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Post by stormymondays on Jan 29, 2019 6:18:13 GMT -6
Ok, so finally I get the chance of testing my new SA2A and it turns out it has a 50Hz hum (I’m in Spain).
The hum is independent of the levels or settings. It starts humming about 5 seconds after power on. It comes in at around -61 dB on my interface.
It’s present on the XLR and TRS outputs. I’ve swapped all cables including the power cable. Visually it all checks out. I’ve checked the continuity of the ground connections and it all seems to be correct. I’m not an expert but the main points seem to be correctly grounded. I have quite a bit of hardware and no hum, it’s only this piece. I have moved it out of the rack, same hum.
What else can I check for?
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Post by kcatthedog on Jan 29, 2019 6:56:50 GMT -6
There have been FB reports of either bad transformers or psu's (I have forgotten which) in the 2a and, at least one that caught on fire. I'd find out who the local tech repair is and get it seriously bench tested under warranty.
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Post by stormymondays on Jan 29, 2019 8:15:04 GMT -6
Oh well. The Stam email hell begins all over again then! I was hoping it could be a bad tube, hopefully not the NOS one.
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Post by kcatthedog on Jan 29, 2019 8:48:05 GMT -6
Maybe not Josh told us a while back he had international tech support set up: fingers crossed you get a contact quickly: they are great sounding units!
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Post by stam on Jan 29, 2019 12:40:07 GMT -6
Oh well. The Stam email hell begins all over again then! I was hoping it could be a bad tube, hopefully not the NOS one. Stam email hell? You only need to email stamaudio@gmail.com and we will send it to our tech who will fix any issue at no cost to you Hardly hell ... |
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Post by drbill on Jan 29, 2019 12:47:04 GMT -6
at least one that caught on fire. Serious??  Makes me curious, are they UL approved? To stormymondays -- Have you made sure that you have no ground loops happening. Different gear presents differently depending on the grounding, patch bays (if any) and star grounding of your studio..... |
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Post by stam on Jan 29, 2019 12:55:21 GMT -6
CE and UL
It happened twice in 1.100 units and we fixed that issue
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Post by stormymondays on Jan 29, 2019 13:07:42 GMT -6
Oh well. The Stam email hell begins all over again then! I was hoping it could be a bad tube, hopefully not the NOS one. Stam email hell? You only need to email stamaudio@gmail.com and we will send it to our tech who will fix any issue at no cost to you Hardly hell ... I appreciate the reply and sorry if this came across as harsh, but come on man, you're the first to admit that you get more than 500 emails per day and can't deal with them! ;-) Your website lists info@stamaudio.com so I wrote there a few hours ago. Just resent it to gmail now. I'll be more than happy to report my good experiences with Stam Audio and not dwell on the not-so-great. Peace! |
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Post by stormymondays on Jan 29, 2019 13:11:43 GMT -6
To stormymondays -- Have you made sure that you have no ground loops happening. Different gear presents differently depending on the grounding, patch bays (if any) and star grounding of your studio..... I did, yes - as best as I could! I have plenty of stuff all in the same racks with no problems. Tube stuff from Retro, Weight Tank, Tree Audio, Black Box, Drawmer. SS stuff from TK Audio, DBX, SPL, Golden Age, Warm, Revive Audio. No ground or hum problems. |
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Post by drbill on Jan 29, 2019 13:18:32 GMT -6
To stormymondays -- Have you made sure that you have no ground loops happening. Different gear presents differently depending on the grounding, patch bays (if any) and star grounding of your studio..... I did, yes - as best as I could! I have plenty of stuff all in the same racks with no problems. Tube stuff from Retro, Weight Tank, Tree Audio, Black Box, Drawmer. SS stuff from TK Audio, DBX, SPL, Golden Age, Warm, Revive Audio. No ground or hum problems. Cool. Sounds like you've done your due diligence. Are your connecting wires telescoped? i.e. ground / shield lifted at one end? Does the hum go away if you (temporarily - don't do it permanently) lift the ground on the AC cable? is the unit racked where it could be sharing chassis ground via the rack rails? Eliminate all paths to ground but ONE, (preferably your AC cable, but could be a dedicated star ground cable to the star point) and see if the problem persists. Otherwise, perhaps its a problem with the unit. Whenever I get a new unit that exhibits a grounding issue, I have to verify that I've crossed all the "t's" and dotted all the "i's" before assuming theres a problem. Not all manufacturers treat ground - audio and chassis - in the same fashion. Hope you find your problem!! bp |
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Post by stormymondays on Jan 29, 2019 13:23:00 GMT -6
Joshua has already replied back - good!  I'm taking it to a local tech in a couple days and we'll take it from there. Connecting wires are all regular balanced cables (tried TRS and XLR). I don't have any device handy that can lift ground from the AC cable. I'll see if I can find one! I guess I could put some electrical tape on the ground connections (remember it's a schuko European plug). |
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Post by wiz on Jan 29, 2019 18:02:15 GMT -6
pull it out of the rack and test it away from the other gear if you havent already.
cheers
Wiz
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Post by bowie on Jan 29, 2019 18:46:14 GMT -6
You could try swapping the positions of the two 12AX7 tubes. Noise (like filament hum) from the gain stage 12AX7 in an LA2A style circuit is "always on", regardless of settings.
However, 5 seconds is a fairly short time for it to warm up enough to start making noise. Still, it's possible to start hearing it within 10 seconds and might be worth the effort to move the two 12AX7s around to see if that's the issue.
