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Old 19th November 2009, 03:15 AM   #1
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Default Guitar amp on the cheap???

Hello again,
My college student brother in law has taken an interest in my hobby and wants me to build him a guitar amp (cabinet/speaker/tube head).

I was wondering if there were any good projects somebody might point me to. I can do all of the cabinetry work myself. I want to try to keep this project around $300 if possible. Any good suggestions? I have built several HIFI tube amps but this will be my first guitar amp. I have seen the speakers for these applications at various places like Partsexpress.com and similar sources but have never really paid much attention to them. I imagine there is a bit of matching of the speaker with the circuit that needs to be observed.

This may sound stupid but does a guitar amp actually have all of the gain in the circuit to take the signal off the cable from the pickups on the guitar? Or is the signal somehow amplified between the pickups and the amp itself?

I haven't even looked at a circuit for a guitar amp, not once that I know of. I wonder if this will be a big departure from my HiFi builds?

Thanks alot!
Jeff
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Old 19th November 2009, 03:37 AM   #2
chrish is offline chrish  Australia
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I have just finished my first guitar amp build for my son (see post "never done this before - guitar amp"). I found the AX84 site very helpful. Not only do they have the schematics, but also .pdf layouts for the turret boards, wiring and chassis. I am sure that you will find the site useful AX84.com - The Cooperative Tube Guitar Amp Project

I found that although the circuits are a little different (distortion is a wanted effect!), the basic circuit building blocks are similar and the techniques you used in a hi-fi amp to reduce noise and hum are all still valid.

Have fun!

Chris
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Old 19th November 2009, 03:41 AM   #3
TheGimp is offline TheGimp  United States
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I've rebuilt a couple of guitar amps and am on my third. They do indeed perform all the amplification from the inductive (magnetic) pickup to the output speaker.

Best to look at Schematic Heaven

Schematic Heaven. Where All Good Amp & Effect Designs Await Resurrection...

or some such to see what was done in the past by Fender, Marshall, etc as a starting point.

What power range are you looking at?

One big price advantage for a guitar amp vs audiophile is the guitar amp does not need the bandwidth of the audiophile amp and the output transformer requirements are much more relaxed, resulting in lower cost transformers.

Personally, I'd start with a late 60s through 70s Fender design for a classic amp.

Transformers, speakers, etc are available from AES (Antique Electronic Supply) and others:

https://secure.tubesandmore.com/

Good luck.
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Old 19th November 2009, 03:54 AM   #4
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I just found a couple of kits at Triode electronics HERE: Guitar Amp Parts
Any thoughts about these kits? I can buy one with all the tubes (the cheapest "Blackface") for about $215. I figure another 40-50 bucks for the speaker and I am golden. I was wondering though, if I went with this cheapest amp, what would be a good cheap speaker to go with it. I have no real idea of what the power output of these amps are but I figure in a push pull circuit with a couple of 6V6's it probably gets in the range of 10-20 watts. They also have a few Jensen speakers on the site at Triode and the ceramic modles are around 50 bucks. Would one use a 8, 10, or 12" speaker for an amp of this caliber?
Jeff
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Old 19th November 2009, 04:44 AM   #5
chrish is offline chrish  Australia
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I went for the "modest" budget approach and used a Celestion Rocket 50 12" speaker for my 20W 6V6 amp, $55 at AES.

I am not a player though, so some others may have some good specific advice.
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Old 19th November 2009, 09:32 AM   #6
Enzo is offline Enzo  United States
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There are all kinds of guitar amps you can build. The above suggestions are good. SChematic Heaven has a huge library of schematics for commercial amps. A early Fender Deluxe is a very popular project - look for model 5E3 in particular.

You can find an old Bogen "PA" amplifier for cheap, and rewire the innards to the same circuit as some Fender and have a nice amp cheap. This is done all the time. Nice thing is, the heater wiring and stuff can stay in place. And you already have the transformers and a chassis, even if it doesn't look guitar-ampish. This sort of project can be very cheap to build.

Kits are great, they usually have everything you need. None of this get all your stuff and find yourself smacking your forhead because you reaslize you forgot a fuse holder or a power cord, or tube shields, whatever. it is all thought of and there. And having a nice finished chassis in a kit saves you the trouble of making one.

One thing to keep in mind with electric guitar amplifiers, particularly if you come from hifi world, is that the guitar amplifier is part of the instrument, it is a fundamental producer of sound, NOT a RE-producer. You want to hear what an electric guitar sounds like? Plug it into the aux input of your home stereo. Kinda dull, thin, and lifeless. The whole point of a guitar amp is that it adds some character of its own to the sound. They are anything but flat. Most guitar speakers roll off in the 3kHz-5kHz range. You will hear guys say I play a Marshall or I play a Fender. They sound different and suit different tastes. They work the same as hifi amps, but the design parameters are different.

Looking at the Triode Electronics kits, the Champ kits are single ended. Champs are nice little amps, but are pretty much "practice amps." Your bud would probably prefer a little push pull amp like the "Tweed 5E3." Note that the kits ther do not include a chassis. You can build your own chassis of course, and if you are making a separate head and speaker cab, then no problem. A "combo" amp is a combination amp and speaker - very common form. There you need to make sure the chassis can fit and be mounted in the cabinet.

Compare to the kits at Ted Weber's site:
https://taweber.powweb.com/store/kits_50a.htm#5E3H

scroll down to "5E3 Head" Costs a lot more, but includes the cabinet and chassis. It may be confusing, but you can check off things you don;t want and save money, for example no cabinet reduces the price $75 in this example.

These are complete kits.


Whatever you do, a 5E3 or something similar is a great little amp. It wants a 10" or 12", or hey, go nuts and make it a 2 x 10". I like the 2x10 sound. And you can decide if you want a closed back or open back speaker cab. Each has its place and fans.

AX84 is a cool site. I don;t recall if they have any kits sold there, but there may be some good links.

ANd another very supportive forum aimed at guitar amps is
Music Electronics Forum


If you are experienced, you could probably build one from a schematic, but if you do I suggest finding some transformers from one of the guitar amp part sellers.
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Old 19th November 2009, 04:14 PM   #7
m6tt is offline m6tt  United States
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Like Enzo said, rebuilding an old Bogen etc. is a great way to go, since these PAs were closer to guitar amps in some ways than hifi (they didn't often try for 20hz as the -3db, that's for sure). Plus they come with fun parts sometimes.

$300 is good for a build if you already have a chassis, but cabinets & custom "guitar amp" chassis get expensive fast. Use something close to a classic fender or marshall tonestack for sure, most guitar players are familiar with this. Otherwise just use a high cut and set the low frequency -3db with the coupling caps, opt and feedback.

A guitar amp is in many ways a malfunctioning hifi (and vice versa! ). Just build a nice simple power stage and preamp from memory and stick a tone stack in there. Use a high resistance power supply in the preamp and screens. If it's too clean, turn the volume up. A 6SN7 or russian equivalent makes a *MEAN* push-pull reverb driver.

Cheers!
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Old 19th November 2009, 11:37 PM   #8
jjman is offline jjman  United States
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I agree that a kit is the way to go. The budget sounds tight, and not adequate if you want reverb. Partsexpress has way too many speakers to choose from IMHO and there are now way to many brands marketed for guitar amp use. 10 years ago you could basically buy a Weber or a Celestion. Now you've got many more. Warehousespeakers.com speakers get very good reviews by budget minded guitar guys and the 10" is $41.00.
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