I have the feeling Tubelab is going to get the 1st prize. 
bst - this was your idea so you make your own rules, I'm not interested in getting my money back because I already have the parts. Fun of this for me is to see if I can design a very nice sounding 5W amp with junk parts. Haven't tried to do this before. Problem would be the output transformer, normally I would use the Hammond 125ESE but....I have to try cheaper ones. We'll see how this turns out.
You're right.
bst - this was your idea so you make your own rules, I'm not interested in getting my money back because I already have the parts. Fun of this for me is to see if I can design a very nice sounding 5W amp with junk parts. Haven't tried to do this before. Problem would be the output transformer, normally I would use the Hammond 125ESE but....I have to try cheaper ones. We'll see how this turns out.
You're right.
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Probably chiming in when not wanted, BUT...the best low power amp i have made had a 6sn7 as a push pull triode. It had the AX84 4-4-0 front end, which is a bit tricky for a first build, and it was also not cheap, however....it is a really sweet loud versatile little amp. Its my all time favorite. Its supposed to be one watt, i have had experienced muso's asking for the same amp but half as loud. Perception is a funny thing
I do have the remains of plenty of guitar amps sitting around, but I intend to create something new since I haven't built a new guitar amp in a long time. It's about time.
I would imagine that silicon diodes in the power supply and maybe a CCS in the audio path somewhere are OK, but do we allow for sand state designs, hybrid designs, or should the audio path be all tube? I'm sure that you could build a 12AX7 into LM3886 amp for less than $100, no wait I have one of those too. Built it at least 10 years ago, it rocks too, makes about 75 watts.
I'm no guitarist, but i've been considering making an amp and cabinet for my musician friends to use. Was thinking of using two eminence beta 12lta drivers i have spare in a 3ft2 sealed box in a bipole arrangement. I'm thinking that having one driver firing backwards into the wall or corner of the room would reduce the rising top end of the beta 12lta.
For amps i was considering either the SE-5a or WF-55 from Amp Maker for guitar amp kits and parts
For amps i was considering either the SE-5a or WF-55 from Amp Maker for guitar amp kits and parts
Some excellent suggestions. Let's revise and extend the challenge a bit.
I would think that a simple, bare-bones design like this could be brought to a working prototype in sixty days of spare time. Let's round off the deadline to August 15th.
I'll start a separate thread with the 'Hundred Buck Amp Challenge' as the title.
We can make it a collaborative effort, and people can augment or critique each others' designs. I'll include a poll, and at the end of the challenge, we'll tally the votes for the best amp (design, innovations, sound). Winner still gets his/her amp paid for (and bragging rights), and diyaudio still gets a $250 donation.
Feel free to chime in on the new thread with specifics for the contest rules; after a day or two we'll post them, and let the breadboarding begin.
This little amp will sound like a big Fender. Output will be made on 6J6 phase splitter and 2x6BA6 output tubes. 6S17B-V in preamp. small 240V CT power transformer for output. To save on chassis everything except PS, control pots and sockets can be mounted on a spring reverbarator tank.
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I do not play electric guitar or build guitar amplifiers so the following is really just to start the ball rolling on "Guitar Amplifier Sound" requirements.
An electric guitar if amplified through a perfectly linear amp will sound quite boring as the body of an electric guitar does not add any interesting tones. The "interesting" sound comes from distortion in pickups, amplifier and speaker.
Crunch
High levels of upper harmonic distortion, F5, F7, F9... This distortion is caused by grid current in the preamp tube(s). The amp must recover from this or you can get blocking distortion.
Compression
Speaker efficiency drops at peaks. It happens when the speaker is pushed. You have to "right size" your speaker so that it distorts at low wattage.
It also is derived from the current limits of the power supply as the tube rectifier has enough resistance to cause voltage drop on high current demands.
Bluesy
Output iron distorts from too much current. Use one that is "too" small for the output tube bias current. It may also be related to high levels of second harmonic distortion (F2) in single ended amplifiers.
Jim
An electric guitar if amplified through a perfectly linear amp will sound quite boring as the body of an electric guitar does not add any interesting tones. The "interesting" sound comes from distortion in pickups, amplifier and speaker.
