Need advice on building an amp with tons of clean headroom

[Zero4]

Hi all! First post. Please go easy on me. Nice forum you have here. Clearly there's a lot of knowledge and experience so I'm here to learn.

I've built four tube amps with great success. One kit, and then three from scratch. I'm starting to get the hang of this.

This next build has been commissioned by a friend who plays jazz guitar. He's been using a solid state amp for portability/reliability and the fact that it's super clean.

What he's looking for is 15-20watts with tons of clean headroom. He did ask for the ability to control mids, so I guess that means it needs a TMB stack. (was thinking to avoid that - but want to give it the tone shaping he desires)

I am up for mixing various amp designs and experimenting to get it right. I just need some advice on where to start looking.

Thanks in advance for any help!

[Gibsonman63]

Welcome Zero4.

Here's a recent thread on the same subject.

http://ampgarage.com/forum/viewtopic.ph ... n+headroom

Speakers help a lot to, but can add significant weight. I restored a Twin with JBLs once. Super clean and tons of headroom, but it weighed a ton.

[brewdude]

I'm no expert, but I would think if he really wants tons of clean headroom it should have as much power as possible. 15-20 watts doesn't seem enough to have much headroom unless played at very low volume.

[Phil_S]

I designed and built this for a young and talented finger style player, actually the daughter of a friend. She requested an amp with "no distortion" which I interpreted as unlimited clean headroom and enough power to get over the drummer in her band.
http://home.comcast.net/~psymonds/Maxie-tone.htm

This uses a two knob tone stack and the knobs are interactive. The tone controls are a little counter intuitive, but I think you can find just about anything you want in them. Here's more about the tone stack. http://www.freewebs.com/balijukka/roybeanstack.htm Also, search TAG for "Roy Bean" and you'll find a few threads.

If I had this to do over, I think I would look for a way to boost the power, maybe to a quad of 6L6's, and maybe I'd add another gain stage after the tone stack (OMG, an unused triode is the result).

I gave her my Stancor A-3801 output transformer. I figured she'd put it to better use than I could. Sometimes you just need to give away the good stuff. I think a great OT is a key component in the design.

[xtian]

Here's a recent thread on the same subject.

http://ampgarage.com/forum/viewtopic.ph ... n+headroom

And I'm following up with a build log:

http://ampgarage.com/forum/viewtopic.php?t=19742

[Zero4]

I'm no expert, but I would think if he really wants tons of clean headroom it should have as much power as possible. 15-20 watts doesn't seem enough to have much headroom unless played at very low volume.

Oh, no kidding! I hadn't thought of it that way.

So how about two 6L6's and a good speaker that can handle the power?

He wants a single 10". I might be able to push to 12" if we have too... but I see some high power 10" speakers that would likely work out.

Weight is definitely a consideration, because it needs to be very portable. I'm a little worried about the transformers for this application.

[Zero4]

I designed and built this for a young and talented finger style player, actually the daughter of a friend. She requested an amp with "no distortion" which I interpreted as unlimited clean headroom and enough power to get over the drummer in her band.
http://home.comcast.net/~psymonds/Maxie-tone.htm

This uses a two knob tone stack and the knobs are interactive. The tone controls are a little counter intuitive, but I think you can find just about anything you want in them. Here's more about the tone stack. http://www.freewebs.com/balijukka/roybeanstack.htm Also, search TAG for "Roy Bean" and you'll find a few threads.

If I had this to do over, I think I would look for a way to boost the power, maybe to a quad of 6L6's, and maybe I'd add another gain stage after the tone stack (OMG, an unused triode is the result).

I gave her my Stancor A-3801 output transformer. I figured she'd put it to better use than I could. Sometimes you just need to give away the good stuff. I think a great OT is a key component in the design.

Wow. That wasn't enough power?

Hmm... I see the weight of this little combo steadily rising.

That looks like it would be a perfect setup. What made you choose that tone stack over the typical one?

