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Post by svart on May 9, 2017 20:01:16 GMT -6
Now I'm also sure a fair number who have built it are more tolerable to noise than Dan Scott and Bill! I wonder about this as well. Compared to any vintage tube mic I've used or my other clones, the noise floor is still much higher even with the lower noise tubes I've found. If I was recording drums or a rock band it wouldn't really matter. But on a vocal in a acoustic track the noise floor of the tubes is to high to use. Since the last few records I've done have been mostly acoustic music these mics haven't been used at all. My mic sits around -80dB in a quiet room with the preamp around singing gain.
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Post by dandeurloo on May 9, 2017 20:19:05 GMT -6
The tube data sheet even says that. But no one seems to read those. Haha Data sheet explicitly says that it is suitable if (filament) microphonics is not a concern. www.westernelectric.com/spec_sheets/408A.pdfFirst page, last sentence in the Description section. Guess nobody reads those, indeed. That is a different data sheet. I'll look to see if I can find the one I was looking at. I do have a number of the WE branded tubes here. They are a little lower noise but a more boring tone. So, maybe they did something in their version of the tube to lower the noise a little. I also have as stash WE's that pop and crackle and sound like breakfast cooking randomly. I do like breakfast however!
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Post by svart on May 9, 2017 20:35:45 GMT -6
Data sheet explicitly says that it is suitable if (filament) microphonics is not a concern. www.westernelectric.com/spec_sheets/408A.pdfFirst page, last sentence in the Description section. Guess nobody reads those, indeed. That is a different data sheet. I'll look to see if I can find the one I was looking at. I do have a number of the WE branded tubes here. They are a little lower noise but a more boring tone. So, maybe they did something in their version of the tube to lower the noise a little. I also have as stash WE's that pop and crackle and sound like breakfast cooking randomly. I do like breakfast however! Link sausage and pancakes.mmmm. Damn. I'm hungry now.
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Post by kcatthedog on May 10, 2017 3:59:32 GMT -6
have peeps tried the Ericsson I think I prefer them . I suppose it's true of all good tube circuits that different tubes tailor the sound. I find the rca gold warm with a nice body and Erickson add a dimensionality ? Interesting with tubes that you can make a good mike more versatile sonically .
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Post by sll on May 10, 2017 6:00:27 GMT -6
I'm glad the tubes have worked for most. I found it too difficult and time consuming to sort through enough to find a decent pair. Neumann rejected most of the new VF14s right from the factory. They would have Telefunken send them over, test them, and send back the unsuitable ones. Most of them were returned. That tube was designed for radios to run off the provisional 105VDC grid at the time. A 12AY7 will work in a C12 in place of a 6072, same tube except they are not microphone grade and have too much noise. You can get lucky and find one that is acceptable once in a while. The 6072a is the one that's consistent enough pull from batches and have decent tubes. Assuming NOS. If these tubes were still being made, it might make sense to buy large batches and sort them. Not anymore. The tube supply is dwindling and who knows what shape they are actually in. Used, leaky vacuum? Who knows? It's a gamble.
That's all the energy I care to spend on this subject.
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Post by svart on May 10, 2017 7:46:38 GMT -6
What transformers were everybody using for their noisy builds? What capsules?
I used the smaller BV8 from AMI and a blueline.
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Post by sll on May 10, 2017 7:59:44 GMT -6
Data sheet explicitly says that it is suitable if (filament) microphonics is not a concern. www.westernelectric.com/spec_sheets/408A.pdfFirst page, last sentence in the Description section. Guess nobody reads those, indeed. That is a different data sheet. I'll look to see if I can find the one I was looking at. I do have a number of the WE branded tubes here. They are a little lower noise but a more boring tone. So, maybe they did something in their version of the tube to lower the noise a little. I also have as stash WE's that pop and crackle and sound like breakfast cooking randomly. I do like breakfast however! I have one more thing to add. I think the filament microphonics is the issue. The random noises are similar to the noise you get when the filament and cathode are heating up during initial power up. Almost like a spring stretching. These tubes need a long burn in to boil the crud off the filaments. When temps stabilize, they settle down. However, remnants of that same noise can happen randomly after hours of being on. Dan and I finally found some quiet tubes. I guess my original point was I would not want the responsibility of the customer service for offering this config as a mass produced product. Additionally, I think I addressed what capsules we used and the transformer. Red and Blueline Thiersch M7 and Beezneez M7 with Max's BV8 transformer changed out resistors to metal film, cleaned everything multiple times. Also bypassed the capsules with a 47pf cap to rule out the cap for any noise. Since a pair of tubes were found that are quiet and put in the same mic, it's not anything else contributing to the noise. It's just too hard to find a pair of useable tubes.
