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Old 7th April 2012, 02:46 PM   #91
Bensen is offline Bensen  Belgium
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Hi Andrew,

I've swapped the resistors. I matched the 47Ohm resistors with my multimeter => to 1/10 Ohm reading.

I've measured and collected all currents from LTP/CCS and VAS, this with and without DC-servo.

When running without the servo I did one other test ==> I had to lower the CCS resistance for the positive LTP from R430 to R315 to have an offset of 0.

Greetz
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Old 9th April 2012, 07:59 PM   #92
Bensen is offline Bensen  Belgium
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I understand it, the only option to avoid big DC-offset's at startup is to adjust the bias of the LTP.

But, I don't like trimmers on the amp pcb. So I turned another way with this.

I regulate the CCS for the LTP, with;
- A 10K trimmer (P21/22) with a voltage devider (R100/101/102)
With this I can set the startup DC-offset to 0V, this avoid a startup thump
due to 600mV offset when the relay kicks in.
- A DC-servo for the dynamic DC-offset ==> Phase shift of this DC-servo is 0
and has 75dB at 10Hz.

At the moment is running in real life.
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Old 10th April 2012, 08:42 AM   #93
AndrewT is offline AndrewT  Scotland
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when setting up the amplifier you need to trim the voltages so that Ir1= Ir2 and that Ir3=Ir4

That gets the two LTPs into balance.

Then set DC output offset to zero by adjusting input Rin or adjusting VAS or setting the DC servo to work if offset is already low when the amp is cold.
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Old 5th June 2012, 08:18 PM   #94
Bensen is offline Bensen  Belgium
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Default Update

All pcb's are ready except the protection board based on the TA7317 chip.
The heatsinks have to be ordered: 4 pieces 200mmx165mm from modushop.

Pcb's are all made with the toner transfer method, cleaned and varnished afterwards.


Enjoy the pictures.
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File Type: jpg SAM_0727-2.JPG (163.1 KB, 218 views)
File Type: jpg SAM_0666-2.JPG (134.7 KB, 215 views)
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Old 5th June 2012, 08:21 PM   #95
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Is the amp approved by you and ready to be build?
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Old 12th June 2012, 08:17 PM   #96
Bensen is offline Bensen  Belgium
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Default Compared with DENON PMA700V

I had the opportunity to do a listening test of my amplifier compared to a DENON PMA700V.

I must admit, the DENON sounded warmer and had more depht in the music.

I wonder what the mean reason is for this?
Could it be the open loop bandwith? This is according to simulation +-7Khz.


Still, I will finish the amp completely and doiing some research for the next.

Greetz
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Old 14th June 2012, 04:10 AM   #97
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Wink Simple the best!

Hi guys!
Why complicate the schematics for subwoofer, subwoofer percent for the frequencies below <150Hz!?
Go to something simple, but powerful (200 ... 400W)!
Cheers!!
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Old 14th June 2012, 06:12 AM   #98
Bensen is offline Bensen  Belgium
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If I could edit the thread title, I would have done it.

Yes, the idea is to use it for a subwoofer, and indeed the complexity is a bit overkill for a sub amp.


But, this was for me a learning project for a next amp.


Concerning power, there are two amp PCB's which are delevering more than 250Wrms/8r for my peerless xls12 sub,this is more than enough for me.

Greetz
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Old 14th June 2012, 09:14 AM   #99
AndrewT is offline AndrewT  Scotland
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Ask the Moderators to adjust the Title.

Maybe
" Amp design for subwoofer and wideband duty".
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Old 3rd August 2012, 07:08 PM   #100
Bensen is offline Bensen  Belgium
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Default Update: one channel finished

Andrew, I've asked one of the operators to change the thread title, sofar I haven't received an answer.

Regarding the comparisation with the Denon PMA700, I noticed when I increase Bass and treble on my equalizer, my amp sound much more like the Denon.


The heatsinks have arrived. I use 4 heatsinks of 165x200mm from Modushop.
With a welded metal construction I connect two heatsinks to eachother and can mount them on the bottom plate.
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