Mini amp circuit

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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Fri Feb 05, 2010 6:02 pm

Thanks for the explanation, Robert. This is actually just an exercise in education. I am learning about
something that is a passion for me - good old analog audio. Starting with the basics (discrete) and
moving toward the all-in-one chip solution. I wanted to have a good understanding before moving on.

CeaSaR
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Robert Reed
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Re: Mini amp circuit

Post by Robert Reed » Fri Feb 05, 2010 9:55 pm

Well I have to say that this posting of yours is certainly reviving my love of audio design again. Years ago I was deep into Hi-Fi design and components, but when good music and singers died off years ago, I eventually lost my passion for it and most of that equipment is stored away in the attic. But being currently involved in an audio project and concurrent with your postings is reviving some of that old thrill of "rolling your own". I should be saying thanks to you :grin:

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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Sat Feb 06, 2010 1:32 am

Good music and singers have not died off, they've just moved away from the corporate machine. This past year was
an exceptional year for me regarding music in that I had the pleasure of seeing some legends:

Peter Frampton - D*MN can he still put on a show. Met him afterward for autographs, along with the wife and son #1.
Very down to earth and cool. I thanked him for one of the best birthday presents ever. He was surprised that it really
was my birthday as he normally wishes anyone in the audience a happy Bday.

Blue Oyster Cult - they played very locally, within walking distance. Again, met them for autographs with the wife and
son #1. He got his Epiphone Les Paul signed by them. All very nice guys.

Renaissance - Annie Haslam still has her voice. Holy cow, can she ever sing! This time it was only the wife with me for
autographs. It's a shame son #1 didn't come as the opening act left my wife and I speechless. The guy who opened for
them was Jann Klose (Myspace). He opened his mouth and we had a rare moment where we were actually floored.
I went out to the lobby right after he went off stage and bought his CD. Son #1 was thoroughly impressed when he heard
it, and it is now in his rotation of albums.

Also, son #1 has found quite a bit of good music that can really only be heard on the 'net. He has shared tons of stuff
with us that he has found. Thank goodness for YouTube.

I suggest that you take a look around there (YouTube). Type in a genre and see what pops up. Type in an old song you
love and see what is related. The good stuff is out there, you just have to find it through different channels.

Who knows, you may empty out some of the stuff in the attic and put it back into service.

CeaSaR

P.S. I am hoping I can get tickets to see Richie Havens and Ottmar Leibert (with Luna Negra) when they perform their shows
locally. Now there's some history and quality you don't see/hear anymore through "Big Corporate".
Hey, what do I know?

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sofaspud
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Re: Mini amp circuit

Post by sofaspud » Sat Feb 06, 2010 7:25 am

BÖC, one of my all time favorites.
A good singer? I'll throw in William Topley. Corporate calls it "contemporary British blue-eyed soul." Can't really be pigeon-holed, though. It varies from pop to r&b to
country to rock to pure folk. I call it "Van Morrison meets Bob Seger in News Orleans to play songs about cities and oceans." :smile:

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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Sat Apr 10, 2010 8:57 pm

Richie Havens was awesome! We were second row left, excellent intimate seating. Singer, songwriter, storyteller,
and all around humble being. His sound was spot on, playing perfect, voice sounds like it did back at Woodstock.
Not bad for a man of 69. :grin:

Many of us at the show met him afterward at the purchase/signing table. He is a man who has held on to his core
beliefs from so long ago, who still imparts his wish for all humankind to come together as a true family. And so
gracious, talking with everyone, signing all manner of things, posing for pictures, shaking hands, etc., taking the
time to really connect with those who wanted to. Wife had his CD signed, I had my ticket signed, and my eldest
had his Epiphone Chet Atkins Signature signed. He said he heard my son playing while we were waiting in line, and
that next time he was in town, he should come jam with him. How cool is that? A 15 year old asked to jam with
the man who defined a generation (with a spontaneous song) at the greatest concert ever put together.

