What path to choose for Hamonica amplifier?

[Overgaard]

I've only been playing the Harmonica for about three months now
but I thought this would be a great project putting together a little
tube amp for use with the harps.

I want this amp to be built from scratch for hamonica playing.
I will only use it for playing at home, in an apartment so no
big watts needed. (No reason to give the neighbors or wife reason to smack me in the head)
My question is (since I cannot make up my mind on this one,
and we're talking topology here. Right word?)

Anyone with good ideas? SE or PP?
I was thinking of using 807's and 6SN7's (maybe some 12A*7)
Not to many stages. Perhaps only two to keep the feedback problem with harp mics tamed.

Without going too deep on this maybe I'll just let you tell me your thought on an harmonica amp.

Regards // Jörgen

[jjman]

We used my '74 Fender Vibro Champ for harp at a jam once.

http://www.el34world.com/charts/Sche...HAMP_AA764.pdf

'74 Vibrochamp

Trem is not really needed since the player can blow his own, but it did sound cool. I'd probably go with a simpler tone control with just treble bleed-off. More breakup that way too. Low wattage is the key so you can get nice breakup when wanted w/o overpowering the band's mix. Then mic it if needed. The last instrument that needs a loud amp is harp.

I'm sure there are more appropriate circuits for harp, but the VC sounded pretty appropriate to me. I think many say use a 12ay7 in the front instead of a 12ax7, but the rest of the circuitry could be adjusted for either, I would think.

[taj]

Hey Jörgen,

Should we assume you're looking for a distorted blues type sound? If so...

Keep the output power quite low so you can turn it up into the distorted area. Low power means REALLY low, even 5 watts can get really loud when driven into distortion.

Limited bandwidth is also part of that sound. So no expensive output transformers, cheapies are perfect. Look for a replacement guitar amp output transformer.

One thing NOT to do, is use a circuit from an old AC/DC desktop radio from the 50s'. They have no power transformer in them so the unisolated power could be live on the chassis (and mic!). I mention this because I saw some moron on eBay selling such a radio as a potential harp amp conversion. He could kill someone saying that. Idiot. They are easy to spot; the tubes they use usually have 35 and 50 volt heaters wired in series.

..Todd

[Overgaard]

Hi,

Looks very interesting! Good tip! Thanks!

Originally Posted by jjman

We used my '74 Fender Vibro Champ for harp at a jam once.

http://www.el34world.com/charts/Sche...HAMP_AA764.pdf

'74 Vibrochamp

Trem is not really needed since the player can blow his own, but it did sound cool. I'd probably go with a simpler tone control with just treble bleed-off. More breakup that way too. Low wattage is the key so you can get nice breakup when wanted w/o overpowering the band's mix. Then mic it if needed. The last instrument that needs a loud amp is harp.

I'm sure there are more appropriate circuits for harp, but the VC sounded pretty appropriate to me. I think many say use a 12ay7 in the front instead of a 12ax7, but the rest of the circuitry could be adjusted for either, I would think.

[Overgaard]

Hello Todd,

Thanks for the reply!

Yes, I was thinking the "Chicago Blues sound".

Maybe I should shoot for a SE amp with about a watt or so of power then?
Cheap transformers is a word I like.

About that AC/DC desktop radio warning.
You will not see such a thing happening here.
Why would someone suggest that selling a radio? Dangerous!
One hand on the mike and your foot on the radiator or something.
Horrible thought!

I actually restore old tube radios as part of my hobby and always rebuild them with an isolation transformer if needed for safety.
Also, I do not have the heart to destroy any old tube radio.

So, I guess I'll just put a 6SN7 plus a 807 into LTSpice and
get a pencil, ruler and some sheets drawing some loadlines and
see what comes up.

All suggestions, flaming and critics are welcome!

Thanks for the info!

Best regards
Jörgen

Originally Posted by taj

Hey Jörgen,

Should we assume you're looking for a distorted blues type sound? If so...

Keep the output power quite low so you can turn it up into the distorted area. Low power means REALLY low, even 5 watts can get really loud when driven into distortion.

Limited bandwidth is also part of that sound. So no expensive output transformers, cheapies are perfect. Look for a replacement guitar amp output transformer.

One thing NOT to do, is use a circuit from an old AC/DC desktop radio from the 50s'. They have no power transformer in them so the unisolated power could be live on the chassis (and mic!). I mention this because I saw some moron on eBay selling such a radio as a potential harp amp conversion. He could kill someone saying that. Idiot. They are easy to spot; the tubes they use usually have 35 and 50 volt heaters wired in series.

..Todd

[ChrisA]

Originally Posted by Overgaard

I want this amp to be built from scratch for hamonica playing.
I will only use it for playing at home,...

