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Old 4th May 2005, 08:49 PM   #1
PSz. is offline PSz.  United States
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Default Tripath hotrodding

Hello all,

Anyone try this stuff yet on the small tripath amps...

Has anyone bypassed the internal opamp with a better one (like opa627)? It looks possible and fairly easy.

How about trading the output filter network for ferrite beads (Fair-Rite # 2512067007Y3) like Texas Instruments does on the tpa3001? http://focus.ti.com/lit/ds/symlink/tpa3001d1.pdf
See page 14

Is there anything better than Os-Cons for power supply decoupling on these amps?
Check out part #s 08J0805 and 20C2913 at newark.com for the lower voltage tripath chipsets

Sorry if these things have already been discussed.

PSz.
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Old 5th May 2005, 06:40 AM   #2
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Default Re: Tripath hotrodding

Quote:
Originally posted by PSz.
[B]Hello all,

Anyone try this stuff yet on the small tripath amps...

Has anyone bypassed the internal opamp with a better one (like opa627)? It looks possible and fairly easy.
The opamp is not bypassable from what I can see, at least on the TA2024. The chip only provides the pins for changing the feedback level on the opamp.

Quote:
Originally posted by PSz.
[B]
How about trading the output filter network for ferrite beads (Fair-Rite # 2512067007Y3) like Texas Instruments does on the tpa3001? http://focus.ti.com/lit/ds/symlink/tpa3001d1.pdf
See page 14
The ferrite beads in the TI chip are acting as a filter for the EMI radiated by the device. The inductors on the tripath serve a different purpose.

Quote:
Originally posted by PSz.

Is there anything better than Os-Cons for power supply decoupling on these amps?
Check out part #s 08J0805 and 20C2913 at newark.com for the lower voltage tripath chipsets

Sorry if these things have already been discussed.

PSz.
Not sure about Oscons even being the best. Most capacitor afficiandos only believe in using oscons on digital devices.. I think any low-esr cap will work well, whether Panasonic FM's, Elna Cerafines, Blackgates, Nichicon HE/UHE, or whatever floats your boat. Mainly the exotics aren't the best choice due to their size.
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Old 5th May 2005, 04:54 PM   #3
PSz. is offline PSz.  United States
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The opamp is bypassable. Set up a unity gain device (buffer, opamp, tube…) and use pins OAOUT1 and OAOUT2 as inputs. Remove Ri and Rf from board.

I know why we have been blessed with the output inductors, and I was just rambling out loud. I think that using the ferrite beads without the LC combo would stand a chance of sounding pretty good while maintaining a little EMI respectability.
Kind of like taking a 1930s vintage Ford car chopping its top off, building up its motor, bigger tires, etc... but leaving a muffler on it.

A hotrod Tripath.


I was thinking that since the t-amps are digital devices that oscons would be best. But I suppose you are right, it really is subjective.

PSz.
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Old 5th May 2005, 06:37 PM   #4
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Quote:
Originally posted by PSz.
[B]The opamp is bypassable. Set up a unity gain device (buffer, opamp, tube…) and use pins OAOUT1 and OAOUT2 as inputs. Remove Ri and Rf from board.
I suppose you could do this, but I don't know if Tripath has any compensation circuitry in there or not. I also don't know how the internal opamp would behave being run wide-open. I suppose nobody will know unless someone tries it.

Quote:
Originally posted by PSz.
[B]
I know why we have been blessed with the output inductors, and I was just rambling out loud. I think that using the ferrite beads without the LC combo would stand a chance of sounding pretty good while maintaining a little EMI respectability.
Kind of like taking a 1930s vintage Ford car chopping its top off, building up its motor, bigger tires, etc... but leaving a muffler on it.
I'm not sure if the amp would even function without the inductors. The purpose of the inductors is to demodulate the switching frequency into the audio waveform.. The RF Beads wouldn't even come close to providing the inductance needed to do that.

I'm guessing that you have to think of it as sort of a switch-mode powersupply.


Quote:
Originally posted by PSz.

I was thinking that since the t-amps are digital devices that oscons would be best. But I suppose you are right, it really is subjective.

