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Old 9th December 2012, 02:10 PM   #2511
palmito is online now palmito  United States
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Quote:
Originally Posted by Salas View Post
A parallel output with 100 Ohm buffer resistors in line.
I have double outputs to the amp and a self powered subwoofer, didn't use the 100R resistors. Seems to sound ok so far, have had no issues with it. Should I put the 100R resistors in anyaway?
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Old 9th December 2012, 04:11 PM   #2512
Renron is offline Renron  United States
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I was wondering the same thing. Wouldn't the 100R just act like an attenuator?
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Old 9th December 2012, 04:51 PM   #2513
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I have had my 100R in for years, no gain problems. And not just in this project. I imagine it will tweak impendence a bit. I've had some very large resistors in line 10k on input before - you can calculate the voltage drop and gain with a t-network. Do not know the formula off the top of my head.
you can always do without, unless you run into some issues- then put them in.
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Old 9th December 2012, 06:10 PM   #2514
Salas is offline Salas  Greece
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If there are no oscillation issues in a system without the buffer resistors, then leave it at that. Their purpose is to counteract against more capacitance by the double cable runs towards the biamping configuration.
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Old 9th December 2012, 06:12 PM   #2515
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Renron View Post
I was wondering the same thing. Wouldn't the 100R just act like an attenuator?
Quote:
I have had my 100R in for years, no gain problems. And not just in this project. I imagine it will tweak impendence a bit. I've had some very large resistors in line 10k on input before - you can calculate the voltage drop and gain with a t-network. Do not know the formula off the top of my head.
the reason TB has not notice any gain issue, or more correctly lack of gain is due to attenuation =
20*[log 10k/{10k+100}] = 20*log0.99009 = 20*(-0.004321) = -0.086dB
The attenuation created by the 10k input impedance is less than 0.1dB.
If there was a 100k stage to be fed by the DCB1, then the attenuation <0.01dB, (actually -0.00868dB).

Stop worrying about next to nothing.
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Last edited by AndrewT; 9th December 2012 at 06:14 PM.
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Old 7th January 2013, 09:00 AM   #2516
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Hi all.. Thanks for this great thread.
I received Tea Bags package some time before christmas and started soldering yesterday..
Some pics attached.

I have a couple of building questions:

As some people has mentioned before. The direction of the led's. I got a bit confused and have not soldered them yet. But they have been matched..

Is this correct?
Where 5 are gathered together. the square solder marks connects to the Cathode?
Where 3 are gathered together. the square solder marks connects to the Anode?

I have (on hand) 2 pcs identical 2*12v secondaries 15va toriods. Is this enough for testing purposes? I could maybe parallell them so I get 30va?

What is recommended V and va value on transformer for dcb1?

That is enough for now..
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Old 7th January 2013, 09:10 AM   #2517
Salas is offline Salas  Greece
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Quote:
Originally Posted by bambadoo View Post

Is this correct?
Where 5 are gathered together. the square solder marks connects to the Cathode?
Where 3 are gathered together. the square solder marks connects to the Anode?
Vice versa.
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Old 7th January 2013, 09:14 AM   #2518
Salas is offline Salas  Greece
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Quote:
Originally Posted by bambadoo View Post

I have (on hand) 2 pcs identical 2*12v secondaries 15va toriods. Is this enough for testing purposes? I could maybe parallell them so I get 30va?

What is recommended V and va value on transformer for dcb1?
For testing purposes and your 10 Ohm setting resistors, one Tx will be enough. To parallel successfully they should be well matched. A 50VA 15+15V Tx is good in general up to medium hot rod.
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Old 7th January 2013, 09:21 AM   #2519
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Originally Posted by Salas View Post
Vice versa.
Hehe - sorry of course - At work now and my mind is elsewhere...
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Old 7th January 2013, 12:46 PM   #2520
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Quote:
Originally Posted by Salas View Post
Square hole is Led's anode in this pcb as crt designated that half circle symbol over the 5 Led groups, when its the cathode in the 3 Led groups. If you put just one in reverse they will not shine, but no reason to blow a reservoir cap. In fact its the first time I hear someone blows a reservoir cap. Could it be it was reversed for polarity by accidental insertion or just very unlucky to chance on a dodgy one?
Yes it was this post I was thinking of..

Sincerely
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