Wanted 36ohm 1/4 Watt 1% Metal Film Resistors

[isobarik]

Perfect!!!

[Barry]

Hi Barry, from this:

9.1 Ω (Stock): Gives standard 0.375V sensitivity.18 Ω: Lowers gain, raising sensitivity to 0.775V.27 Ω: Lowers gain further, raising sensitivity to 1.0V.36 Ω: Lowers gain to the ideal level for a 1.25V target sensitivity.

Resistor 13 on the Quad 306.

Well it's not the way I would have done it. But then I don't understand how you calculate the various values of R13 for a given sensitivity. Good luck with the modifications.

[isobarik]

How would you do it Barry?

[Barry]

As I said, I don't understand how you calculate the new value or R13 for a given input sensitivity; perhaps you could explain as it would appear to be an elegant solution.

My approach would be less sophisticated. The full output from the DH101 is 3V. The input voltage required by the 306 is 0.375V for full output; which is 1/8 of the Hafler output. Thus we need an 8:1 voltage divider (or an attenuation of 16dB), so with a Quad 306 input impedance of 22Kohm, we need a series resistance of 7 x 22K = 154K (or 150K in round figures).

[isobarik]

Hi Barry,
I followed this but it has been documented on other sites i.e. diyAudio https://dadaelectronics.com.au/doc/A...anual-V1.4.pdf

I'm not going to do the full DADA upgrades as I want to leave it stock. Just the R13 change.

Regards,
Ray

[Firebottle]

Ray is altering the gain, not attenuating the input Barry.

[Barry]

Ray is altering the gain, not attenuating the input Barry.

Yes, I realise that, but how are the new values of R19 calculated?

[isobarik]

Ray is altering the gain, not attenuating the input Barry.

Thanks Alan, I'm hopeless at explanation sometimes.

[isobarik]

Hoping this sheds new light. Change R13 to modify the overall sensitivity of the amplifier,

The Mathematical RelationshipThe core AC voltage gain (\(A_{v}\)) of the Quad 306 input feedback loop behaves roughly proportionally to the ratio of the feedback resistor (R22, which is 330 Ω) and the gain-setting resistor (R13, originally 9.1 Ω or 9R1)Because it is an inverse relationship, increasing the value of R13 lowers the amplifier's internal gain, thereby requiring a higher input voltage (lower sensitivity) to achieve the same full output wattage

Regards,
Ray

[Barry]

Thanks Roy,

Now that I understand, even though I would not be able to derive the mathematical relationship from first principles. Despite working in the research department for a major UK electronics company for thirty years, my speciality, amongst other things, was microwave technology and radar, not electronic circuitry.

So the voltage gain is 330/9.1 = 36.26, for that to tally with an output voltage of 20V for an input voltage of 0.375V (the gain being 53.3) the constant of proportionality is 0.68.