Purpose of this capacitor in discrete amplifier?

[tlf9999]

But the problem is very real with any Class AB amplifier (see thumbnail). Is this what you want to listen to?

Depends. After a few beers on a Thursday night, listening to a THD plot as the above is no different than listening to Eric Clapton.

 

[CBS240]

Drums? If it can handle Tool, then it is, I suppose, OK.

 

[amplifierguru]

Whether you're listening standing on your head with a drip feed of your favourite libation, it's still preferable to finesse the cct and, for a few cents more in componentry and science based design effort, be listening to JUST the music, yes? 😀 😀

That's my preference, anyhow.

Cheers,
Greg

 

[tlf9999]

Science? did you say science?

I only need the music to sound fine. Where it is 0.03% thd or 0.00001% thd it doesn't matter as long as i cannot tell one from the other.

 

[amplifierguru]

Ahhh..

You should try my homebrew then, you won't feel any pain just a warm glow!! And only garbled technospeak.

Cheers,
Greg

 

[tlf9999]

homebrew technospeak? is that 99.997% pure or 99.999999% pure?

 

[amplifierguru]

Who cares there's plenty more!😀

 

[CBS240]

Whether you're listening standing on your head with a drip feed of your favourite libation, it's still preferable to finesse the cct and, for a few cents more in componentry and science based design effort, be listening to JUST the music, yes? 😀 😀

That's my preference, anyhow.

Cheers,
Greg

I here you on that. If you are going to make homebrew, whether it be an amplifier circuit or "homebrew": drink, smoke, whatever suits you, there is no reason not to strive for the best. Otherwise it would fester bordem. Cost is a relative factor of course and learning from those with more experience than you is always key to the ending effect. That is what I like this forum, most people here are quite learned people.🙂

 

[dimitri]

2BJT CC sources

2 transistor current source

What ?

 

[amplifierguru]

Hi Dimitri,

Yes, in fact what you pictured was only part of the 2BJT CCS - it just has an extra diode in the sensing leg over the standard configuration! The other transistor wansn't visible.

Cheers,
Greg

 

[andy_c]

Here is my version of the two-transistor current source.

As you can see, the two transistors aren't visible.

Always glad to be of help!

 

[amplifierguru]

Hi Andy.

Very funny 😀 😀 😀

Out of context mate. The post was about the PSRR of various diff'l tails. everyone knows what a 2BJT CCS is, but dimitri had to highlight a partly shown piece of the schematic. that's all. It was simply an experimental lash up and had nothing meritorious in itself to display so there was considered no need to show it.

cheers,
Greg

 

[mastertech]

with diode is not as precise as with transinstor base connected to collector
high precision is mastertech guys

cheers

 

[amplifierguru]

Hi Mastertech,

The diode in question was added to the 2BJT CCs for a reason - I needed a 1.2V active component across the 1.2k so I built up the BJT Vbe junction voltage with a diode. Why? because the CCS is temperature comp as well and either the diode or BJT were to be relocated to the heatsink. As the thermal comp required was half that of a std BJT I added an equal but non thermally connected component with a much smaller dynamic impedance than a resistor which would dramatically impair the CCS performance.

So I got my 2mV/degree in 1.2V, temp comp CCS.


Clear as mud.

Cheers,
Greg

 

[dimitri]

so the CCS current can be calculated as Ube plus Diode drop divide on 1200 Ohms

What about thermal stablity?

oops, you are fast - but why 2 mV/deg, 2 pn junction - 4.4mV/deg

 

[amplifierguru]

Hi Dimitri,

I wanted a CCS that had a -Ve tempco of half that of a BJT so put the diode in the sensing leg and EITHER the sensing BJT or diode can go to the heatsink while the other monitors ambient. Simple low cost solution! As you're aware the simple BJT CCS has a normal 2mv/deg tempco of output current , this was simply my way of halving it.

Cheers,
Greg