And I have no problem with you keeping things under wraps if you plan on producing it. Really was teasing with my first post. Still am curious what you ended up with.
At least something worthwhile would have come out of 100+ pages. Yeah I was there from the beginning, well at least withing the first couple. Had no problem posting schematics since I have no interest in hawking anything. Even made up a parts and price list for one design using the 70V OT and 12AQ5's, made it under the $100 limit including knobs. And only two sources so shipping does not eat up all the gains made whittling down every nickle and dime. Should have my current incarnation of the amp up and running soon. Sanding down guitar tops took much of my time lately. Pretty much set for life in that regard, need a cheap source of decent hardwood though.
At least something worthwhile would have come out of 100+ pages. Yeah I was there from the beginning, well at least withing the first couple. Had no problem posting schematics since I have no interest in hawking anything. Even made up a parts and price list for one design using the 70V OT and 12AQ5's, made it under the $100 limit including knobs. And only two sources so shipping does not eat up all the gains made whittling down every nickle and dime. Should have my current incarnation of the amp up and running soon. Sanding down guitar tops took much of my time lately. Pretty much set for life in that regard, need a cheap source of decent hardwood though.
I posted the schematic and a brief description of how each stage works in post #1622, last November. I made a PC board which turned out very ugly, but worked. Post #1625. The board and transformers were seen in post #1648. Nothing has changed since then. I just turn it on and play when I get a chance.
I have been having some serious numbness and pain in both hands recently, kinda screws my guitar playing. I can't seem to find a doctor who can figure it out. The diagnosis used to be arthritis, since it was only my left hand. Then when it moved into my left arm, it was HEART ATTACK.....go to the ER NOW. Dude, if it was a heart attack I would be dead by now, this has been happening for 2 years, and I have no problem running a mile or two while pushing two grandkids in a stroller! Now its both hands and left arm, they just want to feed me pills that make my brain number than my hands!
When I'm having a good day, I'll try to record the sound and post it. It ROCKS.....and it does mellow pretty good too. The only thing it really needs is reverb.......I got this thing for 60's surf music........
Somewhere in a box near me....I have several hundred used 6AQ5's, and an equally large collection of 6AU6's. There were also two or three large boxes full of twin triodes with 4 digit numbers on them......I have been saving them for something, just not sure exactly what yet.
Nice score!
Our jam sessions have just expanded from four to six microphones. I have a little Mackie mixer with only four microphone inputs (and a few line inputs). It looks as though I'll have to use my little ART USB Dual Pre as a two-input mic preamp (it has 1/4" analog outputs as well as the USB output). Great, one more piece of kit to haul around!
I do, and I also remember all the noise about, err, noise from valves being somehow a non-issue, unlike those noisy nasty low-caste semiconductors with their nasty low-brow crystal structure.
You would think that someone who builds and sells amps for a living (I got curious, and checked; the guy who originally triggered this thread is still at it, selling kits on Ebay) would know that Johnson and shot noise voltage both depend on the square root of temperature, and a valve cathode operating at roughly 1300 Kelvin is inevitably going to be at least 6 dB more noisy than a semiconductor at 300 Kelvin, like it or not...
-Gnobuddy
I just took a look. I like the MOSFET that is a voltage-source at DC and turns into a sorta-current-source at audio frequencies! I was curious about the corner frequency of that transition, but the value of trimpot R9 seems to be missing.
I am very sorry to hear that. I hope you do get a good diagnosis and some help soon.
Surf music or not, in a typical home environment (a small room with limited natural acoustic reverb), a bit of electronic reverb in a guitar amp is a wonderful thing!
Biyang's "Tri Reverb" pedal can be found for around $50 - $60 new, and IMO is a decent-sounding reverb ( I have one, and use it.)
A used Zoom G3 multiFX pedal off Craigslist for $100 or so may be even better - it has some really good reverbs, as well as delays, EQs, chorus, compressors, a usable looper, and a lot more. I think the simulated amp models reek, but many of the modulation effects are pretty good.
