Headphone daughter board for ruby/noisy crickett

[Locrian99]

Hey,

So I've already built one ruby which once I got to vero and realized I had a 25k instead of 10k volume pot on it works great for what it is.   I'm building a second one.   The first one I used a daughter board for the headphone out.   As seen here...




I was putting together the second one and it dawned on me that the resistor and cap seem somewhat redundant to what is already in the ruby schematic.  Here...






Seems like the 10r is taking the output to ground via the 47 nf cap and the output cap is there for the speaker out with the 220uf cap.   Am I missing something here our should I just be able to run the speaker out straight to the tip of my headphone jack and then connect that to the sleeve. 

[PRR]

> the 10r is taking the output to ground via the 47 nf cap

That is needed for '386 stability. Otherwise it may sing supersonic and screw-up the sound. Don't omit that. Don't ask "why", this is fairly advanced feedback theory.

The 220uFd is to block the 4.5V of DC at the '386 output, which would silently burn-up your headphone (maybe your speaker, though the '386 is a lame speaker-burner, it would just distort bad).

[Locrian99]

> the 10r is taking the output to ground via the 47 nf cap

That is needed for '386 stability. Otherwise it may sing supersonic and screw-up the sound. Don't omit that. Don't ask "why", this is fairly advanced feedback theory.

The 220uFd is to block the 4.5V of DC at the '386 output, which would silently burn-up your headphone (maybe your speaker, though the '386 is a lame speaker-burner, it would just distort bad).

Why then would I  need the 10r on the headphone daughterboard (which is from a noisy crickett layout but is as I'm sure you know essentially the same thing.   There is a 47u in there as well.   I just thought it seemed redundant to need the headphone daughter board. 

[amptramp]

In answer to the OP's question, I don't think the items on the daughterboard are a repeat of the Zobel network (R3-C3).  The daughterboard connects tip to ring so you get sound out of both sides of the headphone but the 47 µF cap across the headphones and the 10 ohm to ground from the sleeve doesn't look right.  I don't see why the headphone daughterboard is necessary at all.

PRR is right about the Zobel network being necessary.  If you look at the impedance of a speaker, it starts low at the lowest frequency, has a peak at a low frequency (usually in the 70 Hz range), goes low to about 300 Hz than starts rising after that.  The rising impedance above 300 Hz means the load is inductive which is reasonable as it is a coil of wire wound in the gap of magnetic material.  The Zobel network is intended to be in parallel with that and present a falling impedance as the frequency rises so the feedback network doesn't have to contend with an inductive phase shift in the load.  Leaving the Zobel network out would cause oscillation, probably above sonic frequencies.

[Locrian99]

Awesome thank you both for the info.     I had no doubt about the necessity of the "zobel network".  And thank you for the name and information.    So I ended up making it without the daighterboard and it worked fine through my 32 ohm headphones however when I plugged in my 4 ohm little jbl blue tooth speaker then (used aux jack) it distorted horribly.   It doesn't do this on the one I made with.    So I made it with and it doesn't distort.   Should note this is a 4 ohm speaker, works great for its purpose of a small test amp for the bench. 

[GibsonGM]

Hey did anyone ever figure out what the R-C on the daughter board is supposed to do??

[duck_arse]

I was thinking it was shorting safety for when a mono plug was inserted into a stero jack, but the way it's connected is just whack.