Does anyone have a reference for ribbon mics active circuits that don't use transformers ?
The main problem with the ribbon mics is their low output impedance, of about 0.02 ohm, but I think it should be solvable.
So, any exiting circuits ?
The main problem with the ribbon mics is their low output impedance, of about 0.02 ohm, but I think it should be solvable.
So, any exiting circuits ?
Nobody knows ?
Another question is this: if an active circuit would replace the transformer that the ribbon mics use for impedance matching, would that be a significant improvement ?
I think it might, since the transformers are usually too non linear if one is looking for minimum distortion but I'm looking for other opinions ...
Another question is this: if an active circuit would replace the transformer that the ribbon mics use for impedance matching, would that be a significant improvement ?
I think it might, since the transformers are usually too non linear if one is looking for minimum distortion but I'm looking for other opinions ...
Because of the extremely low output levels and very low source impedance the transformer is almost an ideal step up device translating the large available current into a higher voltage without introducing significant noise. Distortion is easily enough managed. In this case I think the transformer is the best choice from a noise performance standpoint. You may need to shield it to protect against stray magnetic fields, but this may also be a problem with the ribbon itself.
Nope, the ribbon's OPZ is no problem at all - what is the problem is the TINY output voltage...
Without using a transformer - which is against my religion - the noise aspect can be handled by a large parallel arrangement of common base arranged low noise bipolars.
Then the current output of the ribbon is fully utilised. A look over the prolific thread MMP here on DIYaudio should give you some ideas to start with.
Be aware you can't pass the bipolar's running currents throughthe ribbon, or you will either; 1 damage it or 2/ at least move it out of it's idea position wrt the magnets.
Regards, Allen
Hi fireworks,
I've gotten good sound by adapting a low noise moving coil preamp to a ribbon mike. Take a look at Erno Borbely's:
"All JFET MM/MC Phone Preamp" part 1 and 2 which includes description, schematic and component values. Google the title for the pdf or visit Borbely website.
Borbely's website contains lower noise implementation topologies that Erno sold kits for in the past. All of Erno's articles are a great education.
The diyAudio parts forum has seveal suitable JFETs for sale.
I found it important to purchase several Id graded JFETs and then also hand match for good performance. I found it necessary to mount the preamp very, very close to the ribbon and to avoid any extra aluminum-copper metal diodes. I built my own ribbons and could run the ribbon foil directly to the JFET input. The diyaudio post by John Curl Blowtorch preamp is a good refresher on low noise techniques.
I've gotten good sound by adapting a low noise moving coil preamp to a ribbon mike. Take a look at Erno Borbely's:
"All JFET MM/MC Phone Preamp" part 1 and 2 which includes description, schematic and component values. Google the title for the pdf or visit Borbely website.
Borbely's website contains lower noise implementation topologies that Erno sold kits for in the past. All of Erno's articles are a great education.
The diyAudio parts forum has seveal suitable JFETs for sale.
I found it important to purchase several Id graded JFETs and then also hand match for good performance. I found it necessary to mount the preamp very, very close to the ribbon and to avoid any extra aluminum-copper metal diodes. I built my own ribbons and could run the ribbon foil directly to the JFET input. The diyaudio post by John Curl Blowtorch preamp is a good refresher on low noise techniques.
Attachments
You will need to parallel a lot of BJTs because of the base spreading resistance. Toshiba has transistors with a specified base spreading resistance of 2 ohms, but that resistance is still 100 times the impedance of the ribbon mike. This base spreading resistance is in series with the ribbon mike and will have a very detrimental effect on the SNR.
Ray
Ray
This is more of a noise figure way of looking at it. The ribbon has .02nV of noise. We hooked the classic RCA ribbon to a complimentary bi-polar preamp that only had two pairs of npn and pnp's paralleled and noise was not an issue. This was about .4 to .5nV input noise which technically compared to .02nV is a horrible noise figure.
You would be better off working backwards and computing the output signal for an equivalent SPL and using that number as a target. Once you are down to 10dB SPL noise you have a very quiet mic.
Thanks for the schematics and the other infos, I'll take a look at them.
I'm quite interested in your ribbon mics: do you have pictures or construction techniques or audio samples ? How noisy are your mics compared to an identical one with a transformer ?
Scott, thanks for the info. Do you have a reference for the 0.02nV noise ? Can it be computed from some other available data ?
Hello
How about using a low noise fet input opamp like the OPA637 or LT1037 ?
I don't remember which chip number, but I think Linear Technology made opamp with lower noise than the LT1037.
Btw, how much milivolts output a ribon mic will have without transformer ?
Thank
Bye
Gaetan
How about using a low noise fet input opamp like the OPA637 or LT1037 ?
I don't remember which chip number, but I think Linear Technology made opamp with lower noise than the LT1037.
Btw, how much milivolts output a ribon mic will have without transformer ?
Thank
Bye
Gaetan
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It may work, but it's the wrong approach IMO. As is a low nise opamp. They are voltage amps, and a ribbon has only microvolts of output, but because of it's low impedance, quite a lot of current.
A common base type of circuit can utilise all that current directly, hence better S/N.
Regards, Allen
This is a common problem with what we need to do to improve noise. It doesn't matter whether you use common source or common gate for noise. What really matters is the basic noise of the input fet combination. More fets, lower noise.
Transformers made EXACTLY for this application can be very good, BUT expensive. The real problem there is intrinsic winding resistance, and usually primary, is the key factor. There is an AES paper given at the London AES just this spring. Very good paper on ribbon microphone transformers.
