Hey guys!
My friend got himself a new microphone, a Sennheiser e935.
While he loves that mic, he wants to connect it to his iPhone, or laptop via jack.
I want to build him a preamp, which amplifies the signal coming from his mic to the maximum of the phones/laptops input.. Using batteries.
I was wondering if there is any op amps which I could use with a single 9V battery (Or maybe 2 AA batteries (3V)?)
I have found a schematic on Elliots page (attached)
Do you think this could be enough for this case? (Of course with variable gain [R6 = pot])
How could one limit the maximum voltage output for not destroying the phones mic input?
Thanks for your help
Daniel
My friend got himself a new microphone, a Sennheiser e935.
While he loves that mic, he wants to connect it to his iPhone, or laptop via jack.
I want to build him a preamp, which amplifies the signal coming from his mic to the maximum of the phones/laptops input.. Using batteries.
I was wondering if there is any op amps which I could use with a single 9V battery (Or maybe 2 AA batteries (3V)?)
I have found a schematic on Elliots page (attached)
Do you think this could be enough for this case? (Of course with variable gain [R6 = pot])
How could one limit the maximum voltage output for not destroying the phones mic input?
Thanks for your help
Daniel
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You need a single supply circuit, which also requires input and output coupling capacitors
to block the DC offsets. Instead of a noisy pot, use a switch to select 20dB or 40dB gain.
To protect the laptop or iPhone inputs, use a 5V (three series 1.5V batteries) or a 9V supply,
which automatically limits the absolute output level (rather than adjust the gain, which does not).
A good 5V mic preamp chip is the TLV2772, which will work on a single 5V supply,
similar to this circuit. Op-Amp Microphone Preamp.
A 9V single supply circuit would also work, and you could then use the NE5534 op amp.
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I would use a 150 ohm to 15,000 ohm transformer to provide 20 dB of gain and then follow that a low noise low voltage op-amp set for a voltage gain of unity to thirty.
Mouser will have low cost small signal transformer for quite reasonable prices.
For some use the transformer by itself may be enough.
Mouser will have low cost small signal transformer for quite reasonable prices.
For some use the transformer by itself may be enough.
All microphone amplifiers on this thread produce a noise far above the thermal noise of a 350 ohm dynamic microphone. Does your friend require a low noise floor?
simon7000's version with a step-up transformer (post #3) is indeed an exception, or at least it could be when his low-noise op-amp has a low equivalent input noise current.
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These are schematics of a battery-powered microphone preamplifier that I built in 2004. The potmeter works the wrong way around, but you soon get used to that. The circuit is useless if you need something very small.
The monostable multivibrator and LED are for indicating clipping. My amplifier also has a 48 V phantom supply with a step-up converter, but I didn't include its schematic because you don't need it with a dynamic microphone anyway.
The CA3046 is out of production, but it can be replaced with the LM3046, which is still available. The 2SC2547 is a high-hFE, low noise transistor that is also out of production, but there are some low-noise SMD transistors that are nearly as good.
Edit: sorry, I just reread the thread title. For a pocket amplifier this thing is probably way too big, even when you use SMDs wherever you can.
The monostable multivibrator and LED are for indicating clipping. My amplifier also has a 48 V phantom supply with a step-up converter, but I didn't include its schematic because you don't need it with a dynamic microphone anyway.
The CA3046 is out of production, but it can be replaced with the LM3046, which is still available. The 2SC2547 is a high-hFE, low noise transistor that is also out of production, but there are some low-noise SMD transistors that are nearly as good.
Edit: sorry, I just reread the thread title. For a pocket amplifier this thing is probably way too big, even when you use SMDs wherever you can.
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The particular microphone is supposed to be operated into a minimum termination impedance of 1k-ohm: http://www.diyaudio.com/forums/digital-line-level/314935-es9038q2m-board-240.html#post5526080 (click on 'show more'). Often mics similar to this such as Shure SM-57 sound better operated into a load of at least 2k, maybe even a bit higher.
Also, this is a dynamic vocal mic, not a condenser mic used in situations where low noise is a strong consideration. With dynamic vocal mics often it is more important to have a switchable 20dB input pad to avoid clipping the preamp.
Also, this is a dynamic vocal mic, not a condenser mic used in situations where low noise is a strong consideration. With dynamic vocal mics often it is more important to have a switchable 20dB input pad to avoid clipping the preamp.
It has a reasonably flat far-field response, though, so you could use it for far miking when there is no need for an extended bass response.
All in all, we need to know what the thread starter's friend uses his/her microphone for: does he/she shout at it from 2 cm distance, record bird sounds with it from 100 m distance, both, something else entirely?
All in all, we need to know what the thread starter's friend uses his/her microphone for: does he/she shout at it from 2 cm distance, record bird sounds with it from 100 m distance, both, something else entirely?
Sorry, I somehow pasted the wrong link. The Sennheiser page is here: Sennheiser e 935 - Vocal Dynamic Microphone - Fully professional
and here: https://assets.sennheiser.com/globa...36.1355323841.1535157752-385582374.1535157752
Perhaps worth mentioning, the 'presence rise' at higher frequencies is common in close up vocal mics. Single-D Cardiod mics tend to accentuate bass at very close distances, such as in close-up vocal use. The heavy bass in that case can work with the presence rise to give a perhaps enhanced vocal sound. Selection of a given mic in that regard should be based on how it sounds with the particular vocalist. Just sayin' But, the big bass effect can be one reason for overpowering some preamps.
and here: https://assets.sennheiser.com/globa...36.1355323841.1535157752-385582374.1535157752
Perhaps worth mentioning, the 'presence rise' at higher frequencies is common in close up vocal mics. Single-D Cardiod mics tend to accentuate bass at very close distances, such as in close-up vocal use. The heavy bass in that case can work with the presence rise to give a perhaps enhanced vocal sound. Selection of a given mic in that regard should be based on how it sounds with the particular vocalist. Just sayin' But, the big bass effect can be one reason for overpowering some preamps.