We bought his last album, 2008's Nobody Left to Crown, an organically produced album - no processing other than
minimal EQ and levels. What you hear is what they played. The man has it! If you ever get the chance, I highly
recommend seeing him.

Richie Havens Official Site

Next month, Ottmar Leibert and Luna Negra. Stay tuned...

CeaSaR

**Oh yeah, now I really need to get one of these amps built so I can listen to the album on my (our) own creation.
:mrgreen:
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ramsey75
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Re: Mini amp circuit

Post by ramsey75 » Mon Apr 12, 2010 7:04 am

The whole purpose of the diodes is to limit excess current. In commercial amplifiers, the diodes are usually mounted to the same heat sink as the output transistors, so the diode junction temperatures track the output transistor temperatures.

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Re: Mini amp circuit

Post by ramsey75 » Mon Apr 12, 2010 7:10 am

:)

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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Sat May 08, 2010 9:02 pm

Ah, just got back from the Ottmar Liebert & Luna Negra concert at The Colonial Theatre.
Very clear, precise and relaxing. Great show. The wife and son #1 were with me and thoroughly
enjoyed it. Picked up The Scent Of Light and had it signed. Son got his Austin 12 string signed
on the headstock. Very nice man, extremely encouraging to my almost 16 year old. If you want
check him out, go to OttmarLiebert.com. Been listening to him since '93.

Night all,

CeaSaR
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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Thu Jun 13, 2019 6:34 pm

Well, it's ten years later and I have a question about this and many other very similar circuits.

Being that this type of circuit is class AB, wherein the B section is supposed to split the amplified signal in half, with each respective transistor amplifying their respective polarity of the wave form, with just enough bias / voltage drop between then to reduce cross-over distortion. That means that for each positive half of the waveform, the NPN side will do the amplifying and for each negative half of the waveform, the PNP side will do the amplifying.

Simple, right?

Now, if you were to scope the bases of Q5 and Q6 as shown in the schematic on page 6 of this thread, you'll see that Q5 is being driven with a Sine wave (not the positive half, but the full Sine wave) at about supply minus 2 volts swing and Q6 is driven with about 1 volt and the form.looks like a really bad , jagged hump and a wide "flat" at just above 0 volts.

I thought this really wierd since the output is pretty much a beautiful sine wave. So I decided I'd model some other amps with the same type of topology, and they all exhibited similar traits. Can anyone explain why this is and why it has worked this way for so long?

CeaSaR
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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Fri Jun 14, 2019 6:14 am

I think I see why I get that reading. Mostly they are used with a split power supply and a GND point between them. Thus, in this particular case, the negative transistor (PNP) never really has the chance to go more negative than the ground reference point.
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haklesup
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Re: Mini amp circuit

Post by haklesup » Fri Jun 14, 2019 12:11 pm

scoping those nodes, you are really looking at the current flowing through the base bias resistors, Since the PN junction (B-E) of the NPN transistor and the NP junction (B-E also) of the PNP are non linear, the current flow into the bases is non linear (due to the diode characteristic of the B-E junctions) when driven by linear voltage input. For bipolar, you really need to be thinking current especially at the base or collector.

A good AB amp needs a well matched pair of transistors, (same Gain Hfe) or else you get into trouble trying to bias each one differently and crossover distortion gets worse or one side of the waveform suffers.

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Re: Mini amp circuit

Post by dyarker » Fri Jun 14, 2019 1:59 pm

?? AB?? Both Q5 and Q6 are NPN.

Only Q4 is PNP. It does not need a negative supply. It's collector is toward the most negative which in this case circuit common. And the base can go negative RELATIVE to the emitter.

Cheers,
Dale Y

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CeaSaR
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Re: Mini amp circuit

Post by CeaSaR » Fri Jun 14, 2019 7:44 pm

It's based on the old style Quasi-Complentary AB amps of old when high power PNP transistors were rare. Yes, I could use lovely modern units and not go that route, but, nostalgia, ya know. It all works out in the end.

I was just trying to figure out why it looked like that.
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