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Andrew Cockburn
post Aug 14 2007, 07:49 AM
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Hi All,

Some of you will probably have seen my posts pestering MickeM and Tonymirro endlessly about the finer points of Amplifier knowledge and terminology. Yes, I am on a quest for tube tone - I have been convinced that there is more than Line 6 and I am setting out to find it.

I was pondering Carvin and Bogner, Marshall and Vox when I saw this post on the forum - AdamB put up a picture of a tube Amp he had made ... then it hit me, why couldn't I do the same? (Thanks for the inspiration Adam, and your Amp looks incredibly cool!).

So with that goal in mind, I am going to build an amp, maybe several, until I get the sound I want. I have a lot of experience in electronics (built all sorts of gadgets as a kid) but I have absolutely no experience with tubes and tube circuits, althouthg I do understand the physics of them.

Research

I have been looking around the net and have found a lot of websites that sell kits, but I wanted a bit more than that - I wanted to understand how it all worked and maybe tweak things a little to get the sound I have in my head. Adam pointed me to 18watt.com - they have a number of projects on the go, their first design was an 18 watt arshall like tube amp. I had a look around but found the website a little hard to navigate, didn't really want a Marshall sound and was generally uninspired by it all. After some more searching, I happened upon http://AX84.com. A really cool website with a very active community. Over the last 10 years they have designed a prototype tube amp (the P1), along with many variants, and are now on a grander work of prividing a library of reference designs consisting of Pre and Power amps you can mix and match. I liked the site and decided to build one of their simple designs - the simplest have just a couple of tubes and a few tens of components, but building a tube circuit can be tricky and I wanted an easy place to start.

The Amp For Me

Part of what I wanted was to explore the different sounds out there. I have zero tube amp experience. None, NADA. I don't know Marshall Brown from HiGain from Vintage from a Vox - so this is a huge learning curve for me. I have had some good advice from Mike and Tony and know that:

1) Tube Amps are loud
2) they have to be played fairly hard to get all of the tube benefits.

A 35 watt amp with an efficient speaker at 10 feet can rival a jet plane landing for decibels, so something that you can play high enough to get the right sound yet record and practice with needs to be pretty small indeed. The AX84 P1 is a 5 watt design based on a 12ax7 double triode for the preamp and an EL84 for the power amp stage. I loooked at it initially, but although it was simple, it was basically a crunch type of amp, and I am looking for something higher gain, although not monstrously high.

The P1 has a couple of variants, the Extreme, and the High Octane. High Octane is a more complex build but has an EL34 or 6V6 power tube, a 3 stage preamp with cathode follower which makes it a high gain amp. The Extreme still only has 2 preamp stages like the P1 but does benefit from an EL34 or 6V6 power tube. This was appealing as I like the voicing of an EL34 based amp but would also like to experiment with 6V6 - normally hard to do as to exchange tubes you need to re-bias which needs knowledge of the workings of the circuits. The Extreme also keeps the simplicity of the P1, but can be upgraded to be more like the Hi Octane if I need more gain.

So, my choice was made, and I ordered the parts this weekend. I got a kit and a pre-drilled chassis, since my metalwork is dire. I also upgraded to a better output transformer and a variable bias option so I can easily swap power tubes. It has cost me around $300 so far, and counting ...

The Speaker

What little research I did on the internet seemed to point to the Celestion Alnico Blue speaker being the holy grail - they were used extensively in Vox amps for a while where they gained their reputation. Not cheap at $250 a pop, but I am doing this to get tone, not necessarily to save money so it seemed worth it.

Other Bits and Pieces

I'll need something to put all of this in, and I am looking into building a combo cabinet - unfortunately my woodworking skills also totally suck, but maybe this is a chance to learn some other stuff and do it right, I'll think about that some more. I could get a nice tweed style combo cab ready made for about $300 - could probably build it for 75 - 100. Still thinking about this.

Some Links

AX84.com

Schematics for the P1 Extreme

A couple of soundclips, here and here (next sound clips will be from the one I built!)

That's the end of my first update - if there is interest I'll keep the story running smile.gif

This post has been edited by Andrew Cockburn: Sep 25 2007, 08:56 AM


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shredmandan
post Aug 14 2007, 08:26 AM
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Looks like that would be a fun experiment to do Andrew. smile.gif Have you decided which one you would like to build?If you think of it a tube amp for $200.00 US isnt bad at all,even if the speaker is weak you can always just buy a new one.Let us know what you decide and how it goes if you order one.


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Saoirse O'Shea
post Aug 14 2007, 08:52 AM
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Well I don't regard it as pestering Andrew - more great banter biggrin.gif .