PSz.
Pretty much. I'm sure an oscon might work well, especially since the Tripath is a lower voltage device (or at least the TA2024 is). One of the main problems with using OScons, from my understanding, is that it's difficult to get them at voltages higher than 20-25v.

Mike
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Old 6th May 2005, 07:10 PM   #5
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Default Input op amp

I have been thinking of bypassing the input op amp in the TA2024 and have a few questions.

I wonder what would be the best thing to do with the internal op amps – leave the inputs floating, short the inputs together, tie them to ground through a resistor – what are your thoughts?

I notice that some of the Tripath products, for example the TA041, have the + input to the input op amp biased at 2.5V. I wonder why this is? Does the “Processing and Modulation” circuitry run at 5 volts and would like to see the analog signal at half of that. Of course the 2.5V is reflected back to the – input and to the input, thus the need for a capacitor on the input. But then the TA2024 data sheet shows a capacitor in its input and that chip is not shown biased at 2.5V. I wonder what is going on there?
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Old 6th May 2005, 09:48 PM   #6
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Bypassing the opamp sounded like THE next step with these t-amps, but I just spoke with a tech rep at tripath (very helpful, didn't catch his name) and he told me that while the data sheets show a single opamp for the input stage there are actually two. The second converts the single ended signal to differential. I was told that all of their chips (single ended and diff output models) do this. Further, he advised against driving the OAOUT pins as we would be driving the output of the first opamp.

I am still intrigued by the idea of bypassing the first input stage, but I am probably not the one who could pull it off.

My thoughts had been to cut the analog 5 volt input and shut down the opamp. But with TWO in there...I dont know.

Any ideas?

PSz.
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Old 6th May 2005, 11:04 PM   #7
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Hmmm, a second opamp? That complicates things because now you really don’t know what is going on in there. The combination of the two may work together to provide a desired result and bypassing one would upset something or other. That also screws up another idea that I had which was to force the opamp into class-A operation; but now who knows what that would do? Did the rep say anything about a 2.5V bias?
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Old 7th May 2005, 12:06 AM   #8
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Default Re: Input op amp

Quote:
Originally posted by David Davenport
I have been thinking of bypassing the input op amp in the TA2024 and have a few questions.

I wonder what would be the best thing to do with the internal op amps – leave the inputs floating, short the inputs together, tie them to ground through a resistor – what are your thoughts?

I notice that some of the Tripath products, for example the TA041, have the + input to the input op amp biased at 2.5V. I wonder why this is? Does the “Processing and Modulation” circuitry run at 5 volts and would like to see the analog signal at half of that. Of course the 2.5V is reflected back to the – input and to the input, thus the need for a capacitor on the input. But then the TA2024 data sheet shows a capacitor in its input and that chip is not shown biased at 2.5V. I wonder what is going on there?
The input is biased at 2.5 volts. This is needed to do a push pull output with a single rail supply. The output stage is bridged, neither side is grounded.
A transformer could do the same thing, but would cost more than a Tripath chip.
I continue to be amazed how a circuit with so many drawbacks and sonic no no's can sound. Guess there is still a lot to be learned about how to amplify voltages into real world loads.

George
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Old 7th May 2005, 03:31 AM   #9
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Quote:
The input is biased at 2.5 volts. This is needed to do a push pull output with a single rail supply. The output stage is bridged, neither side is grounded.
I suspected as much.

Quote:
A transformer could do the same thing, but would cost more than a Tripath chip.
Sure, but then a transformer costs more than a tube.

I would not hesitate to use a transformer with these chips if I thought it would pay off with great sound.

Dave
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Old 27th July 2005, 11:31 PM   #10
PSz. is offline PSz.  United States
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Ok,
next crazy idea. How about using a tube amp output transformer INSTEAD of the standard output filter, and using the natural frequency roll off provided by the transformer for filtering. Has anyone tried it?

Oh, I just had another one (crazy idea)! How about just using a cap across the output for a 6dB/octave rolloff and do away with the inductors. We would still have filtering in place, just lower order.

Sorry guys, I have an uncommon, unexplainable urge to be rid of the inductors!

regards,
PSz.
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