A little more twisted than usual....

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Hey Folks,

I have a few projects that have a lot in common, and they are beginning to run together in terms of concerns. In fact the ideas are modular, and build on each other.

Examples:

Twisted Sibling - A balanced line driver/preamp and SE/BAL converter.
Twisted X Overture(TXO) - A balanced symmetrically bridged power amp.
Twisted X Symphony(TXS) - Same as TXO but with two OPA549 working at much lower gain (the gain is handled more by the THS41xx in this case).

Anyway, I have made a whole lot of progress on this stuff, but it does not belong in any single thread, until now. I have decided to launch his thread to discuss the modular approach to all three projects. More projects are planned and in the works based on the modules contained here.

Using the modules I have designed one could create a power amp project of anywhere from 50W to 300W or more....

Anyway here is an article to get people started. I am very interested in feedback from the community here, and ideas. This document is pretty high level. I don't want to lose people in details just yet. :) But this is the place to talk about it, and expand on things. Any important info will be added as a new revision of the document.

I will probably write more detailed articles later should people be interested.

A Very Twisted Missive

Cheers!
Russ
 
Ed Lafontaine said:
Is it appropriate to ask if DC blocking can be addressed in a coherent fashion?
For instance: "If your XX pre output contains no DC component you may omit the caps."
Is there a "best" place (or way) to manage DC content?

I really like what you're doing Russ.


Thanks Ed!

My first choice to block DC would be at the source which is what we do on the Opus.

If you used Opus --> TXD --> JT --> TXO you would nothing other than DC blocking caps which are already on the Opus DAC.

For another source, if you thought you needed it you could add an external CAP. In most cases this will not be necessary, when it is that caps people want are widely varied, and are probably best handled off the PCB.


Cheers!
 
Russ, count me in.

Do the twisted amps handle low impedance loads? I'd like to build an pair of amps of 60 to 100 watts each to drive ESLs. Will the amp's protection circuit handle an overcurrent condition well?

Thanks to you and Brian for your work so far.
 
BillH said:
Russ, count me in.

Do the twisted amps handle low impedance loads? I'd like to build an pair of amps of 60 to 100 watts each to drive ESLs. Will the amp's protection circuit handle an overcurrent condition well?

Thanks to you and Brian for your work so far.

Your welcome. :) Its a lot of fun for me too.

If you run the TXO with 2 output (TPM-LM3886) PCBs in parallel per side (4 total TPMs) then you could easily drive just about any load. And would be able to do 200+ watts.

As for overcurrent protection there is nothing I have designed explicitly for that on the PCBs, as that would limit the design somewhat, but the LM3886 itself does afford some degree of protection.

BTW, PCBs have been ordered... we will keep you all posted.

Cheers!
Russ
 
Hi Russ,
I thought that your SuSy schematic with OPA549 (http://www.diyaudio.com/forums/attachment.php?s=&postid=987634&stamp=1156203340) would be nice for a 100W/8 Ohm amp my friend wanted me to help him with so I prototyped it quickly today ("fly by wire" - not even a decent p2p). I only changed it so that OPA549 works as an inverting amp and I used OPA1632 (according to datasheet it has a bit more voltage swing than THS4131).
The result was so good that I thought I have to report it back. It was a quick, couple of hours listening and comparing with two designs based on LM3886 (one single chip NI, the other bridged with OPA1632) and I'm almost sure that this one even surpasses them. The OPA549 amp was powered by regulated (LT1083) +-26 V supply. The next step is to build it properly (my friend insists on PCB although I'm a p2p believer).

Thanks for your inspiring effort.

Here is the schematic I used:
 

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Russ White said:

I would run it at even lower gain then you are. You are not really even coming close to pushing the driver.

Hi Russ,
I was thinking like this:
Typical source output = 2V RMS = 2.82 V peak
OPA1632 amplifies it 4.4 times = 12.4 V peak (realistic voltage swing with a bit of a headroom)
OPA549's gain = 3.03 (bandwith cca. 300 KHz)
So, gain per side of bridge = 4.4 x 3.03 = 13,33 V/V (10K / 750 R)
Total gain = 26,66 V/V - pretty much standard value for this power but can be even lower, as you said.
Inverted configuration is reported to have less distortion and sounds better, and I can only agree.
 
juma said:


Hi Russ,
I was thinking like this:
Typical source output = 2V RMS = 2.82 V peak
OPA1632 amplifies it 4.4 times = 12.4 V peak (realistic voltage swing with a bit of a headroom)
OPA549's gain = 3.03 (bandwith cca. 300 KHz)
So, gain per side of bridge = 4.4 x 3.03 = 13,33 V/V (10K / 750 R)
Total gain = 26,66 V/V - pretty much standard value for this power but can be even lower, as you said.
Inverted configuration is reported to have less distortion and sounds better, and I can only agree.


Yes I actually thought better of my remark and edited it. I think your gain is fine. :)

Good work!
 
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