Quad 34 Pre Upgrades

[arupg]

I have a Quad 34 Preamp from the mid 80s and was looking inside to find several Op Amp (less than a dozen) mostly all of them being TL071 & a few TL072 (the same family).

I would like to get inputs from fellow members & also the Op Amp master 'Carlos' as to what would be a good Op Amp to substitute in place of these TL071 / TL072.

Thanks in advance!

[analog_sa]

Almost anything would be an upgrade. The 34 otoh is such a disaster that simply opamps won't help it that much. Bad analogue switches, lots of tantalums in the signal path...

[dcd]

Arupg

The 34 is not that bad at all but as mentioned, op-amps are not the answer, I have posted some information:

http://www.dc-daylight.ltd.uk/Valve-...D-34-Mods.html

I hope you find it interesting

Keith

[Thomas001]

Hi Keith,

I too have a Quad 34 with MM phono card. Is there a way to change the gain on the phono card from the standard 3mv to about 1.5 mv. Thx for your help in advance.

Regards
Tom

[Zombie]

Frankly, if you're not into modding things for fun and to see what can be squeezed out of a construction, sell the 34 and buy smth else.
I sold the 34 to a Japanese trader and bought a Quad 99 pre and my mega-super-duper-hot-rodded 34 suddenly wasn't that good.
But it was fun and I learnt a lot and the 34 is really neat and nice.
Check out K. Snook's web page, lots of info on the 34 there...
Good luck!
t

[dcd]

Tom

You could change R23 to 110R (100R) which should double the gain, also if not already done you may consider changing C14, C15 and C22 for 2.2uF solid aluminium or better still a poly type as they are small enough nowadays.

Zombie

I guess you have read the web article.... part modding for fun but mainly an investigation into cross-talk that got out of hand. I've never listened to a 99 for any length of time but lived with a 66 series for about 7 years, miss the extra inputs but the modified 34 is simply much better, although it's main role is as a volume control and switch between CD and radio both of which require me to get up off my ......... I'm getting old! maybe i need a 99 or something with a remote control again.

regards

Keith

[Thomas001]

Hi Keith,

Thanks for the reply. Just to make sure that we are on the same page, R23 is located on the phono board (no component # on the underside) and its value is 220R to ground. Can you confirm that please. BTW you also mention changing C14,15,22 but I only counted a total of 4 caps on the phono board.

Regards,
Tom

[dcd]

Tom

values were for right hand channel as a guide,

Left channel has R21, C12 and C13 and right channel has R23, C14 and C15 on the plug-in PCB.

C18 and C22 are on the main PCB.

Change the resistors R21 and R23 for 110R or 100R.

A change of capacitors may make a noticeable difference but perhaps do it some time after the gain gain change to see if it makes a difference, and lets us know what you think.

regards

Keith

[Thomas001]

Hi Keith,

Thanks for the infomation, i just change R21 & R23 and it works. Now, about the cap, I have some problem reading the schematics, so can you confirm the following : C12,13,14,15 = 1.5uf ;
C18,22 = 2. 2uf. Also, can I use slightly larger cap value?

Regards,
Tom

[dcd]

Tom

You are correct, I am suggesting that they could all be 2.2uF - no need to go higher - also listen a lot with the new gain setting before you change the caps.

Regards

Keith