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Thread: New to the forum. Looking to build a 1/4 watt tube amp.

  1. #1
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    New to the forum. Looking to build a 1/4 watt tube amp.

    I am wanting to find out what the best tube amp design is to get distortion and great tone at low volume. I have heard good things about the
    "Little Lanilei" but only from guitar players. Any harp players try these out? Any other low watt tube amp reviews. Although I am no tube amp technician I can build anything with the right schematic so ultimately I am looking for feedback on great sounding low watt tube amps and schematics. Thanks

  2. #2
    Old Timer soundguruman's Avatar
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    The reason for this is that we want the amp to max out constantly with very low volume.
    It's no good for a live band unless your amp is micd thru the PA system. The amp is very low level volume.
    For learning about building tube amps, you should get a kit first to become familiar w/ building. It's like all the parts in one place.
    And saves a lot of parts orders.
    But be careful not to electrocute yourself please.
    Many harp players use 14-30 Watts, or even more. The trick is the microphone, which does not cause squealing feedback. To find a good harp mic may be expensive. There is high isolation, to reduce the feedback problems, Or multiband EQ is very handy indeed.
    Without a good harp mic, you will not get the result you are looking for.
    http://tube-tech.com/eq-1a-parametric-equalizer-12.html
    http://www.ebay.com/itm/Shure-Vintag...item53f41902ed
    Last edited by soundguruman; 01-30-2013 at 11:18 AM.

  3. #3
    Supporting Member eschertron's Avatar
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    Quote Originally Posted by Flounder View Post
    I am wanting to find out what the best tube amp design is to get distortion and great tone at low volume. I have heard good things about the
    "Little Lanilei" but only from guitar players. Any harp players try these out? Any other low watt tube amp reviews. Although I am no tube amp technician I can build anything with the right schematic so ultimately I am looking for feedback on great sounding low watt tube amps and schematics. Thanks
    Of the amps described on their website, the one is a hybrid amplifier, with a tube preamp feeding a transistor power stage, allowing the user to dial in from 1/4W to 50W of acoustic power. The other amp seems to be just the preamp section and a recording output, still with the box's 6 1/2 inch speaker. As an alternative to a combo amp, if you're looking for tube tone in a small package there are a range of 'micro amps' and stompbox-sized tube preamps available. Also there are DIY amp builders that champion a 'firefly' and related designs if you are set on rolling your own.
    +1 to SGM for bringing venue into the discussion. You didn't mention where you'll be playing. A grea-sounding amp is no good if it can't be heard over the rhythm section. So consider where you're going to play and if there is a PA system available, or whether you'll need to bring the horsepower with you.
    Quote Originally Posted by Steve Conner View Post
    If it still won't get loud enough, it's probably broken.

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    Quote Originally Posted by eschertron View Post
    Of the amps described on their website, the one is a hybrid amplifier, with a tube preamp feeding a transistor power stage, allowing the user to dial in from 1/4W to 50W of acoustic power. The other amp seems to be just the preamp section and a recording output, still with the box's 6 1/2 inch speaker. As an alternative to a combo amp, if you're looking for tube tone in a small package there are a range of 'micro amps' and stompbox-sized tube preamps available. Also there are DIY amp builders that champion a 'firefly' and related designs if you are set on rolling your own.
    +1 to SGM for bringing venue into the discussion. You didn't mention where you'll be playing. A grea-sounding amp is no good if it can't be heard over the rhythm section. So consider where you're going to play and if there is a PA system available, or whether you'll need to bring the horsepower with you.
    Thanks Guys,
    First off I play through a Shure C.M. mic with volume control. I also have a wonderful Silvertone 1471 that I have completely redone a few years back. I never gig except for occasional open mics (always a P.A. there) and mostly play with friends. Most of my friends all play acoustic guitars and we will sing without mics so I am wanting to get the tone without stepping on everyone. The Silvertone sounds great but only at volumes that are to high most of the time. So a small head or stomp box with tone and volume and possibly gain if needed that I can run through any P.A. or external speaker. I know about the Firefly and from what I understand it is still quite loud for what I am needing thus the interest in 1/4 watt.

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    http://soundcloud.com/mwjb/sets/half...rding-practice

    This is a 0.4W design, the latest (& best) in a string of tiny harp amps I have built/converted, I used an Eminence Alpha 8A speaker. Bear in mind nearly any single ended champ style amp (6V6 or EL84) can be converted to use a 6SN7/12AU7/12BH7/12AT7/12AY7 as a power tube without much difficulty (though my design is push-pull...I do have a SE 12AY7 powered amp lined out into my hi-fi that I play most days at living room/apartment friendly volume). For the P-P 6SN7 amp I used a 190-0-190 VAC PT with solid state rectification for ~265vdc on the plates), but I have in the past used 260-0-260VAC and a tube rectifier (~300-335vdc on the plates, with a 330ohm to 470ohm cathode resistor) for 6SN7/12AT7/12AU7/12BH7.

