balanced input

[vitalstates]

This may be a naive post..if so then please shoot me down..

would it be easy to convert the input on Steve's(Shadow) el34 SE amp and if so could/would somebody post a simple sketch of the input circuit.

I am just ordering parts to build this and wanted to use it with an ECHO layla(studio DAC) as a front end. The layla has many balanced outputs(although it does provide unbalanced as well) and with some experience of studio ground loops I wanted to stay one jump ahead of the game and avoid the issue from the outset.

regards

Ed

[James D]

The best way to give it a balanced input would be to fit an input transformer. Tis would solve the potential ground loop problem too.

Try Sowter or Lundhal for a suitable trannie.

James

[vitalstates]

Thanks James

I have started to look at some of the wiring suggestions that accompany the transformers but at they moment they look a bit out of my league(electronically), and I've also been derailed by the discovery of inter-stage transformers/ coupling transformers.....sheesh, whats that all about??

just when I was getting my head round understanding SE fundamentals!!

Ed

[NickG]

There are two main threads to SE design, there is the James D way which could be said to be "there can be only one one driver, and its name is pentode". And there is the way I am going, which is "you can't have too much iron in an amp". As to which works best, dunno. but I do know the pentode way doesn't weigh as much.

PS, the above is not to be taken as anything other than a joke, unless you have a amp with a pentode, or at least one interstage transformer, in which case you already have your own answer anyway.

PPS. Oh, and there are the 14 other ways I haven't refered to.

PPPS, its not hard using a TX to convert balanced to SE, have a look as James suggested at the Sowter and Lundahl sites you will find examples.

[Paul Barker]

Or just get an in line phono plug, take your balanced lead, cut correct end off connect hot (red) to centre pin and join shield and cold (blue) to outer part. Then you have made a balanced to unbalanced connector.

With an SE amp you are not treating the signal as balanced anyway, and although a balanced to unbalanced input transformer protects the receiving item from ground loops preceding it, the problem doesn't usually exist. Unless you are maintaining the balanced topology inside the amp (which means you can't use se) you have little to gain.

There are possibly benefits from transformer input though, in which case you could benefit further by using a balanced to unbalanced line level transformer.

I use chokes and transformers for anode loads and interstage coupling like Nick, but they are not essential to good sound, if you use good resistors like Riken for anode loads or Tantalum (but actually even Holco sound a lot better than what I call washing machine resistors, the standard stuff you get with your kit). Use a quality (determined by what sounds good to you) wire wound for cathodes, or a light bulb a battery or diode (valve not solid state).

Others will advise on coupling caps I'm pants at them. I will just say smallest is best but not at the expense of base (hi pass filter effect o0f coupling cap and grid leak resistor).

Grid leak resistor holcos are fine, smallest is best, though not at the expense of base and adequate load to former stage (1:20 impedance ratio is ideal, less is common). Be aware of not using a value greater than the receiving stage valve is specified for.

Don't bother with fixed bias using batteries it's pants.

Grid chokes are a minimal improvement, though there is one oh so small.

Throw away the square wave generator and scope if you do go transformer route, it'll just depress you. Forget all about slew rate you can't get a good one, pretend it isn't the key to good sound. Your ears will confirm you know what you are doing, trust those.

But before all the above save up for Black Gate wkz's power supply caps and use choke input.

[vitalstates]

wow!!!!

Thanks Paul, you've just anticipated and answered my next 20 questions. Thats saved a lots of posts. Much appreciated......

Unfortunately I'm still a bit in the dark about what to do with those 3 wires that come in vis an input transformer...The jensen docs all refer to loads of op-amps...and the Lundahl 1544 doc shows a number of different suggested configs.....I am guessing here, but is it:

input: hot and cold to the 2 trannie i/ps and ground to chassis(or earth bus?)
output: pos to grid and neg to earth bus


regards

Ed

[Paul Barker]

Yes hot and cold go to the transformer primary which must be floating, screen goes to signal ground, transformer secondary goes to grid and circuit ground, and a load resistor goes across the transformer secondary or not according to taste. In the event people with scopes look for a resonant frequency and damp it with a resistor or zobel network, people without scopes listen to it and almost always prefer the sound without a resistor (more lifelike).

By the way I've had loads of scopes, and do have a couple of working scopes at the moment. I just don't find any need for them.

[vitalstates]

Hi paul

if your looking to part with one of them at a reasonable price I'd be v.interested. I have been looking at them on ebay recently but quite honestly they are a mystery to me and I'm a bit scared I might end up with something thats faulty and can't be mended.

Ed

[John Caswell]

Hi Ed
I feel that Paul has made a lot of sweeping statements that can give many of you the wrong impression ie he wrote "people without scopes listen to it and almost always prefer the sound without a resistor (more lifelike)." But not necessarily correct.
Now I know why we engineers are so poorly paid, we are just no good at our job. If I had adopted that attitude at whilst working the first thing I would have received would have been my P45

John aka Dr John

[Paul Barker]

You don't want my scopes Ed, no good to you. Ask Richard he's probably have something suitable.

John mine is one perspective, and not a lonely one. Yours is another, and you probably are among many more than I. We all deserve our voice, let the listener decide.