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Post by jcoutu1 on May 10, 2017 8:07:12 GMT -6
I bought 4 "matched" tubes from England just in case I ever have mine go out in a session, but at that point, I'll probably trash it. Let me know when your tubes go bad and you're tossing it in the garbage.
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Post by kcatthedog on May 10, 2017 8:20:47 GMT -6
I used blue cap and max's build bv8 (mk-u47), sll, which brand of metal film resisters did you use ? thx !
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Post by svart on May 10, 2017 8:30:19 GMT -6
That is a different data sheet. I'll look to see if I can find the one I was looking at. I do have a number of the WE branded tubes here. They are a little lower noise but a more boring tone. So, maybe they did something in their version of the tube to lower the noise a little. I also have as stash WE's that pop and crackle and sound like breakfast cooking randomly. I do like breakfast however! I have one more thing to add. I think the filament microphonics is the issue. The random noises are similar to the noise you get when the filament and cathode are heating up during initial power up. Almost like a spring stretching. These tubes need a long burn in to boil the crud off the filaments. When temps stabilize, they settle down. However, remnants of that same noise can happen randomly after hours of being on. Dan and I finally found some quiet tubes. I guess my original point was I would not want the responsibility of the customer service for offering this config as a mass produced product. Additionally, I think I addressed what capsules we used and the transformer. Red and Blueline Thiersch M7 and Beezneez M7 with Max's BV8 transformer changed out resistors to metal film, cleaned everything multiple times. Also bypassed the capsules with a 47pf cap to rule out the cap for any noise. Since a pair of tubes were found that are quiet and put in the same mic, it's not anything else contributing to the noise. It's just too hard to find a pair of useable tubes. That's fine. I deal with instability in high speed mixed signal design day-in and day-out. I do run into the situation where parts are "iffy" a lot, and I hear the same things you're saying from other engineers. Most of the time the parts are not the cause of the problem, just the key ingredient in the problem happening. The 408A is a UHF tube, so it's bandwidth is high as is it's gain. That's a dangerous mix as the GBW can stimulate oscillation without proper controls. It's the same situation as using a low speed opamp without compensation and experiencing no problems with feedback but then swapping in a higher speed opamp and suddenly being able to listen to mexican radio through your mixer. The problems described sounds an awful lot like oscillation that's being mixed down into the audio band through the non-linearities in the passive parts and connector junctions. This is a common occurrence in high-speed devices that are left uncompensated for HF gain. One situation I ran into once went like this: Designer built a prototype of a high speed phase comparitor that worked exactly as expected. Manufacturing built a short run of production test boards that worked exactly as expected. Full production quantities were built, but failures in test/calibration were extremely high. I was brought in to help troubleshoot the issue. Some boards worked great. Some boards did not work. Some boards worked sometimes, but not other times. Narrowed down the issue to a single high speed amplifier. Turns out that manufacturing couldn't get enough amplifiers from a specific company, so they bought the EXACT same part number from a second manufacturer. The parts from the second manufacturer had a slightly higher bandwidth, and in conjunction with the parasitic components of the signal traces, would kick the amp into oscillation. The parts from the first manufacturer had a lower bandwidth (even though they were the same model part) and wouldn't oscillate in the circuit under any normal circumstance. Their packaging was slightly different and these minuscule differences were enough to keep the part from oscillating. I gave the amp circuit a little change to lower the bandwidth and now both parts work in the design. The moral of the story is that an "iffy" part usually points to a marginally stable design, not a "bad" part. It's my belief that the design is on the edge of stability due to the high gain and bandwidth of the tube, and that the tubes that "work" are slightly lower gain/bandwidth. The tubes that don't "work" are busting into oscillation when stimulated by certain inputs and conditions.
