Re: after multiple headaches...
Adding a 'Master' gain is a v. good move. I find that adjusting the gain (preamp and master) gets me more dramatic and interesting changes in tone than playing with a tone stack anyway. (I generally get to where I want by using the treble cut on the guitar, and the pu selector anyhow.)
Happy New Year
John
Brad-geekysuavo said:
Adding a 'Master' gain is a v. good move. I find that adjusting the gain (preamp and master) gets me more dramatic and interesting changes in tone than playing with a tone stack anyway. (I generally get to where I want by using the treble cut on the guitar, and the pu selector anyhow.)
Happy New Year
John
i'm currently waiting for the final few parts (two resistors and the OPT) in order to finish the amp, but here's what i've finished so far, as an update. (sorry, i know the thread is old.)
http://blackelbowfoot.livejournal.com/104167.html
(pictures are towards the bottom of the post.)
thanks again for all the help guys!
~ brad.
http://blackelbowfoot.livejournal.com/104167.html
(pictures are towards the bottom of the post.)
thanks again for all the help guys!
~ brad.
Brad,
That's one of the nicest looking breadboard tube ampliifiers I've ever seen.
I hope it turns out to be quiet. If it had been me I would have lined the inside of the wood chassis with a groundplane/Farady cage made of thin sheet copper or heavy duty BBQ kitchen foil and contact cement.
Make sure you don't play any gigs in old bars that may have termites.
That's one of the nicest looking breadboard tube ampliifiers I've ever seen.
I hope it turns out to be quiet. If it had been me I would have lined the inside of the wood chassis with a groundplane/Farady cage made of thin sheet copper or heavy duty BBQ kitchen foil and contact cement.
Make sure you don't play any gigs in old bars that may have termites.
hey all,
i hate to resurrect this thread, but i wanted to ensure everybody the amp will be finished soon. 🙂 i'm anxious to get home, since there should be an OPT arriving soon that i can shove into the thing and finally get some test readings.
i suppose i'll just use this thread to post updates/progress as i go.
~ brad.
i hate to resurrect this thread, but i wanted to ensure everybody the amp will be finished soon. 🙂 i'm anxious to get home, since there should be an OPT arriving soon that i can shove into the thing and finally get some test readings.
i suppose i'll just use this thread to post updates/progress as i go.
~ brad.
well that took long enough!
after much needless waiting, the connections in the amplifier are completed! i'm forced to wait a while before i can turn it on, perform the old "see if it blows up" test, and try to play some tones (err... tunes) through it, since the tubes i need for testing are in another corner of texas right now... 😉 by mid-october i should either have some terrible awful gory pictures of a charred dorm room, or some lovely scope output shots. 🙂 🙂
~ brad.
after much needless waiting, the connections in the amplifier are completed! i'm forced to wait a while before i can turn it on, perform the old "see if it blows up" test, and try to play some tones (err... tunes) through it, since the tubes i need for testing are in another corner of texas right now... 😉 by mid-october i should either have some terrible awful gory pictures of a charred dorm room, or some lovely scope output shots. 🙂 🙂
~ brad.
I looked at this. First off you might want to double to B+ voltage, maybe with a voltage doubler. This will greatly reduce the current but maybe the PT is up to it?
Next, the main problem with a new design guitar amp is not getting it to make noise any reasonable design will do that. The hard part is getting the tone "right".
It is kind of like brewing beer or making wine. It is very easy to simply make alcohol but if the goal is a certain exact style well that is harder. Are you looking for a kind of blues "crunch" sound, class British rock. "death metal" or what?
The choice of a pentode as the first gain stage and a cathode follower drive tone stack followed by a high current, low gain recovery stage will certainly have a sound un-like most common common amps. I'm guessing that maybe it will be a clean sound with no preamp over drive but certainly not a "Fender style" clean.
Maybe what you are looking for maybe not. But almost certainly you will need to adjust the design after you listen to it. This adjustment is where it become an art.
In a way HiFi amps are easy to design because you know what they have to do. Everyone wants the same thing in a HiFi -- low distortion and flat frequency response. Bot guitar amps really need to color the sound. Guitars produce no sound below 80Hz so you don't need'/want bass response and also have no sound higher then about 8Khz so you can roll off to high end too. Most player want to ability to clip the waveform asymmetrically so as to add large amount of second harmonics. Most but not all guitarists don't like third order harmonics.
You are building a musical instrument, not a hifi. All good musical instruments (Pianos, saxophones, flutes,..) have rich harmonic content. This is what makes guitar amp building a creative project and makes it different from hifi amp building.
