TONELUX

[Jeff Goodman]

I am only a doctor of luv...

beware of his tiny little stethoscope.


couldn't resist...


Jeff

[TinderArts]

Paul has had nothing but great reviews of his "knob".

[TinderArts]

How about we give PW some input as to the products we want.

[ToneLux]

no

[Beauarts]

I'm sure the man has enough work ahead of him finishing up the products he already dreamed up. Leave him alone for a while to get it done and production up to speed. I'm more interested in the price and performance of those than hypotheticals. If you need a beta tester Paul, send it my way!

[ToneLux]

See Tinderbut... Even though your a good friend, other people that don't know you even think your ideas are, well...

Now, lets get back to great sounding stuff.

My first version of the new discrete op-amp is almost finished. It slews better than 10v/usec and the distortion is almost at the limit of my AP. .0012%. This will be nice, as I will be able to get all the tone out of my new transformer. All this with only 6 transistors. Damn...

[Tim Farrant]

Originally posted by ToneLux
My first version of the new discrete op-amp is almost finished. It slews better than 10v/usec and the distortion is almost at the limit of my AP. .0012%. This will be nice, as I will be able to get all the tone out of my new transformer. All this with only 6 transistors. Damn...

Hi Paul,

10V/uS is not particulary fast but the comment made me wonder what the slew rate of the API 2520 opamp actually is?

Thanks in advance
Tim.

[ToneLux]

Originally posted by The Buzz
Hi Paul,

10V/uS is not particulary fast but the comment made me wonder what the slew rate of the API 2520 opamp actually is?

Thanks in advance
Tim.

Actually, 10V/usec is very fast, and most don't even know what it means, and that it, for the most part, is pointless.

10v/usec means that it will begin rolling off the high frequencies at around 100KHz. It is not really distortion, it just begins to round off the upper frequencies. It also doesn't mean that everything just stops there either. It's where it begins. It shows up as distortion because it is rolled off, much like a tone control would. It is widely known that the 2520 is only 5v/usec. How about that. Now I guess all those records sound like crap. The real test for an op amp is what they call trasient intermodulation distortion. That is what effects the sound the most. That is what the op amp does to peaks. The 2520 is unusually LOW, as is this one. Additionally, using a 2:1 step up transformer doubles the slew rate.

The 990 is 12v/usec in one direction and 11.5 in the other. These are actual measurements. It has chokes on the diff pair to keep it stable.

Another test is where the first pole of the inner stages are. In most op amps, the open loop pole is in the area of 100 to 300 Hz. My amp is around 10KHz. What does that mean?

It means if you run the op amp without feedback, it will roll off at that frequency. It also means that if you run the op amp at hight gains, you have to make sure that the feedback cap is well within the maximum gain area that you will be using, like in a mic pre. If you don't get the cap right, the op amp will cross zero before the cap will and the op amp will oscillate at what ever that frequency is. I have been doing ALL of my tests WITHOUT a compensation cap, because it is so stable and at the 0 to 40 dB of gain ranges, it is so stable.

Also, do you know what the standard slew test is? Most don't.

AND, did anyone know that the famed 5534 op amp was internally tweeked so it would look better with the slew test? That's why is sounds like rolling be bes down a metal pipe.

So, as to being "not particularly fast" is a meaningless statement, since most of the older stuff was slower, which is what everyone tries to copy or emulate. I don't think the original 741 made it much past 20KHz. There are 100 things that effect the way things sound these days, slew rate is near the bottom.