One bit quickly - (I'll try to come back to you about your Q regarding speakers tomorrow - just back from a 12 hour stint at the beach and so am a bit knackered) - beware the quality of components.

It's possibly a bit simplistic but if you use cheap grade components you will build noise into your circuit however good the paper design. Not just for the tubes but for all of it. You might also want to seriously think about separating out and isolating the pre and power sections - there's years wortth of argument in hifi that if you don't you will build residual noise (for want of a better description) into the amp/s. Further, particularly for a hand built amp - good soldering is important. I'm rubbish at soldering and would advocate that anyone who has never soldered/is out of practice does a few dummy circuits before letting themselves loose on expensive parts wink.gif .

Apart from 18amp.com might also be worth looking at Torres and - more widely for a really good in-depth view on amp tone.

Cheers,
Tony

btw - really looking forward to following your progress on this thread biggrin.gif . Best of luck.


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Andrew Cockburn
post Aug 14 2007, 08:55 AM
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QUOTE (shredmandan @ Aug 14 2007, 03:26 AM) *
Looks like that would be a fun experiment to do Andrew. smile.gif Have you decided which one you would like to build?If you think of it a tube amp for $200.00 US isnt bad at all,even if the speaker is weak you can always just buy a new one.Let us know what you decide and how it goes if you order one.


Hi Shredman - the post escaped before I finished it - some more details in there now smile.gif

Being able to mix match and upgrade is a big part of the appeal to this, you are right!


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The Uncreator
post Aug 14 2007, 09:00 AM
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Great, maybe ill build my own amp someday to smile.gif

Cant wait to see how your quest goes Sir Cockburn!!


















Thast right, i said quest, Big Whoop, wanna fight about it?

/End family guy reference

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Andrew Cockburn
post Aug 14 2007, 09:08 AM
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QUOTE (tonymiro @ Aug 14 2007, 03:52 AM) *
It's possibly a bit simplistic but if you use cheap grade components you will build noise into your circuit however good the paper design. Not just for the tubes but for all of it.


Yeah, I agree. I was going to source it all myself and get good quality stuff, but then I noticed that the guy that rund AX84.com also sells kits for some of the amps - he basically puts in a kit what he would use to build it himself, so I am pretty comfortable about that aspect of it, a guy called Chris Hurley - we emailed back and forth several times and he helped me out on the AX84 forum before I bought the kit, very helpful guy.

QUOTE (tonymiro @ Aug 14 2007, 03:52 AM) *
You might also want to seriously think about separating out and isolating the pre and power sections - there's years wortth of argument in hifi that if you don't you will build residual noise (for want of a better description) into the amp/s. Further, particularly for a hand built amp - good soldering is important. I'm rubbish at soldering and would advocate that anyone who has never soldered/is out of practice does a few dummy circuits before letting themselves loose on expensive parts wink.gif .


I'll think about the preamp power amp thing for sure- I think the recomended construction is all on one board, but it wouldn;t be hard to separate it out.

Although I am useless at metalwork and woodwork, my soldering is fortunately pretty competent, so that is the piece that worries me the least, but thanks for the warning smile.gif

QUOTE (tonymiro @ Aug 14 2007, 03:52 AM) *
Apart from 18amp.com might also be worth looking at Torres and - more widely for a really good in-depth view on amp tone.


Thanks - good info there!



QUOTE (The Uncreator @ Aug 14 2007, 04:00 AM) *
Cant wait to see how your quest goes Sir Cockburn!!
Thast right, i said quest, Big Whoop, wanna fight about it?


Nope, not me! In fact I think its a great idea to dignify this activity with the epithet of Quest, I thank you!

All of which leads to the obvious question, what do I call my amp when it is done? Its only 5 watss so it doesn't really deserve a name of power, maybe I should call it "The Fart Box" or similar, and save the names of power for my ultimate amp, yea, I speak only of the amp that will come after this, the one and only, the all playing all distorting .... phew, got carried away a bit there, sorry ...


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shredmandan
post Aug 14 2007, 09:29 AM
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I agree with what some of you have said above.There is alot to take into consideration.Ofcorse soildering is VERY important i have found that out when installing a humbucker in my guitar.I kept wondering why it had such a weak sound and finally found out i had just did a bad soilder,im not very good either at it but it;s something you just have to practice to master.

As for the parts same deal they will make a huge difference pending on what you use.If i was the one buying an amp to make i would first look up all the parts needed to build and research them all.Find out any detail and difference in quality i could see.

