# How do you choose which quad amp to use for a microphone amp

1. Sep 24, 2016

### d_rock

I'm building a microphone amplifier for a bot that will respond to frequency commands between 1kHz and 3kHz. I have an ADMP401 mic but need to choose an op amp. Someone in class told me the LM348 quad amp is best but not why and I need to know how to make that decision.

2. Sep 24, 2016

### Averagesupernova

A schematic would be helpful. Welcome aboard BTW.

3. Sep 24, 2016

### rootone

Why do you think a quad amp would be necessary?
It's just four standard 741 op amps on a single chip, why not use just one?

4. Sep 24, 2016

### rbelli1

Please don't use that amplifier. It is ancient technology. It has so many of its characteristics extremely far from ideal that you will pull your hair out compensating for them.

You will first want to decide on how you are powering it. What voltage? Is it battery powered? That narrows down your selection considerably.

Next you want to focus on frequency and gain characteristics. What gain are you shooting for at 3kHz? Hopefully you can select a slow enough part that you don't have to calculate much further than that. You can use something that has most of the parameters close enough to ideal that the rules of thumb will be OK. If you want or need to do the calculations someone else will have to help you as I know just about enough to get myself into trouble.

I usually find a part that has an application note close enough to what I need and use that to get me where I need to be.

BoB

5. Sep 24, 2016

### jim hardy

6. Sep 25, 2016

### yungman

I tested a few of the high quality audiophile opamps, here are some I used for my audiophile preamp.

http://www.digikey.com/product-search/en?keywords=opa2134

http://www.digikey.com/product-search/en?keywords=opa2604

http://www.digikey.com/product-sear...entation-op-amps-buffer-amps/2556125?k=lm4562

These are opamps that are suggested by the utmost audiophile, most likely are way over killed for just mic. I would not use quad opamp as it just make it harder to layout the pcb. I find duel are the best of both worlds.

Believe it or not, theory say an opamp is an opamp as long as you have to slew rate to cover the highest attack, low enough noise and low distortion. BUT I actually put them one by one into my system and they do sound different with LM4562 sound the coldest.

Be aware, they are not cheap by any stretch. People did use TLO72 in the older days and they were happy. It might be good enough for you.

Alan

7. Sep 25, 2016

### rbelli1

Be careful of the TLO72 and similar op amps. They exhibit phase inversion. If you overdrive them and tell them to produce a voltage outside of what they can they will produce an unexpected result. Some newer j-fet amps have solved that problem.

BoB

8. Sep 25, 2016

### yungman

You never want to run opamp even close to clipping. TL072 is quite popular in guitar amp that have high signal level even in the preamp as guitar pickup gives out way over 100mV of signal.

That said, TL072 is really cheap stuff. I never try it, I did put a TL082 in for comparison for the fun of it, I could here distortion on some notes of fluke. Instantly reminded me of guitar distortion paddle sound. No where close to the same league as the few I mentioned.

Off the subject on this. Someone suggested the ultimate discrete opamp to try:

http://www.ebay.com/itm/141461456047?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

I actually bought one for comparison. It did have a touch more transparency and give ever slightly better image than the ones I suggested, but for over $60!!! I settled with the 2604 which gives me a slightly warmer sound as I am more the video guy. It might be beyond the quality of my system, I don't think it worth the money. 9. Sep 25, 2016 ### rbelli1 True. But for anomalous signals in you get anomalouser signals out with the phase inversion instead of just some distortion from clipping. You can't run so close to the edge with that part. That ebay contraption looks an awful lot like a$500 power cord to me.

BoB

10. Sep 26, 2016

### yungman

I used to think all the audiophile stuff are baloney, but the more I get into it, there is a lot of stuff that is hard to explain. It is a very narrow and specialty field in electronics. You won't believe until you try it. I have been an EE for over 30 years, a lot of things can be explained, but there are things I just cannot explain. Sound is one of those.

Human ears are so much more sensitive than any of the instrument can measure. I actually custom build a test fixture with two identical preamp boards, layout is good for RF with ground plane and bypass so I get all the distraction out of the way and just compare opamps. I have a switch that I can instantaneously switch from one board to the other. to compare the two opamps. Everything is scientific. I was surprised how much difference each opamp sounds. Identical circuit, identical system, instant switch back and fore to compare.

One thing is you have to have a good system, if you have just a normal Adcom etal amp and Energy/Polk Audio/Klipch etal speaker type of quality system, you'll never hear any difference. I am talking about high end audio. I don't know about power cord, but I can tell you I spent hundreds of dollars on the speaker cables and interconnects. They make a difference. I ended up having 4 pairs of monster like cables per speaker to get the sound out. It make such a difference even my wife who knows nothing about hifi can point out right away. I still don't believe any brands of speaker cable, but I believe in massive thick cables to lower the impedance, inductance and capacitance. System is only as good as the weakest link of the system.

I used to be here advising people for a long time, I just spent the last 4 years study deep into audio electronics, designing guitar amps and hifi amps. It's a different world. It's a niche in the field.