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#41
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dynamic mic self noise (and my re15)
hank alrich wrote:
Mike Rivers wrote: On 1/21/2015 12:05 PM, Scott Dorsey wrote: That adds a shunt resistor in parallel with the input. So the microphone sees a lower impedance load, but the noise is not decreased (and is actually slightly increased). The only way to get a real adjustable input Z that maintains noise performance I've only found one microphone, a CAD ribbon, that sounded better with a low impedance load than it did with a conventional 1.5-2.5k ohm mic preamp input. I think it's a gimmick, but if it makes a too-bright mic sound less bright, I suppose it's good for those who have that problem (or that mic). The thing is that overall, adding 20 dB of output level to the preamp input when you need it while increasing the preamp noise by only a few dB, is better for most everyone. The only reason to fuss with that is if you insist on only using the best designs (or nothing). Look at the input impedance of the Gordon preamp. Never heard one that sounded that good, more there there than I'd ever realized before. http://gordonaudio.com/specs.htm The specs don't tell you the full story, though. The input impedance of the Gordon is pretty resistive and does not change at all with level. I don't think that's a big secret to the transparent sound but it's certainly a contributor. That said, if you're using Schoeps mikes or something else with a super low effective output impedance, it doesn't matter much at all. The low output impedance of the mike means variations in input impedance on the preamp are less of an issue. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#42
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
On 1/22/2015 9:54 AM, Dave Plowman (News) wrote:
Don't all classic ribbons have a built in transformer? If so you'd expect that to be designed to work best with the normal input impedance of the day. "Impedance Of The day" sometimes was directly into the grid of a tube. -- "Today's production equipment is IT based and cannot be operated without a passing knowledge of computing, although it seems that it can be operated without a passing knowledge of audio" - John Watkinson Drop by http://mikeriversaudio.wordpress.com now and then |
#43
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
In article ,
Mike Rivers wrote: On 1/22/2015 9:54 AM, Dave Plowman (News) wrote: Don't all classic ribbons have a built in transformer? If so you'd expect that to be designed to work best with the normal input impedance of the day. "Impedance Of The day" sometimes was directly into the grid of a tube. Never seen that with a low impedance mic. I'm surprised you could get enough gain. -- *Forget about World Peace...Visualize using your turn signal. Dave Plowman London SW To e-mail, change noise into sound. |
#44
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
In article , Mike Rivers wrote:
On 1/22/2015 9:54 AM, Dave Plowman (News) wrote: Don't all classic ribbons have a built in transformer? If so you'd expect that to be designed to work best with the normal input impedance of the day. "Impedance Of The day" sometimes was directly into the grid of a tube. Well, through a step-up transformer... but not a very high ratio transformer because making high ratio transformers with any high end at all is hard. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#45
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
Mike Rivers wrote:
On 1/21/2015 10:19 PM, Jason wrote: This may be a silly question - squelch it if so, but what makes "good" preamps so expensive? I presume all the designers know of the good parts to use and of good designs (wrong?) but beyond that what accounts for the price? ..better design? good testing? careful component matching? j Mostly it's the last little bit of performance in one or a few different ways that people who want something different. Part of the reason why we have so many expensive mic preamps is that 20 years ago there were a lot of mediocre preamps because that was all they could do for the price that would allow them to sell a whole lot of them. If you wanted good preamps, you bought a whole console. There've probably always been bespoke preamps but it really picked up in the '90s, when people started being unhappy with DAW preamps. Today, you can make a very serviceable preamp for $25 worth of parts. Putting it in a box with a power supply, connectors, switches, etc. can add another $100, add in marketing and profit and $200 per channel will get 95% or more users a good recording, all other things being equal. The other 5% are willing to pay 5-10 times that for a special color, another 10 dB of gain without noise, and bragging rights. If you look inside a Gordon preamp, you'll easily see why it's worth $2500. If you look inside your heart, you'll wonder if you'd get more bang for your bucks with something else. Some will, some won't. I've done mixes from studios with good preamps, and I've done mixes using my own modest prosumer preamps ( say, Symmetrix quality ) and in neither case was it clear the preamps were the bottleneck. But I'm not exactly recording finely crafted acoustic instruments with expensive mics. -- Les Cargill |
#46
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
Dave Plowman (News) wrote:
Mike Rivers wrote: On 1/22/2015 9:54 AM, Dave Plowman (News) wrote: Don't all classic ribbons have a built in transformer? If so you'd expect that to be designed to work best with the normal input impedance of the day. "Impedance Of The day" sometimes was directly into the grid of a tube. Never seen that with a low impedance mic. I'm surprised you could get enough gain. Although a step-up transformer was pretty much always used, it was seldom more than 1:10 and often just a 1:5. You could get 1:20 transformers for communications applications where trading bandwidth for noise was worthwhile. As far as I know, the only commercial preamp using a tube front end without a step-up transformer is one made by Fred Forssell. It uses a long-tailed pair in a trick circuit and sounds amazingly clean. Noise floor with a low-Z condenser mike is higher than a Millennium but way better than a Mackie. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#47
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
In article ,
Scott Dorsey wrote: Never seen that with a low impedance mic. I'm surprised you could get enough gain. Although a step-up transformer was pretty much always used, it was seldom more than 1:10 and often just a 1:5. You could get 1:20 transformers for communications applications where trading bandwidth for noise was worthwhile. I've seen two lower ratio transformers daisy chained. -- *Cover me. I'm changing lanes. Dave Plowman London SW To e-mail, change noise into sound. |
#48
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
Dave Plowman (News) wrote:
In article , Scott Dorsey wrote: Never seen that with a low impedance mic. I'm surprised you could get enough gain. Although a step-up transformer was pretty much always used, it was seldom more than 1:10 and often just a 1:5. You could get 1:20 transformers for communications applications where trading bandwidth for noise was worthwhile. I've seen two lower ratio transformers daisy chained. I have too. Normally, this is not a win. It is a big, big lose. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#49
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
Be mindful when talking about transformer turns ratios
A transformer with TURNS ratio of 10:1 Will have voltage ratio of also 10:1 And a current ratio of 1:10 Which results in an impedance ratio of 100:1 Mark |
#50
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
And back in the old days, when ribbon mics were most common in studios, there were indeed transformers with step-up ratioa 1:10 -- sometimes 1:20 or 1:30. They showed up in some RCA mic preamps and consoles -- sometimes driving pentode tubes as amplifiers (yeah, really). One RCA circuit used a 1620 pentode, which I believe is really a power tube, for an input tube with a high-ration transformer.
Mind you, I make no claims that these high-ratio transformers actually measured flat or sounded good. I don't know, not having heard them, but I suspect they didn't. Peace, Paul |
#51
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
In article ,
Scott Dorsey wrote: Dave Plowman (News) wrote: In article , Scott Dorsey wrote: Never seen that with a low impedance mic. I'm surprised you could get enough gain. Although a step-up transformer was pretty much always used, it was seldom more than 1:10 and often just a 1:5. You could get 1:20 transformers for communications applications where trading bandwidth for noise was worthwhile. I've seen two lower ratio transformers daisy chained. I have too. Normally, this is not a win. It is a big, big lose. --scott True - but in the days when it was common, it may have been the best compromise. -- *Work is for people who don't know how to fish. Dave Plowman London SW To e-mail, change noise into sound. |
#52
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dynamic mic self noise (and my re15)
PStamler wrote:
And back in the old days, when ribbon mics were most common in studios, the= re were indeed transformers with step-up ratioa 1:10 -- sometimes 1:20 or= 1:30. They showed up in some RCA mic preamps and consoles -- sometimes dri= ving pentode tubes as amplifiers (yeah, really). One RCA circuit used a 162= 0 pentode, which I believe is really a power tube, for an input tube with a= high-ration transformer. Mind you, I make no claims that these high-ratio transformers actually meas= ured flat or sounded good. I don't know, not having heard them, but I suspe= ct they didn't. Want to try some if I can find where I put them? I have some 600-80k RCAs here out of some broadcast gear. (There are here because I put Jensens in.) --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
#53
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
On Friday, January 23, 2015 at 7:46:00 AM UTC-6, Scott Dorsey wrote:
Want to try some if I can find where I put them? I have some 600-80k RCAs here out of some broadcast gear. (There are here because I put Jensens in.) Thanks, I'll pass. Those transformers are only 1:11.5 or so, which isn't much greater than 1:10. Unless they have the option of a 50 ohm primary, which makes them 1:40. Now that would be fun. Not good audio, probably, but fun. Peace, Paul |
#54
Posted to rec.audio.pro
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dynamic mic self noise (and my re15)
"PStamler" skrev i en meddelelse
... On Friday, January 23, 2015 at 7:46:00 AM UTC-6, Scott Dorsey wrote: Want to try some if I can find where I put them? I have some 600-80k RCAs here out of some broadcast gear. (There are here because I put Jensens in.) Thanks, I'll pass. Those transformers are only 1:11.5 or so, which isn't much greater than 1:10. Unless they have the option of a 50 ohm primary, which makes them 1:40. Now that would be fun. Not good audio, probably, but fun. I have one or perhaps two Sennheiser TM514x cable transformers that I soldered a jack and a male switchcraft on for use as step down and balancing around 1977. I don't want to rush things, but some day I hope to get to test them with guitar and a bass, I expect them to mellow things a wee bit and it may be an advantage. I think it was the tape recording utensils shop in Elmegade in Copenhagen, I found them in. Peace, Paul Kind regards Peter Larsen |
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