VOX AC10-TWIN Regrets

Z

zozoe

New member
Greetings,,, I'm at 'that' point where reading about amp that used to be my All-time #1,
is creating great agida, especially since I lost the amp to some untimely life related upheaval.
Not really wanting to spring for anything close to what these originals actually command, I'm thinking (trouble) about having one of the reputed amp builders ála Trinity, Lil Dawg, or countless similar companies to build me a VERY close head only rendition of this circuit, using all the tubes native to that AC10-Twin circuit... I don't really need the tremolo circuit, but if I recall correctly, 'THAT' channel was the one where the MOJO lived, but my memory fails me,, so please jump in to refresh me, but equally as important, who should I go to for such an undertaking? It's a tad beyond my existing intermediate technical smarts & abilities, so I need to commission some company who's able & willing...
ANY thoughts or suggestions that may lead me to a faithful reproduction of my lost treasure?? Many thanks in advance for all your great thoughts & insights.
Kenny
kslewitt@gmail.com
 
While I can't comment on what some of the more popular builders would charge to do that, I can tell you a one-off amp won't be cheap. Surely not any cheaper than acquiring a vintage unit. I would charge $5,000 to take such a job. Removing parts of amplifier circuits changes the way the amp works, thereby changing what made that MOJO work. This means I would have to build a mock head as the circuit was, fine tune it, then remove the desired circuits and then tune it again so that it sounds as you expect it to. For $3,500 I could just build it as you wish, but without an A-B comparison, I can only tune it to sound good, not necessarily the way a vintage unit would sound.

Why so much? Well, like any artist, it is mostly in the time spent. It would take a day to simply build a parts list and source the parts. It would take a full day to just build it assuming I can find a pre-drilled chassis that would work; two days if I had to drill the chassis myself. Then tuning the thing... My latest build took three weeks to sus out what I wanted from it. I had to buy LOTS of parts to try. I have never heard an AC-10 in person and would have to spend a week sifting through examples to even get a good idea of what it should sound like. Then I would have to tune the build to approximate that and still sound good. I value my time at $550 per day, or $55 an hour for a 10 hour day if you will. I suspect, based on what I do know of the AC-10 that it would be about $500-700 in raw parts depending on what iron you wish for. For a basic, just build it and tune it, I can see an easy week of work from start to finish. I can't really charge too much for fine-tuning ( it takes hours and you have to take breaks to rest your ears ), so I can cut a break there, but all in all, I couldn't build you one for less than it would cost you to buy a vintage unit.

There is surely someone out there that will do it cheaper, but I can't imagine that it will be of the highest quality that your money can get. I build amps that have the same circuit, but no two are the same. Each one has its own soul if you will. I use the best stuff I can find and I spend time making things as clean and precise as it can be. Then I spend time tuning the amp to be happy, not just me. My last two builds have 10 different component values in an amp that only has 50 total parts to build. They sound very similar but have rather differing values of components in several different spots to do so.

The biggest challenge for the AC-10 circuit is the EF86 part of it ( the cannel everyone wants ). EF86's are finicky and truly making a good EF86 circuit is not simply cut and paste. If you can live with not having a VOX, a Morgan AC-20 Deluxe will get you in the ballpark for less money.
 
What do you know, an AC-10 replica! The street price is around $2,000 as of 2019. As I mentioned, one-off prices are going to be higher, so finding a production model is usually cheaper. The Henry model SRT+ is a pretty killer-sounding amp as best I can tell. So that may be a way to get that sound without spending over $3k?
 
Yes, Ewiz,,, Very nice sounding, that SRT+, oh, & BTW, I already own a Morgan AC20Deluxe, and you're correct in what mire could I want!?! 20201209_190749.jpg
 
Nice!!! While I am not a huge fan of Morgan's build quality ( a little sloppy if you ask me ), but they do make some nice amps. The AC-20 was the only one that really ever called to me. My own amplifier design was in a way driven by the idea behind the AC-20. As I was trying every circuit I could think of that utilized the chassis I had to work with, I stumbled upon the AC-20 and it gave me the idea to simplify my circuit. After re-building my design with that idea in mind, I saw the light! A few revisions later and I now have what I feel is a truly unique amp design. It is more closely related to a JMP 18Watt Lite IIb than anything, and even still it is pretty far removed from that.

