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

[isobarik]

I need just 2. I know you can buy them online but I only need two and I don't want to be left with loads I'm not going to use just to be thrown in a drawer.
Anyone help me out? Obviously I'll pay for the components and postage.
Thanks.

It's times like this that I miss Maplin's. Only a short bus ride from me!
Thanks for looking.
Regards,
Ray

P.S. Could Mods please move this post if it's not in the right category.

[Barry]

I'll have a look in my spares box. All of my electronic components are stored in my garage, along with a whole load of other stuff which needs sorting out, so it might be some time. What are the resistors for Raymond?

[isobarik]

I'll have a look in my spares box. All of my electronic components are stored in my garage, along with a whole load of other stuff which needs sorting out, so it might be some time. What are the resistors for Raymond?

Hi Barry,
I'm in the process of buying a Quad 306 to partner it with my Hafler DH 101 (I think you know the 101) Lol
As you know the 101 delivers 3 volts where the Quad only needs 375mv for full output.
The 27 ohm resistor will increase the Quads input to 1 volt to a far more satisfactory level

Regards,
Ray

[isobarik]

Hi Barry, having a senior moment, it's 27ohm I need.
Sorry about that.

P.S. Any chance you could amend the title so it reads 27ohms.

[mik_rik]

Hi Ray
I have a couple of 27ohm and a couple of 22ohm also if you want ,can post thm today if you want (f.o.c)

[isobarik]

Hi Mick,
It's a small World! Thank you so much Mick, that would be brilliant!
I think you've got my address lol.
I think you know what I want them for?

Cheers,
Ray

[Barry]

How do you derive a figure of 27ohm, and where will the resistors be fitted?

[isobarik]

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.

[isobarik]

Thanks to Mick, I've obtained the parts I need.
Thank you too Barry for your help, much appreciated

[mik_rik]

Checked on the 2 digi meters I have,readings were 26.9 ohms for each

[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/Audio/dadaelectronics.eu/downloads/Dada%20Service%20Kit%20Instructions/Quad-306-Upgrade-Revision-Manual-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.

[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/206138-cornwall-iv-which-mc/), [2] (https://www.diyaudio.com/community/threads/quad-306-revamp-i-am-in-awe.395708/)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.:doh:

[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!