Modded LA-610 Needing Repair

[TilburyMusic]

Howdy,

I'm in a bit of a pickle with my modded MK1 LA-610 and my tube guy pointed me toward this forum to see if I could find anyone to help me with it.

The preamp was modded by a company called CC&E a few years ago, but the company no longer exists. So obviously I can't send it to UA for repair, due to the mod, but I'm having a hard time finding anyone else to look at it and hopefully fix it.

I'm not sure if it's an issue with the modded components or something just went out and needs to be replaced. I actually never used it after the mod, aside from some quick tests during which things seemed to be fine, as I ended up having to pack up my gear shortly after and wasn't able to set it back up at a different location for a while. When I began working with it, I noticed the issues: There seem to be some gain problems (output too quiet), distortion where it shouldn't be, some of the pathways from the mod aren't working (you can bypass the EQ or Preamp and rearrange the order), and when I open the unit up after it's been running, there's an unusual smell of burning electronics or something. But it still turns on and passes audio through, sounds like it could be really great if it were working properly. Something may have just gotten damaged in transit, it may be something super simple, I'm really not sure.

I have a list of all the modifications made, if that would help any.

If this is something you think you could work with me on resolving, please let me know and how much you would charge.

Also, I'm in Colorado.

Thanks!

 

[hooman]

hi
open and Remove the tubes .... put them back in place.The smell of burning may be normal and is related to the heating of the tubes.
regards

 

[TilburyMusic]

hi
open and Remove the tubes .... put them back in place.The smell of burning may be normal and is related to the heating of the tubes.
regards

Hi, Thanks for the response. Yeah I've tried that, you may be right, but given the other issues, I haven't wanted to risk it.
Also, I never noticed any smell before getting the mod, and I changed the tubes frequently as I experimented with different NOS configurations..

 

[hooman]

I have two cases like your device and the customer's complaint about the very low sound output. I just did what I said.I didn't understand, can you change the tubes yourself or do you consider it a risk? I think your device has no Special problem except for the tubes. If there are still jj.. there is a way to change them with new ones. At least you just need one nos 12ax7 + one nos 12at7 .
regards

 

[13engrsapper]

Reseat the t4 as well.

Most tubes do not like to be moved around when they are still hot either - do be careful with that. There are some exceptions - some automobile types and Nuvistors (1500 G's while running I think), etc.

Embarrassingly, during a tube test here on an old Gates SA-38 we got really excited when we put in an old red matched pair of tubes "sounds amazing!, let's try some more pairs." We excitedly turned off the unit and without waiting at all removed the tubes carefully (we thought) from the sockets, and replaced them with another pair... "meh, not as good as the red pair." So back went the red pair, "WTF!>?! Sounds like crap - still worked but NOISEY!" Barely worked, so back in went the mediocre pair we had also excitedly pulled out, and guess what? Those were "effed" as well. So, we now have a standard practice of waiting 15 minutes or more before pulling tubes.

Sometimes the good lessons are the expensive ones.

I am looking through the list of mods now, thanks.

 

[TilburyMusic]

Oh that's good to know, I haven't done that with the 610 but I have with a microphone, yikes. Hope I didn't mess any of my fancy Nos tubes up, some of them I haven't checked since I hot swapped them...

I'm trying to track down a 12BH7 to test as I have no extras, the mod changed the output stage to use a 12BH7. That wouldn't explain some of the routing issues, but it might be part of the output gain problem.

I did reseat the t4 already, and based on the meter it seems the compressor is working fine.

I am looking through the list of mods now, thanks.

Thank you!

 

[TilburyMusic]

I have two cases like your device and the customer's complaint about the very low sound output. I just did what I said.I didn't understand, can you change the tubes yourself or do you consider it a risk? I think your device has no Special problem except for the tubes. If there are still jj.. there is a way to change them with new ones. At least you just need one nos 12ax7 + one nos 12at7 .
regards

I'm goin to change the tubes and see if that changes anything, I just wasn't sure at first if I should be messing with it. The smell might just be because I didn't use the unit much since the mod was completed and the new wires/connections/solder is burning in or something. I seem to remember other new electronics smelling similar, an electronic rice cooker I had once...