I have thought about doing an EF86 design as I really love the 18-Watt ( read that as low wattage EL84 amps ) vein of amplifier designs, and it seems that the EF86 is predominately used in EL84 driven amp designs for some reason? I don't like amplifiers that go beyond about 50 watts ( too loud, too heavy, and not enough character ) and feel that 18-30 watts is the ideal amplifier power range. An EL84 is perfect for that design metric. Having done JCM, Bogner, and even Dumble style designs, I keep coming back to the 18-watt platform. I would love to do more Supro and Harmony designs but am trying to not utilize non-standard or dying tube breeds, which leads me to my resistance to introducing EF86 tubes into my designs. They are on a resurgence in the past several years, but they are finicky, hard to find off the cuff, and considering the way they are typically utilized, don't really add that much mojo.

Going back to the AC-20, my biggest gripe about it is the variable wattage part of the circuit. It is a very basic and readily available design that works but is a failure point. The design also uses Mercury Magnetics trannies with a choke! So most of the money in that amp is in the iron. I don't feel that MM is that great and considering the rest of the build quality, it seems that the amp was built to a price point more so than simply building a great amplifier. Dr. Z amps are kind of the same way. Great designs, built well enough, but the money you spend is just not in the spots that make the amp what it actually is. If I had to choose between a Morgan and a Dr. Z of the exact same amp design, I would go with Dr. Z. Having played with perhaps 20 of my own designs, I can say with ease that 7/10ths of the sound is the speaker used and the last 3/10ths are a split between the circuit topology, the components used and the layout. The layout is not really a game-changer so much for the sound, but more so how quiet the amp will be and how clean the amp will look when built. My circuit design was easy, but it took me weeks to come to an ideal layout that made for an amp that was clean-looking and absolutely silent when you weren't playing.

Most of my time spent with the designs I do is simply trying to tune the amp to an ideal range of operation. A JCM design for instance is not hard to implement, but making it have a good sound that can do cleans and grit is the hard part. Same with the simpler 5E3 inspired designs. Getting to sound good doing one thing is easy, but trying to make it work from clean to mean takes a lot of tweaking and parts swapping. I can design an EF86 amp that I know will sound great, but trying to copy an unknown circuit is hard to do. It sounds like even the Henry SRT+ is a rendition of the AC-10 that was tweaked to go beyond the original design. Once you have that worked out and can see what your cost of production will be after R&D factors, you can price the amp to meet a market. That is why one-offs and custom amps are so expensive, you are paying for the time to design it and the parts to get it there. When I was initially building my design, I was looking to get its price point down into the $1,200 - $1,400 range. This was very hard to do because a LOT of time was being spent making sure the build was A+ work. It took two weeks just to build the headshell, so ultimately I had to scrap the idea of affordable and price the amp for what it was, a premium class amp. So now the amp sells for $2,500, which is still too cheap from a bean-counting standpoint. That is why I am not an amp builder for my day job, I can't sell enough fast enough.

Here is a picture of my prototype:
IMG_0593.jpg
 
Ewizard: Your posts are always full of quality, and an awesome read! :) Just wanted to thank you for hanging around. :) ♪

-E
 
Ewizard said:
Nice!!! While I am not a huge fan of Morgan's build quality ( a little sloppy if you ask me ), but they do make some nice amps. The AC-20 was the only one that really ever called to me. My own amplifier design was in a way driven by the idea behind the AC-20. As I was trying every circuit I could think of that utilized the chassis I had to work with, I stumbled upon the AC-20 and it gave me the idea to simplify my circuit. After re-building my design with that idea in mind, I saw the light! A few revisions later and I now have what I feel is a truly unique amp design. It is more closely related to a JMP 18Watt Lite IIb than anything, and even still it is pretty far removed from that.

