LA3220 Schematic electret pre-amp need help

[audioguru]

H Jose's Dad!
Your circuit is missing the outputs from pin 2 and pin 13 and the negative feedback they deliver to pin 4 and pin 11.
The datasheet shows a 10pF capacitor added between pin 2 and pin 3 or between pin 12 and pin 13 to prevent high frequency oscillation when the gain is less than 100.

 

[josedad]

One month ago, before I started the project, actually I bought bunch NOS preamp head tape kit, and desoldered it and rebuild with your schematic with prototype pcb. After everything working nice, I go back to the wasted PCB that had been desoldered out, and I try to adapt the lay out with the new schematic. Its not easy but worth to try rather using prototyping pcb or make a new one. And I did it, not even cut any trace.

A weeks ago I study what really opamp is and how it works, Then I thought the head tape kit, must be a preamp too, why dont I use that preamp and tweaking it. it would be more efficient using the actual design rather than re design it. so I go back to the head pramp kit I bought before. Then I found the head tape preamp schematic different with the opamp theory I got ( I learn from Dave Jones EEV blog ). The last schematic I upload is from the actual head tape preamp I bought. After searching trough internet what inside LA3220 is, I found PC1 adn PC2 are connected to the output of the opamp. Its makes me confuse, I dont think that pin 3 and pin 12 is GND, since it on pin 1, right? But Im not sure.

 

[josedad]

this is my last works, using wasted PCB, the last schematic circuit is for the original preamp kit below

 

[josedad]

the original circuit from the kit

 

[audioguru]

The schematic from the kit is completely wrong.
The LA3220 is a very old preamp made by Sanyo who are gone today (bought by Panasonic). In those days tape players were used and needed a lot of amplification. Opamps provide a lot of amplification but have phase shift that causes high frequency oscillation when negative feedback is added so all opamps have a "frequency compensation capacitor" to cut high frequency gain so that oscillation does not occur. The LA3220 preamp IC is designed with a small frequency compensation capacitor so that with a gain of more than 100 (40dB) then its audio frequency response is good and it does not oscillate. But when you use a gain less than 100 an additional frequency compensation capacitor can be added between pin 2 and pin 3 (or pin 12 and pin 13).
An NE5534 is another old audio opamp de-compensated for gains of 3 or more and an additional capacitor can be added for less gain.

 

[josedad]

Thank you for your clear explanation Audioguru. In your opinion what is the pros cons of this chip?

I plan to try to make a baxandal using another channel op-amp using rod elliot schematic. will it works?

regards

 

[audioguru]

Thank you for your clear explanation Audioguru. In your opinion what is the pros cons of this chip?

You are welcome.
I would never use an LA3220 chip because it is very old, is not available anymore and needs an additional capacitor if you want medium gain. The datasheet says " When closed loop gain is below VG=30dB, it should not be used." Use a modern audio opamp like an OPA2134 that works perfectly with gain from 1 to hundreds without adding a capacitor.

I plan to try to make a baxandal using another channel op-amp using rod elliot schematic. will it works?

I could not find Rod's tone controls circuit on his website. Please provide a link to it.
Its parts values are different to the 3-band tone controls circuit I have. Note that it must be fed from a very low impedance like the output of another opamp.

 

[josedad]

I did make a tone control using transistor earlier, it did works but for some reason it invested humm when the bass is too high and hiss when the treble is too high. Then when I learn about opamp i think it should works with opamp too. Then I search on rod elliot equalizer project and found the schematic. BTW, i got suspicious that Rod Elliot love transistor rather than op amps

**broken link removed**

When I use the transistor version actually I really pleased with the result, unless the humm and hiss.

Actually I already got TL071, LM324, NE5532p. Perhaps I will buy OPA2134 later on, its a little bit pricey though . But, since I learnt this preamp thing from the scratch, I want to know how far this obsolete chip would go. You said its very old, how old anyway?

 

[audioguru]

The old LA3220 IC was used in a tape player. How old is a tape player?
My first job in about 1965 was in Philips car radios manufacturing and they used 8 track tape players then Philips introduced compact cassette tape recorders and players. We never used the Sanyo LA3220 IC. The lousy old 741 opamp was introduced in about 1968 and we did not use them.

 

[josedad]

wow, respect for you Audioguru. It would be great if you share your experience which op amp you prefer to use and give review of `em. Few month ago I know nothing about microphone or any electronic circuit, I really appreciate many expert that share his expertise on the net, since electronic hobby seems like fade away nowadays. I my self interested on microphone specifically since its related with my job as video producer/director. I believe even technology changed, microphone technology would n`t changed drastically. The component may changed but the principle will stay the same, that`s what I think.

 

[audioguru]

About 3 years ago I blamed "bad sound" on the video producer/directors for hiding the microphones too far away or under a thick sweater which made them sound muffled with no high frequencies. Then I had a free hearing test which showed that I had normal for my age severe high frequency hearing loss (I was 69). Then I got hearing aids that are programmed so that my hearing is the same as when I was young. The hearing aids do extra things that ordinary hearing cannot do like noise reduction, extra sensitivity, directionality, compression of loud sounds and muting when I want. They play telephone sounds in both ears.

Today the new MEMS microphones are so small that they do not need to be hidden.

 

[josedad]

Just as I thought before, You are as same age as my father. In my country, we give respect to the elder or senior expert by kissing his/her hand. So I send my kiss for your hand, sir. . Your information about high frequency loss due aging give me another consideration, thanks you.

Actually me myself fond on old microphone technology. Ribbon mic is one intriguing mic for me, for the wide dynamic range. But since its not easy to get the part (especially the transformer) it become hard to be learned. Another mic capsule like wide diaphragm condenser capsule is also very hard to find here. The only capsule available on local store are electret and dynamic mic capsule. And all the product is china brand too with no datasheet included. Luckily I got Panasonic WM-34 and Panasonic WM 58. That are the best capsule I got so far from local shop. I did try to do linkwitz mod on the capsule, as far as I got it does n`t expand its dynamic range. from what I read is more like to adjust its SPL and not its dynamic range. But I might be wrong. That`s why I try to manipulate it using baxandal.`

I still seeking for information how to wind a transformer like lundahl transformer, if there is.

 

[audioguru]

The Linkwitz mod on an electret mic allows louder sounds to play without distortion then the modified mic sounds better in a drum or in a piano.
I don't use tone controls. They are used to try to correct cheap speaker problems.