My 550A Project

[horvitz]

Great job Brian..... a braver man than I.

No so.. just not married and no kids

I do actually owe you a credit on this one.  I rather.. umm.. borrowed your concept of the small resistors up front and underneath on the EQN.  Couldn't have done it otherwise!  Sometimes the right idea is just right, so thanks.  I'll get you on the liner notes.

i'll have a glass of Champagne  8) 8)

I'll have a whole bottle please!

And guys, I do plan to make this available hopefully sometime soon.  I never really had any intention of being in business doing this but the idea of other people using my stuff to make music is just too damn cool.

 

[canidoit]

That looks mad!

Do you know how much current does your model take up? I have a space left on my original lunchbox next to the power supply, but I do not know if I have enough current left???? Will this be advisable to be installed near the power supply?

Also, is your HF and LF functioning the same as the original? I thought the switch was to go from Shelf to Lo/High pass filter and not Shelf to Peak. That's what API told me when I emailed them on how the 550A switches work.

I really didn't want to do another DIY journey except for maybe a Buss compressor but this looks really tempting, I really like the API sound and heard great things about their EQ.

What will be the callibration process for this unit and will this be newbie friendly in terms of build manual, BOM and support?

What is the degree of difficulty on this, in regards to other builds?

 

[Nobru]

I have extra space in my lunch box...
Great Job!

 

[joro]

Very cool!

 

[horvitz]

You ask good questions!  I don't have all the answers right now but will try to provide some insight.

Do you know how much current does your model take up? I have a space left on my original lunchbox next to the power supply, but I do not know if I have enough current left???? Will this be advisable to be installed near the power supply?

Haven't figured this out yet.  Shouldn't be too bad.  If memory serves, a loaded 2520 draws about 800mW.  There are two of those.  Add 4 discrete voltage followers and the LED in normal operation.  In bypass, also add the two relays at 500mW each (although, the unloaded 2520 will be about half at this point).  So a totally rough guess, 3-4W on the very conservative side?  Of maybe call it about 200-250mA?  I'll get some better numbers on that.

Also, is your HF and LF functioning the same as the original? I thought the switch was to go from Shelf to Lo/High pass filter and not Shelf to Peak. That's what API told me when I emailed them on how the 550A switches work.

Yes, exactly the same operation as the original.  If you look at the front panel pic on the first post, you'll see the peak/shelf switch for the HF and LF.  In the middle is the Filter switch which enables a bandpass filter from 50Hz to 15kHz.  That's actually one of the things still on my to-do list.  The HPF side of the bandpass filter is a little steeper than I'd like it, although it may be OK as is.

What will be the callibration process for this unit and will this be newbie friendly in terms of build manual, BOM and support?

What is the degree of difficulty on this, in regards to other builds?

Calibration is the easy part - there is none unless you want to tweak with the gain structure. If you build it as-is, just fire it up and go and it runs at just about unity.  I made provision to alter the output level just as in the original by adding a resistor between pin 8 (In-) and a pad on the board.  I can't image many folks will want to do this and I haven't even tested it yet.

As for the build, there will be a manual, BOM, and support via a thread here.  It actually isn't a complicated item to put together.  The difficulty comes in the fact that there are a LOT of parts in different values and it is extremely easy to put something in the wrong place.  Finding your mistake after the fact will be a painful affair.  I've gone beginning to end on a couple by now and it still takes me about 8 hours to put it together.

To be comfortable building it, you should be able to look at doing something along the lines of a DOA with confidence.  There is a lot of real tight, small work and again, it's easy to make a mistake.  I will endeavor to make a very clear manual.  Just work slowly and patiently and I think anyone with decent soldering skills could build this.  It's not electrically complicated, just mechanically so.

  Brian

 

[BladeSG]

Nice work. will watch this thread 

 

[wowi]

Great !  8) Specially your solution for the switch problem.
Congrats

Wolfgang

 

[jsteiger]

I just checked a 550A's current consumption for fun. My guess was well under 100mA. With no cut/boost, EQ switched in, driving a 600 ohm load, with a +4dBu signal at it's input, a vintage module will hover round 55mA. Now, if you wanna really push things like send it a +24dBu 50Hz sine wave and apply full boost with a peak setting at 50Hz, the module will reach around 125mA. Some frequencies will draw more and this is just a sine wave not full program. I would bet that under typical program material applications, you would hover in the 60-80mA range maybe up to 100mA at worst case. Does API have any of this on their site?

The gain compensation is interesting on their EQ modules and smart as always. I don't know what you found Brian but typically, when driving a 10k or lighter load, a +4dBu signal will come out around +5.25 to +5.3dBu. When you change that load to 600 ohm, it will drop right down to +4dBu. Remember, the EQ modules in the console were directly driving the channels faders which were 600 ohm. Unity gain baby! All others must compensate.

All FWIW.
Cheers, Jeff

 

[horvitz]

Cool, Jeff.  Good info.  I'm still tweaking around with just a couple of the frequencies here so as soon as I get that sorted I'll be getting into the performance-type testing and will post all that as soon as I have it.

  Brian

 

[3nity]

how much can this build cost aprox??
I counted around 350-400$ in parts no pcbs....
Let us know please!
Thanks.

 

[[silent:arts]]

... I need a new name.. TB55A isn't doing it for me ...

Brian, the name is clear:
NC550A  ;D ;D ;D

 

[horvitz]

how much can this build cost aprox??

No clue yet.  All I can say is that this will not be a budget project.  I'll have a better handle on the costs over the next couple of weeks and will let you all know then.

 

[horvitz]

Brian, the name is clear:
NC550A  ;D ;D ;D

NC?  Regarding my comment to Peter?  If so, I like it! 

TB I've put on everything for a long time.. it was Totally Bitchin' to start but I've heard plenty of alternatives that I like too..  Taco Breath, Typically Bearded, etc.. some I can't say here.

I think it was the 55A part that was bugging me.  The first 5 isn't a significant digit so at least it should be 50A but then I don't like way that looks.  TB550A is much better but didn't fit so nice on the front panel.

I'm so finicky sometimes it's a wonder I get anything done at all!

 

[[silent:arts]]

Brian, the name is clear:
NC550A  ;D ;D ;D

NC?  Regarding my comment to Peter?  If so, I like it! 

and at the same time "Not Concentric" 550A 8)

names are always difficult - even more for children

 

[horvitz]

and at the same time "Not Concentric" 550A 8)

Ohh.. that one's sneaky.  I like it!

 

[okgb]

Yes , Brave is the word I would use as well , and successful
plus persistent as well , Well done
I have a pair of 550 b's which i like , but often wonder about the " Mojo " of the 550A's

 

[jsteiger]

TB makes me think of the Three Stooges...Two Bellies!  Or even Three Boards.

I suppose this project will cost what it will cost. It's no budget, low dollar module. Those switches are not cheap.

 

[okgb]

May need economy of scale grp buy , perhaps ran through your store ?
preorder ?

 

[horvitz]

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.

 

[jsteiger]

...perhaps ran through your store ?

If you meant me Greg, no probably not. This is Brian's baby. I am just a groupie on this tour.