Experience with this DIY DAC ? - Page 49 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th May 2009, 11:37 AM   #481
legarem is offline legarem  Canada
diyAudio Member
 
legarem's Avatar
 
Join Date: Jan 2005
Location: Quebec city
Quote:
Originally posted by fordgtlover
Sorry for the silly questions.

In legarem's diagram in post #418, the black wire is connected to the ground connection. Is that the analog ground of the DAC?

http://www.diyaudio.com/forums/attac...amp=1241223954

Also, on the same diagram, is the type of capacitor across the transformer primaries important (0.0047uF)?
Yes, it is connected on the analog ground

In my diagram, I forgot a 0 on the cap value. The good value is: .00047 uF not .0047 uF. Sorry.

If you keep the ,0047 uF, you can also change the 1K for 100 ohms and you'll get a lot more gain with the right cut off frequency.

The capacitor can be polypropylene, polystyrene, mica.

I had emali exchange with Bill Whitlock from Jensen transformers. Here is some interesting things related to the schematic included in this message:

1. The low-pass filters are used to supplement the characteristics of the transformer itself. Since the Faraday shield in the JT-11SSP-8MA (or any transformer with such a shield) functions well only below a few MHz, the two 220 pF capacitors and 249 Ω resistors function as a 3 MHz low-pass filter for common-mode to insure that RF energy does not interfere or cause strange intermodulation distortions in downstream equipment. The differential filter, consisting of the 2.2 nF capacitor and 249 Ω resistors, is set to be -3 dB at 160 kHz. This frequency is sufficiently high to add negligible phase distortion (that's deviation from linear phase, not phase shift) while low enough to control ultrasonic artifacts that can also cause strange distortions in downstream equipment (see the 1988 AES paper by Deane Jensen and Gary Sokolich for details on "Spectral Contamination").

2. The differential voltage across the transformer primary must be kept to an absolute minimum (<1 mV) to prevent a shift in the magnetic operating point of the core material. Any significant dc flow in the transformer will alter its distortion characteristics. Normal (for Jensen-selected core materials) transformer distortions consist almost entirely of 3rd harmonic, but adding a dc component creates a series of even-order distortion products (2nd, 4th, 6th, etc.).
Attached Images
File Type: jpg jensen.jpg (32.1 KB, 1541 views)
  Reply With Quote
Old 16th May 2009, 02:21 PM   #482
udovdh is offline udovdh  Netherlands
diyAudio Member
 
Join Date: Jan 2009
About the voltage across the primary: how?
The DAC chip has a certain offset.
Or will it be bear-zero? (no opamps)
  Reply With Quote
Old 16th May 2009, 02:41 PM   #483
legarem is offline legarem  Canada
diyAudio Member
 
legarem's Avatar
 
Join Date: Jan 2005
Location: Quebec city
Quote:
Originally posted by udovdh
About the voltage across the primary: how?
The DAC chip has a certain offset.
Or will it be bear-zero? (no opamps)

As stated in a previous message, after modifying 6 of these dacs, there is always 0mv between the + and - of each output. You don't have to bother with any voltage across the primary of the transformers with the CS4398 and CS4397.

Use matched resistors at the primary of the transformers.
  Reply With Quote
Old 16th May 2009, 02:42 PM   #484
RIP
 
Join Date: Oct 2005
Location: Central Florida
All the ones measured so far have had less than 1mv but thats with DMMs. I dont think anyone has measured with a voltmeter sensitive enough to really see anything. I have assumed that the DC level is not high enough to be a concern, but I may be wrong, as I often am.
  Reply With Quote
Old 17th May 2009, 02:46 AM   #485
diyAudio Member
 
Join Date: Apr 2007
Quote:
Originally posted by Bill Fuss
Those aren't silly questions.

The caps should be good quality polypropylene film.

Bill
Thanks

Quote:
Originally posted by legarem


Yes, it is connected on the analog ground

In my diagram, I forgot a 0 on the cap value. The good value is: .00047 uF not .0047 uF. Sorry.

If you keep the ,0047 uF, you can also change the 1K for 100 ohms and you'll get a lot more gain with the right cut off frequency.

The capacitor can be polypropylene, polystyrene, mica.