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Post by drbill on May 10, 2017 9:37:33 GMT -6
I bought 4 "matched" tubes from England just in case I ever have mine go out in a session, but at that point, I'll probably trash it. Let me know when your tubes go bad and you're tossing it in the garbage. Will do, but I'd have a hard time SELLING it to anyone if it's acting up. It might have bullet holes in it. But at this point, all is good/
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ericn
Temp
Balance Engineer
Posts: 14,934
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Post by ericn on May 10, 2017 10:03:03 GMT -6
Let me know when your tubes go bad and you're tossing it in the garbage. Will do, but I'd have a hard time SELLING it to anyone if it's acting up. It might have bullet holes in it. But at this point, all is good/ Bullet hole might raise the price!
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Post by sll on May 10, 2017 14:48:38 GMT -6
I used blue cap and max's build bv8 (mk-u47), sll , which brand of metal film resisters did you use ? thx ! Vishay/Dale resistors.
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Post by kcatthedog on May 10, 2017 15:41:01 GMT -6
thx sll !
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Post by svart on May 12, 2017 20:21:18 GMT -6
A quick update..
I got my WE408A in the mail today.
Put them in, let them burn for about 15 minutes.
No strange noises, clicks, pops or anything out of the ordinary.
I played around with it for about an hour. Never had a single issue. The noise floor (his) dropped from about -60 to -70 over the course of the hour, and I'll bet it'll drop to around -80 like the other set with more time.
I'll keep messing with it, but I think the chances of me buying two back-to-back perfectly noiseless sets is pretty much impossible if there really are so many bad ones out there as folks say.
I'll even go one step further. I'll make a file of the mic using these tubes, and then offer to trade someone out my We408a tubes for their "bad" tubes. I'll bet that whatever tubes I'm sent will work nicely in my mic.
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Post by wiz on May 13, 2017 0:34:46 GMT -6
A quick update.. I got my WE408A in the mail today. Put them in, let them burn for about 15 minutes. No strange noises, clicks, pops or anything out of the ordinary. I played around with it for about an hour. Never had a single issue. The noise floor (his) dropped from about -60 to -70 over the course of the hour, and I'll bet it'll drop to around -80 like the other set with more time. I'll keep messing with it, but I think the chances of me buying two back-to-back perfectly noiseless sets is pretty much impossible if there really are so many bad ones out there as folks say. I'll even go one step further. I'll make a file of the mic using these tubes, and then offer to trade someone out my We408a tubes for their "bad" tubes. I'll bet that whatever tubes I'm sent will work nicely in my mic. great stuff.... and a great idea about trying others problem tubes in your mic... really hanging on the outcome here... cheers Wiz
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Post by svart on May 13, 2017 8:18:26 GMT -6
A quick update.. I got my WE408A in the mail today. Put them in, let them burn for about 15 minutes. No strange noises, clicks, pops or anything out of the ordinary. I played around with it for about an hour. Never had a single issue. The noise floor (his) dropped from about -60 to -70 over the course of the hour, and I'll bet it'll drop to around -80 like the other set with more time. I'll keep messing with it, but I think the chances of me buying two back-to-back perfectly noiseless sets is pretty much impossible if there really are so many bad ones out there as folks say. I'll even go one step further. I'll make a file of the mic using these tubes, and then offer to trade someone out my We408a tubes for their "bad" tubes. I'll bet that whatever tubes I'm sent will work nicely in my mic. great stuff.... and a great idea about trying others problem tubes in your mic... really hanging on the outcome here... cheers Wiz I'm not sure anyone will take me up on the offer. People seemed kinda put off that I might suggest other possibilities. There's something to be said for sweat equity. The repeating actions cost time and cement the belief that the ends justified the means. Therefore swapping tons of tubes must have been the correct action because it caused the correct outcome. Right? I wonder how many folks just swap engines in their cars when things go wrong? Imagine going to the used parts place and swapping engines until you found one that worked.. In any case, we need to see what a known good set of tubes does in a mic that's had issues. We then find out what "bad" tubes do in a good mic. Then, if I can get "bad" tubes, I can figure out why.
