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Old 27th July 2011, 05:44 AM   #111
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Hi Pete,

your transformer will roughly give +-76V DC at idle and up to +-80V considering the mains voltage variations. the lower limit depends on the transformer size and load, and can go down to +-60V in worst case. thus a 600W module can be used if the under-voltage threshold is set to about 60V and the bias resistors as well. no need to unwind the transformer unless you want to use a lower power module such as the 400W or 250W one(s). what is the size and power rating of the transformer ?
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Old 27th July 2011, 09:07 AM   #112
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This is the PA amp I have, was in the process of repairing but the pcb's on the output stages are in very poor condition.
Click the image to open in full size.

The power rating of the transformer is not written on it but the amplifier its from was class AB producing 400Wrms 4ohms and 240Wrms 8ohms per Chanel.

Separate transformer etc for each Chanel. Each transformer weighs about 8kg

Each 54V output before rectification has a 10 amp fast blow fuse.

My mains voltage is 244-247V so this probably explains the high rail voltage.



Im glad to know I could use the 600w module with a couple of components changed

Do you think I could maybe use 2 per transformer?
 
Old 28th July 2011, 03:08 PM   #113
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Would I be right in calculating these transformers are roughly 1000VA?
 
Old 29th July 2011, 12:43 AM   #114
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well if it's 400wrms into 4ohms and its class-ab

I'd guess they are about double the output power ideally so 800va each at the most i would guess, because I doubt they would overrate it.
 
Old 29th July 2011, 07:20 AM   #115
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Pete,

that amplifier looks very rugged, and i think it deserve one more chance to fix-it. if cannot be fixed, then you can consider replacing the power stages. being a class AB amplifier, the transformers are rated to probably double the output power. using class D modules instead, will allow you to get at least 1000W on each channel, considering their higher efficiency and the fact that the power drawn by the amplifiers is not continuous and this transformers have a long enough thermal constant to allow short time overload.
so, i assume that 2 class D IRS2092 modules for each transformer is not too much and they should supply them without too much voltage sag. if the amp was not used for a long time, check the big electrolytic capacitors, see if their capacitance hasn't drop and if there are no leaks.
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Old 31st July 2011, 02:20 PM   #116
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Thanks for all the help!

Allot of the tracks on the pcb are broken, the working output pcb has been repaired before and has allot of bad looking jumpers where the tracks are broken.

When the output broke I was playing a 50hz sine wave into it and measuring the output voltage with no load with the gain all the way up, So i could set the limiters on my dcx2496. A friend who repairs lots of amps tried replacing the large transistors but it broke 4 when switched on so he just told me to replace everything on the board apart from resistors as they have not been damaged.
 
Old 11th October 2011, 04:52 PM   #117
cOz is offline cOz  United States
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Is the input impedance of the ScaleD IRS2092S 3.3k ohms?
 
Old 11th October 2011, 05:58 PM   #118
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yes. same as in the ref. design. if the source has higher impedance, a buffer will be required. on a next revision i could add an OP amp on the board if will be required.
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Old 11th October 2011, 07:22 PM   #119
col is offline col  Australia
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Hi Cristi,

Does the single channel IRS2092 Modular Amplifier take a balanced input? Also, will the 250W version work well with the A350SMPS?

Edit: I also can see a black relay on the PCB, is that speaker protection?

cheers,
col.
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Last edited by col; 11th October 2011 at 07:24 PM.
 
Old 11th October 2011, 10:27 PM   #120
cOz is offline cOz  United States
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Quote:
Originally Posted by Cristi View Post
yes. same as in the ref. design. if the source has higher impedance, a buffer will be required. on a next revision i could add an OP amp on the board if will be required.
The source that I am looking at has 600 ohms.
 

 


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