OK, the quick answer is that the only difference is the black injection mold plastic knobs, and the black and gold faceplate.

The longer answer is that back when the 737 first came out it had purple injection mold plastic knobs and a sort of cream colored face plate. When they brought it over to 'Babyface's place [Brandon's Way] they quite liked the unit, and thought it was a nice complement to all their other Avalon gear...except it didn't look like their other Avalon gear.

So...the Avalon folks made a version with the aluminum knobs and face plate that had the look of all the other Avalon stuff...and while they were at it put in a 'higher headroom' microphone input transformer.

Now, I could hear the difference in the mic input transformer, but not in the knob caps. If I ever get to a point where I can hear a difference in the composition of a knob cap, I think it'll be time to hang up my guns and find a new profession.

A set of the aluminum knob caps was about $150- more expensive than the injection mold plastic knob caps...sooooo, being the cheap bastard I am, asked Avalon if we could get the higher headroom mic input transformer with the less expensive plastic knobs, to me, the sound of the unit was all that mattered .

They said 'sure', and we charged the appropriate amount more for the unit with the purple knobs and the better transformer...but after a while it became a tad confusing which was which...so we worked out a deal where Mercenary would buy the knob caps and Avalon would get the face plates annodized black. While we were at it, we had a silk screen made up that said "737sm", and screened the units with gold ink.

A couple of years ago the original purple knobed 737 was discontinued and the 737sp was the only 737 in the Avalon line. We still had black injection mold plastic knob caps, which were still less expensive than the aluminum knob caps...so the 737sm lived on.

In other words, the 737sm has less expensive knob caps than the 737sp, so it can sell for less than the 737sp. Other than that, there is no difference what-so-ever, in fact the 737sm says 737sp on the back.

Hope this clarifies the difference and the derivation.

And in other events...I had a long chat with the Avalon folk today...seems it's going to be time to pony up and get more faceplates soon...and more knobs, and frankly...it doesn't look like it's going to happen.

The fact of the matter is that there are about 40x 737sm's left, then they'll be gone for good. So, if you're on the fence, looks like they'll be sold out around September or October.

Just thought I'd mention it...not really trying to 'plug' the product.

Thanks Fletcher,
I appreciate the info, and warning. I'm hoping to get a 737sm, I'm saving my pennies!
:D