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Post by jcoutu1 on May 13, 2017 8:29:29 GMT -6
great stuff.... and a great idea about trying others problem tubes in your mic... really hanging on the outcome here... cheers Wiz I'm not sure anyone will take me up on the offer. People seemed kinda put off that I might suggest other possibilities. There's something to be said for sweat equity. The repeating actions cost time and cement the belief that the ends justified the means. Therefore swapping tons of tubes must have been the correct action because it caused the correct outcome. Right? I wonder how many folks just swap engines in their cars when things go wrong? Imagine going to the used parts place and swapping engines until you found one that worked.. In any case, we need to see what a known good set of tubes does in a mic that's had issues. We then find out what "bad" tubes do in a good mic. Then, if I can get "bad" tubes, I can figure out why. When nobody takes you up, let me know how much you want for the good pair. I'll probably need some for the Stam mic. Hopefully, his build is quiet.
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Post by m03 on May 13, 2017 13:56:01 GMT -6
People seemed kinda put off that I might suggest other possibilities. It sounds like some people were using a trusted 3rd party to do the selecting for them. Is it possible that the wrong selection criteria was being used in that testing?
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Post by Johnkenn on May 13, 2017 22:30:32 GMT -6
While I get what you're saying, you're kindve coming off condescending, svart.
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Post by svart on May 14, 2017 7:56:15 GMT -6
While I get what you're saying, you're kindve coming off condescending, svart. I even re-wrote it like 3 times to try not to sound preachy, lol. I apologize for coming off as condescending. I just want folks to realize that swapping tubes is a symptom of an issue, not the fix, and that we can probably fix this with a little troubleshooting.
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Post by Ward on May 14, 2017 9:23:24 GMT -6
While I get what you're saying, you're kindve coming off condescending, svart. I even re-wrote it like 3 times to try not to sound preachy, lol. I apologize for coming off as condescending. I just want folks to realize that swapping tubes is a symptom of an issue, not the fix, and that we can probably fix this with a little troubleshooting. When you know what you're talking about, and know the absolutes of the topic, completely, it's kind of hard not to. I understood you well and really enjoyed your sermons here. LOL But it was a little jarring every time you smacked your cane down on the desk, and broke into swearing in High German. LOL
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Post by Johnkenn on May 14, 2017 9:39:19 GMT -6
Well, some would argue the absolutes. Dan and Scott both kinda know what they're talking about too. The unwavering need for absolutes is what made GS what it is today. Not saying you're wrong.
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Post by Martin John Butler on May 14, 2017 10:05:05 GMT -6
Haven't been to GS more than twice in a year, and that's just to see if there are any messages.
I'm excited about the Stam 47. Stam's done some good things already, so it's highly possible he'll equal or better the other name brand clones at a much more reasonable price.
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Post by illacov on May 14, 2017 11:45:20 GMT -6
Ok so I will chime in here since this is the world I'm from (mics).
It sounds like a qualified engineer feels they have data that proves the work they did with a public design has solved a rampant problem experienced by other engineers when building the same design which is a paint by numbers application.
So let's be straight forward. Svart are you willing to disclose if you've done something different? I refuse to believe such a large portion of techs left their circuit boards filthy and a simple deflux will solve the issue. Thats still leaving it up to chance. If youre able to repeatedly try different tubes without problems then it sounds like a welcome parameter change.
Do you need compensation to disclose your findings? Are you engaged with Stam and have implemented these design changes already? This is an easily obtainable pcb so either something is wrong with it sans mods or adjustments to operating voltages or you know something we don't. Why send a tube to see if it's bad if that still doesn't point out what you did different? As a U47 admirer and a good friend of Oliver's, politely I ask what do you need in return from us or Stam to spill the beans?
Thanks -L.
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