Hi,

I'm thinking about building a small guitar amp from scratch (Preamp/Power Amp/Power Supply/Cabinet). What I'd like to do is build my own one, not doing one of those DIY projects found on the internet. What I'm looking for is a great learning experience and a usable project for home playing (great sound > output power). I'm not pretty sure what I'd like to do so I'm looking for some advice here first.

My goal would be a 15W practice guitar amp. I really prefer the warmth offered by a tube amp, but I'm a bit concerned about the availability of parts here in Canada (Quebec). Also, I never used tubes in any circuits before. I hear the 12AX7 and EL86 are great tubes to use in guitar amps. My current setup is more of a "metal" setup (Line6 solid-state with active pickups on my ESP KH). But the classic rock/blues sound is not so great on this rig at low volume. That's why I'm leaning towards a tube amp.

Can I obtain relatively good results with the aforementioned tubes? Should I go with a solid-state amp for a first project? What kind of driver should I use? Anyone had success stories on the board?

 

Hello,

On this page you will find the schematic of several guitar amps:
http://www.schematicheaven.com/index_HTML.htm

Greetings,
Bertus

 

A picture is worth a thousand words.

 

A picture is worth a thousand words.

Its true... And how many words does it take to describe how to run a wire through broken BX?

I hope thats a ground.

 

What are those big glass tubes??



I heard that they have a much warmer sound than silly solid state amplifiers.


What are they called again?

Dustbuster tubes?




I used to play guitar (about 7 years worth, a few bands and shows here and there) and i had a Marshall jcm900 SL-X tube amp. After using nothing but solid state fender amps until that point - i was just blown away by the tube sound - my band mate had a Peavey 5150 - heavenly as well.

enjoy the end result if you go through with it!


http://en.wikipedia.org/wiki/Peavey_5150_Amplifier
http://www.marshallamps.com/heritage/jcm900/jcm900_01.asp

 

retched

1) That's not part of a guitar amplifier.
2) That's not a wire hanging out of a piece of armour.
3) It's not there any more so I can't tell what it used to be.
4) Thank you for noticing all the hard work I did on that amp.

 

ok, ok, ok, I was just playing around with you. Sorry grump.

I had tried my hand at tube amp repair. Not an easy task. Very VERY beautiful RICH sounding amps.

 

OK. I'l forgive you.

 

awwwww

how cute!

 

Wow! Nice work Bychon. I guess I'll go with a tube amp finally, a pretty tempting experience. How about the availability of those tubes in Canada?

 

Oh look, I'm an inspiration!

I don't know about how to buy tubes in Canada. I got mine at www.tubesandmore alias Antique Electronic Supply in Arizona. I also got the Tolex, tube sockets, transformers, and knobs there.

 

Here's the wood part. You have to make a sled to go on the table saw to make the finger joints, or buy something commercial.

 

A tube amplifier sounds "rich" because it has poor high frequency response, poor low frequency response, a high output impedance that does not damp the resonances of a speaker and has high even-order distortion. Also it does not clip harshly when its volume is too high.

Years ago, my tube amplifier needed its tubes replaced every 3 months. Some groups replace the tubes for every performance.

I still have my first solid-state receiver that is 46 years old. It has been used every day and still works perfectly and sounds pretty good.

 

I built a tube amp for a musician, 13 years ago, and it's still being used every weekend with the original tubes that I put in it.

 

Thanks for the pictures. I'll jump in that project pretty soon and update this thread. I need to calculate how much money I can invest in this. Time is not a problem since I'm planning to do this in my spare times, no stress.

 

Time is a huge part of this, way more than the price of parts. You have to learn all the different skills that go into the finished product, from carpentry to Tolex, from sheet metal to tone controls. But isn't that most of why a person would do this?

ps, my biggest mistake was that I didn't know the metal corner protectors you can buy are only made for rounded corners. Probably a router with a 3/8ths round over bit. The rest of it was making up for lack of skills by being really meticulous. You don't know any short-cuts on your first try!

