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

[Barry]

Have you thought of increasing the value of R13 further, so as to reduce the sensitivity of the 306 to 3V for full output? This will match the 3V output of the DH101.

[isobarik]

Might take the value up to 36ohm to achieve 1.25v. I shouldn't have any problems. Not too sure about increasing it further.
Regards,
Ray

[Barry]

Might take the value up to 36ohm to achieve 1.25v. I shouldn't have any problems. Not too sure about increasing it further.
Regards,
Ray

Fair enough Ray. I agree, the recommended values for R13 for a given sensitivity do not seem to follow an exact mathematical rule, so to extrapolate beyond 36ohm is not at all clear; if at all desirable.

[isobarik]

Hi Barry, after general consensus, I'm going to go with 27ohm.
I have to agree, where they get these figures seems a little vague.
Guess I'll have to go with the flow.
I'm looking forward to listening to the Quad through the Hafler 101 (thanks for the Hafler Barry)
I'll let all know on here how it sounds.

Regards,
Ray

[Barry]

I've been doing some research and it seems no-one knows how Dada derive the values of R13 for reduced sensitivities. You probably won't go wrong with using a 27ohm value to achieve a sensitivity of 1V, but some have expressed concerns.

These being that increasing R13 increases negative feedback, which in turn increases the loop gain, and this results in a lower stability margin and a greater chance of ringing on transients.

The preferred method is to fit an attenuator between the Hafler pre and the Quad 306. A simple series resistor of 47Kohm will reduce the source voltage fed to the 306 to 1V. That is still around 2 and half times the base sensitivity of the 306, but will allow more of the range of the volume control to be used.

(Suggest you keep the 9.1Ohm resistors in case you are unhappy with Dada's suggested scheme, so you can restore things back to the status quo. If you don't want to mess around fitting 47Kohm resistors to either the input of the 306 or on the output of the DH101, then you can use a 10dB in-line RCA phono attenuator.)

[isobarik]

Hi Barry,
I'll try the 47Kohm resistor as you've mentioned, easy to implicate than lifting a resistor off the board.
Thanks for the information Barry.
I'll order the said resistors tomorrow.
I'd like to know how DADA arrived at the values too, unable to ask now as DADA have ceased trading.
Regards,
Ray

[isobarik]

Hi Barry, I've been researching a bit more.

The Issue 3 Sensitivity Modification. On the M.12890 ISS.3 board, the input gain is determined by a voltage divider network consisting of resistors R11 and R12.To shift the sensitivity to roughly 1.0V–1.2V, you change the value of R11 on both channels: [1] (https://community.klipsch.com/topic/...l-iv-which-mc/), [2] (https://www.diyaudio.com/community/t...708/)Component (Left & Right Channels)Factory Stock ValueModified Value for ~1.0V–1.2VR11 (Feedback Resistor)180 Ω560 Ω (or 620 Ω for slightly lower sensitivity)R12 (Ground Loop Resistor)330 ΩKeep Stock (330 Ω)

[isobarik]

Hello Barry,
Even more confusion! Their is no resistor 11 fitted to my board it's vacant.
I believe the information given earlier is not factual and it's for the 606.

The circuit board in mine in M.12890 ISS 3


Regards,
Ray
Something simple to implicate is becoming to be a nightmare.

[Barry]

Hi Ray,

If you look on the website ukhhsoc.torrens.org (*), and go to Directory 'MANUAL' contents, you will find four pages:

Page 20 The PCB layout of M 12890-2 Issue 2

Page 21 Circuit Diagram Issue 2

Both show R11 (= 47R) and R12 (=2K2), for both channels.



Page 22 M 12890-2 PCB Issue 3

Page 23 Ciruit Diagram Issue 3

Again these show

R11 (= 47R, as for Issue 2)

R12 (= 330R, different from the 2K2 of Issue 2)


You say that R11 on your board (M 12890-2 ISS 3, is missing, that is, the position is unpopulated. Are there signs that a component there has been removed? And yet despite this the amplifier works as it should.

Are there any resistors soldered on the track side of the PCB? If you look at the circuit diagram for ISS 3, there are notes stating that R11 may have an alternative connections to the +ve supply rail.

So check the value of R12 (330R, colour code: orange, orange, brown) and look for R11 (47K, colour code: yellow, violet, orange).


* If the url doesn't work, simply type in "Quad 306 circuit diagram", and a few hits down will be the torrens website. click on that and you will find the pages I cite there.

Good luck.

[Barry]

Don't confuse the PCB and the component values for R11 and R12 of the Quad 606 with those for the Quad 306, they are completely different!