    If you go up to 1-2W or a little over, things like possible OTs widen in choice. I have another amp loosely based on a 5D3 Deluxe/Gibson style push-pull amp that uses 2x 6SN7 or 2x6SL7 as power tubes (depending on speaker tap used) that could be built using most of the parts in a tweed 5E3 deluxe style kit (with lowered B+ ideally).

    PM me and I can send you a XL file with a layout & BOM for the amp in the schem above.
    Last edited by MWJB; 01-31-2013 at 08:20 PM.
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  6. #6
    Senior Member mozwell's Avatar
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    Flounder
    I built this for the harp player in our band. Its just a simple preamp, but might do the job you want, when it is plugged into a small PA.
    Its based around runoff grooves "professor tweed" but with a different tone stack. (runoffgroove.com)
    I added a balanced output driver for connection to a PA.
    I thought as many low wattage amps are used for harp amps, i would try the jfet emulation of a small fender amp as a starting point.
    I used a DC plug pack power supply and a voltage regulator to keep the DC supply as ripple free as possible (to keep the noise down).
    The op amp i used TLC2262 is only rated for 16V max on its power supply, so i used a 12V reg. If you use a different op amp such as NE5532 (as it can drive 600 ohm loads) you can easily bump the power supply up to 24VDC (add a 12V zener in the "common" leg of the 7812 regulator & use a 30VDC wall wart) for more gain & level. Make sure all capacitors have suitable voltage ratings (use 35VDC types).
    With no input signal & with teh input shorted, adjust each trimpot so as to measure 1/2 the power supply voltage at each jfets drain pin.
    The 47uF capacitors in the balanced output driver are bipolar types

    Its quite easy to dial in the amount of "growl" you want, and if you set it right you can get extra growl when you blow harder, so you can control the growl by the way you play. Set the tone stack to all knobs at maximum & reduce them to taste, or to get rid of any feedback frequency. A graphic woudl be better here but that was beyond what i was after as i can set that by the EQ on the PA we use.

    Our harp player seems to like it quite a lot, and the first time he used it, he said it was like his harp finally started to "sing" & "growl" the way he heard in his head.....

    Enjoy.....
    Attached Thumbnails Attached Thumbnails harp_j.gif  
    Attached Files Attached Files

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    Thanks Mozwell, So is this able to get the nice tube tone at low volume? For jamming with acoustic guitar and mic free vocals, that kind of low volume?

  8. #8
    don't forget the joker g-one's Avatar
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    To be louder than the harp is acoustically, yet not drown out "mic free vocals" may be a bit of a balancing act. How strong is the vocalist?
    Hopefully others here will have input on this scenario.
    "Thank you. Now on this next one , ladies and gentlemen, I'd like you to pay attention to my tone - not so much my singing or the band... " - JP Lepage

  9. #9
    Senior Member mozwell's Avatar
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    Its just a preamp, designed to go into a mixing desk or a PA. You cant plug a speaker into this.
    It will be as loud as you turn the PA up to.
    You could make a small amp on the end (instead of the TLC2262 circuit), using a LM386 power amp IC......
    Check out Ruby as an example

    You can get a nice sound, pretty much like a tube amp (not exactly, as the only way to get a real tube sound is to use a tube amp)
    With mic free vocals & acoustic guitar, i have the feeling the harp will be loud enough already without having to carry around a little preamp, small PA & a harp mic.

    I just thought i woudl offer this up as a possible alternative.

    Our harp player is very happy with it, as its easy for him to get the growl & tube amp sound he likes without overblowing & shortening the life of the reeds in the harps, and he likes that he can go from clean to a little dirty, just by using the volume control on his harp mic. You could of course set this box to go to "really dirty" but thats not what our harp player likes.

  10. #10
    Senior Hollow State Tech Bruce / Mission Amps's Avatar
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    I can't imagine a 1/4 watt amp being anywhere near loud enough to overcome the natural acoustic volume of a harmonica.

    You probably could do it in spades with a 2-3 watt amp and a single 8" speaker, as the 8A previously mentioned.

    In that case a 12AU7, 12AV7-12AY7, 5751, 12AT7, or 12AX7 and 12AT7 in the final output with both triode sections in parallel would be more then enough.
    So I'd use the small output tranny found in a stand alone reverb unit using a 6V6 or 12AT7 to drive the tank, but instead, drive an 8 ohm speaker.
    If finding a suitable power tranny is hard, two small 120v to 12v@3a PTs wired one 12vac to the other 12vac for isolation might do it.... that would give you 120vac on the output of the second PT, rectified with a full wave bridge and a 100uF@250v cap... you could see up to around 160vdc at the B+ rail.
    I think the 12v secondary of the first PT would be enough to run the two 12A?7 filaments.
    Have not done this myself but isn't that part of the fun?
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    Quote Originally Posted by Bruce / Mission Amps View Post
    I can't imagine a 1/4 watt amp being anywhere near loud enough to overcome the natural acoustic volume of a harmonica.