One thing you need to make sure the box amp is built in is very good quality and is sealed very well.All the other things (parts) you can replace but if the box isn't good your stuck with nothing to build in. sad.gif I would be allover Ebay right now looking at prices for parts laugh.gif .I am an Ebay junkie and have found all my stuf on there cheaper than any store.I would think it would be a better place to buy your tubes and upgrade parts.


You have done this once before Andrew smile.gif so im sure you learned afew things since then.Just do alot of research that way you built a amp that you will always be satisfied with and remember the cheapest route isnt always the best but,there are deals to be found especially in bulk and used buys.

Good Luck Keep us posted biggrin.gif


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JVM
post Aug 14 2007, 10:33 AM
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Very interested andrew, I'm still going to be building my guitar, so maybe I'll do an amp as well 8) Keep us posted.


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MickeM
post Aug 14 2007, 04:33 PM
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QUOTE (Andrew Cockburn @ Aug 14 2007, 08:49 AM) *
I am going to build an amp

laugh.gif that's so funny because I've been discussing with another amp kit guy since before the summer, then he went for vacation and returned yesterday and I placed the order.

It will ship from abroad so it will take some time before I get it I suspect.

Mine is "smaller", it's 1/2 W with a British flavor mod and I will make it a combo. The speaker will be a Vox-kind 12" Cheramic.

I will see how your blog works out Andrew, I may open a thread aswell about my build or post a "how to" afterwards. Only hope it will work or it will be a "how not to" laugh.gif

I'll come back with all the details on which kit and speaker in a few weeks when I get started biggrin.gif


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Andrew Cockburn
post Aug 14 2007, 06:52 PM
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QUOTE (MickeM @ Aug 14 2007, 11:33 AM) *
laugh.gif that's so funny because I've been discussing with another amp kit guy since before the summer, then he went for vacation and returned yesterday and I placed the order.


Cool! We might have to Pester Kris for an Amp building forum for the three of us smile.gif


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Smikey2006
post Aug 14 2007, 10:43 PM
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Ahh id love to do this smile.gif I've always wanted to just build all my own gear but it sounded too time consuming and expensive smile.gif. Let me know how long this whole indever takes smile.gif i might wanna try it someday.


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Hardtail
post Aug 16 2007, 12:53 PM
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Andrew, sounds like your going to have a lot of fun! Lemme lend some advice:

- The maximum plate dissipation of an EL84 is 12 watts.

- The maximum plate dissipation of an EL34 is 25 watts.

- The maximum plate dissipation of an 6V6 and 6L6 is about 30 watts.

The above information will come into play later.

Tone vs. Gain

ALOT of people confuse gain with tone. To make things quick and simple I will explain it this way. Gain comes from your Preamp tubes. Tone comes from your power tubes. The flavor of your tone is altered by everything from your guitar, amp circuitry, effects, etc. A 12AX7 based preamp breaks up (or saturates as the pro's call it) exactly the same in every amp. Your unique tone will come from the power tubes and circuitry.

What does this all mean? This means if you want a tone that is unique and saturates smoothly you will want to drive your power amps into saturation (and not ride the gain nob like a noob biggrin.gif ). Find someone with a low wattage (5 to 15 watts) tube amp and leave the "Gain" relatively low and crank the volume to 10. You will most likely hear a distortion so sweet and butter smooth you'd think you were in tone heaven.

SRV did this on the clean channel of his Fender Twin Reverb by cranking the volume insanely loud.

SO... coming back to plate dissipation in power tubes. If you don't drive the wattage into the power tube hard enough it won't saturate correctly and all your distortion will come from the preamp tubes. In that case you might as well just play a solid state amp with a decent preamp section.

Most power tubes don't saturate well until you reach at least 70% max plate dissipation. So I would think in my humble opinion that a 5 watt EL34 based amp won't give you that unique tone you may be looking for because you're hardly pushing the power tube at all. Just some food for thought.

Example Amp design calculations:

Fender Blues junior (rated 15 watts) - 2 EL84 - 12 watts x 2 = 24 watts - 24 watts * .70 = 16.8 watts

Fender Hot Rod Deluxe (rated 40 watts) - 2 6L6 - 30 watts x 2 = 60 watts - 60 watts * .70 = 42 watts

Marshall TSL 100 (rated 100 watts) - 4 EL34 - 25 watts x 4 = 100 watts - 100 watts * .70 = 70 watts

The TSL100 is biased lower for the EL34's to work but is designed to move 100 watts because you can always swap up to 6V6's with a professional rebias.