I have thought about doing an EF86 design as I really love the 18-Watt ( read that as low wattage EL84 amps ) vein of amplifier designs, and it seems that the EF86 is predominately used in EL84 driven amp designs for some reason? I don't like amplifiers that go beyond about 50 watts ( too loud, too heavy, and not enough character ) and feel that 18-30 watts is the ideal amplifier power range. An EL84 is perfect for that design metric. Having done JCM, Bogner, and even Dumble style designs, I keep coming back to the 18-watt platform. I would love to do more Supro and Harmony designs but am trying to not utilize non-standard or dying tube breeds, which leads me to my resistance to introducing EF86 tubes into my designs. They are on a resurgence in the past several years, but they are finicky, hard to find off the cuff, and considering the way they are typically utilized, don't really add that much mojo.

Going back to the AC-20, my biggest gripe about it is the variable wattage part of the circuit. It is a very basic and readily available design that works but is a failure point. The design also uses Mercury Magnetics trannies with a choke! So most of the money in that amp is in the iron. I don't feel that MM is that great and considering the rest of the build quality, it seems that the amp was built to a price point more so than simply building a great amplifier. Dr. Z amps are kind of the same way. Great designs, built well enough, but the money you spend is just not in the spots that make the amp what it actually is. If I had to choose between a Morgan and a Dr. Z of the exact same amp design, I would go with Dr. Z. Having played with perhaps 20 of my own designs, I can say with ease that 7/10ths of the sound is the speaker used and the last 3/10ths are a split between the circuit topology, the components used and the layout. The layout is not really a game-changer so much for the sound, but more so how quiet the amp will be and how clean the amp will look when built. My circuit design was easy, but it took me weeks to come to an ideal layout that made for an amp that was clean-looking and absolutely silent when you weren't playing.

Most of my time spent with the designs I do is simply trying to tune the amp to an ideal range of operation. A JCM design for instance is not hard to implement, but making it have a good sound that can do cleans and grit is the hard part. Same with the simpler 5E3 inspired designs. Getting to sound good doing one thing is easy, but trying to make it work from clean to mean takes a lot of tweaking and parts swapping. I can design an EF86 amp that I know will sound great, but trying to copy an unknown circuit is hard to do. It sounds like even the Henry SRT+ is a rendition of the AC-10 that was tweaked to go beyond the original design. Once you have that worked out and can see what your cost of production will be after R&D factors, you can price the amp to meet a market. That is why one-offs and custom amps are so expensive, you are paying for the time to design it and the parts to get it there. When I was initially building my design, I was looking to get its price point down into the $1,200 - $1,400 range. This was very hard to do because a LOT of time was being spent making sure the build was A+ work. It took two weeks just to build the headshell, so ultimately I had to scrap the idea of affordable and price the amp for what it was, a premium class amp. So now the amp sells for $2,500, which is still too cheap from a bean-counting standpoint. That is why I am not an amp builder for my day job, I can't sell enough fast enough.

Here is a picture of my prototype:
Click to expand...

Beautiful, look at that real estate! is that extra height for extra cooling?
 
The height is for heat and aspect ratio. There is not much air movement in there and of course wood above that glowing glass.

