Simplest preamp for Aleph-X?

[leadbelly]

There have already been some posts in the Aleph-X group buy thread on this subject, but I do not like to threadjack.

My question is, since I would like to get my Aleph-X up and running soon (as in sooner than I could concurrently build a high quality preamp), would it best to throw together a simple preamp built on perfboard with something like an LM6181 to convert from unbalanced to balanced input? Or is this not really worth the effort and expense and it is best just to run the Aleph-X with an unbalanced input until I make something fancier?

[leadbelly]

Sorry, I realize my idea was silly after a bit more research.

But now *seriously*, how about a first, buffer stage using an LM6181 or NE5532 driving an SSM2142 balanced line driver second stage? Good idea, or is this a case where "less is more"?

[GRollins]

One, you don't need a balanced input.
Two, is there some reason that a BOSOZ, perhaps with a current source to improve unbalanced/balanced conversion, wouldn't do the trick? Discrete, too.

Grey

[leadbelly]

Originally posted by GRollins
Two, is there some reason that a BOSOZ, perhaps with a current source to improve unbalanced/balanced conversion, wouldn't do the trick?

Only ease of construction. The circuit I envisioned was one resistor, then op amp, then a pot, then the other chip. No other resistors, no caps except for the PS filtering. Much quicker to construct than a BOSOZ with CCS.

[leadbelly]

As shown in the attached schematic:

[GringoAudio]

So why Grey don't you need a balanced connection between pre-amp and amp? How do you connect an unbalanced pre to a balanced amp without a balun? Thanks I am kind of new to the balanced world.

[GRollins]

A differential (i.e. the first stage of the Aleph-X where the two IRF9610s have their Sources connected) makes a spendid phase splitter if there's enough resistance under the Sources/emitters/cathodes. The extreme endpoint of the resistance game is to use a current source (one of the few times you'll see me use one happily--it's delivering DC in that application). A current source is a fair approximation of an infinite resistance. Once you've got a current source under a differential, you can stick a signal in one side of the differential and--as if by magic--the opposite phase comes out the other side.
Okay, so there's no such thing as magic...Harry Potter notwithstanding. What happens is that the current source will literally force the current into the differential. It's easy enough to see that the driven side will use a varying amount according to whatever the signal is telling it to do. No problem, right? But what happens to the rest of the current--the unused part? It gets stuffed into the rump end of the other half of the differential. Sounds kinda rude, but they're consenting adults and what they do in the privacy of their own amplifier is their business, right? Well, that creates a signal once it gets to the load resistor for that side of the differential, even though there's no signal at the Gate.

Grey

[jh6you]

Originally posted by GRollins

... Sounds kinda rude, ... Well, that creates a signal once it gets to the load resistor for that side of the differential, even though there's no signal at the Gate.

Grey

Rude? No, not at all.

By the way, the remaining part does not give me clear meaning. In other words, please?

[Fred Dieckmann]

"Well, that creates a signal once it gets to the load resistor for that side of the differential, even though there's no signal at the Gate."

Since you have built the amp and I am afraid that I will never convince you otherwise by trying to explain the circuit, go measure the signal at the gates of the input pair with a single ended input signal. I think you are in error and I know you would not want to confuse others. Hint: Think about the current in the feedback resistors for both sides of the amp and remember no current can enter the very high impedance gates. Remember Kirchoff's Current Law: The sum the currents entering a node is equal to sum of the currents leaving a node or that all the currents in a node must equal zero. This law is as basic and as important as Ohm's law. Please don't come up with name calling and questioning my motives. I am honestly trying to help you and others understand this mode of operation. (see post above for example)

http://www.geocities.com/~supertrooper/kirch_i_n.html

[Panelhead]

I picked up some opamps to do the single ended to balanced conversion a while back. I think they are DRV134. Might be DVR134.
They run on +/- 15 volt rails and recommended application notes are on the net.
I decided to go discrete and use a transformer to do this instead. But I have been told that these opamps are very nice sounding. They are fairly cheap - 4.00 USD each.

George