noise issues with Tube Tech SMC-2B Multiband Comp

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z11111

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Hi all,
We have had an SMC-2B at my work for many many years which sounds phenomenal… when it is behaving properly, which is usually isn’t.

For the past several years, we have encountered noise issues with ONE channel on the unit and as of right now it’s totally unusable. Hiss, crackles, pops, always a little different

last year, I went through with the guidance of Tube Tech via email and blindly replaced a number of parts they told me to replace. They wouldn’t share a schematic or any service docs with me (which I understand why!) so we went back and forth replacing random parts around the summing amplifier until the noise issue (sort of) went away. I figured out some parts based on PCB traces but obviously not how they work within the circuit, which wasn’t very helpful.

after fixing this up, the unit would just randomly blow fuses. I replaced the bridge rectifiers within the units as they looked super toasty and even started running the unit with a bucking transformer to drop our wall voltage from 125vac~ to 113~115vac. I had replaced the PSU electrolytic caps the first time I serviced it (when I was trying to solve the noise issue) because several had developed bulges. Replaced PSU dropping resistors as well. Fuses stopped blowing after this and the unit behaved fine for almost one year.

At some point, a different tech worked on the unit, repairing some burnt traces on the underside and likely a different OT on one channel. I have to take the unit apart again to double check but if I remember correctly, the channel with the noise is the same one the previous tech worked on

this is a really phenomenal sounding unit but the fact that it is so unstable is really sad for us. Hopefully our unit isn’t completely cursed and can be remedied.

to cut to the point: does anyone have a schem for me to reference or has had similar problems with this piece?
 

beatnik

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Not the same model, but a friend reported similar intermittent noise problems with a Tube Tech comp and it was a bad output transformer.
You should inspect the unit with an oscilloscope and understand where the noise is generated
 

z11111

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Not the same model, but a friend reported similar intermittent noise problems with a Tube Tech comp and it was a bad output transformer.
You should inspect the unit with an oscilloscope and understand where the noise is generated

Good to know. The noise was originally coming from somewhere in the summing amp section, according to Tube Tech when I was in correspondence with them over a year ago. I assume the single OT replaced by a previous tech was for similar reasons to what you describe. I will get it up on the scope soon and see what I can find .
 

guy_4

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Good to know. The noise was originally coming from somewhere in the summing amp section, according to Tube Tech when I was in correspondence with them over a year ago. I assume the single OT replaced by a previous tech was for similar reasons to what you describe. I will get it up on the scope soon and see what I can find .
Hello z11111,

I did service for Tube-Tech products here many years ago.
I encountered several times the same issues as you, with very few help from Tube-Tech office.

The solution that I found and giving good results for my clients was to remove and replace the tube sockets with high quality gold plated sockets.

After this I replaced the full set of tubes with brand new ones, whatever their age,
( I mainly use JJ Tubes ), the bridge rectifiers and filtering caps too.

These Tube-Tech have a good sound reputation, but badly designed and they generate lots of troubles when aging, because of the heat generated inside the chassis and no airflow, then the components are " cooking ".

Six, seven or eight tubes in an (almost) enclosed 19"/2U is a shitty design, sorry !

I also replaced the cover with some " small spaced hens fence " to allow the heat to exit the unit, and still keep the shielding effect as much as possible.
I also told the owners to let - at least - half a unit of air above their Tube-Tech to cool it.
I would recommend you this " upgrade " ...

Good luck !
Best,
Guy
 

z11111

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@guy_4 , huge help. Glad to see I am not the only one who hasn't had luck with their support department. I have ordered new sockets and a new set of tubes and will see what happens. The sockets were the one thing I haven't replaced and figured could be the next move, so it is nice to hear someone else had success doing this.

We keep ours with 0.5RU of empty space above and below and the rack is completely ventilated in the back and both sides (custom console desk) but the thing still gets crazy hot. Will probably take the top panel and machine some more vents in it.
 

kags

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Nov 2, 2019
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56
Same issues here with Cl1bs and MP1. Replacing tube sockets and repairing cooked traces on the board helps a lot. Bridge rectifiers run very hot, so keep they cool the board and the traces, too. Great sounding units, but limited lifespan without heroic rebuilding at some point. Our units are in commercial rooms with cooled racks, but things are on 10 to 15 hours every day.
 

Matt Syson

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Dec 17, 2005
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France
I used to service TubeTech units in the UK years ago and emailing the 'right' person at TubeTech got fantastic assistance. The management was changed some years back which may have resulted in some 'issues' with service. Rectifiers should have had heatsinks fitted which I often did even if the unit had come to me for other reasons altogether. The fuses are rated very close to what is needed when used on 240 Volts (UK) mains and although Europe is nominally 230 Volts they can actually receive more in some situations. Thus when linked for USA would in theory be 115 volts nominal but what actually appears on American wall sockets?
 

guy_4

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Hello All,
I forgot to say that I used gold plated contacts tube sockets with a Porcelain ( Ceramic) socket.
Also the gold contacts are round, then the tube pins are in contact over a full circle.
They are high quality, not like the original sockets from Tube-Tech.
I also replace the bridge rectifiers with higher electrical specs than the originals.
And like Matt, I use fuses higher rated, as the original sometimes blow without reason.
The most important action is to lower as much as possible the temperature inside these units, because that "kills" all the components around, and generates lots of issues.
I quickly decided to remove the top cover ( no holes on it ! ) and after some trials I ended with some fine mesh fence to replace the cover.
It was a big improvement to let the heat escapes.
Since years, I got no return of Tube-tech units where I made all of these mods.
Guy
 

z11111

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Status update: replaced all tube sockets with nice ceramics (gold pins because sure why not) and all tubes a couple of months ago, as well as a few toasty looking resistors I missed previously. Currently running it with the lid off and it has been great ever since. Keep in mind I have also replaced all of the rectifiers, every electrolytic cap, and every power supply / high voltage resistor in the thing over the past 2+ years as well...
 

guy_4

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Dec 23, 2004
Messages
305
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Near Paris, France
Status update: replaced all tube sockets with nice ceramics (gold pins because sure why not) and all tubes a couple of months ago, as well as a few toasty looking resistors I missed previously. Currently running it with the lid off and it has been great ever since. Keep in mind I have also replaced all of the rectifiers, every electrolytic cap, and every power supply / high voltage resistor in the thing over the past 2+ years as well...
Bravo : you did it the good upgrades !
So, it is " better than a new one " now ! :))
Best,
Guy
 

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