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Matching BJT's

Posted 27th January 2010 at 08:27 AM by Cro maniac

Yeah, my first blog entry !

I have spent whole day in matching output transistors for poweramp I'm building for a friend.
I found out that Vbe tracks gain pretty good (the transistors with higher gain have proportionally higher Vbe), so I think the painful matching of Vbe at various collector currents is pretty much useless because Vbe spread can be already seen in DC current gain.

If I think of Vbe tracking gain, it is good, because transistor that needs more Vbe will be less opened, but it has higher gain, so collector current will be more equal between devices.
I have 10 pairs of MJ21193 / MJ21194 and plan to use 4 pairs per channel.
Transistors are ordered directly from Onsemi and the NPN's all come from the same batch but PNP's are from 2 different batches and that can be clearly seen from measurements because there is a big mismatch in gain between the 2 batches.

Fortunately, the ones from the same batch are pretty...
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Inductor Evaluation Help

Posted 27th January 2010 at 04:40 AM by audi0

[FONT="Verdana"][SIZE="2"]Over the last couple of years amongst other things, I have been playing around with T amps changing and upgrading components, noting changes etc. When I saw the ‘Inductor Evaluation Help’ thread by ICE_Mag it was of immediate interest to me.
I have read a fair bit about the audible effects of different inductor types used in these amplifiers, some people liking air core and others ferrite core toroids etc. so I registered my interest with the supplier.

It then occurred to me which of my amps (I had three T amps at that stage) would be the guinea pig for my trial; I pondered on this for a while thinking that although all were modified, they are all in a condition where they could be sold if they became surplus to my needs.
I therefore looked on eBay and saw an Hlly amp at the right price, so I bought it.

The inductors arrived, two each of three different sizes (all 10mH) hmmm I thought, how am...
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andy_c is banned?!

Posted 24th January 2010 at 07:50 PM by gootee

Dear diyaudio,

I was shocked and very much saddened, today, when I discovered that andy_c has been banned from

I know that Variac and the moderators have a sometimes-difficult job to do, that is necessary and is appreciated, overall. And I have gathered that they felt that they had no choice. But this seems like much too great a loss for this community!

And I cannot seem to find out what actually happened, which leaves me feeling very unsatisfied with the sparse explanations that I did manage to find.

This is a _major_ loss and it needs a major explanation. I believe that that much is owed to all of us, in some sense, especially since I am not aware of anything in andy_c's posting history that hinted that he might ever even be a candidate for banning, or even binning; quite the opposite in my opinion.

And now I can't help but fearfully wonder: Who's next?! AndrewT? Janneman? Bob Cordell? (to...
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Tech note: Balanced lines-1

Posted 13th January 2010 at 05:54 PM by jan.didden
Updated 13th January 2010 at 05:57 PM by jan.didden

Why would one use balanced interconnects, and how can we make them work well?

Balanced lines came about at a time where very long signal lines were coming in use for telephone and later for large audio performance venues. If you use a single screened line for your signal, and the line is long, the ground current through the screen causes a voltage between the ground points of the cable ends. Since the signal send out (and received) is the difference between the voltage on the signal wire and the ground wire, the unwanted signal (noise, hum) is effectively added to the wanted (music) signal. We don’t want that.

The trick is to use TWO signal lines in parallel. You send the signal over the two lines in such a way that the signal you want to transmit is the difference between the signals on these two wires, and then at the receiving end you have an amp that reacts to the difference between the two lines, so your signal at the far end is the difference between...
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CSS bias

Posted 12th January 2010 at 03:32 PM by DougL
Updated 13th January 2010 at 08:52 PM by DougL

I found a great comment in post post #10.

Very few details were given, but it caught my imagination.
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Confessions of an audio DIYer

Posted 11th January 2010 at 12:58 AM by Damon Hill

Current projects:

P. Millett's Sound Card Interface

Long term projects


I'm a DIYer, and that means for me a lot of test equipment. I bought a lot of Heathkit gear in my day and still have most of it, supplemented with a Hewlett Packard oscilloscope and Tektronix audio distortion test set, but the Heathkit gear is still my mainstay.

Since an Audio Precision test set seems to be forever out of my reach, I'm taking a crack at a sound card based analyzer, as above.


My main amplifier is based on Marshall Leach's design, version 4.4, with a massive power supply (about 1/4 farad!) on a dual mono chassis. I've been building his amplifiers since the late 70's with excellent success, to the point that I've neglected making a serious effort to build anything else.

At the moment I'm considering Jan Didden's design using Hawksford error correction...
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Finaly did some DIYing again

Posted 10th January 2010 at 09:26 AM by wintermute (Wintermutes Rantings)

With the Silly season and general busier than normal work shedule (working a lot of weekend) I haven't made any progress on anything much at all lately.

Last week my Mother In Law put my 2 YO daughter in the bathroom basin. It was only attached with what looked like tile grout. It didn't hold... Today My Father in law assisted to glue it back in with some marine polyurethane adhesive/sealant . Hopefully it holds! This stuff was similar to the glue I had bought a while back to seal my 3 ways (see the leaks are stealing my bass blog entry) but hadn't got around to using yet. It seems perfect, it remains flexible, seals, sticks incredibly well apparently, and even claims to dampen sound and vibrations . As the tube was open, I pulled one of the Three ways out and basically sealed every interior joint. I then put a slight 45 degree chamfer on the back of the woofer cutout and glued in the front baffle (it has always only been screwed and didn't even have a gasket). ...
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A Decision

Posted 8th January 2010 at 07:40 PM by tomtt
Updated 14th October 2011 at 10:45 AM by tomtt


"The best way to control the opposition is to lead it ourselves."
- Vladimir Ilyich Lenin

"First they ignore you, then they laugh at you, then they fight you, then you win.
- Gandhi
in light of these quotes, from Famous Men,

I no longer care what my psychiatrist says.

I'm glad I'm a Jedi


Click the image to open in full size.



ImageShack Album - 36 images

Imageshack - dscn95063168587.jpg

ImageShack Album - 36 images

ImageShack Album - 36 images

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The white van is in Tucson

Posted 8th January 2010 at 04:27 PM by relder (Rob's active 3way with transconductance chipamps build blog)

I haven't been propositioned for white van speakers for several years (outside of a home depot.) But a guy I know was taken in this last week after leaving the ATM.

Why always a white van, why not mix it up with a red one or something?

They are a lot more sophisticated it seems now.

It might be fun to borrow his newly acquired $300 sound system and measure them, but I think I'd rather use my time on real audio projects.
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Tech note: voltage regulators-1

Posted 7th January 2010 at 05:10 PM by jan.didden
Updated 11th February 2010 at 03:31 AM by Jason

There are lots of types of voltage regulators, but in this installment I’ll talk about series regulators.

What’s a regulator? It’s all in the name: it REGULATES the voltage to the circuit to be powered to keep it constant and as free of noise and ripple as practical. The ‘regulation’ means that there is some circuitry that compares a reference voltage, like from a zener diode, to the regulated output voltage, and then uses the difference between the two to adjust another element to null that difference. The ‘compare-and-correct’ is crucial for a regulator, and is done by negative feedback….

Look at Fig 1: is there a regulator in there? No, they are all circuits that try to give a constant, ripple free voltage, but if you start to draw varying currents from them, the output will vary with that current and there is no mechanism that somehow tries to null out that variation. Fig 1c is better than 1b, because Q1 buffers the voltage from the zener reference, so...
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