[BUILD] TB550A

[horvitz]

Hang on, even easier.  The input doesn't have to switch at all.  Soft bypass need be nothing more than parallel path from the input (pins 8/10) going to relay, relay switching either output transformer or input parallel path to output pins.  Input condition stays the same, output is either the amp, or the parallel input path.

Right, but then you are changing your output condition rather than your input condition.  EQ in, the transformer would be driving a balanced out.  In bypass, low out would be grounded.  You've traded your situation on one side of the circuit for the other side.  I think?

 

[Unit7]

Paul,

What we're seeing is oscillation at A2.  Makes a nice huge signal at about 80-85kHz, which explains why you can see it but not hear it.  I can -only- cause this to happen with GAR2520 in my v1.1 board with the output plugged directly into the Avocet.  Every other combination of stuff I try doesn't exhibit this symptom.  Lucky you, eh?  I'm glad we found it, though.

Figuring out why this is happening might take a little longer.  I would recommend that you do NOT leave the EQ on in this configuration.  Probably will cook the DOA eventually.

I'll be back with you when I have something.

  Brian

Thanks a LOT for looking into this Brian!

Awesome that you have an Avocet there... and yes what an odd thing!..

But this is really great news for me as I never meant to use the analog inputs of my Avocets for more than testing, instead the eqs will be on the inserts of my Harrison console. I didn't have the console powered up yesterday when testing but I will have tomorrow. And as it looks now the eqs will probably work fine in that setup. Will let you know how that works.

Great news also that it seems I've managed to build my three first DIY project ever without any errors. Very rewarding... I feel quite proud here! 

I'll contact Crane Song shortly to hear what they say.

Thanks again for all your effort and your dedication Brian!

 

[horvitz]

Thanks a LOT for looking into this Brian!

Awesome that you have an Avocet there... and yes what an odd thing!..

But this is really great news for me as I never meant to use the analog inputs of my Avocets for more than testing, instead the eqs will be on the inserts of my Harrison console. I didn't have the console powered up yesterday when testing but I will have tomorrow. And as it looks now the eqs will probably work fine in that setup. Will let you know how that works.

Great news also that it seems I've managed to build my three first DIY project ever without any errors. Very rewarding... I feel quite proud here! 

I'll contact Crane Song shortly to hear what they say.

Thanks again for all your effort and your dedication Brian!

You did a great job, Paul!  Really, you're a fantastic example of what a determined builder can accomplish, even with little or no experience.  Very well done, indeed.

Definitely let me know how it goes with the console.  Like I said, I can't reproduce the problem any other way, so I think you'll be fine there.  I'll continue to work to mitigate this, though.  I may not always be possible, but of course I'd like a solution that works for everyone.

 

[emrr]

Maybe it matters what the next input sees, maybe not. 

Output condition follows input condition, so a balanced output that doesn't like to drive an unbalanced input loses 6 dB as-is when passing through the amp, and the V1 hard bypass disconnects that unbalance, giving 6dB more level in bypass, effectively making bypass useless.  Leave the input connected and the loss will follow, even in bypass. 

 

[horvitz]

Well.. useless only if you are actually seeing that condition.  This is why I built the option for both hard or soft bypass on the v1.1 boards.  But, I see what you are saying now about the loss following through.  Basically, if you are in a situation where there will be loss, make it permanent so at least you stay at a consistent level.  Makes sense.

 

[emrr]

Right, only useless when there's a 6 dB change.  It seems totally hit and miss here, depending on what I've patched.  I hit bypass more to see what's going to happen, than to listen to bypass.  : ) 

I think you're right, the output condition is probably going to cause similar problems, especially since I'm talking about flopping transformer to no-transformer coupling.    1240 daughter board may still be the real answer.  Easy enough to test with a Y cable, when I get the chance. 

 

[Unit7]

Thanks a LOT for looking into this Brian!

Awesome that you have an Avocet there... and yes what an odd thing!..

But this is really great news for me as I never meant to use the analog inputs of my Avocets for more than testing, instead the eqs will be on the inserts of my Harrison console. I didn't have the console powered up yesterday when testing but I will have tomorrow. And as it looks now the eqs will probably work fine in that setup. Will let you know how that works.

Great news also that it seems I've managed to build my three first DIY project ever without any errors. Very rewarding... I feel quite proud here! 

I'll contact Crane Song shortly to hear what they say.

Thanks again for all your effort and your dedication Brian!

You did a great job, Paul!  Really, you're a fantastic example of what a determined builder can accomplish, even with little or no experience.  Very well done, indeed.

Definitely let me know how it goes with the console.  Like I said, I can't reproduce the problem any other way, so I think you'll be fine there.  I'll continue to work to mitigate this, though.  I may not always be possible, but of course I'd like a solution that works for everyone.

