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API Graphic EQ - 560, 560a, 560b?
Old 17th May 2006
Gear Nut
🎧 15 years
API Graphic EQ - 560, 560a, 560b?

I recently purchased (new) a 560, as seen on the API website. What's the deal with the 560b as seen on Mercenary's site? Is there a sonic difference between the current 560 and the 560b?
Old 17th May 2006
Lives for gear
electric's Avatar
🎧 15 years
not an expert here but this is my understanding. (I own two vintage 560's myself).

-sonically i think the vintage 560 and modern 560b are close. they both have the API opamp. however, i have heard the modern 560b (for the last couple of years at least) uses surface mount ic's so they are less repairable than the vintage units because you cannot simply remove the ic's out of their sockets. however many of the vintage units have scratchy sliders.

-the 550a did not use the famous api opamp and has some sort of alternative amp design that gives it a different vibe. i have not compared. i hear they kick ass also.

you can do a search. there is tons of info on these units. however, some conflicting. others please correct me if i am wrong. i wouldnt get too hung up. they all are awesome. i am sure others will have more feedback. best of luck with them.

Old 17th May 2006 | Show parent
Gear Nut
🎧 15 years
hey electric, thanks. I did search, and lots of 550a vs 550b, but not as much on the various generations of 560 modules, which is what I'm interested in. As it appears, there are two 560s available new, the 560b and the unlettered 560. I have the latter, and freaked out for a second when I saw the "560a can be damaged by 48v rackmounts" before seeing that it's the model currently on the API website... mostly curious about it vs. the "b" model some retailers are selling.
Old 18th May 2006
Lives for gear
electric's Avatar
🎧 15 years
hi weatherbox,
thats interesting. i didnt know API was also making new units bearing the "560" logo.... did you purchase directly from api? oh well, without confusion where would the fun be ! the issue with the 560A's has to do with the pin that supplies phantom power in the modern api racks was used for something else with the 560a. therefore with 560a's you need to make sure that pin is modded correctly before you drop in the standard api rack. this issue does not apply to 560 or 560b. you can call the guys at brent averill about this stuff. they are experts who will give some time over the phone and are real cool. they would probably also know the answer to your other burning 560 questions. maybe someone else can answer your other questions better.

Old 18th May 2006 | Show parent
Lives for gear
Steamy Williams's Avatar
🎧 15 years
There are some posts kicking around on Gearslutz that suggest that the 560A is to be avoided (because of the sound rather than 48V issue) although I can't remember anything more specific about the differences. I have one of the new 560 'reissues' too - they definitely seem to have got this one right!
Old 18th May 2006 | Show parent
Gear Addict
Surfkat's Avatar
🎧 15 years
Here is some great info I found on the web while researching API 560 EQs a couple years ago. This was written by Al Davis, the guy who designed the original 560.

From: Al Davis ([email protected])
Date: 2002-08-04 22:09:39 PST

I don't normally read this group, but this thread caught my eye, and I
did some snooping in the archives. I figured I would leak a few more
API secrets.
I am responsible for a few API products, pre-Datatronix, including the
original 560.
In the comments on eq's there was mention of "proportional-Q" and
"fixed-Q" designs, in reference to the variants of the 550. It was also stated (more than once) that the 550A-1 is essentially 3 bands of the 560. This is not true. The 550A-1 is fixed-Q. The 560 is proportional-Q. The 560's Q actually varies more than the original 550 does. The 550A-1 design is really more like the 554, but with significantly lower Q, and single op-amp filters instead of 3 op-amp filters. Also, the 550A-1 has first order shelving, contrast to the 554's second order shelving.

Most graphics have some ripple in the response when you boost or cut.
This is because the Q is too high. Although it was not specified, I considered it to be a requirement that at most reasonable settings there would be no ripple. The idea is that if you boost two adjacent bands you get a single hump, not two. You can boost a band and use the adjacent ones to broaden it. If you really want peaking, use a parametric where you can tune the frequency.

Another factor is that with any tuned circuit, if the Q is sufficiently high, there is ringing. The higher the Q, the longer it takes for the ringing to damp out. If the Q is low enough, it is really more like a pair of RC circuits, and there is no ringing. The 560 is designed so that unless the setting is full boost or cut, the Q is low enough to not get ringing.

The 560A was not intended to be an API product. It ended up being one
because of the way Datatronix got into the scene. It began during the
period between when the original API went bust and the acquisition by
Datatronix. That one was my design, too. Ideally, it would have been
the same, but there were some key parts that were not available. The
change from the 2520 is well known. The reason for that change is
simply that the company that made them went bust.

