AD1865 tube i/v converter

[drobert]

Hi,

I have a short question:

I found this schematic on the web. This is a very simple i/v converter for the TDA1545.
Can I use this schematic with AD1865? If yes, how?

drobert

[poynton]

Hi,
The answer is yes.
DAC in goes to the AOL / AOR ( pins 6 /8 ) on the TDA1543. R8 is used as the I/V converter.
On the AD1865, it would go to the equivalent output - pins 4 / 21.
Andy

[drobert]

Hi,

It is sure?

I don't understand something.

If I connect the AD1865 output to R8. The output of the AD will be about 3,3V.


Robert

[philbyx]

Originally posted by drobert
Hi,

It is sure?

I don't understand something.

If I connect the AD1865 output to R8. The output of the AD will be about 3,3V.


Robert

Sure, it is not right!!!

The I/U resistor in this shematic is the 22 kohms
ad1865 1 ma full scale will give 22 Volts at the output of this circuit (called common grid).

There is a problem with this common grid : the dac input is not 0V :
then the ad1865 can blow.
You have to reference the 375 ohms resistor to a negative supply, to have 0V on the dac input.

Go to this post and the rest of this thread :

http://www.diyaudio.com/forums/showt...684#post696684


Philippe

[drobert]

OK, I understand it.
But can I use this schematic with TDA1543? What will be a correct value of the Vref?

drobert

[ThorstenL]

Konnichiwa,

Originally posted by philbyx
Sure, it is not right!!!

Well, not for the AD1865, but then, it was explicitly designed for one DAC chip and ONE only, simply because this DAC chip will not work with the normal solutions.

Originally posted by philbyx
The I/U resistor in this shematic is the 22 kohms

No, it is not. The U/I Resistor is 375R in parallel with around 800R, so around 250R. This with the intended DAC which has when used as instructed with the original version of the schematic 2mA Peak-Peak full scale output current will give a voltage of 500mV Peak-Peak on the ECC88 Cathode, which as observed works as grounded grid amplifier.

All in all the circuit used with the DAC it is designed for gives a bit above 2V for full scale.

Originally posted by philbyx
There is a problem with this common grid : the dac input is not 0V :

That is intentional, the DAC this output stage is designed for likes to have it's output at 3.3V, not 0V and will not work well otherwise.

Sayonara

[ThorstenL]

Konnichiwa,

Originally posted by drobert
can I use this schematic with TDA1543?

Not really, you may be able to adapt it, but changes would be needed. But given that TDA1545 this circuit is designed for is so dramatically superior to the TDA1543 sonically and given that it is readily available for the same sort of money as a 1543, I'd ask "Why bother with 1543?".

The key attraction of the 1543 is that it actually works very well with just a resistor as I/V and an output coupling capacitor to give nearly 2V RMS @ 0dbfs, in other words, no active output stage. Adding an analogue stage only detracts from that.

Sayonara

[philbyx]

Originally posted by Kuei Yang Wang
Konnichiwa,



Well, not for the AD1865, but then, it was explicitly designed for one DAC chip and ONE only, simply because this DAC chip will not work with the normal solutions.



No, it is not. The U/I Resistor is 375R in parallel with around 800R, so around 250R. This with the intended DAC which has when used as instructed with the original version of the schematic 2mA Peak-Peak full scale output current will give a voltage of 500mV Peak-Peak on the ECC88 Cathode, which as observed works as grounded grid amplifier.


Sayonara

Bonjour

I agree with you because this 250 R is in fact the input impedance. Then the dac current will flow in this impedance and will give this voltage (2vpp) on it.
But replace the 375 R with a constant current source, and then, the I/U resistor will be the plate resistor.
Feed 1 ma on the cathode, you will find 1 ma in the plate Resistance, then U = 1ma x plate resistance.



http://www.tubecad.com/april_may2001/page24.html

http://www.diyaudio.com/forums/showt...684#post696684


Au revoir

Philippe

[ThorstenL]

Bonjour,

Originally posted by philbyx
I agree with you because this 250 R is in fact the input impedance. Then the dac current will flow in this impedance and will give this voltage (2vpp) on it. But replace the 375 R with a constant current source, and then, the I/U resistor will be the plate resistor.

Yet I designed and published the circuit using a Resistor and not a CCS (for very good reasons as well). BTW, when I published the circuit it was also made clear that it is to match the TDA1545 in a Philips CD-720/21/22/23 and included some other notes, all in German.

It is a poor idea to just copy something without understanding it (and it is not nice to publish others IP without consent or at least attribution), yet it seems a number of Website owners seem happy and even keen to do exactly that.

As for the theory of such circuits, I am reasonably well versed in it, thank you very much.

At any extent, as is the Circuit is designed for the TDA1545 and ONLY for the 1545 and non else and it works as intended in that application and rather well if I may say so myself.

See Ya....

[drobert]

I ask you then designer of this schematic.

Is it possible to use this (or other very simple common grid) schematic with TDA1543 or not?

drobert

Sorry, but my English is not to good.