Things like way under spec'd power supplies contribute to the sound if you like that kind of compression (musicians call it "sag") but add more and bigger caps to the power supply filer for tighter bass sound.
Think about things like if you want strings # 1, 2 and 3 to over drive an AX7 tube but the bass strings to come through clean when you play a loud open chord. You can choose a cathode by-pass cap value to make this happen or not. It's an art not a science.
This is why people suggest to copy an exiting amp so you can predict the tone of the amp befor you start.
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i completely agree chris. thanks for the input. 🙂 after testing for smoke the fun part will be tweaking the amp until i fall in love with the sound. we'll see. 😛
~ brad.
I sent this as a PM but maybe best to bring it up here again let others comment too.
The photo shows the amp built on a wood chassis. Normally a metal chassis is used. The metal provides an important back-up safety ground function in case of component failure or loose wires.
Without a metal chassis you will need to make 100% sure every switch handle, jack and screw head exposed to the outside is grounded with a very secure mechanical connection. This should be in addition to the signal grounds and should be designed in such a way that even if any wire breaks or a transformer shorts out or the spring inside the standby power switch fails, the ground system is still in place.
The reason for being so careful as to provide a redundant ground is that you don't get a second chance with lethal voltages.
The normal method is to enclose all the HV inside a conductive box and then ground the box with a wire that is (1) at least the same size as the conductors on the AC mains power cord and (2) is as short is practical. Doing just this makes it very safe.
The photo shows the amp built on a wood chassis. Normally a metal chassis is used. The metal provides an important back-up safety ground function in case of component failure or loose wires.
Without a metal chassis you will need to make 100% sure every switch handle, jack and screw head exposed to the outside is grounded with a very secure mechanical connection. This should be in addition to the signal grounds and should be designed in such a way that even if any wire breaks or a transformer shorts out or the spring inside the standby power switch fails, the ground system is still in place.
The reason for being so careful as to provide a redundant ground is that you don't get a second chance with lethal voltages.
The normal method is to enclose all the HV inside a conductive box and then ground the box with a wire that is (1) at least the same size as the conductors on the AC mains power cord and (2) is as short is practical. Doing just this makes it very safe.
Don't fire this thing up just yet. I see an issue that will cause your 12au7 to die a horrible death. They are dc coupled to the cathode of the 6au8 triode which will have roughly 150V on it. For the au7's to bias up properly they will have to dump 70+ma across the 2.2k cathode resistors = instant death. Gonna have to capacitive couple those bad boys or the smoke will get out.
wow, you're right! thank you so much for catching that mistake! i've already cut the wire in question in preparation for the addition of an ac coupling capacitor. once my tubes come in, i'll be able to add in a cap (for a rolloff around 10khz, i'd need 15pF i think... may have to order one, it looks like the amp doesn't have any suitable caps...) and *then* test. 🙂
chris, as for your recommendation of a metal case, this project is too far along for that. obviously in a serious design i would consider such a thing, but connecting the earth ground to the amp ground seems reasonable enough here. thanks for your input!
please let me know if there is anything else i have missed in the design of this amplifier.
thanks everybody!
~ brad.
no lost magic smoke! 🙂
good news!!
i got the tubes today and did a smoke test with a signal generator and dummy 8 Ohm load to see if anything fried after only a few (tested for 10 at most) minutes, and good news: all is still well! in fact, running a signal through the amp shows a clear amplification of the signal, as well as quite a bit of even-harmonic distortion, and a bit of odd-harmonic distortion.
it should be interesting to try the amp on a test (i.e. cheap) speaker and actual guitar...
~ brad.
good news!!
i got the tubes today and did a smoke test with a signal generator and dummy 8 Ohm load to see if anything fried after only a few (tested for 10 at most) minutes, and good news: all is still well! in fact, running a signal through the amp shows a clear amplification of the signal, as well as quite a bit of even-harmonic distortion, and a bit of odd-harmonic distortion.
it should be interesting to try the amp on a test (i.e. cheap) speaker and actual guitar...
~ brad.
sorry it's taken so long to test this amp... school has been killing me. 😛
well, i finally got around to testing the amp with a loaner les paul and some cheap 8 ohm speakers. the result? not bad for a first try: the amp has a warmish tone, a little on the clean side, but can still clip when the output stage is driven adequately.
the four-capacitor can used in the rectifier setup gets WAY too hot, so i'm thinking this build was more of a proof of concept than a true everyday-use amp. if i were to rebuild around modern components, however, i'd be quite comfortable using it regularly. 🙂
~ brad.
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