Noob Amplifier question

[dax]

Can Anyone help me modify my amp to have better bass response
i am playing bass guitar through an amp designed for guitar???


Here is a schematic
http://us.f13.yahoofs.com/bc/43ec0dccm9bc8c2a8/bc/Mts+Schematic.pdf?BCSyVrEBkimpeW8M

thanks in advance

 

[amorris]

change your speaker setup. add a 15" to it.

 

[amorris]

cant get your schem. but does it have audio transformers? you could be outta luck if it does.

 

[PRR]

> i am playing bass guitar through an amp designed for guitar???

Bad Idea. Get a bass amp.

> Here is a schematic http://us.f13.yahoofs.com

yahoofs.com is not a public server. You may be able to see files on it because you have an account or cookie with Yahoo, but nobody else can.

But a Bass Amp is a very different beast than a Guitar Amp. Guitar can play through a bass amp: this is the roots of Heavy Metal. But a bass through a guitar amp is just lame, until you kill the speakers or amplifier with tones lower than they were made to handle.

 

[pstamler]

Well, now, that's a different story, and a fairly respectable-looking amplifier.
Assuming, this being bass, you'll mostly be playing through the clean channel, I think your project is not out of line. You'll probably want to increase the size of some coupling capacitors (at first glance, C2, C37 and C39 look like good candidates to start with) and cathode bypass caps. And you may decide to replace the tone stack with one designed more for bass instruments (but maybe not; I still love the sound of my Fender Deluxe Blackface with its stock tone stack and an external bass cab).

Enjoy!

Peace,
Paul

 

[PRR]

It's not about "cheesy". A good Guitar Amp is no joke. But it is extensively designed to work above the range of the bass. The Tenor does not try to compete with the Baritone. It's different work.

> Changing ... caps ... for better bass response or someting???

Electric bass needs guts.

If you ignore the gimicky "Lead" channel, the Carvin 3200's "Clean" channel appears to have plenty of bass response, even to 42Hz. I don't see any radical tone-shaping. There is a lot of treble boost available, but also enough treble cut.

The limit could be, as amorris says, the iron. Is the Output Transformer bigger than or smaller than the Power Transformer?

Have you tried the amp with a heavy-duty PA subwoofer? A hundred watts is a lot of bass guitar for a 15". We used 15" with 50Watt Ampeg B15s; 100 Watts may deserve an 18" or twin-15".

 

[Kit]

It all depends on your style of playing.

If what your after is classic "rock sound" you can most definitly get away with a 100w tube guitar amp. (4X12 enclosure is a must.)
Crank it.

 

[pstamler]

That's actually a respectable output transformer (Carvin probably sourced only one for guitar and bass amps).

Here's what's up with cap sizes. Capacitors are often used as coupling capacitors: a capacitor in series with the signal, with a resistor on the output side. This stops DC from passing, but lets the signal pass, above a particular frequency. That frequency is deternined by this formula:

f = 1 / (2 x pi x R X C)

where f is the cutoff frequency in Hz (the frequency at which response is down 3dB), R is in ohms and C is in farads, and pi is in your face ... er, well, you know what pi is.

C37 on the schematic is a good example. It's equal to .01µF, which is the same as 10^-8 farads. The following resistor is 1 megohm, or 10^6 ohms. Plugging the numbers into the formula, we get:

f = 1/ (2 x 3.14159 x 1,000,000 x 10^-8) = 15.9Hz.

That's a reasonable cutoff frequency for a guitar amp, but maybe you should extend it a bit for a bass. It's considered a good rule of thumb that you want response to extend to 1/10 the lowest frequency to be handled. In the case of a 4-string bass that's about 42 Hz.

You can turn the equation around to figure out what capacitor to use:

C = 1 / (2 x pi x f x R)

Same units; for a cutoff frequency of 4.2Hz,

C = 1 / (2 x 3.14159 x 4.2 x 1,000,000) = 3.79 x 10^-8. That's the same as .0379µF; the closest standard value would be .039µF.

The bypass capacitors on the cathodes of the tubes follow the same formula; do the arithmetic and see what their cutoff frequencies are -- oh, here's something that will help you:

f = 1,000,000 / (2 x pi x R x C)

In this version of the formula, f is still in Hz and R is still in ohms but C is now in µF, a much more manageable unit. And pi is still...

Note that all these formulas compute how deep the bass goes, not whether there's "more bass". Admittedly, that's a subtle distinction.

Peace,
Paul