There is another change that I have never seen mentioned, that is more
important than it might seem at first. Both the 560 and 560A use
special S-taper controls. The resistance curve has an "S" shape. It
is symmetric but is steeper in the middle, and relatively slow at the
ends. If it used linear pots, the control would be all scrunched toward the ends. The use of the S taper also allowed a higher resistance, resulting in lower noise and the "proportional-Q". The 560 used Alps pots. The 560A used Noble pots. The Alps pots were not available in the small quantities we needed. The taper is a little different, but the same at the calibration points. The Alps taper really looks like an "S". It is all curved. The Noble taper looks more like piecewise linear with rounded corners. This was not a conscious decision, and was considered to be a negative at the time, but we really didn't have a choice. It points out an issue that is often overlooked in products like EQ's ... A production change beyond the control of anyone who should know can significantly affect the sound.

Now, back again to the fact that it was not intended to be an API product ... Since it was unknown what would happen to API, and we didn't own the design, we could not just use the same design. This meant doing it over without access to the original drawings. Even though the goals were the same, and they use essentially the same topology, this makes for some subtle differences. One of these is that the Q in the 560A is a little lower than the 560. Also, it varies a little more, or in other words it is a little more proportional.

In the actual business deal, I was not "hired to do it" but rather it was a joint venture between me and Studio Consultants, where we split the profits and risk.

Now, back to the 550A-1 ... I wanted to call it something else, maybe 551, because it obvious to me that nothing could really replace the 550A. It should be marketed as a lower cost alternative. The original design was incredibly expensive to produce, and a significant money loser. Something had to be done. The final reason for not calling it something else was that they had a huge stock of front panels that said 550A.

API did not have good listening facilities, and the people we sent the
prototype to really liked it, so the problems slipped by. I became aware of it during the dead period between the bust and Datatronix, and made a modification to the design that would make it proportional-Q without raising the cost. Datatronix wasn't interested, and they continued to make the fixed-Q design. Most of them were made after they were aware of the problem and the fix they didn't use.

The 550A-1 design used filters in the feedforward or feedback path, with a summing node, giving a fixed-Q design.

The 560 (and 560A) uses a completely different gyrator based design. The "filter" simulates a series R-L-C circuit. When the pot is near the middle, its resistance is in series with the gyrator's R-L-C, lowering the Q. It was actually designed as an LC equalizer, then an active circuit was substituted for the L.
Old 18th May 2006 | Show parent
Gear Addict
Surfkat's Avatar
🎧 15 years
here's what Paul Wolf wrote about the 560.

Search Result 40From: Paul Wolff ([email protected])
Subject: The secret 560 story... View: Complete Thread (2 articles)
Original FormatNewsgroups:
Date: 1999/04/05

OK, Here is the story, once and for all...(but don't wait to buy any,
they are still a ways off)

The 560 was made by API while in NY.
It had some coupling caps, 4558 opamps, and one inverting 2520 with
xformer. The pots were linear and had a dead spot in the middle for "true zero". It was designed to replace the APSI switchable graphic eq that sounded like ****. (but good for matter where you set the bands the guitar sounds like its all the way up)

API closes shop. Studio Consultants in NY want to keep it alive, but
cannot get 2520's so they hire Al Davis to design a new one without a 2520 and DC coupled (no caps) OOh AAh B.F.D...Dataronix gets API stuff and continues the design with Al. The 560A is released without 2520 and the transformer is an option (****ing hell). I buy API from Datatronix and sell the last 28 original 560's to Shelly at A&M, then next make the transformer standard on the dreaded 560A, then get rid of the piss-amp with a 2520 and call it the 560B.

There it has sat, DC coupled and all. The pots are linear, but with no
center dead spot. They don't jump when slid, which many think "the old ones seemed to do more", but not true. They are more gradual. Circuit is the same except for the caps and a couple of other senseless changes that Jeff and I are just now getting around to changing back. There is not much to change, and I hope nobody thinks that they will see the lord with the re-issue comes out. The tests show very little difference. The big problem is better parts now days. They sound different than the old ones.

Next week, maybe I'll tell the story of the 550A-1...

Old 22nd January 2014
Gear Nut
🎧 5 years
Hey guys, can someone tell by sn which re-issue it is ?


Old 22nd January 2014
Gear Nut
🎧 5 years
nevermnd just got my answer. latest revision is 560b right ?
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