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Old 2nd November 2011, 05:19 PM   #1
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Default AX84 kits

It'll be a while before I get to it, I've got a few other projects to keep me busy in the meantime, but I've started thinking about trying to build myself a couple amps. I've done some diy electronics stuff in the past and I've been spending some time reading up on amplifier design and I think I understand well enough and have the requisite skills to take a shot at it. I have no desire to design an amp from the ground up, I'll be starting with a schematic and buying parts or maybe just buying a complete kit.

I've been looking around at AX84 and I like the looks of what's there. I thought the HO looked like it would be a good beginner/intermediate project. Complicated enough to teach me a few things as I go, but not so complicated as to frustrate me and end my interest prematurely.

At some point though, I might like to try a more advanced project (maybe more than one). The two that interest me most are the "October" and the "4-4-0." The october because it looks like it's got more sophisticated tone shaping circuitry and would make for a very flexible amp able to do a lot of styles. The 4-4-0 because I really want to hear what all the trainwreck hype is about, and I do like the idea of a responsive, touch-sensitive amp.

So what's the question? Well, I wonder if anyone has experience with these three or any of the other projects listed on AX84. Better yet, do you have experience with more than one of the project amps? I'd love to see some compare and contrast kind of commentary on the various builds from people who have built them. How do you like the tone, playability, responsiveness to different inputs, tonal variety, does the 4-4-0 live up to its pedigree? As far as the build, how would you rate the degree of difficulty. How much fine tuning is necessary after the initial build is complete? Were some kits more difficult to tweak than others? Any information is good information.
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Old 2nd November 2011, 05:38 PM   #2
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Oh yeah, one more thing, how would any of these take to a VVR-type circuit. I definitely like to open 'em up when it's appropriate, but as often as not, I need to pull my volume way back.
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Old 2nd November 2011, 11:44 PM   #3
Enzo is offline Enzo  United States
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The AX84 site has designs that have been around a while and a LOT of discussion, so if you decide to do one of their projects, you won;t be alone. That's good.

MY advice to you would be decide on one and build it. Once you have that experience, you will be better equipped to make decisions on further projects and modifications. In my view there is no point in pkanning changes before you know what you have in the first place.

Building from a schematic is a character builder. Building from a kit can be just as rewarding, but the added advantage is that someone has already thought of what you will need. You won't get halfway through it and slap your palm to your forehead because you overlooked the need for - whatever, a fuse holder. Also, depending upon the level of kit you buy, if it comes with a chassis, especially a drilled chassis, that will be a lot of work and planning saved.
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Old 3rd November 2011, 01:39 AM   #4
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Enzo - Thanks, that's sound advice. I will most likely do the HO first though, I'm kind of torn between that one and the higher output SEL. It is not likely that I will ever be playing anywhere outside of my house, that phase of my life has passed I think, but if the master volume works alright it might be nice to have the extra power on tap.

One nice thing about the ax84 projects is that board and chassis layouts are posted on the website. I'd rather have a nice neat board than a rat's nest. I think for a first build I'll use someone else's well thought out layout and learn how to do it right. Maybe I'll be more adventurous later on. I do wonder how much I might save if I shop around for components and fashion my own board and chassis using the templates. What are some good places to find cheap components?

I'd still love to hear what anyone thinks of the various designs posted there.
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Old 3rd November 2011, 06:47 AM   #5
Enzo is offline Enzo  United States
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For general parts, companies like Mouser are a pretty common choice. Or Digikey or Newark or Allied...

What those places won;t have is much tube related stuff. Likely no tube sockets, and alimited selection of high voltage electrolytic caps, and no tubes. They do have some transformers, but they will be generics like Hammond, not specific like for Fender Tremolux or something.

For amp parts, ther are a number of places, but one that is reasonable and has a good selection is AES at:

Antique Electronic Supply

A good selection of the sort of caps we use, and tubes and sockets. Not to mention grille cloth and speakers and cabinet handles and volume controls and and and. Oh and a nice selection of books too.

Go ther and request the paper catalog be sent. That way you can page through it and familiarize yourself with what is available. That is a lot harder to browse online. Online is good if you know what you want and want to look it up.

When AES has a dozen different 9-pin sockets to chose from, you can find one that mounts to the chassis the way you want, or one that fits on a pc board, or one with or without a tube shield flange. And if they come in both 3/4" and 13/16" - I made those up - and you have a 3/4 hole punch but not a 13/16 one, then it pays to get the socket that fits the hole your tool makes. Saves an hour and a half with a file.

Look at a kit parts list and find them at one of thoe supliers and make a list to compare prices. A bag of exactly what you need has a certain time saving value, at least would to me. Of course at this point in my own life, I am sitting in a commercial amp repair shop, so I could just turn my chair around and find everything I need to build an amp. Not patting myself on the back, just that we may have different needs while shopping.
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Old 3rd November 2011, 02:34 PM   #6
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Thanks again! I hope you don't mind if I pick your brain a little more.

Quote:
A bag of exactly what you need has a certain time saving value
This is certainly true. In addition to the fact that I'm not too savvy about component selection, but I'd like to learn a little.

So resistors seem easy. Certain resistors in the parts list have specified power ratings. I need to get resistors for those spots that can dissipate enough heat. Other than that I guess you can pay more or less depending on the manufacturing tolerances. Easy.