    You probably could do it in spades with a 2-3 watt amp and a single 8" speaker, as the 8A previously mentioned.

    In that case a 12AU7, 12AV7-12AY7, 5751, 12AT7, or 12AX7 and 12AT7 in the final output with both triode sections in parallel would be more then enough.
    So I'd use the small output tranny found in a stand alone reverb unit using a 6V6 or 12AT7 to drive the tank, but instead, drive an 8 ohm speaker.
    If finding a suitable power tranny is hard, two small 120v to 12v@3a PTs wired one 12vac to the other 12vac for isolation might do it.... that would give you 120vac on the output of the second PT, rectified with a full wave bridge and a 100uF@250v cap... you could see up to around 160vdc at the B+ rail.
    I think the 12v secondary of the first PT would be enough to run the two 12A?7 filaments.
    Have not done this myself but isn't that part of the fun?
    0.2W to 0.4W output is easily loud enough to overcome an acoustic harp. I have built a bunch of these style amps, P-P & parallel SE running 12AU7/12BH7/12AY7/12AT7/6SN7/6SL7. I think you'll want more than 200vdc on the B+ rail, the lower voltage amps I have built were ~260-270vdc on the plates, up to 400vdc+. There are plenty of 190-0-190VAC 5W SE EL84 style PTs about that would work well with SS rectification, even a low voltage 125P1A champ style PT @ 250-0-250VAC, or a little more, will work well too with tube rectification, or even SS with 12AT7/6SN7.

    My day to day pactice rig is a EL84 SE amp converted to SE 12AY7 (265vdc on the plates, 270ohm cathode resistor, 0.33W out at the speaker/load) parallel triodes & I need to line that out via a dummy load box to get it quiet enough for apartment practice levels! :-0

    My 2-4W (switchable via a PI driven to self-split switch) P-P amp (2x6SN7 @ up to 440vdc, or 2x6SL7 @ 375vdc for lower power still) is simply way too loud for home use where I live & can be heard all around the apartment block. In practical terms this is pretty much as loud as many SE EL84 amps & lower voltage 6V6 champ style amps which may only measure 2-3W at the speaker...and are certainly loud enough to attract unfavourable comments from neighbours.

    Don't forget the acoustic harp sound is damped considerably when cupped up to the mic.

    These tiny amps tend to be very flexible regarding tone settings too, no need to use roll on/off tone pots of less than 1MegA, as is often done on harp amps.

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    Thanks Bruce and Mark for the input. Hey Mark I sent you a P.M. way back after your first reply maybe I screwed it up. Yes I would love a layout and BOM for that amp schematic. Looks like just what I am wanting to build! I will P.M. you also.

  13. #13
    Noodle of Reality Steve Conner's Avatar
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    Quote Originally Posted by MWJB View Post
    That's a cool looking amp! Did you make the cabinet?
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    Thanks Steve,

    Alas "no". My woodworking skills are better left unmentioned. I did a rough design & sent it to Mark Phillips at AF Custom Cabinets (in Ammanford, Wales) who has made a few cabs for me, as well as many others. Mark even picked the colour scheme.

  15. #15
    Noodle of Reality Steve Conner's Avatar
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    Interesting, I take it he made it to fit the Ampmaker Woodface chassis? Would he make another one for me?
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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    The chassis & fascia are both direct from Amp Maker: Guitar amp kits and parts, the 4 hole wooden fascia for his AC04 chassis is something that Barry at Ampmaker keeps in stock but the 4 hole versions aren't listed AFAIK on the site, you have to order as a "custom" part, the fascia was 4.50 at time of ordering. The one in the pic is "blonde spruce", you can see the mahogany variety on the Ampmaker site with the WF-55 4W "tweed style" amp kit.

    The larger chassis' at Ampmaker have traditional Marshall style gold & silver fascias.

    Mark Phillips @ AF http://afcustomcabinets.weebly.com would certainly make you a cab, mine are a tight fit on the chassis at the baffle (had to fit the chassis, then put in the baffle), so I'd make sure you have 52mm depth at least for the chassis cut out.

    Just to clarify (for any other interested parties) the circuit is not one that is offered by Ampmaker. I started off building this kind of amp in 5F1 Champ chassis (Mark also made me a compact 1x12" 5F1 cab to airline cabin stowable dimensions) with tube rectifiers (the Ampmaker PT will fit 5F1 chassis also, but you'll need to use SS rectification), but going with the Ampmaker parts allowed me to considerably cut back on build costs...
    Last edited by MWJB; 02-25-2013 at 01:22 PM.
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  17. #17
    Supporting Member tubeswell's Avatar
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    Building a better world (one tube amp at a time)

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    Thanks Tubeswell, it's Nat Adderley's "Worksong"...about the only thing I can play on both diatonic & chro! ;-)

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