[snip]
The compound device DOES have a good NF... I've used it to advantage in a sonar design.
As applied in this case, all advantage was lost... big time. "Engineering" via pasting never works.
In spite of Win's exaltations, the circuit IS "crap".
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Like I said before, I AM a PERFECT asshole ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
I make the biasing of Q1 about 1ma, and Q2 about 2ma. Q1 is constant, where as q2 has the full swing. Q1 can be biased for optimum noise, Q2 biased so to avoid clipping.
With non compound differential pair the non linearity of the change in vbe with input voltage adds distortion. Q2 removes almost all of the change in Q1 current and hence the distortion.
Im surprised this point seems to be so hard to see.
Colin =^.^=
Who needs the input stage at all?
R1 and R3 would imply that a high input Z is not needed.
Any NF advantage was tossed in the transition to the OpAmp.
The circuit is CRAP ;-)
I certainly enjoy rubbing Win's nose in his pomposity ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
Why exactly is it lost ? explain it to the dummies, give us formulas for its loss.
Colin =^.^=
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
The signal fed to the op amp has been amplified upto 100 times, this means the op amp contribution to SNR is probably negligable.
Colin =^.^=
If you had written out the gain equation as a single statement you would have seen it immediately ;-)
That's why I kept pushing for a full analysis.
You only learn if you do the work yourself ;-)
Hint: The "designer" himself said an overall gain of 6 - 15 dB.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
That's not as expressed by the "designer". Read his post.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
the gain equation has been written out many times so far by several people. what does this prove ? just that its not a good relationship for vr1 to follow.
Colin =^.^=
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
I read the article, not sure wich of many posts you refer to,
I behind so many posts here lol,I should realy be trying to work out how the missing points in my FFT will affect the result and compensate for it, but ive got bogged down in the code.
so anyway at maximum gain is when the ip noise is most noticable, but if the gain is turned right down the gain of the input stage is
The "designer" said 6-15dB of gain, so the first stage is lossy and its use pointless.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
6-15db gain for a mic preamp is pointless. must be some mistake. The gain range is from about 1 to well over 1000, thats 60db. 15db is nothing compared to that, maybe thats its minimum gain ...Colin =^.^=
[snip]
Agreed. But 6-15dB is what was stated.
Still, the implementation is lousy (as well as lossy ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
well I would agree if it realy was only for 6-15db, but if that figures wrong/misleading then I dont see why its that lousy. so far your point is that the low input noise is wasted if the gain of the ip stage is low.
If this is truly the case I would agree.
I was thinking just now about alternatives and had the bright idea of a common base stage with volume control in collector, at least thal give beter relationship and stil good comon mode rejection, but then thats gona be hell with input impedance...
come on give us a better circuit show all those dummies up !
Colin =^.^=
Why don't you provide a circuit?
What's the need for input impedance? The 3K3 resistors kill it.
What are the specification for a good microphone preamp anyway? I don't know, I'm not involved with audio at this level. All I do now-a-days are hearing aids with MEM's microphones.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
Ive just read the bit in the link in the original post where it says "6 or 15db for the stage" that is just for the output diff op amp stage ! and thats not 6-15db that is 6x or 15db wich is the same it then says .... "Full gain is 1000 times or 60dB"
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
now I gues youl blame it on your eyes ...
Colin =^.^=
"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
Bah I dont know whats needed for a good mic amp input spec either. like i said I lost interest in audio ages ago. I bought a huge box of 2n3055s cheap to make an enormous amp then lost interest, I stil have the box lol. I tend to deal with very wideband pulse stuff, and now robotics or mechatronics as it seems popular to call it, anything else doesnt interest me enough to get involved, software keeps me in bread and butter for far less effort, electronics has been delegated to mostly a hobby, pity cos I put to shame most electronics engineers whose projects I have to write software for lol. its kind of fun when they aproach me with the attitude oh your only a software engineer what the heck could you know about it lol. although its all mostly off the shelf chips and asics these days. gone are the days of boards stacked full with ttl chips.
but seems the mics being talked about for use with this are about 600ohms.
I dont see why I should have to provide a better circuit as ive said I dont see why this ones as bad as you sggest. its up to you to come up with better if your the one criticising it.
a few suggestions ive made same as other people probably dont alter the real life performance a great deal.
btw see my other post about the artical says the gain is 60db not 15db !
Colin =^.^=
OK. But there's still a far better way to do it... with far better PSRR.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Save some of it for yourself.
-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85.
Michael A. Terrell Central Florida
Always full of shit?
-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
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