Transformers made EXACTLY for this application can be very good, BUT expensive. The real problem there is intrinsic winding resistance, and usually primary, is the key factor. There is an AES paper given at the London AES just this spring. Very good paper on ribbon microphone transformers.
Allen, how much current? If the output is microvolts and the ribbon resistance is on the order of an ohm, that seems like it's pumping just a few microamps.
FM condensers are starting to look good right about now...
FM condensers are starting to look good right about now...
Where did your one ohm figure come from? Ever seen a mike ribbon - very unlikely to be anywhere near as high as one ohm. The OP was talking about 0.02 ohms or so. I was just working with his number - I don't have a ribbon mike to pull apart and measure.
My experience is with MC cartridges, which are reputed to have far more potential energy output as current than voltage, hence your trafo approach works as well as it does, and the prevalence of summing junction/common base MC phono pre's. Check the MPP thread...
Regards, Allen
That's why I asked, I don't have one around here to measure. 😀
So really, as far as current goes, we have something on the order of 50 microamps at full steam?
So really, as far as current goes, we have something on the order of 50 microamps at full steam?
Hello guys
I've wrote to arround ten ribbon mic making companies to get some ribbon mic specs (specs without the transfo).
Some companies, like Shure, reply me that those number are secret, others reply me that they don't know those numbers, some never reply me.
But, hopefully, Audio Engineering Associates and Shuaiyin did reply to me with the numbers.
Here is the numbers.
Bye
Gaetan
----
The ribbon mic company, Audio Engineering Associates, give me lot of infos, here it is;
Audio Engineering Associates, AEA R84:
The aluminum ribbon thickness are 1.8 microns
The voltage ratio of the transformer are 1:28
The ribbon output voltage are 0.09 mV/Pa without the transformer
The dc ribbon resistance are .2 ohm
The ribbon resonance frequency are 12 hz
The ribbon AC impedance without the transformer are ; .9 ohm at 20 hz , .4 ohm at 50 hz , .3 ohm at 100 hz , .2 ohm from 500 hz to 10 khz
Here is a little explanation they give me about the transformer.
"When you're looking at the impedance of a ribbon microphone. The transformer itself doesn't have an inherent impedance, but it reflects the impedances on both its sides. Furthermore, the transformer reflects those impedances with the square of its voltage ratio. So instead of 1:28 you're now looking at 1:784. Most importantly, the impedance of a ribbon motor is not purely resistive, but has a reactive component giving it a complex impedance."
----
The chinese mic company, Shuaiyin, give me those numbers;
Shuaiyin SYR80 microphone: 2.2 microns aluminum ribbon, the impedance is 0.5 Ohm and the output voltage is 0.04mV/Pa without the transformer.
----
I've wrote to arround ten ribbon mic making companies to get some ribbon mic specs (specs without the transfo).
Some companies, like Shure, reply me that those number are secret, others reply me that they don't know those numbers, some never reply me.
But, hopefully, Audio Engineering Associates and Shuaiyin did reply to me with the numbers.
Here is the numbers.
Bye
Gaetan
----
The ribbon mic company, Audio Engineering Associates, give me lot of infos, here it is;
Audio Engineering Associates, AEA R84:
The aluminum ribbon thickness are 1.8 microns
The voltage ratio of the transformer are 1:28
The ribbon output voltage are 0.09 mV/Pa without the transformer
The dc ribbon resistance are .2 ohm
The ribbon resonance frequency are 12 hz
The ribbon AC impedance without the transformer are ; .9 ohm at 20 hz , .4 ohm at 50 hz , .3 ohm at 100 hz , .2 ohm from 500 hz to 10 khz
Here is a little explanation they give me about the transformer.
"When you're looking at the impedance of a ribbon microphone. The transformer itself doesn't have an inherent impedance, but it reflects the impedances on both its sides. Furthermore, the transformer reflects those impedances with the square of its voltage ratio. So instead of 1:28 you're now looking at 1:784. Most importantly, the impedance of a ribbon motor is not purely resistive, but has a reactive component giving it a complex impedance."
----
The chinese mic company, Shuaiyin, give me those numbers;
Shuaiyin SYR80 microphone: 2.2 microns aluminum ribbon, the impedance is 0.5 Ohm and the output voltage is 0.04mV/Pa without the transformer.
----
Hello
I forgot to write in my previous post, for those who are not familiar with microphones sensitivity number, 0.09 mV/Pa means the mic produces an output of .09 mv when presented with an input of 1 pascal (94 dB SPL)
I would also say that Julian David, from Audio Engineering Associates, wrote a very good paper about ribbon microphones, in the AES 128th convention paper 8126, May 22-25 2010
P22-6 Analysis of the Interaction between Ribbon Motor, Transformer, and Preamplifier and its Application in Ribbon Microphone Design
AES London 2010: Paper Session P22: Microphones, Converters, and Amplifiers
Bye
Gaetan
I forgot to write in my previous post, for those who are not familiar with microphones sensitivity number, 0.09 mV/Pa means the mic produces an output of .09 mv when presented with an input of 1 pascal (94 dB SPL)
I would also say that Julian David, from Audio Engineering Associates, wrote a very good paper about ribbon microphones, in the AES 128th convention paper 8126, May 22-25 2010
P22-6 Analysis of the Interaction between Ribbon Motor, Transformer, and Preamplifier and its Application in Ribbon Microphone Design
AES London 2010: Paper Session P22: Microphones, Converters, and Amplifiers
Bye
Gaetan
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This is the paper John C referred to earlier.
AES E-Library: Analysis of the Interaction between Ribbon Motor, Transformer, and Preamplifier and Its Application in Ribbon Microphone Design
Recommended reading!
T
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