Crunch
High levels of upper harmonic distortion, F5, F7, F9... This distortion is caused by grid current in the preamp tube(s). The amp must recover from this or you can get blocking distortion.
Compression
Speaker efficiency drops at peaks. It happens when the speaker is pushed. You have to "right size" your speaker so that it distorts at low wattage.
It also is derived from the current limits of the power supply as the tube rectifier has enough resistance to cause voltage drop on high current demands.
Bluesy
Output iron distorts from too much current. Use one that is "too" small for the output tube bias current. It may also be related to high levels of second harmonic distortion (F2) in single ended amplifiers.
Jim
Dumb question: Is there anything inside the power supply of older personal computers that is useful? Just guessing that caps and power diodes are probably leaded components and could be scrounged, forget the surface mount stuff. My real question is whether the iron could somehow be used, maybe in the new amp's supply, maybe as a poor-man's OT? New old-style power supplies can be found cheaply everywhere. Brand new ATX supplies sell for $5.
If the price is any greater than "free", then probably no. You might be able to scrounge some mains caps and diodes, as well as a switch and IEC jack. The transformers inside are designed for high frequency, if you got very lucky one might be marginally useful for an OPT, but would probably need to be re-wound and/or used as parafeed. Far easier, safer, and more reliable to do like Tubelab and I and just use an inexpensive Antek toroid ($10-13) for the OPT. A high voltage switching PSU built with cobbled together parts sounds like a recipe for trouble, especially since a proper PSU isn't that expensive.
Right from the start PC computers came with switching power supplies and they do not have any iron that we can use. But what is usable is the diodes and capacitors used to feed the switching circuit. The generally use a bridge rectifier and a set of capacitors, I have one here with caps that are 220uF and 200V. 200 v may seem on the low end of usability for guitar amps but these power supplies are designed to operate on 120V or 240V. They do this by using a voltage doubler configuration on 120V and a regular bridge power supply circuit for 240V. They use a switch to select which line voltage you have, this can be put to good use in our case.
Say you use a 120v to 120v power supply transformer, you can get about 180v out or in the range of 300v. Switch it one way you have full output, the other you have an amp with a lower power setting.
Now I doubt I would go pick up a ATX power supply for $5 since I could get a bridge rectifier and a couple of caps for that price. But stripping an old computer makes sense, don't forget the switch, cord and socket are also parts you can use.
HI,
I see bst, you have not so small requirements about guitar sounds, but you want small power amp, isn't that? So, it is interesting thread about good sounding guitar amp like many here, but we are maybe went topic of this thread. Because i wanted to build one for me, finally I found schematic for HH combo 212 VS Musician guitar amp which I want sincerely to recommend here again on DIYAudio.
I don't want to shake this all pervading and traditional tube fashion, but if you really like to get results in sound like you asked, I sincerely recommend to you go there:
freestompboxes.org (off-shore) • View topic - Build an HH VS musician AS00015/A tone correction module
It is solid state, but excellent guitar amp where you can change only output stage for smaller power. This two channel guitar preamp will fulfill far more than your expectations are about guitar sound, and it is of course also far more cheaper and simpler solution than any tube amp. Very soon I will make this amp in complete same conception, but first I like to find appropriate good speakers.
Regards!
I see bst, you have not so small requirements about guitar sounds, but you want small power amp, isn't that? So, it is interesting thread about good sounding guitar amp like many here, but we are maybe went topic of this thread. Because i wanted to build one for me, finally I found schematic for HH combo 212 VS Musician guitar amp which I want sincerely to recommend here again on DIYAudio.
I don't want to shake this all pervading and traditional tube fashion, but if you really like to get results in sound like you asked, I sincerely recommend to you go there:
freestompboxes.org (off-shore) • View topic - Build an HH VS musician AS00015/A tone correction module
It is solid state, but excellent guitar amp where you can change only output stage for smaller power. This two channel guitar preamp will fulfill far more than your expectations are about guitar sound, and it is of course also far more cheaper and simpler solution than any tube amp. Very soon I will make this amp in complete same conception, but first I like to find appropriate good speakers.
Regards!
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