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Old 30th May 2012, 08:50 AM   #1
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Default Is NOS modification bad for the tweeters?

I want to apply the NOS modification for TDA1541A on a Quad CD66.
(bypass the SAA7220 with three wires).

1. Is there any change to damage the tweeters playing without adapted analog filtering?
2. Do I have to remove or modify the existing filter parts for OS from the PCB for the NOS NOFILTER modification.

I looked in the forums but didn't found a clear YES or NO answer to this questions. I mounted already a new clock from LCAUDIO. I'll replace the opamps LM833 later. PLease let me know if I missed an existing thread.
Thanks.
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Old 2nd June 2012, 09:00 AM   #2
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Default Is NOS modification bad for the tweeters?

Quote:
1. Is there any change to damage the tweeters playing without adapted analog filtering?
I read this warning in Dgital Audio Blog:

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http://www.digitalaudioblog.com/2011/01/oversampling-upsampling-and-non.html
Quote:
Take some of the earliest DACS, that were 16 bit and extracted data at a rate of 44.1 kHz / 16 bits. When the DAC converts data in the 20-20kHz range, it leaves some canard above the 22kHz range that must be cleaned up. If it did not, inter modulation distortion and ultrasonic frequencies would wreak havoc on your system
destroying tweeters, midrange drivers and turning mylar into chewing gum. In order to prevent this, a filter is applied.
Is this true for all NOS filterless Dacs? I don't see many schematics with a filter.. Do I need a filter with the TDA1541a?.

Anyone who has done the NOS mod on a Quad CD66?
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Old 2nd June 2012, 08:02 PM   #3
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My impression is that some hotheads leave the filtering to chance, with the argument that there are loads of filter elements between the DAC and your speakers, such as cables, interstage couplings, etc, etc. I feel this is wreckless...and in one case quite bonkers.

Others use rudimentary filters. A transformer, for example, can make a good HF filter due to its series leakage inductance, parallel winding capacitance, and winding resistance.

If you delete the output stages, isn't a Quad the same as any other machine as far as NOS goes?

Has it got an S1 single crown chip, btw? Do be careful...

Ian
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Old 3rd June 2012, 12:00 PM   #4
oshifis is offline oshifis  Hungary
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The unfiltered analog signal at the DAC outpt is a stepped waveform. The steps amplitude is 1 LSB @44.1 kHz. 1 LSB = -96 dB referred to 2 V RMS, so I believe there is nothing to worry about, regarding the tweeter overload.
Intermodulation due to nonlinearities and spurious modulation components folding back to the audible range is another thing. (I don't experience any adverse effect in my system).
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Old 4th June 2012, 12:57 AM   #5
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Quote:
Originally Posted by oshifis View Post
The unfiltered analog signal at the DAC outpt is a stepped waveform. The steps amplitude is 1 LSB @44.1 kHz. 1 LSB = -96 dB referred to 2 V RMS, so I believe there is nothing to worry about, regarding the tweeter overload.
Intermodulation due to nonlinearities and spurious modulation components folding back to the audible range is another thing. (I don't experience any adverse effect in my system).
I interpreted the question wrongly, probably. I need to adapt to European English. I would say "without adapting the analogue filters" rather than "without adapted analogue filtering" which I took to mean with no filtering at all.

I rather assumed that NOS and ripping out analogue stages go together.

Also, I don't follow your argument, quite. If every step of the output is 1LSB, then the waveform would always be the same oblique triangular form, regardless of input.

Not really a question for you. I'll go away and read some more.
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Old 4th June 2012, 03:14 AM   #6
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Can someone please explain to me inter modulation distortion and how ultrasonic frequencies even get enough amplitude to cause any audible distortion?
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Old 4th June 2012, 04:56 AM   #7
oshifis is offline oshifis  Hungary
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Quote:
Originally Posted by PlasticIsGood View Post
If every step of the output is 1LSB, then the waveform would always be the same oblique triangular form, regardless of input.
Sorry, I meant "the step amplitude is at most 1 LSB".
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