[BUILD] TB550A

[Bobby Baird]

Hey Brian,

I have a question. I just traded one of our members for a couple tb550 kits, and it seems I am missing one nut for the small 72 series greyhill switch for the frequancy band.  The nut in question is 1/4" 32 unef. Since this is an extra fine thread it's not something I could find at ace or lowes. Do you know were I could source one of these. Are if you had a spare I would pay for the part. p.s What are the main differences between the first version and the current version? Better layout, added functionality, and do the different versions have sonic differences ie. can they be paired? Thanks in advace for any input.

 

[Winetree]

The first version had a 6db increase in volume going thru it.
It also didn't have a true bypass.

 

[Bobby Baird]

I had another ver.1 eq and it did not have a 6db increase. more like a .25 db increase when engaged, and I pretty sure it was true bypass. Soft bypass I believe was added on later versions as an option from what I have read. Thanks

 

[horvitz]

I had another ver.1 eq and it did not have a 6db increase. more like a .25 db increase when engaged, and I pretty sure it was true bypass. Soft bypass I believe was added on later versions as an option from what I have read. Thanks

So, yes on the bypass.  The v1.1 boards have the option for soft or hard bypass while the v1.0 only had hard bypass.

Regarding the level, there is indeed an increase when running in unbalanced mode (the only option on v1.0).  I had measured that at about .5dB.  If using in a stereo situation with a v1.1 board, I'd put that in unbalanced as well so they match.

As you note, all the other differences are peripheral so sonically they will be exactly the same.

I'll have a look around but I'm pretty sure I don't have any spare panel nuts for those switches.  If you can't find one online somewhere, you'll probably be just fine leaving it off.  I'd leave off either the HF or LF bands since there are two decks soldered to the PCB on those switches rather than the one on the MF.  All six of those switches fastened to the front panel is really overkill.

Good luck!

Brian

 

[Bobby Baird]

Alright, I have one built everything works except 7k peak. No boost or cut.  Not sure how to sort this out. Any help would be appreciated. I think I have narrowed it down to the  hi band section of the filter board because I switched out filter boards from my second eq and all frequencies work so the problem should not be on the main board.

 

[horvitz]

Alright, I have one built everything works except 7k peak. No boost or cut.  Not sure how to sort this out. Any help would be appreciated. I think I have narrowed it down to the  hi band section of the filter board because I switched out filter boards from my second eq and all frequencies work so the problem should not be on the main board.

You're exactly right, Bobby.  A single frequency not working can only be on the filter board.  To narrow it down further, does it not work in both peak and shelf modes, or is it just one of those?  The answer to that should get us to within just a couple of components.

 

[Bobby Baird]

The filter board in question will work in 7K shelf, but no cut or boost in 7K peak. I'm not sure what components govern the 7K peak mode. Thank you for any insight Brian.

 

[horvitz]

The filter board in question will work in 7K shelf, but no cut or boost in 7K peak. I'm not sure what components govern the 7K peak mode. Thank you for any insight Brian.

Please see the attached photo.  The green lines show you where you should have connectivity for the 7k peak to work.  Also, please ensure that when the switch is set to 7k, the common terminals on the switch actually connect to the pins as indicated in red.

Keep in mind that this is the component side of the board so obviously, reverse everything as you test from the bottom.

Brian

 

[Bobby Baird]

Thanks for the heads up reply. I will check shortly as I am busy smoking some tenderloin & ribs.

 

[Bobby Baird]

The red marks you made look to be 12.5K on my switch. Here is what I have reference picture. My 7K would be the grey lines. As far as continuity on what you marked all is good.

 

[Bobby Baird]

I believe I found the cold solder joint by tracing the circuit. 7K peak is now working.

 

[Bobby Baird]

2-TB550a racked Up.

 

[horvitz]

Great!  It's funny, after telling you to pay attention to which side is up, I got it reversed myself.  I'm glad it worked out.  Love the set up!

 

[dandeurloo]

Does anyone have build docs laying around for these?  I specifically am looking at the Filter PCB's.  I have a issue i need to try and find with a unit. 

Thanks

 

[rhythminmind]

Does anyone have build docs laying around for these?  I specifically am looking at the Filter PCB's.  I have a issue i need to try and find with a unit. 

Thanks

http://ericbeam.com/wp-content/uploads/2019/12/TB550A-Assembly-Guide.pdf

 

[dandeurloo]

Thanks guys, I got them going!

 

[AudioGimmer]

I built a couple of these, and really like them.
Hadn't used them for a while, and noticed one was not sounding like the other.
I wondered why...

Replaced cap and all good.
Surprised it went quite so badly tbh