[Phil_S]

I think the amp idles at around 38W, but it sounds so clean, well, I don't know if it's enough or not. Maxie says it is. I've never seen her in a live performance situation. I compare it to the JTM45-ish thing I built which seems much louder to me. Maybe 2x 6L6 is plenty and I'm letting my imagination run away with me.

You might consider the design I posted, but instead of a concertina, use a floating paraphase inverter, like you see in the Ampeg designs. In fact, you might want to look at Ampeg designs in general, as they were made to minimize distortion and give lots of clean headroom. (The ones from the early days.)

My personal feelings about the amp are that the concertina is key to getting clean headroom, but it also limits the amount of signal getting to the power tubes. That's why I suggested another gain stage even though the Roy Bean is supposed to be a lossless tone stack. So, to answer your question, I was looking for a lossless or low loss tone stack to use with a concertina. This was something off the beaten path, so I gave it a try.

[martin manning]

Really cool amp Phil! What kind of effect do you hear switching the treble "color" cap from ceramic vs. film?

[Firestorm]

Hi all! First post. Please go easy on me. Nice forum you have here. Clearly there's a lot of knowledge and experience so I'm here to learn.

I've built four tube amps with great success. One kit, and then three from scratch. I'm starting to get the hang of this.

This next build has been commissioned by a friend who plays jazz guitar. He's been using a solid state amp for portability/reliability and the fact that it's super clean.

What he's looking for is 15-20watts with tons of clean headroom. He did ask for the ability to control mids, so I guess that means it needs a TMB stack. (was thinking to avoid that - but want to give it the tone shaping he desires)

I am up for mixing various amp designs and experimenting to get it right. I just need some advice on where to start looking.

Thanks in advance for any help!

Interesting questions. The jazz amps I've built were stupidly high-powered (for the headroom) and thus stupidly heavy. If your guy wants mids control, I'd suggest the Baxandall/James tone stack, because it's the only passive one that can boost mids. Very lossy though, so you might need more power to get him enough output.

[Reeltarded]

Or.. 2 cathode followers? Ehh?



I have been playing in traffic. It's not a clean amp, but you'd go, "Hey, what's up with that thing?". -pulls visor down and goes back to solder fumes-

[Phil_S]

Really cool amp Phil! What kind of effect do you hear switching the treble "color" cap from ceramic vs. film?

Thanks Martin! It was a labor of love. I took an Organo organ chassis in trade from her parents (friends of mine). It was still inside the piano. http://ampgarage.com/forum/viewtopic.php?t=13788 This included a pristine Jensen P10Q dated 1966. I worked on stripping the chassis and got about half way through it. I still have the PA intact and don't know what sort of project to do with it. That includes what must be a 12lb 12.6V transformer. But I diverge.

I remember putting in the color cap. Alas, it has been long enough that I don't remember how it sounded and I don't seem to have any notes. I only had the working amp for a few days before I delivered it. I do recall it offered some tonal difference though.

[martin manning]

Oh well... You had a nice A/B test of ceramic vs. film there. Does the Maxietone amp still get a lot of playing?

[Phil_S]

I think Maxie has mothballed her amp while away at college. There is a physical limit to what one can bring and store. I know she took the guitars with her.

[topbrent]

This is something of an aside, and nothing against any of the afore mentioned circuits. IMHO, Some circuits do produce nice clean tones very well, but some don't feel that great to play and they don't produce familiar tones that many seek( without directly saying so. ) Sometimes these qualities are overlooked.

The classic Fender blackface AB763 circuit is a natural for anyone seeking a classic clean tone that sounds familiar, feels great to play and takes pedals well.

A no reverb, no tremolo, single channel AB763 is an easy build and a great choice for high headroom work. On my personal amps, I also prefer to keep the voltages high, like that of a super reverb on the preamp and power amp.

On the attached layout/schematic, SLukey's AB763 lite is a great choice for this circuit. With good planning and parts selection it's also easy to package all this in a very small chassis.