modding a headphones guitar amp for bass

[Vince_b]

I would like to mod this amp to be able to use it with a bass:

http://www.jmkpcbs.com/JMK_PCBs/DIY_Projects_files/Headphone%20Amplifier.pdf


Any pointers of what I should try?

[RandomGlitch]

You could increase the 100nF cap on the input. Maybe double it ir more.   But mostly I think you need good headphones that can reproduce bass. Crappy headphines just distort.

[Mark Hammer]

C1...bigger.  C3...bigger.

[Vince_b]

C1...bigger.  C3...bigger.

And what about C5? Shouldn't it be increased too?

[deadastronaut]

i think thats what mark meant.....i would breadboard it first though, may need a bit more tweaking.

btw i'm working on a bass preamp at the mo..its really nice, makes the bass come alive, ive modded it for normal and warm type tonestack too..

just about to build it, if you play bass i  highly recommend it.

http://www.diystompboxes.com/smfforum/index.php?topic=101898.msg903972#msg903972

demo

http://www.diystompboxes.com/smfforum/index.php?topic=101898.msg903014#msg903014

[Vince_b]

i think thats what mark meant.....i would breadboard it first though, may need a bit more tweaking.

I will breadboard it of course, I just wanted to have some basic idea of what I should try first.

I watched your demo of the bass preamp, it sounds really good. But I don't play bass myself. My friend asked me to build her a 9v headphones amp so that she could play during the night without waking up everyone.

[PRR]

C5 R2 is already 0.16Hz. You sure don't need this bigger.

At max gain, C4 R13 is 8Hz which is more than good enough.

Taking worst-case low-low-Z headphones, C3 R7 and a few ohms is 31Hz at -3dB, 62Hz at -1dB. The bottom notes of bass are slightly shaved. However ALL bass *speakers* are falling at 50Hz. -3 at 31 is fine.

I say it is fine the way it is.

If you must fiddle, take C3 to 470 uFd.

R10 C2 offer 50dB of supply rejection; and your source impedance is surely under 100K (probably under 10K for lows) so R2 vs Source give another 40dB supply rejection. If 90dB is not enough, get a better supply.

For headphones over 50 ohms, I'd be inclined to take the supply higher. 12V, 18V. C1 must be rated higher than supply voltage (use 470uFd 35V; not expensive and looks good), the others must be rated well above half supply voltage (so 25V will be fine for all).

I really don't like the R13 C500K R12 network. Max gain is only 13, C500K must be a reverse-taper, and even then half of it is useless. Take C4 to 22uFd, R13 as 1K, short that pot, replace R12 with 100K audio-taper pot. Now gain runs from unity to 100, which will put soft strumming to pretty loud levels. (It won't shut-up completely, but neither did the original, and so what?)

[Vince_b]

Thanks for the suggestions and explanations Paul. I wil try them out as soon as I will be able to borrow a bass from someone.

[Vince_b]

I breadboarded this circuit today to try different components value. But Houston, we have a problem. The noise level is so high on the breadboard that I can barely hear the guitar signal coming through. I thought that I have messed something up but I rebreadborded it from scratch 2 times with the same result.
This circuit ain't noisy on a pcb though.