I'd build a clasic Fender "Champ". They are very simple, have 60 years of history and sound good. You'll need two tubes an 12AX7 and a 6V6. If you follow the scematic exactly, using carbon resistors and the small undersize filter caps and transformers the finished amp will have an authentic sound just like one built in the 1950's They have mostly a clean sound but get into a "crunch" if you turn it up

You will also need a speaker. I just bought a Jenson "mod" in 8" size. It would work. But if you need a small size vintage sounding speakers have Webber build an alnico speaker or get a more vintage soundig one from Jenson. They are not expensive to have them made. The mic you use matters a lot too

If you need less volume build an "L Pad" with two resistors and conect the speaker through that. Much better to use the "correct" tube because it has to sound right when you over drive it. The 6v6 is a good blues tube. But to loud for an apartment so build that l-pad. A low power 6sn6 tube will not have the same sound.

http://www.paleoelectronics.com/blog..._5e1_schem.gif

You can make it simpler, use solid state diode rectifier and just one input jack.

If saving money is the goal it is cheaper to simply buy a re-issue Champ from Fender.
http://www.fender.com/products/searc...tno=2330100000
These sell here for $150.00

The above champ uses a printed circuit board and a small 6" speakers. this one is hand wired.
http://www.fender.com/products/searc...tno=8160500000

[ChrisA]

Double post, deleted

[Overgaard]

Thanks! I will look into the classic Fender Champ. Even found an
"analyze" of that amp on the net.

I am out of 6V6 right now though. I was hoping to put something together
with what I had in stock and also the 807 would look kind of cool
vintage style.

I will let you all know how it goes!

Best regards!

Originally Posted by ChrisA

I'd build a clasic Fender "Champ". They are very simple, have 60 years of history and sound good. You'll need two tubes an 12AX7 and a 6V6. If you follow the scematic exactly, using carbon resistors and the small undersize filter caps and transformers the finished amp will have an authentic sound just like one built in the 1950's They have mostly a clean sound but get into a "crunch" if you turn it up

You will also need a speaker. I just bought a Jenson "mod" in 8" size. It would work. But if you need a small size vintage sounding speakers have Webber build an alnico speaker or get a more vintage soundig one from Jenson. They are not expensive to have them made. The mic you use matters a lot too

If you need less volume build an "L Pad" with two resistors and conect the speaker through that. Much better to use the "correct" tube because it has to sound right when you over drive it. The 6v6 is a good blues tube. But to loud for an apartment so build that l-pad. A low power 6sn6 tube will not have the same sound.

http://www.paleoelectronics.com/blog..._5e1_schem.gif

You can make it simpler, use solid state diode rectifier and just one input jack.

If saving money is the goal it is cheaper to simply buy a re-issue Champ from Fender.
Fender Products: Champion? 600
These sell here for $150.00

The above champ uses a printed circuit board and a small 6" speakers. this one is hand wired.
Fender Products: '57 Champ®

[wakibaki]

I have a little homebuilt 12AX7/EL84 SE guitar amp with a 10" Jensen speaker here. It's very similar to a Fender Champ although obviously it has an EL84, not a 6V6. I took a noname dynamic mic, plugged it in and blew a bit of harp. I could hear the amp over the harp, and I could get it to feed back if I provoked it. It wasn't too loud at about 5W. OK for an apartment I guess. I've got a spring reverb for it but I haven't wired it in yet. The amp has gain and master volume but it stayed quite clean as I think it is a bit underdriven by the mic.

Next I plugged into a little Marshall MG15DFX SS amp with an 8" speaker and (surprise) 15W. I tried the clean and overdrive channels, I liked the overdrive best as there was a bit of distortion although the sound stayed fairly clean and I preferred this amp as it was easy to get a bit more volume. It's more versatile with reverb, echo, phaser and flanger so if I could only have one of them it'd be the Marshall. It actually cost less to buy than the components for the valve amp.

A compromise might be one of the current small Fenders with a valve output stage and SS front end effects.

Depending on the microphone you might want a preamp of some kind, neither of the amps were as loud as when driven by a guitar pickup.

w

[Trout]

If it were me, I would go with a SE design, use the 807, 10-12 inch speaker.

Ideally, I would rather use the blackface AA764 champ circuit. This gives you a bit more control over the bass & treble. Go octal on the front end for that early 50's raw, 6SJ7, 6SC7, 6SN7 all come to mind quickly. Not a lot of voltage needed to get great low powered tones with the 807.

If you want real authentic tone, you needs lots of tiny speakers like Little Walter, 8 X 8" through an old masco amp