[BUILD] TB550A

[rhythminmind]

It seems I'm short two 0.01uF WIMA caps.
I could substitute c208 & c211 (good location) with 0.01uF 100v Polyester Films I have laying around...? Would that cause any negative consequence?

Got your email regarding this.  Responding there.

Got it, thanks.
Great kit by the way, top notch. Really nice layout & well documented.

 

[rhythminmind]

Finished this guy up tonight. Not the easiest of builds, as mentioned patience is key. I made a couple careless mistakes along the way, but all are resolved. TIP - Triple check alignment/orientations at all stages  . For the time being I've loaded it up with a pair of 990's & a CMOQ-2S. I might swap out the 990's at some point, but I have to say it's performing very well as is. Great EQ kit.


DSC_0017 by rhythminmind, on Flickr

DSC_0003 by rhythminmind, on Flickr

DSC_0010 by rhythminmind, on Flickr

DSC_0013 by rhythminmind, on Flickr

LS by rhythminmind, on Flickr

LP by rhythminmind, on Flickr

MF by rhythminmind, on Flickr

HP by rhythminmind, on Flickr

HS by rhythminmind, on Flickr

filter by rhythminmind, on Flickr

THD FR by rhythminmind, on Flickr

THD by rhythminmind, on Flickr

1k Square by rhythminmind, on Flickr

 

[horvitz]

Really nice work!!  Very clean build.  Thanks for posting those sweeps, too.  I can only capture 8 at a time on my software so it would have been real cumbersome to get that all together.

 

[rhythminmind]

Just posted a quick test with the EQ on a solo kick batter mic. With & without the EQ active. Pretty amazing difference, the EQ is last in the chain with no other influence.
http://rhythminmind.net/1313/?p=3790

 

[horvitz]

Man, that is so cool  ;D  I think back to where I started out with this project and everything that's happened to get from there to it actually being in use making music and it makes something like that really satisfying!!

 

[rob61]

Finished building my pair shown here. The EQ sounds great. I use +4 balanced thoughout my studio, and I noticed when I switch the EQs in, there is a drop in level. I'd read the original 550s had an unbalanced input which would explain the drop. Is this the case with these? Otherwise, any idea why I get a drop in level when I switch them in even when all settings are at zero?

I use Gar5250 op amps.

Thanks for making the great kit available.

 

[rhythminmind]

It might be the DOA/resister values. With my 990's it outputs +4.8 dBu when feed +4 with everything stock. You can swap out the resisters that feed the DOA's. I don't know what ones off hand.
Also sweep or play pink to make sure everything is happy/flat.

EDIT: Scratch that, looks like it's not the DOA.

 

[horvitz]

Finished building my pair shown here. The EQ sounds great. I use +4 balanced thoughout, and I noticed when I switch the EQs in, there is a drop in level. I'd read the original 550s had an unbalanced input which would explain the drop. Is this the case with these? Otherwise, any idea why I get a drop in level when I switch them in even when all settings are at zero?

I use Gar5250 op amps.

Thanks for making the great kit available.

You work fast!  Nice job.

While yes, it uses the same unbalanced input as the original, you shouldn't be seeing any kind of significant loss when switching in.  If anything, I usually notice a very small gain (.25db or so with Gar2520 and EA2503).  How much loss as we talking about?  Perhaps double check the leads on the transformer to make sure they are all going to the right place.

  Brian

 

[rhythminmind]

How hot do those exposed DOA's get?

 

[horvitz]

It might be the DOA/resister values. With my 990's it outputs +4.8 dBu when feed +4 with everything stock. You can swap out the resisters that feed the DOA's. I don't know what ones off hand.

If you wanted to show it -2 rather than +4 (although it would have to be on pin 10), you could replace R1 with a jumper.  Haven't actually tried that, though.

 

[rob61]

How hot do those exposed DOA's get?

If you are talking about the Gar2520s, they're in the rack so I don't really know.

 

[rob61]

You work fast!  Nice job.

While yes, it uses the same unbalanced input as the original, you shouldn't be seeing any kind of significant loss when switching in.  If anything, I usually notice a very small gain (.25db or so with Gar2520 and EA2503).  How much loss as we talking about?  Perhaps double check the leads on the transformer to make sure they are all going to the right place.

  Brian

Ran a 1KHz sine trough it and when EQ is zeroed out, but switched in, there is a 4db loss of signal. I read in GS where a guy was using old 550s and said he had a 6db loss because the 550 was unbalanced so maybe that is what is going on. All modules in the rack do get a balanced +4 signal.

Its consistent between the 2 EQ units. I did check transformer wiring and that is wired correctly. It does sound good, but I'd like to figure out if there is a way to keep gain very similar if possible so when I switch it in and out to compare I don't get the jumps in volume. But still, a great kit, and I'm diggin' em.

 

[horvitz]

Well, while true that you get -6 at the input, that loss is made up on the way out so the unit should be at unity gain.  I'm curious about your rack setup.  What is before the EQ in your chain?  Perhaps it's simply wiring with hi/lo swapped on the way in.

Alternatively, you could install a 180R resistor as shown in the attached picture and it would make up about an extra 4db at the output.  That's kind of masking a problem but it would sort it out for you.  Might need to fiddle with it for the exact value.  The range is about +11 with a jumper and +2 with 510R.

 

[emrr]

I took ownership of someone else's built pair recently, and am noticing the same gain discrepancy in my system.  -4.4 dB with eq switched in, relative to bypass.  I had a look on my Audio Precision test set, and got a clue I haven't thought through yet: there it's +6 dB with the eq in, relative to bypass.    Other tests suggest all is well with the units in terms of response, distortion, etc, at least what I've looked at so far.

 

[rhythminmind]

I had a look on my Audio Precision test set, and got a clue I haven't thought through yet: there it's +6 dB with the eq in, relative to bypass.

Are you saying on your system you getting -4.4 while IN, but on your AP your getting a +6 boost while IN?

 

[emrr]

That's what I'm saying.  Relative to bypass level for same interface condition.

 

[horvitz]

Now that's a bit of a head scratcher.  I'll do some experimenting tomorrow and see if I can replicate the symptom.

 

[rhythminmind]

Not seeing it on my end, but I'm thinking it's possibly a balanced symmetry issue. (Differential vs single maybe)

 

[rhythminmind]

Try flopping output pins 2 & 3 and see if the level changes.

 

[emrr]

Switching xlr cabling to AP over to an adjacent MEQ500 channel, set for flat on both, level does not shift significantly. Looks as expected there. 

Reconnected to console patchbay, flopping polarity on either input or output side changes nothing with TB550A, still -4.4 dB when engaged, relative to bypass. 

Gonna try a different 500 rack now....