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Old 25th February 2006, 12:17 PM   #1001
awpagan is offline awpagan  Australia
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i was going to do some test to see the drive capabilities of the dac
just a bit of info for passive filter

so far
removed output caps, muting, headphone, DAMH( ), improved various caps, .1uf bypass caps to get .1mV noise on any rail, iec and rerun earths, opamps-2134's

very much improved for such cheap mods

oh yes forgot to fit opamps in sockets, still got resonable signal out.
yes restricted on frequency
looks promising for the passive filter to buffer

allan
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Old 25th February 2006, 12:21 PM   #1002
awpagan is offline awpagan  Australia
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Quote:
Originally posted by poynton



the future of HIFI ?

LowFI

allan
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Old 25th February 2006, 12:23 PM   #1003
awpagan is offline awpagan  Australia
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ash_dac

you got post 1000

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Old 25th February 2006, 12:45 PM   #1004
ash_dac is offline ash_dac  United Kingdom
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Quote:
Originally posted by awpagan
ash_dac

you got post 1000


haha

You removed the hdam ?

What was the voltage of the signal you got ?
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Old 25th February 2006, 01:17 PM   #1005
awpagan is offline awpagan  Australia
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Quote:
Originally posted by ash_dac



haha

You removed the hdam ?

What was the voltage of the signal you got ?

hdam yes (bypassed all)
suggestion by a fair few on here and elsewhere that with a better opamp, the hdam doesn't help.
i tend to agree with them

on schematic voltage into opamp 1.4v

without opamp, it goes though the feedback caps/resistor circuit
as i said restricted frequency.
will have to measure it.

thinking about making small pcb to plug in opamp sockets

at lest that way i don't have to keep removing pcb to test ideas.

allan
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Old 25th February 2006, 02:27 PM   #1006
6h5c is offline 6h5c  Netherlands
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Quote:
Originally posted by ash_dac
Hi,

Does anyone know anything about pwm signals, and pdm signals ?
A pwm signal comes out the Marantz dac....
Is this pwm signal at 44.1khz or is it higher ?
Does the 1st stage after the dac just generate a voltage from the difference in the +/- left/right output ? (still 0/1 pulse)
..and the low pass filter turns the pulse into audio ?
Hi ash_dac,

I put my scope on the DAC and measured between 0.5 and 1uS for a period, so my guess is the output frequency is pretty high, 32*Fs or 1.411MHz.

The first stage does some passive filtering and the first opamp summs and amplifies both outputs to a single ended signal. At this point it's already more or less analog, with lots of HF residue. Then a second opamp stage filters a bit more. If you take out the opamps, like Allan did, you have reasonable music, with lots of noise.
The HDAM circuit only acts as a buffer, so if you bypass it the amplitude of the output signal stays the same.

Regards,

Ray.
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Old 25th February 2006, 02:36 PM   #1007
awpagan is offline awpagan  Australia
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just changed C605/606 from 1000pF to 470pF
and R611/612/605/606 from 10k to 12k1

listeninig to Nora Jones before and after
much much better balanced sound highs to lows
recommended

Ray's filter suggestions

allan

ps all other caps in filter standard
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Old 25th February 2006, 03:07 PM   #1008
awpagan is offline awpagan  Australia
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Quote:
Originally posted by 6h5c


Hi ash_dac,

I put my scope on the DAC and measured between 0.5 and 1uS for a period, so my guess is the output frequency is pretty high, 32*Fs or 1.411MHz.

The first stage does some passive filtering and the first opamp summs and amplifies both outputs to a single ended signal. At this point it's already more or less analog, with lots of HF residue. Then a second opamp stage filters a bit more. If you take out the opamps, like Allan did, you have reasonable music, with lots of noise.
The HDAM circuit only acts as a buffer, so if you bypass it the amplitude of the output signal stays the same.

Regards,

Ray.
no opamps was a mistake, just forgot to put them in
but gave me better view of dac output hmmmm voltage
used to current out where you need IV converter

not really reasonable music maybe not as good as MP3

Hmmm converts to single ended
I have balanced input capability on my preamp.
why this cdpayer is good for experiments

allan
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Old 25th February 2006, 03:17 PM   #1009
ash_dac is offline ash_dac  United Kingdom
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Quote:
Originally posted by awpagan


why this cdpayer is good for experiments

allan
I've been thinking about that pwm signal, and have been reading up on digital amplifiers.

I've never opened up my Marantz......

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Old 25th February 2006, 03:59 PM   #1010
poynton is offline poynton  United Kingdom
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Quote:
Originally posted by awpagan




Hmmm converts to single ended
I have balanced input capability on my preamp.


Hi.

There's no reason you could not retain the balanced output from the DAC. Possibly build a daughter board to plug into the opamp socket??

Andy
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