Quad 44/405

[Dick Dawson]

I recently obtained a Quad 44/405 combination, believed to be original. Playing vinyl via a Grado cartridge produces almost no sound through the phono input, even at the greatest sensitivity. More sound is provided by the radio input, but all the low frequences are missing and the sound is very thin.

It seems most likely that some components are past their best, but it could be an interconnect problem, or perhaps internal connectors need cleaning. What is the best problem-solving route for a complete beginner, who has never been inside an amplifier case before?

I'd be grateful for any advice - thanks.

[Tajzmaj]

Hi
There is a lot of things which can br replaced or even replaced by some better components. There was a lot of such threads here and you can find a lot of information on net....but. You shoud replace all electrolytic caps.....in 405 it is good idea to replace input op amp.......check output transistors ....and replace them if they are not all the same.......and renew thermal grease.......so a lot of things can be done......
If you want you can email me
taj.pecnikar@gmail.com
and I will send you service manuals for both units........
This site will give you a lot of usefull information......
http://quad405.com/405mods4.pdf
Maybe there are some too radical ideas there.......but if you want cut traces......you can try. But I leave my 405 with input sensitivity like it come from factory and it works fine ........but everything else is ok.......
Just my opinion.
Best regards, Taj

[burbeck]

hi Dick
first thing to do is get the amp up and running before considering any upgrade path.

here is what i would do, 1st connect a cd player or other line level source into the cd or radio input and see what happens. if everything is ok on these inputs then the fault is with the phono stage.

2nd if there is still no sound then the next step is to establish wheather the fault is with the preamp or the power amp or the lead that connects the two.


to check the power amp a signal connected directly to the input socket to test it. caution is advised here as the sensitivity of the power amp is high and there is no means of reducing the volume with the preamp disconnected, i would use a cd player with its own volume control, with the volume turned down very low initially to test.

if there is clear sound just with power amp alone then the pre amp or the interconnecting lead is faulty.

if there is no sound the the power amp is faulty.

at this point you should have a good idea which is faulty and may want to consider your next step, miight be a job for a technician from here.

[Dick Dawson]

Hi Burbeck

Thanks for the advice. I'll carry out some further checks along the lines you suggest and see where I get to.

Many thanks.

Dick

[batteryman]

I recently bought a 405-2 off Ebay and then unexpectedly won a 405-2 with a 34preamp. m12

The 405s work but will be upgraded with new electrolytics, a opa604 and eventually a pair of MJ15003s. (its handy having two - use one whilst the other is being upgraded and then try bi-amping)

The 34 worked fine for 4 days and then the tape button ceased to work and the output level dropped dramatically.
The supply voltages are too low so I'm in the process of changing the 4013 flip flops and also the CD input opamp to a opa2604. (something is dragging the voltages down so have a supply of 4066be's on hand as well!)
The electrolytics will also be replaced, the coupling caps will be shorted and maybe the other op amps changed at a later date.

The cd input is being customised to direct couple to the I/V transformers of my Dac but I am not changing the configuration to non inverting.

[batteryman]

Originally Posted by batteryman

The 34 worked fine for 4 days and then the tape button ceased to work and the output level dropped dramatically.
The supply voltages are too low so I'm in the process of changing the 4013 flip flops and also the CD input opamp to a opa2604. (something is dragging the voltages down so have a supply of 4066be's on hand as well!)

I replaced the bridge rect, increased the smoothing cap to 4700uf, replaced most of the other electrolytics, fitted the OPA2604 (with 22n caps on the supply pins to 0v) and replaced all three 4013s.
Normal button operation has been restored and the supply voltages are correct.