Acoustic amp schematics

[Cliff Schecht]

Can anybody point me at some acoustic amp schematics? I'm interested in both tube and SS styles. I'd actually prefer to see both to see how each style is voiced. Google just hasn't pointed me at much..

[KellyBass]

Try this, Cliff:

http://music-electronics-forum.com/t7659/

about three posts down is one of my favorites...the SWR blonde.

[KellyBass]

Oh Yeah, one more!...The Fender Acoustasonic 30:

http://support.fender.com/schematics/gu ... mat2BB.pdf

[Aurora]

Isn't the idea that an "acoustic" amp should have little or no "voice" of it's own?
In essence, any good quality mic preamp ( or may a mixed 2-3 channel) with decent tone controls should do the trick ???
OK - maybe an effects loop and reverb could be added.....

[Cliff Schecht]

Essentially I'm looking at a single 12AX7 into a 6V6 with a tonestack somewhere in there (just a practice amp for a friend). I think the trick is going to be getting the voicing in the tonestack right. An acoustic amp doesn't necessarily have to be transparent, it depends on the pickups and overall setup you are using. I was just looking for some good acoustic amps to study up on their typical design.

[Structo]

Yeah the California Blond has a very good reputation and a friend of mine has an original.
Really makes his Martin sound good.

Sheesh, I thought those were tube amps!

[labb]

I wish you luck in your search for a good tube acoustic amp. I have been trying to find one for some time now. I think that the main problem is that tubes just want to distort at some point and you really don't want that to happen with an acoustic..That being said, the best I have come up with is the 5F2-A (Princeton). Until you really crank it it sounds pretty good. Now you have to worry about what kind of pick ups are being used..The Princeton gives you the 12AX7, the 6V6 and tone control..

[BTF]

Mister Schecht:

I have the service schematic for the Peavey Ecoustic 112 amplifier. It's solid state of course, but has a very good notch filter. I've been under the weather lately, but will try to scan and upload it in the next couple of days.

I believe Rivera had a valve amp for acoustics called the Sedona or something similar. I know I saw a schematic for it floating around on a European site. I will try to find it and link.

I had to migrate to acoustic amplification after Bluegrass, Traditional and Acoustic Folk moved into our region and killed Rock and most Blues (hopefully not permanently). I built an acoustic preamp using the '59 Bassman as a basis but with a "depth" control at the first stage to control low frequencies. It works very well with piezo pickups.

Aurora's correct in that most of the acoustic amp schematics I've seen generally use the same tone stack for the instrument as for the mic- in other words, flat frequency response. One neat idea for someone planning on building a tube acoustic amp might be to use the late Fred Nachbaur's boost/cut- hi/mid/low arrangement from his tube mic preamp (he used to have a site called Dogstar Music). Flat in the centers, but with boost and cut for feedback control. I've been mulling over trying it.

Good Luck, BTF.

[Furtz]

Vox makes an acoustic amp that uses a 12au7 in one of its preamp channels.
http://www.zzounds.com/item--VOXAGA70

[KellyBass]

When you do get your tube acoustic amp voiced where you want it, you might try plugging a bass guitar onto it...My guess is it will sound fantastic.

[radstringz]

Just wonderin', but what are the requirements for a good sounding acoustic instrument amp? Would it be something like a hifi amp, with clean, flat, PA frequency response? Ultralinear taps for screen supply? I guess a versatile EQ is a must. Plenty of ins and outs for mixer feeds, etc. Did I miss anything?

Also, what sort of coloration do the pickups provide?

jr

[Cliff Schecht]

Just wonderin', but what are the requirements for a good sounding acoustic instrument amp? Would it be something like a hifi amp, with clean, flat, PA frequency response? Ultralinear taps for screen supply? I guess a versatile EQ is a must. Plenty of ins and outs for mixer feeds, etc. Did I miss anything?

Also, what sort of coloration do the pickups provide?

jr

These are good questions which I don't personally have the answer to yet. Some of the things like the UL taps aren't a necessity, I think the real trick here is getting the EQ nailed. As others said, being able to achieve a flat frequency response is important, as is being able to tailor the sound to the pickups/guitar you are using. My only concern is that I don't have any good quality iron laying around, I'm going to just give the guy the tranny set out of my Epi Valve Jr that I recently gutted. Not the best, but this guy is fairly new to guitar and tube amps anyways so he won't necessarily require the best sound ever, he just wants something cool and different.

[greiswig]

I think a lot depends on your goal sound-wise, particularly since a solo acoustic sound needs to be different than that of an acoustic in the middle of a band. But...

While you don't want distortion (I assume), some addition of even order harmonics by pushing a tube a bit can be nice.

I would shoot for clean, with a variable hi-pass filter and a parametric filter, along with an overall phase switch on it. Some of the best sounds I've gotten were using my Demeter tube preamp through my Bergantino powered cabinet. Drive the tube a little bit, and it develops a bit of natural compression and some harmonics, but still sounds undistorted.

But much (much!) depends on your pickup.

-g

[Cliff Schecht]

I'm going to try a standard 3 knob tonestack. The Marshall PA schematics have the same values throughout models so I'm going to start there and tweak as necessary.

[KellyBass]

Here's one that's worth a glance...the Bogen K15. A very cool little 6l6 pa amp with a 6ax5gt rec tube...:

http://www.flickerdown.com/forsale/k-15.pdf