 

Tubes (or "thermionic valves" in the Queen's English) sound great in guitar amps, precisely because of all the various distortion mechanisms. I'll list as many as I can remember with my sleep-deprived head:

• The characteristic non-linearity of valves gives a slightly asymmetric response that is rich in pleasing lower-order even harmonics. Hard clipping tends to produce higher-order odd harmonics that can sound quite harsh.
• The output transformers have their own non-linearities, particularly when driven into saturation, also adding pleasing harmonics. Sometimes this effect was an happy accident, like in the Vox AC30 where it was under-specified to lower production costs.
• Carbon-rod resistors are also a little non-linear, particularly with a large voltage across them. They're also noisy, but it's worth using them in the anode bias line at least as that's where you'll get the best effect. Modern carbon rod resistors are now available, not quite as noisy and wildly inaccurate as the old ones, but still a bit non-linear. The newer ones aren't marketed at choob fanatics (their resurgence is due to their very high surge capabilities), but why not take advantage?
• Valves are also microphonic, as anyone who has ever tapped one can attest. There's an old guitarists lore that says a valve amp design built on tag-strip will sound superior to one built on a PCB, due to the magic electrical properties of the former. The reasoning is nonsense, but the observation is sound. Mount the valve sockets directly onto the chassis and you'll get a good acoustic coupling to the loudspeaker. PCB-mounted valve sockets will have a fair acoustic coupling strength, but it will be coloured with the sound of twanging fibreglass board.
• A flabby power supply also adds an extra load of distortion when cranked right up, so use a hollow-state rectifier circuit on the HT supply for this bonus effect. Also, it doesn't do to bang the HT straight in there before the main valves have warmed up, and valve rectifiers give a gentler wake-up call.

Don't forget the loudspeaker, which can add more tone colouring than the whole of the electronics. If you've got 15 W to play with, then may I recommend the Celestion Blue. Horribly expensive, but worth every penny as it sounds like nothing else, and it makes an enormous difference to the sound. Guitar speakers are designed to be over-driven (up to a point...) and the stiffer surround rolls and magnet saturation properties give lovely breakup modes at high volumes. The Blue is awesomely efficient, and it will be the loudest 15 W you ever heard in your life.

There's my braindump for the evening. For more, get these books by Morgan Jones. Lastly, if I ever come across a musician who discards their valves after one gig, I'll make them eat them. Twice, so help me. Five times forwards and then five times backwards if it's a late-60s NOS valve. That's either the symptom of insane decadence, or a valve that's been so over-biased it's running white hot.

Good luck with the project dsp_redux; do post your workings.

 

I am working on the same project myself. When you finish perhaps you would like to make your own pedals? Anyway, i made a low cost distortion pedal from this site and it seems decent. http://www.runoffgroove.com

I don't really like advertising for other peoples sites so just consider it advice from one musician to another...

I also made a little 1000ma portable guitar amp (ruby) from here based on the lm386. It works great with headphones and only costs about $5-10 to build. Reminds me of the old "rockman" amps that they used to sell.

As far as looking for tubes, if you search around on the internet you should have no problem finding what you need. I am ashamed to admit it but i have been forced to purchase quite a few components from ebay when not available through general sources such as mouser...

Anyway,
Best wishes on the tube amp!

 

I have 5 6v6's matched.. Mesa.

If you need a power tube. and want something good.

I would get a few off ebay cheap to play with in case you blow things up.

 

@Darren Holdstock: Thanks a lot for the input. I was actually looking into the Celestion Blue speaker driver and was wondering if it was any good. That clears out for something, so Celestion Blue it should be.

@oidium45: Since I have a Line6 spider and a floorboard, I guess I'll look for pedals only after the amp is built. I've made a simple mixer pedal which works pretty good (so my brother could jam with me on the same amp). Do you have any pictures of your portable guitar amp? Is it small enough so you get wear it on yourself while playing?

@retched: Do you have any datasheets/manual/curves (Plate current vs plate voltage vs grid voltage)?