
Home  Forums  Rules  Articles  diyAudio Store  Blogs  Gallery  Wiki  Register  Donations  FAQ  Calendar  Search  Today's Posts  Mark Forums Read  Search 
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 

Thread Tools  Search this Thread 
16th February 2019, 06:42 PM  #1 
diyAudio Member
Join Date: Mar 2015

TDA1543 filter capacitor calculation
Dear forum members,
Could you somebody explain please, how can I calculate the capacitance of the marked elements? It's not clearly visible what is above the capacitors. I see LPF, 49kHz (this sould be a cutoff freq., the 6dB/octave, and 1.2nF*8?) What is the relation between its capacitance and the 680o Rout resistors? Is there any affect of the number of the DACIC? The capacitance should be different if I want to use 1 or 2 DACIC, instead of 4? Thanks 
16th February 2019, 08:46 PM  #2 
diyAudio Member
Join Date: Mar 2003
Location: Haarlem, the Netherlands

Neglecting the deemphasis circuit and regarding the DC blocking caps as short circuits for signal frequencies:
On each line you have four paralleled 1.2 nF capacitors, 680 ohm, 47 kohm and whatever the resistance of the circuit connected to the outputs may be. Assuming that last one to be 10 kohm (guess), the cutoff frequency is: f = 1/(2 pi RC) = 1/(2 pi (680 ohm // 47 kohm // 10 kohm)*(4 * 1.2 nF) ~= 52782 Hz where // means the value of the parallel connection, so R1 // R2 // R3 = 1/(1/R1 + 1/R2 + 1/R3). Assuming infinite input impedance of the next stage: f = 1/(2 pi RC) = 1/(2 pi (680 ohm // 47 kohm)*(4 * 1.2 nF) ~= 49466 Hz With fewer DAC ICs, you can either keep the resistances and the capacitances on each line the same (that is, keep 4.8 nF total from each line to ground) and accept that the output signal gets smaller, or you can scale up all resistances and scale down the filter capacitances. That is, use twice the resistance and half the capacitance with two DAC chips. 
16th February 2019, 09:51 PM  #3 
diyAudio Member
Join Date: Mar 2015

Thanks for the explanation

17th February 2019, 10:34 PM  #4 
diyAudio Member
Join Date: Mar 2015

One more question about the DAC. I have attached a picture from the frequency response of my DAC, how can I improve the high freqs.? At 20kHz 4dB, and 18kHz 3dB.

18th February 2019, 02:15 AM  #5 
diyAudio Member

You could try using a CLC filter between your DAC and your I/V resistors. This can be tuned to give a rising response (reaching +3.2dB @ 20kHz) before rolling off to reduce the energy of images.
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant  Alan Greenspan 
18th February 2019, 10:21 AM  #6 
diyAudio Member
Join Date: Mar 2015

Could you help to suggest a design tool or expressions to calculate the correct values? Sorry but I'm mechanical engineer, so I don't have a deep knowledge about the electronics, but I want to learn it

18th February 2019, 10:21 AM  #7 
diyAudio Member
Join Date: May 2007

The drooping HF frequency response is to be expected from a NOS DAC with a crude output filter (or no output filter). Is that what you have?

18th February 2019, 10:57 AM  #8 
diyAudio Member

Here's a starting point  you can download LTSpice (from Analog Devices) and tweak it to your heart's content.
The inductor's a Coilcraft MSS1210 and the caps I've used in such circuits have been SMT NP0 types (good stability).
__________________
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant  Alan Greenspan 
18th February 2019, 11:24 AM  #9 
diyAudio Member
Join Date: Mar 2015

Thanks DF96, Yes I only have the RC filter, same as KusunokiDAC.

18th February 2019, 11:25 AM  #10 
diyAudio Member
Join Date: Mar 2015

Ok, I try to adjust the Ltspice model.

Thread Tools  Search this Thread 


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Low Filter Roll Off Calculation  SyncTronX  The Lounge  48  14th May 2018 08:58 PM 
Asking for choke value or calculation for CLC filter  Groundloops  Power Supplies  5  15th September 2009 07:51 PM 
DC coupling capacitor calculation  luvdunhill  Parts  5  18th December 2007 10:43 AM 
Sime filter calculation help needed.  Nordic  Parts  20  15th November 2006 02:42 PM 
RC filter on TDA1543 inputs  ash_dac  Digital Source  4  4th September 2005 06:01 PM 
New To Site?  Need Help? 