I could go on but I think you see what I am saying. If you want to run a single EL34 or 6V6 I'd plan for more than 5 watts. Cheers and GOOD Luck! I can't wait to see the finished product! biggrin.gif

- Hardtail


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post Aug 16 2007, 12:59 PM
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QUOTE (Smikey2006 @ Aug 14 2007, 03:43 PM) *
Ahh id love to do this smile.gif I've always wanted to just build all my own gear but it sounded too time consuming and expensive smile.gif. Let me know how long this whole indever takes smile.gif i might wanna try it someday.


Often times it can be less expensive actually, from my experience. Relatively anyway, you can build a great guitar for ~600$, for example.

Thanks hardtail for the tone advice!


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Andrew Cockburn
post Aug 16 2007, 08:32 PM
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Great advice Hardtail - thanks, this is all fascinating stuff and point out how complex a subject this it - sounds like you know a lot about this, how did you pick it up? Built an amp yourself maybe?

Anyway, I slightly misspoke about the 5 watts - the original P1 design is based on an EL34 which is much lower power than the Octal EL84 or 6V6. In the course of my deliberations I settled on the P1 Extreme which is an EL84 design, and in my haste forgot to check the change in output wattage resulting form a move from the EL34 to the EL84. The guys at AX84.com know what they are doing so I am pretty sure they will be driving the power tube into saturation, which means as you pointed out, my amp will be LOUD! Louder than I planned in fact.

However, there are a few compensating factors at work here which make it look a little better. Firstly, the P1 Extreme is a single ended design not push pull, which make it a lot less efficient, and ensures you get full tube usage and that lovely overdrive for less wattage (not sure what the conversion factor is exactly but lets say it is something like 0.6. That gives:

Original P1 -> 1 X EL34 -> 12 *.7 * .6 = 5.04W

P1 Extreme -> 1 x EL84 -> 24 *.7 *.6 = 10.5W

So roughly double. When you add to that the logarythmic nature of power increas vs loudness, that actually equates to a 2Log10 increase in volume, which is about 30% if I calculated it right (by no means certain!). So louder, but not disasourously so smile.gif

Another thread to this is that I want to experiment with various ways of attenuating without losing tone so that I can practice and recording, so having a louder amp will actually help with that goal, or maybe I'll build a 2nd amp with an absolutely tiny output - say 1 - 2 W.

Another point that I have discussed with the AX84 guys - whilst they agree that driving power tubes to distortion gives a great sound, they also pay attention to the design of a preamp so that it does add to the overall sonic character with its own subtle distortion. The feeling I got from them was that the power tube thing, whilst important had been blown up a little out of proportion. They may be right or wrong, part of the fun of this is that I can form my own opinions based on experimentation smile.gif

Anyway thanks for your info, I learned something - I look forward to discussing the finer ponts of the design and construction with you some more!

This post has been edited by Andrew Cockburn: Aug 16 2007, 08:34 PM


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Muris Varajic
post Aug 16 2007, 09:18 PM
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I'm not gonna waste your time here guys cause I really don't know this much about small details as you do...
fingers are crossed Andrew,wish you all luck!!!! smile.gif

Muris


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Andrew Cockburn
post Aug 16 2007, 09:20 PM
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QUOTE (muris @ Aug 16 2007, 04:18 PM) *
I'm not gonna waste your time here guys cause I really don't know this much about small details as you do...
fingers are crossed Andrew,wish you all luck!!!! smile.gif

Muris


Heh, thanks Muris - I hope you will listen to some clips when I get it going and give me some opinions on how it sounds relative to tube amps you have played smile.gif


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Effects : Line6 Helix, Keeley Modded Boss DS1, Keeley Modded Boss BD2, Keeley 4 knob compressor, Keeley OxBlood
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Hardtail
post Aug 17 2007, 12:03 AM
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QUOTE (Andrew Cockburn @ Aug 16 2007, 03:32 PM) *
Great advice Hardtail - thanks, this is all fascinating stuff and point out how complex a subject this it - sounds like you know a lot about this, how did you pick it up? Built an amp yourself maybe?

Anyway, I slightly misspoke about the 5 watts - the original P1 design is based on an EL34 which is much lower power than the Octal EL84 or 6V6. In the course of my deliberations I settled on the P1 Extreme which is an EL84 design, and in my haste forgot to check the change in output wattage resulting form a move from the EL34 to the EL84. The guys at AX84.com know what they are doing so I am pretty sure they will be driving the power tube into saturation, which means as you pointed out, my amp will be LOUD! Louder than I planned in fact.