The Lo-cut is a cut only control, and the Hi-cut is a basic VOX style cut control. They are not interactive and you can use the Lo-cut as more or less a control to dial between single-coil and humbucking pickups. Depending on where you set them, you can make the mids more or less apparent. It is a mid-forward amp with no typical tone stack to suck the mids out. The MV is of course Master Volume. It is post phase inverter. This allows you to dial in phase inverter distortion if desired. The input is a parallel triode setup ( the two halves of the 12AX7 work together as one ). This makes the amp a little quieter and gives it a little bit more oomph to drive the Pi. The parallel triode runs straight into the Pi via the Vol pot. The Lo-cut just varies the coupling cap value which is what changes the bass. With the MV all the way up, the amp works just like any typical 18-watt normal channel would with the exception of no tone stack in the way. If you dial back the MV, you can get a nice crunch that is all Pi distortion, or you can blend the MV and Vol knob to get the Pi and power amp distortion you want. When dimed, it has that 18 watt Marshall sound with a well-controlled amount of the fizz and grit prevalent with them and the Vox AC-15 style amps ( even the Matchless amps have a bit of that fizz ). It is there but is very muted and subtle. This amp has BALLLLLLLSSSSS. It sounds very warm and big, the mids are forward but balanced and the highs can be there depending on how you dial it. It isn't really a chimey, bright, and glassy sounding amp, but has enough highs to be bright enough.

The design was meant more to be a clean pedal platform amp ( whatever that means ), which to me means balanced, natural, and works well with pedals. To me, it does that in spades. Ran into a Two Notes Captor X is where it really works well! Because you can dime it, it gives you " that " sound. Obviously, if you have pedals that have " that " sound, it will deliver the goods then too. I have an Egnater Tweaker-15, an Epiphone Valve Jr., and a Peavey XXX that I compare it to regularly. I think is a step above them. Where I feel it really has its thing is dynamic range. The amp is so quiet that when you play quiet, it can literally be whisper quiet, but if you dig in, it will bark and snap at you. It can do country twang with snap and pop, or if you wish it will do very soft and nuanced.

Here is the first production model in the tuning phase:
65838498498__062FDFBE-F79C-40C3-8528-14CF9297BBB9.jpg

You will notice a few differences. I don't like Standby's, this amp doesn't need one, so I removed it. I did include a mute switch ( the little one ) which kills the audio with NO pops of any kind! The pots and tubes were of course moved together. This is a hand-drilled and machined chassis that is now one of three in the world! I still have to finish the shell. I like wood, and as you can see in my prototype picture, I like light and mirrors. This is why it takes a while to build the shells. It is all custom. Each amp is a little bit different, both externally and internally. Each amp is tuned to its strengths. The circuit is the same in each, but values are changed and tweaked to where I feel it makes the amp do what it wants to do. I'm not 100% happy with my transformer choice yet... They sound fine, great actually, but the finish kills it for me. Still looking for a transformer that sounds and looks good.

Here is a gutshot of the above amp just before the tuning stage. I still hadn't finished a few things and several parts are different values now:
IMG_0569.jpg

And this is the panel for the back of the Prototype:
64472390163__8ED03CC8-C2A2-4E47-B685-63326960755F.jpg

This amp costs about $600 in parts, including the wood for the headshell, but it takes several weeks to build it. This is why it is costly for me to build amps. I can build the amp itself in a few days, but the headshell takes the most time. I can't stand to use a pre-made box, my thing is the mirror and the wood. Maybe one day I will post sound clips, I am just horrible at self-promotion and am too picky about things to just wing it. I am never 100% happy with it and always feel it can be better, so I don't ever really feel like a project is done. I don't even capture all stages of production. It just doesn't mean anything to me until the client gets it and is happy. Where I start and where I end with a job is irrelevant so long as whatever the tangible item is, makes the end client smile. Then and only then do I wish I had more documentation to share. But it isn't mine anymore, so again it is not for me to worry about. I have snippets of my work and none of it is good enough.

I have been kicking around doing a YT video series on amplifier design and building, but I just can't seem to get myself to start the project. I have another amp to build and am ready to start on it, but I am so picky about crap, I just don't think I would make a good host to present a series like that. I'm goofy, outspoken, introverted, and super persnickety about stuff all at the same time. Nothing worse than a goofy, neurotic, yet reserved nerd trying to show you how to design and build an amplifier. Most of my friends don't even know I can do that. Anyway, I hope you find your amp. I do feel The Henry SRT+ is the one to go with.
 
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