Which Subamp? (P68,IRS2092,Thermaltrak) - diyAudio
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Old 3rd September 2012, 10:17 AM   #1
superR is offline superR  Netherlands
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Default Which Subamp? (P68,IRS2092,Thermaltrak)

I am currently cleaning up my audio chain. The front-amp's are 99% finished, the Sub-Sat filter is in a nice enclosure too and now I am thinking of cleaning up my Subamp. I have a 8 ohms subwoofer driver so for some power I need quite a lot of voltage.

I currently have a IRS2092 pcb with a psu of 2*70Vdc rails. I can of course reuse that pcb, but I want to look at other options too.
MY DESIGN L20D IRS2092+IRFI4020H 200W8R

I have interest in the ESP P68 amp, since I have some spare MJL21193/4's
300/500W Subwoofer Power Amplifier

Another option is going with Thermaltrak transistors since I have many of them. Maybe combining with a LME49810/1 or LME49830 is a good option.
Initial Series

Going cheap&easy is using the IRS2092 PCB I have
Going easy is ordering the PCB's for the Thermaltraks
Going "all the way" is designing a PCB layout and using the MJL21193/4 in a P68-like design or the Thermaltraks in combination with a LME49810/1

The options are there, but which one should I go for?
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Old 3rd September 2012, 12:22 PM   #2
superR is offline superR  Netherlands
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Hmmz, the "all the way" option is going fast. Maybe that's a sign.
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Old 6th September 2012, 11:34 AM   #3
superR is offline superR  Netherlands
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About P68:
Does any of you have an idea on heat dissipation of +/-70dc on 8 ohms or bridged (+/-50vdc) onto 8 ohms in living room operations?
I am looking for a proper heatsink-method but don't know which to use.

Last edited by superR; 6th September 2012 at 11:54 AM.
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Old 8th September 2012, 07:05 AM   #4
superR is offline superR  Netherlands
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I am still testing the P68. Harmonics are high. Is there a way of improving this. Maybe force the bias up or is this true class B?
Testing is currently done on a powersupply with lax +/- 35Vdc. Will incresin the supplyvoltage automatically increase the bias?
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Old 9th September 2012, 12:15 PM   #5
djk is offline djk
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" Harmonics are high"

What about the woofer distortion?

The bias should not change much with a change in supply voltage, the optimum bias would be about 340mV on the bases of the outputs (class AB+B).
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Old 9th September 2012, 09:25 PM   #6
superR is offline superR  Netherlands
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What I meant was, that it is high compared to for example a P3A or my previous amp. I was expecting lower 2nd and 3rd harmonics. I will make a proper measurement within a couple of days.
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Old 10th September 2012, 01:41 AM   #7
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More open-loop gain will reduce 2nd harmonic, but so what?
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Old 10th September 2012, 07:19 AM   #8
superR is offline superR  Netherlands
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Isn't everyones goal to make a proper amplifier, no matter if it is used to drive a subwoofer or expensive loudspeakers? Now I am not saying that the P68 is bad, but I noticed the hogh harmonics and started to wonder if it could be improved.
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Old 10th September 2012, 08:22 AM   #9
djk is offline djk
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Sure, even harmonics can be reduced with more feedback. Using an active current source with the Vas and a Current-Mirror for the diff pair will raise the OLG quite a bit. Why not just stick a Ne5532 in front of it (as stock), it would be a lot simpler.
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Old 10th September 2012, 09:06 AM   #10
AndrewT is offline AndrewT  Scotland
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bridged +-50Vdc !!!!!
what kind of speaker are you planning to attach?
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