Thanks again Brian!
Just wanted to confirm that the eqs indeed are working just fine on the inserts of my Harrison Series 12! I really really like the eq on the console (grabby and musical, not too clinical IMO) so it was interesting do a quick A/B with your 550As. I tried them on kick/snare. Fairly obvious that they add some nice grit and made the drums smack a tad bit more. Very happy over here! Probably looking at getting at least one more as soon as the soldering obsession kicks in again... ;D

I also emailed the tech support at Crane Song, and Sean replied that he didn't get any ideas why this happens. He suspect it has to do with the eqs though, and not the Avocet as, quote "the Avocet's input amplifiers are discrete class A amplifiers"

 

[Unit7]

I've been browsing Steiger's homepage and Group DIY for comments on the different DOAs available. Found a few comments in the LC53A thread, but would like to bring up the question here to see if anybody would like to chime in.

I've built Brian's 550s to add a new colour on the eq side of my studio. As mentioned I really like the eq on my Harrison console with a nice balance of clean/colored, very versatile. I also have the Cartec Pultecs which sound really sweet. So now I'm looking for bite and attitude to use on drums etc, and after the short test I did with the 550s I really liked what I heard!

Now, looking at a possible order of additional kits I just wanted to get a little more input on which DOAs to choose. I currently have GAR2520/EA2503. Looking for bite, grit and attitude, are there any other options you think I should try? If there's another thread you think I should look at, please tell.

Cheers
Paul

 

[Unit7]

I'm hooked so badly on these kits that I'm planning to fill a whole 10 unit rack with DIY eqs API style this year. Probably LC53As next, and then continue with the ones I like the most. But what after the whole rack is filled...Depression? Emptiness?.. Have to try to avoid thinking about it...

 

[horvitz]

Easy answer: Get another rack!!  ;D

Really nice work, man.  Then second pair went fast!  You didn't put the color inserts in the knobs?  I've seen a few guys leave it that way and I'm torn if I like it better or not.

 

[Unit7]

Easy answer: Get another rack!!  ;D

Really nice work, man.  Then second pair went fast!  You didn't put the color inserts in the knobs?  I've seen a few guys leave it that way and I'm torn if I like it better or not.

Thanks! Another rack is a great idea - 20 eqs!  Don't know why I didn't think about that. Dolly Parton and Jeff Steiger are right: Less is less and more is more.
No, I'm not a fan of those inserts Looks a bit toy'ish to me...
btw, the new face plates looks great! Classy stuff!

 

[Unit7]

I've finally soldered a 1K resistor across pin 2 & 4 on the card edge, but oscillation remains. This is only if I have it plugged in to a hi z input at power up. If I have the unit first powered on, and afterwords plug it into a hi z input, it seems to work.

 

[horvitz]

OK, let me dig into this a bit today.  When I had tested the same previously, it settled right down with the resistor in.  I'll get back to you.

 

[Unit7]

A little update. Of my four units the #1 (also the one I tested above) still has the ringing (only when connected to hi Z input at power up). #2 & #3 was fixed by installing the resistor and finally #4 had no ringing at all. I've swapped op amps between #1 & #4 but still no change. Brian has been very helful as always, and suggested a swap of transformers and voila, the problem moved. Unfortunately I don't have a very accurate DMM, but the transformer from #4 seemed to measure just a tad bit higher than #1. Both were around 8.5-8.6 Ohm. I just measured two more 2503s that I have here waiting for other builds and they were like 8.9-9.0 ohm. Going to install one of them asap, and we'll see if a higher Ohm on transformers is the key.

 

[jimkeaney]

Looking for bite, grit and attitude, are there any other options you think I should try?

turn the knobs further  ;D

 

[Unit7]

Finally got the time to replace the OT in my stubborn unit #1. Now, no ringing with 1k resistor installed! But still ringing without the resistor. Still curious about why unit#4 doesn't need the 1k resistor to avoid oscillatation when seeing high imedance inputs, but this will have to do for now.

 

[Unit7]

Sorry for my spamming of this thread...but the  DIY rack/PSU is ready, and with 4 rubber feet and no rack ears I found the perfect position for these additional eqs on top of my console. Just where you want them! And my 5th and probably last TB550A ready. IMO the undisputable winner of the beauty contest. Love those face plates Brian! Now, four more LC53As, hopefully not too long from now...

 

[horvitz]

Awesome!!  I think you are now faster than me building these things  ;D  That's going to be one great rack full of EQ when you get all the LCs in there, too!  Great work.

 

[cbarrett92]

I have somehow managed to switch a 0.001 and 0.0015 microfarad wima cap on the filter board....  :'(

Judging by how close these caps are in value and the (hopefully wide enough) tolerances of the caps, does it matter if I put the 0.001 in place of a 0.0015? Specifically at C300? If it is that important, I can desolder the 0.001's until I find where I goofed, but I was hoping to avoid this.

How important is the 0.0005 difference here?

Thanks for the help!

EDIT- Found the misplaced one by process of elimination (and a bit of luck). Got it up and running tonight and it sounds great!

 

[horvitz]

Great!  Glad you got it worked out.  Unfortunately, that's kind of an easy mistake to make but that's why we have the sorting sheets.  Real fast too.  I think you give Unit7 a run for his money on build speed!  8)