However, there are a few compensating factors at work here which make it look a little better. Firstly, the P1 Extreme is a single ended design not push pull, which make it a lot less efficient, and ensures you get full tube usage and that lovely overdrive for less wattage (not sure what the conversion factor is exactly but lets say it is something like 0.6. That gives:

Original P1 -> 1 X EL34 -> 12 *.7 * .6 = 5.04W

P1 Extreme -> 1 x EL84 -> 24 *.7 *.6 = 10.5W

So roughly double. When you add to that the logarythmic nature of power increas vs loudness, that actually equates to a 2Log10 increase in volume, which is about 30% if I calculated it right (by no means certain!). So louder, but not disasourously so smile.gif

Another thread to this is that I want to experiment with various ways of attenuating without losing tone so that I can practice and recording, so having a louder amp will actually help with that goal, or maybe I'll build a 2nd amp with an absolutely tiny output - say 1 - 2 W.

Another point that I have discussed with the AX84 guys - whilst they agree that driving power tubes to distortion gives a great sound, they also pay attention to the design of a preamp so that it does add to the overall sonic character with its own subtle distortion. The feeling I got from them was that the power tube thing, whilst important had been blown up a little out of proportion. They may be right or wrong, part of the fun of this is that I can form my own opinions based on experimentation smile.gif

Anyway thanks for your info, I learned something - I look forward to discussing the finer ponts of the design and construction with you some more!


I think you have the EL84 and EL34 backwards but yes everything you said makes sense. I forgot about single tube efficiency but it looks like you got it all biggrin.gif

And yes preamp is important for overall tone as well but I was focusing purely on saturation. Preamp tube saturation is constant depending on where the gain knob is set and does not respond as well to attack. I really never discovered this till I got a lower wattage amp (my Blues Junior) where I could really push the volume. Now I usually set the amp so that I am on the edge of powertube saturation. When I play harder or boost my signal a little via a pedal my amp passes over that threshold and just sounds heavenly.

Most people including myself use preamp saturation in combination with powertube saturation. In any case the point is to play loud biggrin.gif

I have not built my own amp (yet rolleyes.gif ) but I am a Professional Engineer here in the US and I enjoy learning about things like this so I have done a lot of research.

BTW - I think you will be pleasantly surprised by your overall volume. My junior is rated 15 watts running 2 EL84's and I can max out its volume without hurting myself (trust me it is freaking loud). Of course I stand about 20 feet away when I do that but I can't help it, I LOVE tone!

Also! I recommend talking with the folks over at www.eurotubes.com. They might have helpful information to recommend to you as well.

Good luck and keep us updated!

Hardtail


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Andrew Cockburn
post Aug 17 2007, 01:09 AM
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QUOTE (Hardtail @ Aug 16 2007, 07:03 PM) *
I think you have the EL84 and EL34 backwards but yes everything you said makes sense. I forgot about single tube efficiency but it looks like you got it all biggrin.gif

snip ...

Also! I recommend talking with the folks over at www.eurotubes.com. They might have helpful information to recommend to you as well.

Good luck and keep us updated!

Hardtail


Oops, yes I switched them - well spotted smile.gif Looking forward to realising that tube sound, and planning for my next build as well - I'll keep you updated, and thaks for the link.


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Andrew Cockburn
post Aug 18 2007, 01:41 AM
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Update :

Well my speaker has arrived - looks like it survived the trip intact, here it is smile.gif

Attached Image

Lovely and blue, hope it sounds as good as it looks ...

I have been talking to a guy on AX84 that might make me a custom case for the amp. I fancy a tweed style because it looks distinguished - something a little like this maybe:

Attached Image

I might have a go at building it myself depending on price, but my woodworking skills are dire. I have been reading up on cabinet construction though and have almost convinced myself that I could do it (a descision I have regretted in the past!)

Tweed is expensive though, I figured about $100 to cover a mod sized combo. The other alternative is Tolex but that is a little utilitarian for my taste. I can buy a ready made tweed covered cabinet form mojo for around $300 plus any mods I would need to fit my specific construction. Still mulling this over really.

I have also researched a couple of sites that will make faceplates to a desigm so I can get some cool labeling for the controls.

This post has been edited by Andrew Cockburn: Aug 18 2007, 01:50 AM


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Acoustic Guitars : Taylor 816ce, Martin D-15, Line6 Variax Acoustic 300 Nylon
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Muris Varajic
post Aug 18 2007, 01:45 AM
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QUOTE (Andrew Cockburn @ Aug 18 2007, 02:41 AM) *
Update :

Well my speaker has arrived - looks like it survived the trip intact, here it is smile.gif

Attached Image

Lovely and blue, hope it sounds as good as it looks ...




Ahhh...nice biggrin.gif


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