Thanks for the response. No harm done, I haven't ordered the parts yet.

Just to clarify my understanding of this. The Resistor (1K) and Capacitor (0.00047uF) are acting as an RC filter.

My calculations, using the formula F = 1/(2 * pi * C * R), have the cut off frequency at 338691.43 Hz (338 KHz). Is this correct? If it is correct, why does it need to be so high?

Using the value of 0.0047uF for C, gives a cutoff frequency of 33KHz. Is this not high enough?
  Reply With Quote
Old 17th May 2009, 07:51 AM   #486
piero7 is offline piero7  Italy
diyAudio Member
 
piero7's Avatar
 
Join Date: Apr 2009
Location: Matera
Quote:
Originally posted by Franz Gysi
All Digitec's are tested and ready for shipment:


@Xaudiox: I miss your mail, still two pieces reserved for you!

Kind regards
Franz
Hi franz, I'm interested in your transformer, due I'm a new user can't still email to you. Please contact me

tnx
  Reply With Quote
Old 17th May 2009, 11:41 AM   #487
legarem is offline legarem  Canada
diyAudio Member
 
legarem's Avatar
 
Join Date: Jan 2005
Location: Quebec city
Quote:
Originally posted by fordgtlover


Thanks



Thanks for the response. No harm done, I haven't ordered the parts yet.

Just to clarify my understanding of this. The Resistor (1K) and Capacitor (0.00047uF) are acting as an RC filter.

My calculations, using the formula F = 1/(2 * pi * C * R), have the cut off frequency at 338691.43 Hz (338 KHz). Is this correct? If it is correct, why does it need to be so high?

Using the value of 0.0047uF for C, gives a cutoff frequency of 33KHz. Is this not high enough?

You have to do the sum of the two resistors so 338 khz become 169 khz

If you don't have a preamplifier, use 2 X 100 ohms instead of 2 X 1K .
The caps value become 680 pF

33Khz is too low. Remember that the cut off frequency is at -3db
  Reply With Quote
Old 17th May 2009, 06:51 PM   #488
diyAudio Member
 
Franz Gysi's Avatar
 
Join Date: Oct 2007
Quote:
Hi franz, I'm interested in your transformer, due I'm a new user can't still email to you. Please contact me
You have good luck and I sent you a mail

Why?

All Digitec's are gone, just the pair I sent to Legarem for comparison will come back.

His opinion is, they play on the bright side. Soon we will read (hopefully) about Legarem's comparison and I am looking forward for that.

I still like the Digitec's, and I recommend to play with the surrounding parts (i.e. passive filtering at the primary side).

They are very linear over the whole frequency range and Legarem and I could not measure any overringing.

For some sound I still prefer the Digitec's over the Lundahls, for some not.

My theory: because of the bigger core of the Digitecs, they play "cleaner" bass than smaller trannies, wich means lower distortion in the bass area.

Franz
  Reply With Quote
Old 17th May 2009, 08:56 PM   #489
diyAudio Member
 
Join Date: Jan 2009
Quote:
Originally posted by legarem


If you don't have a preamplifier, use 2 X 100 ohms instead of 2 X 1K .
The caps value become 680 pF

Legarem, I am new to this and so would be grateful if you could explain the reason for raising the cutoff if not using a preamp (I used the formula for 2x100 Ohm with 680pF, giving 1170kHz).

I use an integrated amp (Primaluna ProLogue 2) which I guess, by definition, has preamp built in. I am therefore planning to try your original filter (2x1K res, 470pF cap). Am I heading down the right path?

Thanks
  Reply With Quote
Old 18th May 2009, 12:18 AM   #490
johnm is offline johnm  United Kingdom
diyAudio Member
 
johnm's Avatar
 
Join Date: Sep 2003
Location: Hampshire
Franz are you still using 10R resistors (and nothing else) between the DAC and primaries of your Digitecs?

Cheers,

- John
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
A.O.S - Any experience? Keltern Multi-Way 16 26th April 2012 11:15 PM
my t-amp experience Eggzy Chip Amps 35 17th December 2005 06:29 PM


New To Site? Need Help?

All times are GMT. The time now is 10:40 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2