Quad 34 -- No Output

  • No one logged in.

05-Dec-2011 11:07 PM

Rob

Rob

Posts: 8

Hello, I have a 34 preamp that was working fine when put into storage 5 years ago, now my son would like  to use it, and unfortunately we have no output, well almost none, at full volume I am getting a very weak output at the speakers, same on all inputs , tone  controls are working.

We  had hoped to install a DADA upgrade kit  into the 34, but would like to get it running again first, would anyone have any idea of a good place to start as to where the problem may lie on the board, I am suspecting a dry joint somewhere, both channels are effected the same way

 

any advise or help would be greatly appreciated

  Reply

06-Dec-2011 04:51 AM

EJP

EJP

Posts: 1712

Check the power supply first. There should be +/- 7.5VD to the logic chips and about +7.8/-9.6VDC to the op-amps.

Dada Electronics Australia
  Reply

06-Dec-2011 08:52 PM

Rob

Rob

Posts: 8

Right, first of all I was only seeing  0.181v at op amps and logic, so decided to check input and output at the transformer, have discovered that "N1" (.047uf +100 Ohms)has had a very visable failure, after I removed this I am seeing 7.3v at logic and 8.5v at op-amps.  

I have ordered a few from RS

 What is N1`s purpose in the circuit, is it simply smoothing the AC ?

would it be safe to test the pre-amp with N1 removed ?

  Reply

06-Dec-2011 10:25 PM

MJ

MJ

Posts: 55

It's a snubber network, it will eliminate spikes and other garbage from the mains line.

 

  Reply

06-Dec-2011 10:25 PM

EJP

EJP

Posts: 1712

It's an arc suppressor for the switch. You can use it for a short time without it in place but fit it immediately it comes in. There seems to be a world wide shortage of these things: I ordered some in Oct that won't arrive until Jan.

Dada Electronics Australia
  Reply

07-Dec-2011 12:54 AM

Rob

Rob

Posts: 8

Tested without N1 in place, and still no output, found a useful post on another forum which a user had the same problem, Iwent through the tests as described and traced it down to the power supply area, I had power to T14 and T15 which mutes the amp apparently, turns out the LED on the board beside the transformer was dead, luck would have it that I had a few in the tool box, I replaced it with one of the same colour (green) and the amp has came back to life, I am so happy !

Will carry on using my 33 until the smoothing cap arrives, and I have bought a 44 on ebay too because I did not think the 34 would be such an easy fix !

Thank you to all who posted with advice , I have pasted a link to the aricle which helped me, hope this does not break forum rules,

http://www.vintage-radio.net/forum/showthread.php?t=69634                                                                                     

  Reply

07-Dec-2011 12:58 PM

Stefaan

Stefaan

Posts: 628

Hello,

N1 can be replaced with a 100nF 400V film-capacitor in series with a 100R resistor.

http://www.dadaelectronics.eu/shop/components/capacitors/film-capacitors/100nf-400v-15mm-mkt-vishay

Make sure to insulate it well as there is mains voltage over it.

This component is often worn out.

Stefaan

  Reply

08-Dec-2011 07:12 AM

EJP

EJP

Posts: 1712

And make sure the capacitor you use has an X2 rating, otherwise it isn't legal to connect it to the mains voltage.

Element14 have been out of stock of this network for some weeks but I am expecting delivery of a few next week.

Dada Electronics Australia

  Reply

20-Dec-2011 10:48 AM

EJP

EJP

Posts: 1712

"It's a snubber network, it will eliminate spikes and other garbage from the mains line."

To reiterate, this is not correct. The component in question isn't across the mains, it is across the power switch. It is short-circuited by the power switch when the 33 is on. Ergo it can have no effect on the mains line spikes and garbage whatsoever.

It's an arc suppressor.

EJP
Dada Electronics Australia

  Reply

21-Dec-2011 08:49 PM

Rob

Rob

Posts: 8


I ordered 5 from RS components in the UK and they arrived today, so I now have a couple of spares.
  Reply

12-Apr-2019 01:55 PM

digital_Twiddler

digital_Twiddler

Posts: 1

Just to add- I went around in circles with a similar fault which turned out to me the balance control sliders, RV4. When removed and stripped down, the pysical plastic holders for the contacts had broken away thus no pressure available. At first, due to very low output on both channels, the balance seemed to work. It was ony when I used a signal injector to the 'input' and 'output' sides of the slider it was apparent this was the component at fault. A new on cured the issue.

  Reply

28-Jan-2020 04:24 PM

Kalle G

Kalle G

Posts: 4

I had similar problem and it was the balance slider causing it. I removed it and striped wires as described in upgrade doc. And all working fine now. Will replace with the resistors 330ohm and 1,5kohm for right output level.

  Reply