Balanced Phono preamp

There is a neat balanced phono stage in morgan jones - valve amplifiers.

 

You should be able to get some good ideas from the hagarman website as well.

Edited by nikongod - 8/30/10 at 6:14pm

http://www.hagtech.com/pdf/trumpet.pdf

If I recall, the Nelson Pass Ono had balanced outputs. There are usually clones of his gear kicking around the Pass forums. I can't point to a thread there, but it'd be worth digging around there to see if someone built a clone and might have boards available.

Just build it single ended. There is a fair bit more to building a balanced phono stage that putting 4 channels together with some creative wiring.

 

If you need to drive balanced inputs in whatever amp comes next use a phase splitter. Active and passive solutions are both reasonably affordable. Better would be to design a phase splitter into the balanced amp and drive the single ended input without extra stuff in the signal path, but "extra stuff in the signal path" phase splitters arent relly that bad.

 

If you are going to use a phase splitter the phono stage you linked to is either awesome or a waste of time :) It is great because that output stage should be able to drive relatively low impedance transformers very cleanly. If you use an active phase splitter its probably a waste as they generally have very high input impedances.

In general I'd agree with this. It really depends on what the motivation is. I still want to build a balanced pre-amp, but here's why. A big reason is because a cart creates a balanced signal naturally, so it kinda makes sense to build a balanced amp for a balanced source signal. The other, more compelling reason is that I have more than one turntable, and my second table can't be next to the rest of my equipment. If I set that system up as balanced, then I solve the issue of lengthy interconnects. One day I'm going to do this, just not today....

 

Generally yes.

 

A passive phase splitter would be a transformer, which you rarely find with an input impedance of much more than 10Kohms. Every now and again 20K :) But also 600ohms.

 

Lets say the primary is set up for whatever. Input a SE signal from one end to the other.

 

The secondary gets 2 options. 

 

The first is for a single pair of outputs. you take 1/2*whatever the secondary load is (from the datasheet, name{10K:600}, or test) and strap this across the secondary. The center of these 2 resistors goes to ground. This will output a balanced signal. The 2 load resistors need to be matched pretty precisely, but the winder dosnt have to make the center tap exactly right.

 

The second option is with a transformer with a split secondary. The center tap of the transformer goes to ground, and the 2 ends go to the load. You still need a loading resistor here, but it dosnt have to be matched like the other option.

 

six of one, half a dozen of the other. Different vendors have their own preferences.

why not use one of P-A's DRV134 boards on the output?

it's a balanced line driver, or differential output amplifier. It converts a single ended input into a balanced output pair.