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Old 25th May 2007, 09:53 PM   #101
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Brian

Thank you i can finish my parts orders now.

Best regards
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Old 25th May 2007, 10:07 PM   #102
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Sheldon, I feel compelled to explain a few things.

Balanced or SE input is no different for the TPM if you adjust the gain of the TXD(6db) to account for half "input" swing. The output of the TXD will still be exactly the same. So you need not adjust anything on the TPM, as the load it sees and the load the TXD sees are identical either wat. There is no difference at all in the way they work accept that you will not get the same benefit of the common mode rejection at the TXD input which you would get going balanced input. That is literally all.

The TXD is current feedback, so you have to think in those terms.

Adding a SE/Bal converter will do you no good really, as the TXD already handles that marvelously, but adding a balanced source will help a lot.

Be careful about your comparisons, the BPA is a totally different beast from a TXO. The only really similar thing is the servo.

Good luck, and sorry if I left you befuddled.

Cheers!
Russ
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Old 25th May 2007, 10:58 PM   #103
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Russ Thanks for the extra words it helps me to understand the 4131 a lot better.

By the way one thing that has made it tougher is I had to figure out from the BOM as you do not have the components identified
e.g. R1 1.1k, in some cases not all the pieces are listed in BOM .

Right now there is still no 22.k1 resistor in the TXD BOM. it is missing!

So there are little discrepancies from schematic to text to BOM
here and there.

There are no schematics for the LCPS or the TXPS I have read all of the material over and over and even used the pictures to help figure out what was what. TXD in particular.

I know you are working on the DAC which I am sure is quite complex.

The whole TX thing is fairly complex

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Old 25th May 2007, 11:18 PM   #104
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Quote:
Originally posted by SheldonD

So there are little discrepancies from schematic to text to BOM
here and there.

The whole TX thing is fairly complex

Best regards

Yes you are right, and we have tried to fill the voids with the documentation on the site, but I agree it is still lacking a bit. It is something I will personally strive harder to rectify. Thanks for helping me see it through a user's eyes. Sometimes I get "designer's goggles" syndrome.

I am working on more complete TXO documentation. And I am writing DAC documentation even tonight.

So I think you will see some improvement there.

Cheers!
Russ
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Old 28th May 2007, 05:19 PM   #105
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Default txd

the manual for the txd does not say whether to us ro resistor when using it to drive txo. you say it stabilzes feedback and may be jumpered. will that work for txo use. also, does the txd need a balanced input or can it be fed from a single unbalanced rca jack.
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Old 28th May 2007, 05:27 PM   #106
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Default Re: txd

Quote:
Originally posted by tryonziess
the manual for the txd does not say whether to us ro resistor when using it to drive txo. you say it stabilzes feedback and may be jumpered. will that work for txo use. also, does the txd need a balanced input or can it be fed from a single unbalanced rca jack.
RO is there to protect the TXD from capacitive loads. Because the TXD will not always be used to drive Twisted Power modules which are not capacitive loads I wanted to be sure there was a spot there for those resistors should they ever be needed.

For TXO you just use jumpers in place of RO1 and RO2.

For single ended input into a TXO you bring your input into +IN and connect -IN to GND. If you plan on using the TXO this way I would configure the amp for 20X gain.

Cheers!
Russ
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Old 28th May 2007, 10:55 PM   #107
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Default txo 8

has anyone build the txo with 8 lm3886 in bridge parallel mode. i would be interested to know what to expect. as a mono cofiguration and enough heat sink i do not expect problems. if all goes well i will build 3 to 5 more for biamp or tri amp. my grandkids love to play with my toys.
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Old 28th May 2007, 11:00 PM   #108
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Default Re: txo 8

Quote:
Originally posted by tryonziess
has anyone build the txo with 8 lm3886 in bridge parallel mode. i would be interested to know what to expect. as a mono cofiguration and enough heat sink i do not expect problems. if all goes well i will build 3 to 5 more for biamp or tri amp. my grandkids love to play with my toys.

You should have no trouble doing a TXO-8 but I can't imagine why you would need that much current.

I have successfully tested a TXO-6. I doubt a TXO-8 would behave any different. When I get time I may try it out myself. But the only application I can think of is 2ohm subwoofer.

Cheers!
Russ
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Old 29th May 2007, 12:08 AM   #109
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Default txo 8

running 20 speakers in a line array necessitates series parallel wiring in excess. if i use a lower series count ie, increased current, maybe it would make individual speaker characteristics less noticeable. i had thought of buying some 72 inch bohlender ribbons which might need the extra juice. just fun toys, beats watching tv. anyway they would run cooler with more chips in parallel. thanks for the input. first amp almost ready to heat up will be buying another quite soon.
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Old 29th May 2007, 06:43 PM   #110
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Default Import note about parallel TPMs TXO-4 and up

Last night I did some load testing of a TXO-6. When I built the TPMs I closely matched all of the feedback resistors (R1 and R2). That amp performs very well. What I wanted to test was the effect of gain imbalance between the power modules. So I intentionally mismatched one of the feedback resistors to get a little higher gain on that TPM.

What I found was that the module with the higher gain was supplying nearly double the current of the other modules.

The TPM includes an output current sense resistor (it actually works like local feedback). which helps a bit, but at .1R not really enough if the resistors are 1% off.

So if you plan on build a TXO-4, 6, 8 etc be sure you use .1% or better resistors (or resistors hand matched to that tolerance) for TPM resistors R1/R2 and possibly increase the size of the output resistor(R7) to .22R. Both of these measures together will insure that the TPMs distribute the load evenly.

We will be making appropriate changes to the BOM, and we will be in contact with anyone who got a TXO-4 to get you some replacement resistors.

Keep in mind, I listen to a TXO-4 with 1% resistors everywhere, but I hand matched them. This is fine. But I just wanted to make sure people knew the importance of gain matching to optimal performance. Without it one TPM will quickly reach thermal protection, which would sound, well icky...

Another note, this only applies to TXO-4,6,8 etc. TXO-2 because it is not running parallel power modules is not effected in the least.

Cheers!
Russ
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