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Old 22nd January 2011, 10:26 PM   #3591
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Quote:
Originally Posted by fandersen View Post
I was wondering if any one has experimented with different resistance values and types of resistors? For example I have 249 ohm metal film as recommended by Jensen for my JT-11P-1 transformers but the bass could be a little better. Will a lower resistance help? Are some types of resistors better for low frequencies, for example Vishay Nude Bulk Metal Foil?
Hi,

The resistance of R1 + R2 + transformer should be not lower than 1000 ohm according to CS4398 specs. Your Jensen has 600 (?) ohm, so your two resistors on primary should be not lower, than 2x ~200 ohm.

If you are using metal film resistors, than change to carbon resistors, the bass will be thicker and warmer, but no so lean and precise as with metal film.

I found in my diy box two Rikens 180 ohm. Can anybody advice me if going slightly under 1000 ohm (960) will be OK, or is it dangerous for the dac chip ?
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Old 22nd January 2011, 11:11 PM   #3592
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That is entirely incorrect. Crystal is speaking of a DC resistance of 1k minimum to ground, not impedance.

Last edited by Bill Fuss; 22nd January 2011 at 11:13 PM.
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Old 22nd January 2011, 11:24 PM   #3593
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Originally Posted by Bill Fuss View Post
That is entirely incorrect. Crystal is speaking of a DC resistance of 1k minimum to ground, not impedance.
So what is incorrect ? I am a beginner in this matter
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Old 22nd January 2011, 11:39 PM   #3594
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Your interpretation of the CS4398 specs is incorrect. 180 ohms will be fine. Metal film or carbon, whatever floats your boat.
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Old 23rd January 2011, 12:44 AM   #3595
sendler is offline sendler  United States
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Default Without series resistors

Quote:
Originally Posted by sinski View Post
Hi,

The resistance of R1 + R2 + transformer should be not lower than 1000 ohm according to CS4398 specs. Your Jensen has 600 (?) ohm, so your two resistors on primary should be not lower, than 2x ~200 ohm.

If you are using metal film resistors, than change to carbon resistors, the bass will be thicker and warmer, but no so lean and precise as with metal film.

I found in my diy box two Rikens 180 ohm. Can anybody advice me if going slightly under 1000 ohm (960) will be OK, or is it dangerous for the dac chip ?
I run my Jensen JT11-EM or -FM output transformers direct from the dac chip with no resistors or filters with great results. The primarary of a 1:1 transformer will present the same load to the dac as whatever the secondaries are connected to. I my case, my stepped attenuators at the input of my amps, which present a load of 4k to 11k ohms depending on the setting. I started with 20ohms in series with each leg of the primaries but took them out as it sounds better wide open. Without the resistors the sound is just starting to show a slight hint of increased edge. Something around 10 ohms might be ideal in my set up with the CS43122 and Jensens. The fine tuning of damping/ isolation resistors and filters might be quite different depending on dac chip, trans and down stream system. I think the most wide open sound from these transformers comes from running direct and can be tamed down from there with series resistors on the input and a small cap if a less aggressive sound is desired.
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Old 23rd January 2011, 09:42 AM   #3596
brane is offline brane  Croatia
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thanks guys, i will stick to coax input, no problem and sounds good!
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Old 23rd January 2011, 10:33 AM   #3597
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Quote:
Originally Posted by sendler View Post
I run my Jensen JT11-EM or -FM output transformers direct from the dac chip with no resistors or filters with great results. The primarary of a 1:1 transformer will present the same load to the dac as whatever the secondaries are connected to. I my case, my stepped attenuators at the input of my amps, which present a load of 4k to 11k ohms depending on the setting. I started with 20ohms in series with each leg of the primaries but took them out as it sounds better wide open. Without the resistors the sound is just starting to show a slight hint of increased edge. Something around 10 ohms might be ideal in my set up with the CS43122 and Jensens. The fine tuning of damping/ isolation resistors and filters might be quite different depending on dac chip, trans and down stream system. I think the most wide open sound from these transformers comes from running direct and can be tamed down from there with series resistors on the input and a small cap if a less aggressive sound is desired.
Wow, this is highly interesting. I have to make a "fast switchable test setup" and check it.

But why is Jensen proposing two 249R+2.2nF on primary and 1K+1nF on secondaries ?

What about filtering, trafo ringing etc ?
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Old 23rd January 2011, 12:16 PM   #3598
sendler is offline sendler  United States
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Default Which transformer needs correction?

Quote:
Originally Posted by sinski View Post
Wow, this is highly interesting. I have to make a "fast switchable test setup" and check it.

But why is Jensen proposing two 249R+2.2nF on primary and 1K+1nF on secondaries ?

What about filtering, trafo ringing etc ?
Most engineers adhere to the inclusion of a filter to reduce the ultra sonic noise from the dac chip to protect the amp. I initially started working with the direct out scheme using the AK4395 dacs which have no ultrasonic noise so was able to run with no filter which showed me the advantage of getting rid of any un needed series resistance before the interconnects. The CS dac chips may benefit from a filter but I haven't tried it yet as I would rather develope one to fit across the secondary in order to take advantage of the series resistance of the coils. I have to see if this would become somewhat dependant on the load of the next stage though. The Jensen dac output circuit with the 1K+1nF values was based on the JT-11-SSP transformer which may need some correction. The JT-11-EMCF data sheet doesn't recommend any correction components although it does show a JT-OLI-2 isolator on the inputs. My quick change for comparisons is done by having two dac boards which sit on my coffee table right in front of me for fast cable swaps. I do run 8 foot interconnects which may make my system a little more sensitive to the output impedence of the source.
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Old 23rd January 2011, 02:11 PM   #3599
sendler is offline sendler  United States
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Default Post trans filter an option

A post transformer filter should work well with the JT-11 output transformers which have winding resistances of about 40 to 60R each depending on the size. Values of .02uf to .01uf across the secondaries with no added series resistance should give -6db points of about 80KHz to 160KHz depending on the acutual output impedance of the chip which was measured to be about 80R per leg for the AKM chips.
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Old 23rd January 2011, 11:19 PM   #3600
Jim W is offline Jim W  United States
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Quote:
Originally Posted by Bill Fuss View Post
Your interpretation of the CS4398 specs is incorrect. 180 ohms will be fine. Metal film or carbon, whatever floats your boat.
Bill,

I understand what you're saying here, but wonder where you got the specs from. The Cirrus CS4398 datasheet says:
Minimum AC-Load Resistance RL - 1 - kΩ
Maximum Load Capacitance CL - 100 - pF
I assume this means AOUT+ to AOUT-, but I guess I don't know for sure. I didn't see any DC output impedance specs listed.

In any case, the AC impedance presented by the transformer to the DAC will depend on the output loading and will be somewhat frequency dependent. A 600:600 transformer with a high impedance load on the output will present a much higher AC impedance than 600 ohms to the DAC output, so a direct connection should be OK from an AC impedance perspective. However, when I build mine I will have the RC network between the DAC and the transformer to reduce the ultrasonic noise.

I talked with Jensen for a while about which transformer to use and they suggested a JT-11P-1 10K:10K BUT said that it's important to keep the output capacitance low on this transformer. Use a short length of low capacitance cable to connect to the following stage. As soon as I find some free time I'll order a couple of transformers and start experimenting.

Cheers,
Jim
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