Capacitors are more complicated. For the big filter caps on the B+ rail and for the bias caps there is a voltage rating specified. I'm assuming this is a minimum specification right? So if the list calls for a 1uf/25V cap and I see a 1uf/400V for a $1 that's suitable? That doesn't seem too difficult.

What I'm really not sure about is this... in the catalog there are a lot of "special" caps that are quite expensive. The marketing language describing them refers to better or faster transient response. I'm assuming that these are useful when they are right IN the signal path... I guess for use as blocking caps and in the tone stack? I'm not too sure where I can get away with using cheaper caps and when I'd be better off spending a little more.

Everything else seems pretty straightforward to me. I'll just use the recommended hammond transformers. The rest is resistors, connectors, switches and hardware. Is there anything I missed where it's really worth it to select better quality components?

Last edited by clengman; 3rd November 2011 at 02:42 PM.
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Old 4th November 2011, 12:42 AM   #7
Enzo is offline Enzo  United States
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A lot of special caps are selling mojo rather than real improvements in sound. These caps are made by naked virgins out of spun gold, so naturally the soundstaging is stunning and the blah blah blah...

I won;t tell you there is no difference between caps, but think of it like tires for your car. If you want to drive to the store, does it really matter if you have extra stunning stability in curves at over 140mph? Or if the tire pressure is within a quarter pound of each other?

In my opinion, spending a lot of extra dough when you are just beginning is not warranted. If you are just learning to ice skate, you don;t need to look for $1000 skates like olympic skaters and pro hockey players might chose. Learn to skate, and once you have the background to know what differences in sound are there, then think about alternatives. Besides, if you make your amp with dollar parts and get used to the sound of it, then it will be real instructvie to swap those caps out for fancy ones later and hear the amount of difference it does or does not make.

SOmeone else may disagree.

Yes, you can use a 400v cap where a 25v cap is called for, but the higher the voltage, the larger a cap's physical size, as a rule. Caps have gotten much smaller than they used to be, so it may not matter, but a typical cathode bypass cap of 22uf at 25v is tiny and really cheap, so I think in general it will be unusual to find a 400v version of something that is cheaper than the 25v version.
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Old 4th November 2011, 01:06 AM   #8
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Quote:
Originally Posted by clengman View Post
It'll be a while before I get to it, I've got a few other projects to keep me busy in the meantime, but I've started thinking about trying to build myself a couple amps. I've done some diy electronics stuff in the past and I've been spending some time reading up on amplifier design and I think I understand well enough and have the requisite skills to take a shot at it. I have no desire to design an amp from the ground up, I'll be starting with a schematic and buying parts or maybe just buying a complete kit.

I've been looking around at AX84 and I like the looks of what's there. I thought the HO looked like it would be a good beginner/intermediate project. Complicated enough to teach me a few things as I go, but not so complicated as to frustrate me and end my interest prematurely.

At some point though, I might like to try a more advanced project (maybe more than one). The two that interest me most are the "October" and the "4-4-0." The october because it looks like it's got more sophisticated tone shaping circuitry and would make for a very flexible amp able to do a lot of styles. The 4-4-0 because I really want to hear what all the trainwreck hype is about, and I do like the idea of a responsive, touch-sensitive amp.

So what's the question? Well, I wonder if anyone has experience with these three or any of the other projects listed on AX84. Better yet, do you have experience with more than one of the project amps? I'd love to see some compare and contrast kind of commentary on the various builds from people who have built them. How do you like the tone, playability, responsiveness to different inputs, tonal variety, does the 4-4-0 live up to its pedigree? As far as the build, how would you rate the degree of difficulty. How much fine tuning is necessary after the initial build is complete? Were some kits more difficult to tweak than others? Any information is good information.
I built up an AX84, Hi octane, SE amp kit for a client that bought one and
decided not to follow through with the build himself.

The result was one of the best sounding gtr amps I've ever heard, within
it's volume restrictions.

This amp is very sensitive to component choice. For example, I tried a few
different OP tube cathode bypass caps, even a Black Gate and they all had
a different sound.

I did change quite a few component types from standard, and used my own
grounding scheme.

Recommended.
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Old 4th November 2011, 05:37 PM   #9
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Thanks guys. Definitely won't get too fancy to start with.

I was pricing components at Mouser and it looks like there's the potential to save quite a bit of money if I buy most of my components there, buy raw materials (garolite and aluminum) from amazon and just buy transformers tubes and sockets from AES. At mouser, for the most part, I picked the cheapest caps that fit the required values. These included some multilayer ceramic caps for the tone stack and blocking caps and tantalum rather than aluminum electrolytics for some of the cathode bypass caps. Is this too cheap? Are there capacitors that really aren't suitable?
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Old 5th November 2011, 12:37 AM   #10
Enzo is offline Enzo  United States
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I am always nervous around tantalum. They work and sound just fine, but they have ZERO tolerance for reverse voltages and don;t like overvoltages. As a pro audio repair tech, I cringe when I see them in something. But that is just me.

I have no problem with fancier caps, I always think about the caps physical attributes. If you build on a circuit board, then consider the hole patters, but if you build point to point or on an eyelet/turret board then I prefer to look for axial leaded caps. A radial leaded cap can have the leads bent out to either side to go to eyelets, but I'd just as leave have axial leads in the first place. Electrically it doesn;t matter.
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