Building the ultimate NOS DAC using TDA1541A

[Vbenonisen]

Hello Ceglar.

I don't know if you still read this thread, but if you do (or somebody else knows) - what is the purpose of the 56uF capacitor over the I/V resistor in your schematic?

Vidar

 

[niamex]

(6K8 resistor is from DEM to +5V)

Koldby

Hi Koldby.
I hope you are wrong because I have these from DEM to -15 ??
Rgds,

 

[ryanj]

Hello Ceglar.

I don't know if you still read this thread, but if you do (or somebody else knows) - what is the purpose of the 56uF capacitor over the I/V resistor in your schematic?

Vidar

Hi Vidar

This value is actually 56nF from what i can make sense of. 56uF is totally way too high a value to have any practical purpose in this position.

As many of you are probably aware, this cap limits bandwidth into the output stage by providing a low impedance to ground for the fast transient of the square wave coming out of the DAC.

 

[ryanj]

Hi Koldby.
I hope you are wrong because I have these from DEM to -15 ??
Rgds,

Hi niamex,

Koldby is indeed incorrect. 2 x 6k8 resistors go to the DEM pins from -15 not +5.

 

[niamex]

Thanks ryanj,
the actual value is 6k6 /probably I should buy hundreds in order to get four 6k8 - I have two TDA piggybacked// In the meantime do you think I will need this cap- 56 pf in parallel to my 50 ohms I/V res ??
Regards,

 

[ryanj]

No problem,

Probably not necessary to go with a value lower than 6k8 but i guess it wont hurt, although ive had great results with this value.

56pf is too small a value to be using for this purpose. You should be in the range of 50 to 120nF.

 

[niamex]

No problem,

Probably not necessary to go with a value lower than 6k8 but i guess it wont hurt, although ive had great results with this value.

56pf is too small a value to be using for this purpose. You should be in the range of 50 to 120nF.

Sure, mistype. Not easy to get the exact value - it is always 6K8 written on it but

 

[ryanj]

Yeah thought it might be a typo. I dont think the value is as important as the temperature coefficient. I think John recommended those MELF resistors at some stage. But you will still get a good result with any resistor type. Im using carbon comps at the moment.

 

[niamex]

right, it is MELF /at least two of them/but 6k6 even thou

 

[niamex]

I have to try vishay 0.1 % but not easy to find

 

[niamex]

Found MULTICOMP 0.1% in Farnell-seem OK -

 

[Vbenonisen]

Hi Vidar

This value is actually 56nF from what i can make sense of. 56uF is totally way too high a value to have any practical purpose in this position.

As many of you are probably aware, this cap limits bandwidth into the output stage by providing a low impedance to ground for the fast transient of the square wave coming out of the DAC.

I wasn't aware. Thank you for that.

 

[koldby]

Hi Koldby.
I hope you are wrong because I have these from DEM to -15 ??
Rgds,

Yep my wrong. It is -15V

 

[lcsaszar]

2 x 10k works for me. I don't think the actual value is particularly important (within some range).

 

[Eldam]

Hi Oshifi,

Could you tell us again please the DEM values you use with the 14 decoupling caps unpopulated ?

Your conf is on my listening waiting list as you & John said it adds sweet (at the price of a little loss of precision)...

Thank you for that

 

[Eldam]

Hi niamex,

Koldby is indeed incorrect. 2 x 6k8 resistors go to the DEM pins from -15 not +5.

On the distinction-1541 i putted this one : manufacter part number : RG2012P-682-B-T5 (Sussumu low noise resistor RG serie)... You can't go wrong with it... (maybe too small for tweaking EBAY kits !)

 

[esgigt]

2 x 10k works for me. I don't think the actual value is particularly important (within some range).

Did you check the waveform with a scope? I don't doubt that 10K works too...

I remember once asking the question how the 6K8 was determined, but unfortunately I got no answer... Your post is a bit of an answer to that question.

 

[LeonBernieniv]

Here's the tail currents of the integrated emitter coupled oscillator :

 

[Ceglar]

Hello Ceglar.

I don't know if you still read this thread, but if you do (or somebody else knows) - what is the purpose of the 56uF capacitor over the I/V resistor in your schematic?

Vidar

Hi Vidar,

56nF//R forms low pass filter.. at higher frequencies the cap represents the lowest impedance path to/from signal common whilst the resistor has a fixed impedance (within reason).

Shane.

 

[lcsaszar]

Did you check the waveform with a scope? I don't doubt that 10K works too...

I remember once asking the question how the 6K8 was determined, but unfortunately I got no answer... Your post is a bit of an answer to that question.

The waveform is the same as John's in post #5060. My DEM capacitor is 510 pF, the frequency is 172 kHz. My goal was to achive auto-lock to 4x sample frequency, but it did not occur.