Tube-I-zator Professional PCB

[dvb-projekt]

Originally Posted by DQ828

Trying to buy Carbon resistors to meet the requirements (without going to a special OS supplier for 1 resistor) is impossible, can I just use metal film, why the carbon?

It is a recommendation from Salas to use 220R carbon resistors as gate-stoppers.

If you have nothing at hand, use a metal film.

[DQ828]

Originally Posted by dvb-projekt

It is a recommendation from Salas to use 220R carbon resistors as gate-stoppers.

If you have nothing at hand, use a metal film.

Gate-stoppers???

I'm talking about the 820R 2W resistors you recommended I use as a replacement 1kO to raise the input voltage. The 1KO are carbon.

[dvb-projekt]

Originally Posted by DQ828

Gate-stoppers???

I'm talking about the 820R 2W resistors you recommended I use as a replacement 1kO to raise the input voltage. The 1KO are carbon.

Ups... A small misunderstanding!

You could use any 2W resistor you have for this position!

[Crom]

Originally Posted by DQ828

DVD
Do you have any idea what value would be suitable for BIII as the I/V resistors?

Can anyone explain to me how best to work out the best value for the I/V resistor? I've had a play with a few values ranging from 20R to the original 56R and I have to admit that I'm not sure what I'm listening for...and I can't tell what, if anything, changes. Does anyone know what I should be listening for...distortion? changes in output volume etc etc?

Thanks,
Crom

[noizas]

Originally Posted by Crom

Can anyone explain to me how best to work out the best value for the I/V resistor? I've had a play with a few values ranging from 20R to the original 56R and I have to admit that I'm not sure what I'm listening for...and I can't tell what, if anything, changes. Does anyone know what I should be listening for...distortion? changes in output volume etc etc?

Thanks,
Crom

Hi Crom,

sadly to say, but both I/V (more correct name should be I/U) resistor values 20R or 56R compromise TDA1541 linearity and resolution.
However to detect those problems you need perfect set of your ears, loudspeakers and amplifiers , else you need to measure THD somehow.

Value of I/U resistor is possible to calculate from TDA1541A datasheet:
1. "Notes to the characteristics: To ensure no performance losses, permitted output voltage compliance is ±25 mV maximum." - here is P-P values, not RMS.
2. "full scale current: 4 mA (nominal)" - current is negative here.
3. ""zero scale current: 25nA (nominal)"- actually 0 mA.

So there is two ways to calculate maximum correct value of I/U resistor by Ohm law R=U/I :

A. If you have no constant 2mA current injection circuit -
R=[-25mV]/4mA=6.25R , because current is only negative here.

B. If you have constant 2mA current injection circuit -
R=[+-25mV or 50mV P-P]/4mA=12.5R , because current is swinging +-2mA around 0 (compensated by CCS).

So, why most of diyers use I/U resistor for TDA1541 in range 20R - 60R ?

It is because of noise issue as well as amplification factor.

Lets take circuit with CCS 2mA injection, so we have signal of U RMS=0.7*25mV=17.5mV, and we need to amplify it to:
1. For CD player output level (2V RMS): K=2000mV/17.5mV - about 114 (even more than 12AX7 in grounded cathode way can provide, not even mention SRPP - half of mu).
2. For level of professional audio (+4dBu, or 1.23V RMS): K=70 (still not achievable with SRPP and 12AX7 tube, but almost here )
3. For level of customer audio (-10 dBV or 316 mV RMS): K=18 (easily achievable in SRPP with 12AX7 and almost achievable with medium mu tubes as 6N1P or 6DJ8, etc).

But choosing tubes with medium to high mu, do not forget standing current in SRPP - more standing mA you have, less the output will be taxed for charging capacities of interconnect cables and input of preamplifier.
This is also related with output impedance - as usual medium mu triodes have less plate resistance than high mu triodes, so damping factor of interconnection would be better.

Best wishes
Saulius

[dvb-projekt]

For all of you who use the Tube-I-zator with the SSHV-Shunt,
please look at the recommended modification in my blog!

[crobbins5421]

Hi Oliver,

Type and/or brand of 75K resistor?

Thanks

[dvb-projekt]

Originally Posted by crobbins5421

Hi Oliver,

Type and/or brand of 75K resistor?

Thanks

Blog entry is updated.

[crobbins5421]

Perfect. Thanks.

[DQ828]

Does this apply to the Buffalo DAC's as well?