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Old 20th December 2008, 04:51 PM   #1
caine28 is offline caine28  Germany
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Question TDA1540 passive I/U Stage ???

Hello,

I hope there is someone who could help me.
I want to use a older TDA1540 only with a Restistor as the
I/U Stage, without the normaly taken OP-Amp. Has somebody done this bevore ? What Resistor should i take, I tried 100ohm and 330 ohm, but there is a sprankling dirstortion on the less loud passages...

I hope there is someone who could help me.

Best regards from bavaria,
Manfred.
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Old 20th December 2008, 05:46 PM   #2
oshifis is offline oshifis  Hungary
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Similar specs as of the TDA1541A. 10 ohm or smaller I/V resistor + some gain needed.
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Old 20th December 2008, 06:15 PM   #3
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Default Bah humbug ! Manufacturers, what do they know.

Would it not be a good idea to consider the compliance rating of the device ?
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Old 20th December 2008, 07:02 PM   #4
oshifis is offline oshifis  Hungary
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Compliance rating is +/- 10 mV (the TDA1541A has +/- 25 mV). Full scale output is 4 mA for both. Perhaps even 10 ohm is a bit too high.
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Old 21st December 2008, 07:35 AM   #5
dddac is offline dddac  Germany
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Why don't you just work it out?

Attach a 50 Ohm trimmer, play a 0dB Sinus wave and check the output on a scoop with FFT and turn till you have lowest or acceptable distortion (specially d3)

I have done this for the pcm63 for example. you can read it at my Site here

doede
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Old 23rd December 2008, 02:17 AM   #6
Richard is offline Richard  Australia
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Hi Manfred,

I have played around with different resistors, from 7.5 ohms to 47 ohms as I/U with a valve output. I also used a 1:2 step up transformer. I found that the sound with step up by itself was lacking in dynamics and does not produce enough drive. Higher I/U resistors do cause distortion, I think anything above 50 ohms is too much for the 1540.

Iím currently using a 1:2 step up transformer with a valve output which is rather nice, I found the bass is better with the transformer in the chain, rather than just the plain I/U resistor before the valve. I have a 20 ohm which, in parallel with the transformers primary, gives an I/U of about 8 ohms. The transformer Iím using is a vintage one from some medical laboratory equipment (10Hz Ė 60kHz), but I recall someone here using a Lundahl 7905 with good results.

You should adhere to advice from Rfbrw & Oshifi and keep the I/U resistor value low so that the voltage compliance is near the dacís +/-10V limit.

You may also find the following thread useful
AD1865 the best DAC

Cheers,

Richard
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Old 28th December 2008, 09:33 PM   #7
caine28 is offline caine28  Germany
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Hello,

thanks a lot,
and o.k. i will try the prozedure,
i allready have done this with TDA1543.
I know the dddac article. Very helpfull indeed.

Probably I should try the transformer, but they are not cheap I think, and not so easy to get in germany.

Thanks again and I wish you all a good
and interesting year 2009 !
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Old 28th December 2008, 09:59 PM   #8
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"Korkscheibchen" glued on the TDA might help.
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Old 28th December 2008, 10:32 PM   #9
caine28 is offline caine28  Germany
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donīt you think this helps ?
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