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Old 5th September 2010, 12:06 PM   #3121
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Magnetized trafos have hysteresis distortion, low level low frequency odd order harmonics. You can degauss them with a beefy preamp and a signal generator. Feed a 60-100hz signal to them strong enough to saturate them and then slowly turn the signal down to zero.
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Old 5th September 2010, 12:59 PM   #3122
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Good to hear from you Bill, it's good to be back on DAC

Quote:
Originally Posted by Bill Fuss View Post
The filter's still good.
Thanks for confirming, I can eliminate ringing as the cause of harshness heard...

Quote:
Originally Posted by Bill Fuss View Post
... did you see the posts about the incorrect voltage feed on the upsampler board?
I did, but I had forgotten, so thanks for the prod. This could make sense - in bygone posts EI was reckoned to sound better than toroidal, but maybe the 50VA EI is able to push the upsampler feed over the edge, whereas the weaker toroidal cannot.

I will whet my multimeter.
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Old 5th September 2010, 01:16 PM   #3123
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Quote:
Originally Posted by Bill Fuss View Post
Magnetized trafos have hysteresis distortion, low level low frequency odd order harmonics. You can degauss them with a beefy preamp and a signal generator. Feed a 60-100hz signal to them strong enough to saturate them and then slowly turn the signal down to zero.
I think my Tams are probably ok then, thanks, as I do not hear any nasties at low frequencies.

For future reference, might a headphone output of a pc sound card serve as a beefy preamp? That way I could use a software signal generator and not spend any $. If not, how about using an audio power amp with some delicate knob control - or is that very silly?

Thanks
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Old 5th September 2010, 02:51 PM   #3124
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I would be very careful using a power amp, but why not.
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Old 6th September 2010, 02:25 PM   #3125
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Ref: Post 3030
Quote:
Originally Posted by RichLund View Post
...I received this interesting email from Bill Whitlock of Jensen Transformers regarding suitable transformers for current output DAC's:...
I also received a similar email from Bill back in July. I was wondering if Jensen made a suitable transformer for the PCM1798. He seems to say that I could probably use my 10K JT-11P-1s. This would save me from ordering a pair of rather expensive LL1674s or the K&K passive output stage.
Of course I can't figure out the last part about capacitive load etc...

Quote:
Hello Mike,

Thanks for writing. As with virtually all current-output DAC's, the
manufacturer of the PCM1798 does not specify how much voltage swing is
allowable on those pins ... because they're designed to work into the
virtual ground of an inverting op-amp (which keeps the voltage swing at much
less than 1 mV). Some DACs will respond very poorly if the output pins are
allowed to swing even a fraction of a volt. Others will allow substantial
voltage swings in one direction but not the other. Therefore, I must defer
to those "golden ear" types on the DIY and audiophile forums to determine
what "works" and what doesn't.

I appreciate that you're pleased with our JT-11P-1 in a similar application.
I see no reason that, once an appropriate value for the load resistors is
found, the same transformer wouldn't also work just as well with the
PCM1798. In either case, the JT-11P-1 secondary must have less than 100 pF
of capacitive load to maintain its specified high-frequency response. In
practice, this generally means no more than about 1 meter of cable (assuming
about 30 pF per foot of cable capacitance).

Cordially,
Bill Whitlock, president & chief engineer
Jensen Transformers, Inc.
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Old 6th September 2010, 03:31 PM   #3126
sendler is offline sendler  United States
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Default Mono mode connections

Here are a couple threads showing mono mode connections. Interesting in the Ciuffoli tests the PCM1798 in mono mode didn't rate high until he switched to an active output. And, he immediatley ditched the shunt regs after listening to them. He mentions measurements of the PCM1794 in mono mode but doesn't seem to follow through with a listening test of that chip.
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DAC Final
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Comments on PCM1794A DAC design
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Old 6th September 2010, 09:06 PM   #3127
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Quote:
Originally Posted by McCrackers View Post
Ref: Post 3030


I also received a similar email from Bill back in July. I was wondering if Jensen made a suitable transformer for the PCM1798. He seems to say that I could probably use my 10K JT-11P-1s. This would save me from ordering a pair of rather expensive LL1674s or the K&K passive output stage.
Of course I can't figure out the last part about capacitive load etc...
You need a gain of around 20 so you would still have to feed it to some type of gain stage. The capacitance of the cable will act as a low pass filter, keep them very short.
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Old 6th September 2010, 09:09 PM   #3128
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Rich was going to try some 1/10 trafos with the the PCMs but he hasn't posted back yet.
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Old 10th September 2010, 04:12 PM   #3129
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I know this has been discussed before but could anyone please comment/simplify the CS8416 PLL values issue.
What exactly needs to be done and is it a worthwhile intervention?

http://www.cirrus.com/en/pubs/errata/ER578D1.pdf
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Old 10th September 2010, 04:37 PM   #3130
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Hi guys, sorry for late answer about my problems with 50 Hz hum, just recently had time to fiddle with it.
First, I looked inside my amp and saw that it's ground is tied to the case, so, after some argument with myself, I've decided to tie DAC ground to the case also and connect both grouds through the wall socket (followed Protoplasma's advice).
After that the hum was gone, and I was happy, but after re-reading posts with answers to my problem, I think it is not the right way of getting rid of the hum - see this post by Bill. I think Bill is right, and amp's ground should not be tied to the case in the first place. To support this thought, when I connected grounded DAC to my reciever (remember, there was no hum, when DAC's ground was not tied to the case), the hum was back, I guess Yamaha's engineers were wiser than the builder of my amp (which is DIY). After all, I've decided to leave it as it is, i.e. both grounds tied together, although it is wrong, but there's no hum . Next step would be resolve ground problems in the amp.

So, to sum it up - one of possible reasons for hum could be your amp's ground tied to it's case.

Thanks to all you guys for valueable input, and especially to Bill, who is really the guru of this thread.
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