....................................................................................Nigel Goodwin said:Why?, and what are you defining as 'low level'.
And it's not 'my' technique, it's EVERYONE'S technique - can you name a single audio input where impedance matching is used?. If you're thinking of suggesting microphone transformers?, they are simply used to change the impedance, which is then fed into a much higher impedance as normal.
hawk2eye said:Apparently you have not been involved with low level, noisy signals very much.
I am correct and EVERYONE's technique is wrong.
I have emphasized the words "impedance matching"
with ...vvv... marks.
.................||||||||||||||||||||||
.................vvvvvvvvvvvvvvvvvv.................
< Excellent impedance matching between the microphone and the pre-amplifier,
Nigel Goodwin said:Why would you have noisey signals?.
As I said previously, this ONLY matches the microphone to the transformer, and NOT the transformer to the preamp, not even back in the 1940's where that technology comes from!.
++++++++++++++++++++++++++++++++++
Nigel:
I repeat:
the mike impedance to the amplifier is (Npri/Nsec)^2*Rgen
as shown by ANY text book that describes impedance matching.
Look it up. there is nothing wrong in being wrong.
............................................................................
The input transformer serves as an impedance matching device.
mathematically, for the transformer
Nout*Iout = Nin*Iin
Eout/Ein = Nout/Nin
then
Eout = (Nout/Nin)Ein
Iout = (Nin/Nout)Iin
Rout = Eout/Iout
Rout =(Nout/Nin)^2 *Ein/Iin
Rout =(Nout/Nin)^2 *Rin
hawk2eye
hawk2eye said:Nigel Goodwin said:Why would you have noisey signals?.
As I said previously, this ONLY matches the microphone to the transformer, and NOT the transformer to the preamp, not even back in the 1940's where that technology comes from!.
++++++++++++++++++++++++++++++++++
Nigel:
I repeat:
the mike impedance to the amplifier is (Npri/Nsec)^2*Rgen
as shown by ANY text book that describes impedance matching.
Look it up. there is nothing wrong in being wrong.
............................................................................
The input transformer serves as an impedance matching device.
mathematically, for the transformer
Nout*Iout = Nin*Iin
Eout/Ein = Nout/Nin
then
Eout = (Nout/Nin)Ein
Iout = (Nin/Nout)Iin
Rout = Eout/Iout
Rout =(Nout/Nin)^2 *Ein/Iin
Rout =(Nout/Nin)^2 *Rin
And I repeat again as well, what has that got to do with the matching INTO the preamp - quoting formulas from a book doesn't help anything, do you have actual examples of microphone transformers being impedance matched to the preamp input impedance?.
audioguru said:I worked with very high quality PA amplifiers. They used an input transformer for dynamic microphones as a balanced connection for them. The transformers were used at impedances far higher than the mics and as stepup transformers to reduce the noise of the following opamp since then it didn't need such a high gain.
No disrespect Audioguru, but how long ago was that?. Using a VERY high quality transformer on the input stage of a VERY expensive mike stage is probably still the best method available (although it still doesn't use impedance matching to the preamp). However, it would increase the costs VERY substantially for a very small level of improvement. Cheap, and medium price, mike transformers have performance levels below modern electronics.
audioguru said:Hi Nigel,
I worked with TOA brand, a Japanese sound systems company, until 6 years ago. The expensive amplifiers have a high quality input transformer for perfect balancing and for a voltage stepup which feed a very low noise opamp. Although they were small, the transformers have a good low frequency response because they are used with their impedance unmatched.
Their cheaper amplifiers use transistors as an almost balanced input.
audioguru said:The cheap TOA mixer has recently been discontinued. Its mic input S/N spec is 126dB @200 ohms. I don't know the ratio of the input transformer.
Their products were pretty reliable. Very few items were returned during the 2 years to 5 years warranty. Their best power amps had a "no questions asked" 5 years warranty and none came back for repairs. They had 1500 dealers in Canada.
Dr.EM said:I was quite suprised at how good the live sound was on a Massive Attack concert I went to recently. Hadn't seen an outdoor one before and wondered if the bass would come across well. It was in fact the most powerful bass i've ever heard, literally "trouser flapping" and the vibrations in your chest from it actually made it difficult to breathe. The overall quality of sound was good too, a bit too bass heavy, but at least it wasn't bright and nasty, my ears were fine after.
Nigel Goodwin said:< And I repeat again as well, what has that got to do with the matching INTO the preamp - quoting
< formulas from a book doesn't help anything, do you have actual examples of microphone
< transformers being impedance matched to the preamp input impedance?.
[end QUOTE =Nigel Goodwin
.................................................................................
In my final attempt to show that impedance matching is
required for best noise performance the ultimate in low level
amplifiers, I include the following from respected companies
on the Internet
..................................................
1. https://www.electro-tech-online.com/custompdfs/2006/09/an002.pdf
see right side of p2
..............................................
2. **broken link removed**
3. **broken link removed**
.............................................
4. **broken link removed**
quote
Do's and Don'ts of Audio Transformers
Do use a transformer to match impedances.
Do use a transformer to increase or decrease signal level by up to 25 dB.
Do use a 1:1 transformer to isolate problem components in an audio chain.
Do not use a transformer to increase signal level by more than 25 dB.
...............................................
5. **broken link removed**
6. http://www.midi-classics.com/c/c4283.htm
++++++++++++++++++++++++++++++++++++++++++++++++++
It is important to keep an open mind.
Especially when there is so much evidence
that apparently negates what we are sure we know.
hawk2eye
Nigel Goodwin said:Know what you mean about feeling the bassthey always run too loud at Donut gigs (at least for me!).
You have to bear in mind the massive power they run at these gigs!, I remember reading an article years back about the PA for an ABBA tour of Australia. The first thing they had to do was order (well in advance) an independent 3 phase mains supply to be provided, in order to cope with the demand - they also always carried sacks of salt and large metal spikes, so they could make their own earth system if they didn't like that provided. All the amps (banks and banks of them) were top end, Crown and such. Lighting and sound were on different phases, to help prevent any noise from the lighting getting to the amps.
Powers are even higher (and cheaper) these days, if I remember correctly the first band to run 1,000,000 watts was the Rolling Stones - late 60's early 70's?.
Dr.EM said:1000W surely? a million watts is madness!
I did wonder how much power they used at that concert, and then it's not just the sound but lights, equitment etc. I didn't see any generators so presumably they had a special supply, or they were round the back somewhere out of sight.
hawk2eye said:It is important to keep an open mind.
Especially when there is so much evidence
that apparently negates what we are sure we know.
It isn't an opamp. It is a power amp. It is pretty noisy if it has a gain more than 20.systemloc said:I tried out building a new circuit around the LM386, which I found at the RadioShack, since everyone pretty much agreed an op-amp would work out better.
The input DC voltage of the LM386 is 0V so if the capacitor is fed from a grounded volume control then it doesn't matter which way the capacitor's polarity faces.the input 10uF cap is electrolytic, and the second page referenced shows it with the positive towards the input. Looking at the internal schematics LM386, this seems acceptable since that side goes to ground. Is that acceptable?
It is 0.05uF and 10 ohms. 0.1uF might work but I would use 0.047uF instead. It stops the LM386 from oscillating at a high frequency when the inductance of a speaker causes a high load resistance, like your application without a speaker.what's the function of the 0.1uF cap and 100 ohm resistor to ground on the output?
A matched impedance doesn't cause distortion, it causes the output to be half.In response to the discussion of impedance coupling, for microphones, at least, wouldn't having matched impedance create a load on the mic itself, thus causing distorted input?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?