My 550A Project

[mulletchuck]

Greg,

It's a little early yet to discuss what will or will not be included in a kit.  We'll talk about that when we get closer.  At the very least though, I intend to include the switches.  I should be speaking with Grayhill about that this week.  I'll be stocking up for probably 100 kits so the pricing should be as good as I can get it.  Still not cheap, but no matter what it'll be better than folks placing individual orders and waiting 3 months for a factory direct ship.

but will it be cheaper than an actual API 550A module direct from API?  that is the question!!!

 

[horvitz]

Well, most certainly yes.  By a long way.

But just to be fair, this is not the same thing!  This is a modern implementation of a vintage circuit using stuff we can easily buy today.  Whatever API is selling now is their own and unique in its own way.  Thanks to the contributions of people like Ed Anderson and his 2503, our DOA makers, and the efforts of many others, we can really have something that performs very closely to that vintage unit.  It is not an API 550A but a Two Bellies 550A after all, so take that for whatever it's worth to you   It'll be fun no matter how we slice it.

Niagara Falls!

 

[horvitz]

Status update.

I took a vacation and walked around the mountains in Nevada for a little while.. nice to not think about this for a little bit.  When I got back, I had a nice package waiting for me from Jeff with some sweeps from additional vintage units (thanks!).  Since these things do wander a bit, that additional data allowed me to make some component decisions that I'm pleased with.  The short of that is that we'll be using the Elna Silmic II's for the 'lytics in the audio path.  In the BP filter, they most closely resembled the majority of the vintage units that I could compare with (dead on with 3 of the 5).

So now I'm off to do the (hopefully) final proto and we'll be ready to go.

I'd like to get a little feedback from you all on kits.  My intention is to deliver as complete of a kit as possible so that you don't have to source much and we can keep the cost down by buying in bulk.  That sound good?

  Brian

 

[canidoit]

Will your version be great for mastering use and can they pair up easily?

 

[dandeurloo]

The 2 db steps will probably be a bit much.  That has always been my only issue with any API eq.  You may not always want/need that much gain or cut.  But you could probably just change up some resistors and have .5 db or 1 db steps which would work great for mastering and a bunch of other things.

 

[horvitz]

It's an interesting question.. Dan is right, I think it would be a little extreme to try and master with due to the gain steps.

Unfortunately, it's not QUITE as easy as swapping around a few resistors in this case due to the proportional Q stuff.  I have been tossing around in my head a bigger 4 band, 2 channel rack mount version which would probably do the trick but you know, one thing at a time

 

[martthie_08]

it would be interesting to see how API made the gain steps switchable on the 5500 (0.5dB / 1dB / 2dB), I have a unit at hand, but no schematic...

 

[horvitz]

it would be interesting to see how API made the gain steps switchable on the 5500 (0.5dB / 1dB / 2dB), I have a unit at hand, but no schematic...

You know, I have been turning this over in my head a little bit.  It may actually be as easy as swapping out the 6.98k resistors (R7,8,32,33,58,59 on the schem) with a larger value.  The Q stuff wouldn't change.  That is, what the filter was doing in position 1 of the switch would stay the same regardless of how much gain it is making.  Might be a worthwhile experiment.

 

[horvitz]

You know, I have been turning this over in my head a little bit.  It may actually be as easy as swapping out the 6.98k resistors (R7,8,32,33,58,59 on the schem) with a larger value.  The Q stuff wouldn't change.  That is, what the filter was doing in position 1 of the switch would stay the same regardless of how much gain it is making.  Might be a worthwhile experiment.

OK, I had to try and never mind.. it's not quite so simple as all that.  Back to the grind.  Mods later.

 

[horvitz]

Moving right along.. Here's what the thing looks like done.

 

[horvitz]

And to answer the burning question, kits with everything you need to build it except for transformer and 2x DOA is going to be very close to the $400 mark.  Don't have final costs on everything yet, but it'll be near enough to that.  I'll probably receive the switches and be able to start shipping around early to mid November.

 

[haima]

WOW. looking very good. 

I love the clear, utilitarian look of the panel.

I can feel my GAS for an vintage 550A slowly subsiding..... : Thanks Brian!

Looking forward to hearing more about these kits if you do them.

 

[peter purpose]

There's a twitch in my knob.

 

[canidoit]

And to answer the burning question, kits with everything you need to build it except for transformer and 2x DOA is going to be very close to the $400 mark.  Don't have final costs on everything yet, but it'll be near enough to that.  I'll probably receive the switches and be able to start shipping around early to mid November.

How much are the 2 X DOA and tranformer?
Do you know the total average cost would be now that you are closer to completion?

Any recent comparison tests with the original unit and how is it comparing to? What are the sonic differences?

I am a little concerned about the exposed PCB back. I would probably place a plastic sheet over it if I was doing it.

What will be the callibration procedure and what tools will be needed? Will it be similar to Pete's EQN callibration where you really need a high signal to do the callibration?

Really dig how you have pulled this one off!!

 

[okgb]

I'm in for a pair , no questions asked

 

[minor_glitch]

I'm in for a pair , no questions asked

Likewise!

 

[horvitz]

How much are the 2 X DOA and tranformer?
Do you know the total average cost would be now that you are closer to completion?

Well, DOA you have lots and lots of options.  Check the white market for many good choices and their associated costs.

As for the transformer, you need any 2503 or compatible.  I strongly suggest Ed Anderson's EA2503 which Jeff carries at classicapi.com.

Add all that up with the roughly $400 that I mentioned and there you go with your total cost.  Oh, you'll need a little bit of wire and some shrink tube to be neat.. another 14 cents or so there.

Any recent comparison tests with the original unit and how is it comparing to? What are the sonic differences?

I won't comment on sonic differences.. my poor ears are not exactly the gold reference.  The circuit is largely the same as the published version from 40 years ago but our components are certainly different.  The functionality of the EQ is nearly identical from the point of view of curves on a sweep.  Make of all that what you will.

I am a little concerned about the exposed PCB back. I would probably place a plastic sheet over it if I was doing it.

Not a terrible idea.  The nylon screw that you see there is by design the tallest part of the board for just this reason.  If you're a belt and suspenders type, go for it.

What will be the callibration procedure and what tools will be needed? Will it be similar to Pete's EQN callibration where you really need a high signal to do the callibration?

Didn't we talk about this on just the previous page?

Really dig how you have pulled this one off!!

Thanks!

I'm in for a pair , no questions asked

Oh go ahead, ask  ;D

There's a twitch in my knob.

There's life in the old boy yet!

 

[plumsolly]

That is a great looking panel. Nice work all around.

Best,

Ben

 

[earl]

Should be approx. $470 w/ Jeff's doa's and output xformer then.

 

[mulletchuck]

Wow what a deal!!!    You and Jeff should set up a complete kit!