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Building the ultimate NOS DAC using TDA1541A
Building the ultimate NOS DAC using TDA1541A
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Old 21st February 2009, 07:54 AM   #2591
dddac is offline dddac  Germany
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John,

It seems that reoccurring questions are mostly about circuit drawings and how things (modules) are tied together.

I also understand you are not done and things keep changing. So it becomes kind of jig saw puzzle

Would it be an idea, you publish a circuit with everything in it as it is today, give it a revision number and just update whatever is to be updated and increase the revision number?

That would keep the thread readers in sync on what you are actually doing
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Old 21st February 2009, 08:00 AM   #2592
ecdesigns is offline ecdesigns  Netherlands
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Hi ccschua,


Quote:
I wonder how u know the sound is ringing, what best to test it. Is the chrage transfer connected to the output stage of transimpedance circuit?
I measured the output signal on the emitter of the darlingtons in the floating CT supply with an oscilloscope, after measuring slight interference at the series regulator output in the D1M. The voltage across the power-shunts was clean.

The floating CT power supply first drives a capacitance multiplier. Then it's routed to the D1M and enters a 9.6V discrete series regulator.

The series regulator feeds the connected loads through 30 ... 40 mH and 47,000 ... 100,000uF LC filters, the voltage at the loads is kept constant using power-shunt regulators, placed as close as possible to the loads.

The master clock / tracker is fed by the 9.6 volts series regulator, a precision constant current source, a 40mH choke, and finally a 5V power-shunt regulator.

D1M power distribution is as follows:

9V6 series reg > precision constant current source > LC filter > 5V shunt reg. > multi-rate master clock tracker / clock buffer.
9V6 series reg > LC filter > 4V2 shunt reg. > SPDIF cleaner (CS8416), synchronous SPDIF reclocker.
9V6 series reg > LC filter > 4V2 shunt reg. > SPDIF receiver (CS8416), WS generator (counter).
9V6 series reg > LC filter > 3V1 shunt reg. > DAC chip (1xTDA1543), I2S attenuators
9V6 series reg > LC filter > 8V9 shunt reg. > trans-impedance converters / buffers.
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Old 22nd February 2009, 12:43 PM   #2593
ccschua is offline ccschua  Malaysia
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Quote:
Use either a diode like 1N4148, or a 2SC2240 connected as diode.
I connected the transimpedance circuit single ended as below

Click the image to open in full size.

I use R1 = 1K5, R2=2K7, R3 = 510R and U1 = 1N4148. T1 and T2 is C2240. C1=1200uF panasonic FC, Vin = 12.07 V DC.

The DC voltage is shown in RED. When IDAC is left open, I found 0.3V at C2 output. Connecting IDAC to my TDA1541 IoutR give the same. Wonder what is wrong here.
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Old 22nd February 2009, 12:56 PM   #2594
Andypairo is offline Andypairo  Italy
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Hi,
at idle the TDA1541A Iout sinks 2mA, so you should have 9V on T1's collector.
If nothing changes connecting the TDA this means that ther is no current in T1.
Are the Gnd of the circuits connected?

Ciao

Andrea
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Old 22nd February 2009, 01:26 PM   #2595
ccschua is offline ccschua  Malaysia
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Ground is connected. Am I missing something. I even tried connecting the Idac to ground, but still the same.
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Old 22nd February 2009, 03:09 PM   #2596
ecdesigns is offline ecdesigns  Netherlands
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Hi ccschua,

Quote:
Ground is connected. Am I missing something. I even tried connecting the Idac to ground, but still the same.
T1 is not conducting, I suggest checking both T1 and T2 connections.

When viewing the 2SC2240 from the top with the rounded side facing to the right. Upper pin is emitter, center pin is collector, lower pin is basis.

Andypairo is correct. TDA1541A bias current equals 2mA when the code for bipolar zero has been latched in the TDA1541A output latches. This produces .002 * 1500 = 3 volts across R1, so the voltage at the collector of T1 should be around 12 - 3 = 9 volts DC. The voltage at the emitter of T2 should be around 9 - 0.6 = 8.4 Volts.
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Old 22nd February 2009, 03:44 PM   #2597
maxlorenz is offline maxlorenz  Chile
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Dear EC,
I am trying find a good use to my other DI4
I suspect that if I connect each DAC output (NIR, NIL, IR, IL) to its corresponding trans impedance/buffer circuit I could end with a balanced output NOS DAC, and, as I use a TVC as preamp, I could get rid of the output caps, since all the trans impedance circuits will be fed by the same power supply, so I hope DC output will cancel out on the transformer based preamp...am I right?
(using matched parts and transistors, that is...)
Cheers,
M
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Old 22nd February 2009, 06:56 PM   #2598
JC951t is offline JC951t  Taiwan
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HI John,
Question. Would biasing the transimpedance circuit
for a parallel TDA 1541 be of any benefit sound wise ?

Thanks
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Old 22nd February 2009, 08:22 PM   #2599
Terry Demol is offline Terry Demol  Australia
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Quote:
Originally posted by Andypairo
Hi Terry,
I'm interested too in the detailed datasheet, if possible.

Ciao

Andrea
Sorry guys I only had the Philips DEM data sheet.

T
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Old 23rd February 2009, 01:34 PM   #2600
ccschua is offline ccschua  Malaysia
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Quote:
Originally posted by -ecdesigns-
Hi ccschua,



T1 is not conducting, I suggest checking both T1 and T2 connections.

When viewing the 2SC2240 from the top with the rounded side facing to the right. Upper pin is emitter, center pin is collector, lower pin is basis.

Andypairo is correct. TDA1541A bias current equals 2mA when the code for bipolar zero has been latched in the TDA1541A output latches. This produces .002 * 1500 = 3 volts across R1, so the voltage at the collector of T1 should be around 12 - 3 = 9 volts DC. The voltage at the emitter of T2 should be around 9 - 0.6 = 8.4 Volts.
So does this mean that TDA1541a draws min 2mA. and it swings from 2mA to 4mA to give the corresponding ac signal.

Now since the DC is blocked by the coupling cap C2, where does this AC signal come from to give an output of 2V PP for driving the audio amp?
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