007, 01:45 PM   #1055
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Default No..i am not experienced related the mods you want.


Dx amplifier is cheap and simple....also it is already done.

modifications you should make may be under your own risk.

Try Symassym high powered version...or the Linx...they are very good and powerfull too.... and Linx has room to obtain much more power.

regards,

Carlos
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Old 28th April 2007, 01:51 PM   #1056
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Default re. aaa

Thanks any way Carlos,
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Old 28th April 2007, 01:57 PM   #1057
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Default You are welcome Phong.


regards,

Carlos
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Old 30th April 2007, 11:09 AM   #1058
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OK Charlie, last help before we start the fire....

I now have the board mounted, insulated and thermal pasted...
60w lightbulb in series with live wire from mains....
wire harness connected
short connected over intput
3 multimeters with homemade crocodile clip wires...(was way cheap and I can kick myself for not haveing made em before... All you need is a 4mm regular banana plug, the clip and a piece of wire...perfect for low voltage work....)
10R 10W resistors installed in stead of fuses - only connected on amp side, so I can first measure check PSU section voltages... (did mini check with 9v battery last night, seemed fine).

Then I will solder the other lead of the resistor in place.

Install voltmeter on 2V range over the resistors

hide behind pillow, and switch on, then

a.) look for something to extinguish fire with ... eyes cat.

b.) see a voltage in range in the DMM

wait 10 seconds

adjust 10k pot until voltage on V+ rail resistor reads +- 0.5V

SHOULD OFFSET DMM BE CONNECTED ALL THE TIME?

adjust offset to 3mv

readjust 10k pot
adjust offset etc. until stable....

Does this sound right?
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Old 30th April 2007, 11:18 AM   #1059
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Hi Nordic,

It seems like Carlos is having a day off.

Are you following the "Adjust the bias, and trimming DC offset" instructions found here: http://users.tpg.com.au/users/gerskine/dxamp/

To quote step 11.

"Adjust the bias (VR2) to between 800 and 1,100 millivolts (0,8 and 1,1 volts) on each rail. Remember the positive rail will read slightly higher (about 100 millivolts) than the negative rail."

Please let me know if the instructions are not clear, so I can amend them.

regards
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Old 30th April 2007, 11:35 AM   #1060
Nordic is offline Nordic  South Africa
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Hi greg, I have the other PCB type if you remember so I suppose it has minor setup diffirences... won't 1V over 10ohms give me 100mA bias? I thought Carlos said to go for 50mA....

PS. is it ok to have output DC DMM from the start or should I wait till biasing is set up innitialy?
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