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Old 12th May 2013, 11:34 AM   #1
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Default HI-FI amplifier for bass guitar

Hello everyone!

I plan to make an amplifier for my bass guitar (Rickenbacker 4001-1971) 100 to 150 W RMS but I have not found anything suitable yet.
I currently have the woofer and plans for a preamp.
My question is simple:
An amplifier dedicated to HI-FI can he agree or should it be specially designed.
My preference would be to desc mosfet, hexfet, etc ...

Thank you!
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Old 12th May 2013, 02:51 PM   #2
JMFahey is offline JMFahey  Argentina
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You can use a Hi Fi designed power amplifier for Bass; the main difference with Home use lies not in sound but in heavy duty use.

A Home amplifier may have 50 or 500W, it's the same, it will normally be used at, say, 5W , or "the missus" or neighbours complain, while if you are playing close to a drummer you will *continuously* be using it at 60 to 100W (or more) just to match his acoustic volume.
Drummers play *loud*.
So you'll need an adequate transformer because you *will* be pulling current from it , you'll need good heatsinking, either outside or inside a cabinet with air vents (or a fan) and good short protection, because sh*t happens often.
Instrument amps get moved all the time, connected and disconnected, plugs and jacks are horrible connectors but unfortunately the standard, people steps or trips on them often, etc.
Quite a few Hi Fi amplifier designs offered here, while excellent sounding, have NO, repeat NO short protection
Nor offer fans, thermal protection, not even a humble bimetallic switch attached to the heatsink .
Fine at Home, maybe also in a *fixed* installation PA/Theater sound/background Music/Church/etc.) but not onstage.

Which, believe it or not, usually are dark, confusing, and sometimes even contain a couple of drunk/stoned people
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Old 12th May 2013, 02:59 PM   #3
tinitus is offline tinitus  Europe
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I would say, for use at home, ok, fine...but with a band, connected to other gear etc, I wouldnt
but you can use cheap PA amp
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Old 12th May 2013, 03:02 PM   #4
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JMFahey thank you for this answer!

Having already played in a band there in a long time, I know all the issues raised.
I do not intend to replay group, I'm too old!
I thought about 100 W because I have a speaker that can hold twice that power.
For some time I want to emphasize my old bass guitar and make it sound just for fun.
I've sampled the bass and big sound bank is available free on the internet.

Regards!
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Old 12th May 2013, 03:06 PM   #5
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I think most make a amplifier mosfets or hexfets because I have a lot of these components in stock.

Tinitus thank you!
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Old 12th May 2013, 03:09 PM   #6
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Guitar amplifiers generally differ from Hi-Fi amps in a number of ways. Of course you can use a Hi-Fi amplifier for guitar use but compare what you will get using the following ideas:-

(This list is not finite and many guys will probably add to it).

1. Stage amps are generally built to be far more robust than home amps.

2. Guitar amps are often built to deliberately add a "flavour" to their sound.

3. Hi-Fi amps are aiming at ZERO distortion, many guitar amps are quite happy with a small amount of distortion.

4. Cost and weight. Not always true I know.

There is nothing to stop you building a Hi-Fi design in a more robust fashion.

5. A guitar has a particular output level which will not match naturally to a Hi-Fi amplifiers input specs.

So YES, with a small pre-amplifier to match the guitar with the amplifier, of course you can use your Hi-Fi.

6. Stage amps are generally Class B or higher to give them more "Bang per Buck". Hi-Fi amps are generally lower power and better quality.

7. Stage amps are generally more robust, both electronically and mechanically. You can drop a stage amp and it probably wont suffer too much. Drop your stereo and it probably wont work afterwards.

Last edited by KatieandDad; 12th May 2013 at 03:16 PM.
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Old 12th May 2013, 04:58 PM   #7
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5 bis (c'était bien vous qui utilisé une programme de traduction, non?) En plus qu'un préampli HiFi n'est pas réglé pour le niveau d'une instrument (une basse va même un peu fort) il a normalement un impedance d'entrée trop bas (autour de 47k, quand pour une basse j'utilise au moins 1 meg

5. continued (It was you that used a translation program, no?) Not only is the input sensitivity of a Hi-Fi amp not necessarily adapted to instrument level, their input impedance is low, generally around 47kΩ, while with a bass I go for at least 1MΩ

8. Les controls de tonalitie (egaliseurs) d'un ampli hifi sonr assez peu puissant, fait pour compenser les deséquilibres mineurs d'un haut parleur dans une pièce, pendant que dans un ampli pour instrument ils sont beaucoup plus puissant, pour modeller un son.

8. The tone controls (equaliser) for a home HiFi are relatively subtle, for correcting minor imbalances betwee treble an bass for a loudspeaker in a room. Tone controls on an instrument are far more brutal and wider range, as you are building your sound.
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Old 12th May 2013, 05:20 PM   #8
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Quote:
Originally Posted by chrispenycate View Post
(It was you that used a translation program, no?).
It's me, won!

In fact it is especially on the amplification part that I asked myself.
For the preamp section I will point me to this arrangement:

Bass Preamp

Thank you KatieandDad & chrispenycate!
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Old 12th May 2013, 09:25 PM   #9
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Okay, you want 100 W and to use mosfets. Search on google diyaudio.com:"Ampeg SVT 3 schematic" and find the repair thread on instruments and amps forum. The schematic diagram is there. You see the Ampeg logo on stacks behind guitar bands on stage on all sorts of television shows. Setting the bias current is allegedly tricky; read all the tips the experienced repairmen say about setting it up after final test.
You want something a little smaller (100w) and safer look up the MJR7 from Michael Renardson.On diyaudio solid state thread I believe, in a thread on output capacitors. It has an output capacitor, which helps keeps shorted speaker plugs from blowing your output transistors and shorted output transistors from blowing your speaker. The MJR7 requires lateral MOSFETS, but maybe it would work with hexfets. It is a simple topology. Huge heatsinks and a fan, nutrix speaker connectors instead of 1/4 phone jacks, It could morph into a guitar amp.
For power supplies you can either buy a toroid transformer from a European source, or try a switching >400w quad voltage power supply from connexelectronic in the diyaudio vendor threads below. If you use a switching supply don't forget to put it in a separate steel box with hash filters (chokes) in and out to prevent RF (radio) leaking into the analog circuits. That is the way Peavey built my CS800s, the power supply in a separate box. (but it is a bipolar transistor amp.)
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Last edited by indianajo; 12th May 2013 at 09:32 PM.
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Old 13th May 2013, 05:23 PM   #10
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Well, that bass preamp is designed like an input strip to a console; equaliser in/out switch (on an instrument amplifier? I might have liked an alternative equaliser, to be set up for different numbers) the equaliser itself, modified Baxandall, typical HiFi, input sensitivity (unless you're going to be driving it into distortion) and overload lights… (give them points for the tuner out, though). Being me, I'd put an insert break point and a balanced, ground switchable line out.

With a Rickenbacker you're probably not going to need that ultra high switch (which only works at low volumes anyway; how strange).

While HiFi amps do not generally have to sustain power levels like instrument amps, PA amps or studio monitor amps, they should be able to. If their power supplies sag, or their heat sinks are underrated so they catch fire when you're listening to the 1812 while the neighbour passes the vacuum cleaner they're badly designed. More problematic is that they're not built to be transported all the time; resistors crack off, screws shake loose and rattle around inside, fuses lose contact, and this you can't really criticise them about; even though I might do exactly that when remounting them. Mind you, there have some pretty poorly built guitar amps, too, and some which, when run flat out for any length of time you could cook your hamburger on…
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