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The iPhone is said to require a moderate DC source resistance (at least 1k) to detect
and operate with a mic. Be sure to take this into account.
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I just had a look at the TI website for op-amps with low voltage noise that can work on 5 V and are available in SO packages. With the one with the best noise performance on top:
OPA1611 and OPA1612 (noise at 1 kHz: 1.1 nV/sqrt(Hz) and 1.7 pA/sqrt(Hz), 4.5 V to 36 V supply)
OPA1602 (noise at 1 kHz: 2.5 nV/sqrt(Hz) and 1.8 pA/sqrt(Hz), 5 V to 36 V supply)
OPA1662 and OPA1664 (noise at 1 kHz: 3.3 nV/sqrt(Hz) and 1 pA/sqrt(Hz), 4.5 V to 36 V supply)
OPA1611 and OPA1612 (noise at 1 kHz: 1.1 nV/sqrt(Hz) and 1.7 pA/sqrt(Hz), 4.5 V to 36 V supply)
OPA1602 (noise at 1 kHz: 2.5 nV/sqrt(Hz) and 1.8 pA/sqrt(Hz), 5 V to 36 V supply)
OPA1662 and OPA1664 (noise at 1 kHz: 3.3 nV/sqrt(Hz) and 1 pA/sqrt(Hz), 4.5 V to 36 V supply)
You could put one of those in a circuit similar to the one post #2 links to, but with much reduced feedback resistor values, with the resistance from the negative input to ground made either switchable or controllable with a good potmeter and with the value of the capacitor in series with this resistor increased.
All in all, I'd try something like this. The basic operation is explained by Rayma in post #2, but I've changed the dimensioning for lower noise floor and added some stuff.
R1-C1: RF filter to make sure your friend records his own voice rather than the nearest transmitter.
C2: filter capacitor to improve the power supply rejection a bit, not needed when you only use batteries, useful when you occasionally use a mains adapter instead
C6: prevents unnecessary amplification of any RF signals that may have passed through R1-C1
R8: ensures stability when there is a long cable connected to the output
D1: prevents destruction of the op-amp when the battery is inserted the wrong way
R9: I'd rather use a higher value, like 22 kohm, but I understood from Rayma's post #12 that that causes problems with the I-phone. I may have misinterpreted post #12, though.
R7 and C6 may have to be changed: reduce R7 and increase C6 when the maximum gain is (much) more than your friend needs, increase R7 and reduce C6 when the maximum gain is too low.
When RV1 is an ordinary logarithmic potmeter, connect it such that you have maximum gain (minimum resistance) with the potmeter fully anti-clockwise (counter-clockwise). This is a bit unusual, but you get used to it quite fast.
After switch-on, the circuit needs a few seconds to get properly biased.
R1-C1: RF filter to make sure your friend records his own voice rather than the nearest transmitter.
C2: filter capacitor to improve the power supply rejection a bit, not needed when you only use batteries, useful when you occasionally use a mains adapter instead
C6: prevents unnecessary amplification of any RF signals that may have passed through R1-C1
R8: ensures stability when there is a long cable connected to the output
D1: prevents destruction of the op-amp when the battery is inserted the wrong way
R9: I'd rather use a higher value, like 22 kohm, but I understood from Rayma's post #12 that that causes problems with the I-phone. I may have misinterpreted post #12, though.
R7 and C6 may have to be changed: reduce R7 and increase C6 when the maximum gain is (much) more than your friend needs, increase R7 and reduce C6 when the maximum gain is too low.
When RV1 is an ordinary logarithmic potmeter, connect it such that you have maximum gain (minimum resistance) with the potmeter fully anti-clockwise (counter-clockwise). This is a bit unusual, but you get used to it quite fast.
After switch-on, the circuit needs a few seconds to get properly biased.
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Then what does it do when the resistance is less than 1 kohm? Assume a line level signal or assume there is no source at all? What does it do if the DC resistance is very large, like > 1 Mohm? Apologies if these are silly questions, but I know very little about iPhones.
The iPhone assumes that you have plugged in headphones, if their DC resistance sensed
is less than around 1k. (I think it's actually 800R or so.) I don't know what the maximum
DC resistance is for it to still think it's a mic, it could even be open circuit. This may vary
from one iPhone model to another, also.
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OK, so then it's probably a good idea to make R9 a bit larger, but not much. Maybe 2.2 kohm or so.
If the main application is with the iPhone:
Since the iPhone apparently only has a microphone input and no line input, chances are that R7 needs to be reduced and C6 increased. Maybe 2.2 kohm and 1 nF as initial guess? RV1 can then be reduced to 5 kohm, as its upper 5 kohm wouldn't have much effect on the gain anyway (1 + 2.2/5.047 ~= 1.4359 while 1 + 2.2/10.047 ~= 1.219, a difference of only 1.4226 dB).
If the main application is with the laptop's line input:
Keep R7, C6 and RV1 as is for the time being.
If the main application is with the iPhone:
Since the iPhone apparently only has a microphone input and no line input, chances are that R7 needs to be reduced and C6 increased. Maybe 2.2 kohm and 1 nF as initial guess? RV1 can then be reduced to 5 kohm, as its upper 5 kohm wouldn't have much effect on the gain anyway (1 + 2.2/5.047 ~= 1.4359 while 1 + 2.2/10.047 ~= 1.219, a difference of only 1.4226 dB).
If the main application is with the laptop's line input:
Keep R7, C6 and RV1 as is for the time being.
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