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Quad 306 resistor spec for changing input sensitivity

villan

villan

Member
Just picked up a pristine 306 that had been mounted since new at the back of a hifi cabinet so has hardly seen the light of day, let alone been bashed around.
I'm going to replace power caps and the C7 47uf caps (are these electrolytic? I'm assuming so) and leave the rest alone. I'm thinking of copying another member (John_73, hello) to keep things simple and go for Kemet ELGs and Vishay 136 because it's doing my head in trying to make a decision for myself and the Kemets seem readily available and are not too tall. Any other suggestions welcomed however, but the Kendeils everyone seems to favour don't seem to be available.
I want to change the input sensitivity to 1.0V. Dada does this by using a R27 resistor at R13. Quad spec for existing resistor is 9R 0.25W metal film. So my question is if I go for R27 does the wattage stay the same or will this change?
This is a near-field desktop system. I'm planning to output directly from a PC with a Xonar Essence STX card and was thinking about getting one of those little Nobsound passive pre-amps just for a volume control.
 
It's a very bad idea. If you must change sensitivity then use an attenuator such as the Rothwell ones or modify the input R1, R2 and C1 to act as an attenuator.
 
I thought it was pretty standard to change the sensitivity on a 306. I am happy to leave it as it is as long as it will work ok with the output from the PC card, which is line output as I understand it at 1.0V. I'm all for keeping changes to a minimum. Is there any downside to leaving sensitivity alone if the input is 1.0V? The standard input-sensitivity is 0.375 Volt.
 
Great, the little Douk Audio/Nobsound box is basically just an attenuator, so I'll go with that
 
I believe Jez suggested "If you change R1 and R2 to make them both 10K this should approx halve the sensitivity."
 
villan said:
and was thinking about getting one of those little Nobsound passive pre-amps just for a volume control.
Click to expand...

I just hooked up a Nobsound PGA2310 in place of my 20k Little Bear passive because I was sick of not having a remote control for the volume, and it seems I'm going to have to put the 9R resistor back in the 306 because I had to turn it right up to 75 (out of 100 steps) to watch Netflix. Below 50 I can hardly hear a thing.
 
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The one I'm going for is just an Alps pot in a box with RCA in and out, no power. It is literally just a volume knob.

Got my caps, tho not soldered yet. I was going to get Kemet ELG but they seem to have disappeared. I went for Vishay PMG-SI because someone on DIYaudio (am I allowed to say that here?) said they are excellent and his new go-to caps, plus two little Vishay 136. The power supply caps are exactly the same size as the original Spragues (35x30) except the tops aren't blown out and rounded.

My set up will be a PC, with Jriver as the player which I can control remotely from my iphone, including volume, but I would feel safer having a passive pre-amp on my desk between the PC and 306, especially in a Teams or Zoom meeting when I could give everyone a heart attack if I forgot to turn it down.
 
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