KVR Audio

Cuauhtli · Post by **Cuauhtli** » Thu Mar 21, 2013 5:38 am

I have this book (The Audiophile's Project Sourcebook by G. Randy Slone). Anyway, in some of his op-amp circuits (preamps) he uses a couple of capacitors to decouple each of the op-amps power supply connections. A 4.7uf (tantalum) cap in parallel with a 0.1uf (ceramic) cap connected from each of the op-amp's power connections to ground.

Other circuits use only one cap (0.1uf ceramic) for decoupling each of the op-amp's power connections.

Why the need for two caps? Is there a reason one is a tantalum and one ceramic or is it just about cost/availability?

Still have a few chapters before I get to the chapter dealing with frequency effects (which covers bypass and decoupling capacitors) in the electronics book I'm studying.... just getting impatient I guess.

earlevel · Post by **earlevel** » Thu Mar 21, 2013 6:11 am

Cuauhtli wrote: Why the need for two caps? Is there a reason one is a tantalum and one ceramic or is it just about cost/availability?

Two caps to handle high and low frequency power supply noise. Tantalum because the higher-value cap would be quite large otherwise.

Cuauhtli · Post by **Cuauhtli** » Sat Mar 23, 2013 5:27 am

Thanks. I thought you only had to worry about the lowest frequency (from which the cap would act as a bypass cap) and the higher frequencies would also be bypassed.

earlevel · Post by **earlevel** » Sat Mar 23, 2013 7:53 am

Cuauhtli wrote:Thanks. I thought you only had to worry about the lowest frequency (from which the cap would act as a bypass cap) and the higher frequencies would also be bypassed.

In a perfect world, that would be true. But in a perfect world we wouldn't need two- and three-way speakers—a single big one would be fine.

Capacitors do have internal resistance and inductance, and that may be enough on its own, but also I think that electrolytic capacitors in general, of which tantalum is one type, have poor high-frequency characteristics. Tradeoff for density, I suppose. Maybe a giant ceramic cap would do the trick in a lot of cases, but would be impractical due to size. In any case, I've been accustom to the practice of using at least two different sizes since I was building synth circuits as a kid decades ago.

xtp · Post by **xtp** » Fri Mar 29, 2013 4:15 pm

Cuauhtli wrote:Anyway, in some of his op-amp circuits (preamps)

Hi,

A little off topic,

if you are looking into building preamps when you have some spare time try googling triode emulation, jfet

Jfets offer an alternative sound to op-amp preamp circuits.

The j201 is a popular audio jfet

Cuauhtli · Post by **Cuauhtli** » Sat Mar 30, 2013 6:24 am

The preamp I built was my way of avoiding buying a decent preamp. I must say it sounds a lot better than the cheap commercial preamps I have. I'd need to try a good one to compare but I like it.

Anyway, I have been thinking about Jfets and Mosfets for preamp and distortion circuits. Still want to experiment with the plate starved tube distortion pedal design I posted about previously though.

jonnyG · Post by **jonnyG** » Sun Mar 31, 2013 3:29 pm

Any publication with the word "Audiophile" in the title should be taken with a pinch of salt imo.

Here's an interesting read on capacitor characterics:

http://sound.westhost.com/articles/capacitors.htm

It also has proper graphs and stuff, instead of the usual audiophile skewed opinion and flawed listening tests.

A 4u7 tantalum to locally decouple each opamp in addition to the usual 100n does seem a little like overkill (unless those opamps are sinking some pretty heavy currents), but at least it will do no harm or cost a king's ransom (unlike a lot of audiophile snake oil / fallacy). Whether it makes a difference to a sensible circuit on a properly designed pcb is impossible to say without sticking it on the test rig. Non double blind listening tests don't count!

Cuauhtli · Post by **Cuauhtli** » Fri Apr 05, 2013 3:44 pm

Just so you know, Slone isn't a snake oil salesman as far as I can tell. He doesn't present any opinions on the merits of the materials used to create components (as in silver mica caps vs ceramic caps, carbon composite resistors vs carbon film resistors, etc.). the caps used to decouple the power supply are the only place he gives specific types for caps, or resistors, which is why I asked why the use of tantalum caps.

Just thought I should clear that up. His audiophile power-amp cookbook is cool too.

Since you brought it up, is there any difference in the usage(? use? using?) of different types of resistors and caps? I have a Guitar & Bass Classics magazine (the one titled: DIY Amps & Pedals Bible) and they conclude that they do make a difference in one of their projects (overdrive pedal). Looking at the prices of some of those caps I doubt I'll experiment and try to find out any time soon, if ever.

Question about decoupling capacitors