Like I said I don't think it's going to change some of the routing issues where I get no sound with certain selections, but it might simplify things if some of the problem is tube related. In search of a 12BH7 now...

 

[hooman]

12bh7 for la610mk1?

 

[TilburyMusic]

12bh7 for la610mk1?

Yes Sir, the mod changed the output stage. But my tube expert told me today I could use a different one for testing.

 

[andYz00m]

What are the list of mods? Im curious why you would mod the 610

 

[TilburyMusic]

What are the list of mods? Im curious why you would mod the 610

Yeah, I was in my early 20's and regret it. I should have just sold it and bought something else, lesson learned.

The mod was said to lower the distortion significantly, improve headroom, make the 610 more like the original, and allow you to use the compressor as a standalone compressor (in addition to changing it over to use a T4B so it wouldn't be as sluggish), which all sounded really good to me then and like it would make the unit more versatile for me. I just talked to someone else on Gearspace recently and ended up with a similar situation.

Anyway, here are the mods:
- convert the compression element to use a T4B instead of the T4UA
- change the preamp circuitry over to be a copy of the old "green" 610
- change the output stage to a copy of the LA2A output stage
- change level detector and gain control amplifier to be a copy of the '68 TELETRONIX LA2A
- add choke filtration to the power supply
- add bypass capability to each stage
- add EMI TG12413/Siemens U273-derived diode limiter feature ("growl")
- install a Lundahl amorphous core output transformer
- output stage converted to use a 12BH7 tube

- Pre can be On or Bypassed
- EQ can be On or Bypassed
- EQ can be Pre-Compressor or Post-Compressor

http://s470656472.onlinehome.us/cce/la-610-modification/
The website now has this weird address but that's where it was all originally explained. I've submitted messages and no one responds.

 

[TilburyMusic]

These blog posts explain more of the "why" in depth...

http://s470656472.onlinehome.us/cce/blog/

 

[hooman]

It may smell burning. Modification may cause the device to fail. The changes were not interesting to this level.

 

[TilburyMusic]

It may smell burning. Modification may cause the device to fail. The changes were not interesting to this level.

Sigh...

 

[andYz00m]

The mod was said to lower the distortion significantly, improve headroom, make the 610 more like the original, and allow you to use the compressor as a standalone compressor (in addition to changing it over to use a T4B so it wouldn't be as sluggish), which all sounded really good to me then and like it would make the unit more versatile for me. I just talked to someone else on Gearspace recently and ended up with a similar situation.

Welp, sounds like you learned a lesson. Would be hard to troubleshoot any significant issues without a modified schematic of exactly what they did, which is likely unavailable.

I have a pair of very low serial silver face LA-610s and they are awesome stock haha.

 

[hooman]

آه...

If you know how to work with a multimeter, I can prepare you for troubleshooting. Just a cheap digital multimeter is enough.

 

[radeng]

Send to UA. Have unit returned to stock form.

 

[FarisElek]

Idk, if you pull the schematics out for all the different pieces it's modded after, it shouldn't be too hard to find the culprit by checking voltages. Harder than if it wasn't modded...but not impossible.

 

[Forcemusicgroup]

You did that fox mod eh???? I've done it many times. Late to the post. What's the issue.

 

[13engrsapper]

FYI His unit has been repaired and returned to him with a chunk of the mod removed, along with some of our own fixes added. I will let him comment further. His was originally modded by CC&E, not used/checked upon return, then later was found to not function properly at all.

We adjusted the heater voltage to 6 volts (it was still stock). We moved the filament voltage regulator to the chassis so it could cool itself (they run SUPER HOT in stock configuration/location). We moved the Lundahl transformer included in this mod to a better/closer location - and further from the power supply. We fixed everything that did not work (instrument level input, high eq), and got signal to pass properly. Mounts were made for V5, and for the T4b, which was just flopping around on a board. (we have also since designed our own boards which incorporate legs to properly support the T4b.

Anywho - it behaves like a 610 now, rather than a doorstop.