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Post by soundintheround on Jan 29, 2019 20:37:17 GMT -6
I had an issue with my SA-2A, but it was something more obvious... and had to do with the gain reduction circuit.
I can vouch for Stam Audio and say that Josh helped me get it fixed quickly and it was sent to California from what I recall for a free repair, no problems.
I think when Josh gets emails about major issues like these he responds pretty quickly. It's the ones about lead-time/availability/costs/advice/etc that you might experience the 'hell'... lol
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Post by stormymondays on Jan 30, 2019 1:15:24 GMT -6
pull it out of the rack and test it away from the other gear if you havent already. cheers Wiz First thing I did Thanks bowie for the tube tip, will try that. I don’t quite like how the tube sockets are attached to the PCB, seems quite a fragile arrangement. I also have quite a few 12AX7 in my stash that I could try. |
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Post by Ward on Jan 30, 2019 2:34:00 GMT -6
pull it out of the rack and test it away from the other gear if you havent already. cheers Wiz First thing I did Thanks bowie for the tube tip, will try that. I don’t quite like how the tube sockets are attached to the PCB, seems quite a fragile arrangement. I also have quite a few 12AX7 in my stash that I could try. True. Unplug, make sure the caps are discharged then hold the tube sockets as you remove the tubes. Shouldn't be that hard... although I agree with what you're sayin there about PC board mounted tube sockets being fragile in general. |
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Post by stormymondays on Jan 30, 2019 4:24:41 GMT -6
Good news! The tube swap did it. I also tested the tubes with my Orange VT1000, which I know is not “pro” equipment but it has served me well. One of the tubes tested a gain of 7 on both sides (position V1 initially). The other tested 8 and 10, which is not unusual (position V4 initially).
So, which tube was the culprit? V1 I guess?
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Post by stormymondays on Jan 30, 2019 5:02:17 GMT -6
I’ve also noticed that 0VU is calibrated 3dB hotter than it should. I’m sending a test signal at +4dBu, apply some gain around the “20” mark with no compression, so the output meter reads 0VU, and the signal that comes back is +3VU. Is that happening on yours wiz ? |
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Post by kcatthedog on Jan 30, 2019 6:52:50 GMT -6
The tube sockets have legs which go through the through hole pcb. They would simply be soldered in place. While lightly built, the pcb should feel secure: held in place with height standoffs and suitably sized washers and light bolts tightened down securely. Once physically assembled and properly tighten, other than a very severe drop, everything inside should be securely held in place.
If the tube swap sorted things out, that suggests that all the tube sockets are properly soldered, but you could always check and re-flow them, if you have a good iron.
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Post by bowie on Jan 30, 2019 7:26:50 GMT -6
Good news! The tube swap did it. I also tested the tubes with my Orange VT1000, which I know is not “pro” equipment but it has served me well. One of the tubes tested a gain of 7 on both sides (position V1 initially). The other tested 8 and 10, which is not unusual (position V4 initially). So, which tube was the culprit? V1 I guess? Glad I could help! That tester won't necessarily give you any indication of the tube's potential for AC hum. There are many, many ways in which a tube can go wrong and testers only give a glimpse, some more than others. A tube that tests extremely healthy can still hum. Unless it proves to have some other issue, you should be able to use that tube in the comp section's 12AX7 spot as that position is not noise sensitive. BTW, don't worry too much about one testing 7 while the other is 8 and 10. Tubes are built in an attempt to hit a target spec, but they really end up all over the place. A tube that starts at 7 won't necessarily have a shorter lifespan that one that starts at 10. |
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Post by stormymondays on Jan 30, 2019 7:34:15 GMT -6
Awesome, thanks for the help everybody! And I got to say that the unit sounds great and it's not noisy at all!
Now let's see if I can get the VU meter calibrated. It's not that big of a deal anyway since most of the time it will be showing gain reduction, but I always like my analog equipment to be correctly calibrated all over the board.
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Post by soundintheround on Jan 30, 2019 8:55:57 GMT -6
If anybody knows the LA-2A and especially how the tubes work in that unit....its Bowie!
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Post by stormymondays on Jan 30, 2019 16:21:07 GMT -6
Tomorrow I will try to check the calibration with my tech, but first I need to do some tests at the studio. I want to see if it's only the +4 setting that's wrong, or also the +10 and if they are consistent. And I should also test the gain reduction meter. I've read that the gain reduction meter can't be consistent at all settings, so I'm planning on checking a 5 dB reduction and see what happens with the output. I could also use my ears, but I want that VU meter to be a little bit more than a decorative bouncing needle  |
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Post by wiz on Jan 30, 2019 17:24:08 GMT -6
I’ve also noticed that 0VU is calibrated 3dB hotter than it should. I’m sending a test signal at +4dBu, apply some gain around the “20” mark with no compression, so the output meter reads 0VU, and the signal that comes back is +3VU. Is that happening on yours wiz ? I dont think so, but I havent checked though it seems to be operating like that. I never actually move the meter switch from Gain Reduction. It operates around the same levels as my other LA2A though...nothing out of the ordinary cheers Wiz |
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Post by stormymondays on Jan 31, 2019 3:28:26 GMT -6
I found some “unofficial” calibration instructions and got my VU properly calibrated. Gain reduction was not too far off. I calibrated it using 10dB of reduction and it does the trick.
I know VU meters are fiddly affairs and “real” VU meters are expensive. The Stam’s VU didn’t strike me as a very high quality unit. My pair of Golden Age Comp 3A came properly calibrated from the factory and the VU is more precise.
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I'm taking it to a local tech in a couple days and we'll take it from there.