-Gnobuddy
I remember the circuit, did not understand the pentode mosfet then, got it now. I have been looking into distortion pedals and want to build an all semiconductor amp with Class D output. Promises I won't post it here.
Yeah doctors, found out how much they know about pain symptoms without the cause staring them in the face. Once they get you on pills to control it they are happy enough to forget about it. Really hope your issue is not related but look up allodynia.
Reverb, right, that was what I went out for. I picked up some PNP (you would think I would have some) transistors to drive a reverb tank. The lumberyard was a street over so I checked out what was new and came home with 70 guitar tops. Just finished sanding them down to 0.120", realized my hands have issues also. Wonder if they will outlast the wood or the wood will outlast them. Carving the necks is the most physical operation and also the most satisfying. Hate to collect all this wood and not use it.
Yeah doctors, found out how much they know about pain symptoms without the cause staring them in the face. Once they get you on pills to control it they are happy enough to forget about it. Really hope your issue is not related but look up allodynia.
Reverb, right, that was what I went out for. I picked up some PNP (you would think I would have some) transistors to drive a reverb tank. The lumberyard was a street over so I checked out what was new and came home with 70 guitar tops. Just finished sanding them down to 0.120", realized my hands have issues also. Wonder if they will outlast the wood or the wood will outlast them. Carving the necks is the most physical operation and also the most satisfying. Hate to collect all this wood and not use it.
R9 is the front panel "saturator" knob. It adjusts the gain of the stage. The parallel combination of R6 and R7 sets minimum gain, and that plus R9 sets maximum gain. The amp now has a 1 meg pot, because I didn't have anything bigger. C3 sets the corner frequency, which moves with the gain knob.
The oddball tubes are from the last generation of the AA5 radio before it got a silicon injection. The input pentode is essentially an 18 volt 6AU6, the triode is a 6AV6 (1/2 a 12AX7) and the output tubes are similar to a 50C5. 6AQ5's work far better, but need more voltage.
Some have called this circuit a "gyrator" because of it's inductor like characteristics, but it is not a gyrator in the classic opamp sense.
This concept comes from a series of experiments I did back in high school electronics class (1967 through 1970, and they taught tubes!). There was a circuit in a magazine (Popular Electronics maybe?) that used a 1 meg resistor as the plate load on a 6AU6 pentode, fed by some stupidly high voltage, and buffered by a cathode follower, to achieve a ridiculous gain number.
Attempts to duplicate this design for a tube based guitar fuzz pedal in class failed. It made a muddy sounding awful tone, probably because none of us, including the teacher understood the high impedances, stray capacitances, and the effect of our crappy breadboarding skills at the time.
I had forgotten about it until Gary Pimm started posting experiments using partial CCS loads on pentodes in some of his designs to boost the gain and lower distortion about 10 years ago. Experiments at that time showed promise.
During the time that the challenge ran, I had lost both parents, and Sherri's mother was losing her 5 year battle with cancer. We both spent too much time in a car, airplane, or hospital waiting room. I carried my laptop and played with LT Spice, or laid out many of my ideas in Eagle. Some of those old board designs are now being tested.
I can tell you that this circuit doesn't work like it simulates, probably due to less than perfect pentode models. You have to "play with parts." It will work notably better, and it is easier to get working with more B+ voltage. It can be a total terror to make stable if you try to use a pentode with a lot of Gm. It makes a great TV and radio jammer, especially when you plug in a guitar cable.
I briefly tinkered with a Belton module during the challenge, but I think I want a real set of springs....and I have a few tanks for the next amp. There is always a "next amp" the only questions are when and what.
I do have something about half built that many will consider a crime......Microsoft Windows in a "music machine"....Yes, it has tubes.
I have not heard that word yet, but it doesn't seem to apply to me. The days that I am the most physically active are pain free. Sitting around relatively immobile, say at the workbench or in front of the computer seems to be the trigger, then the symptoms appear later that night. Looking back this has been going on for many years, it's just gotten much worse in the last year or two.
I built a guitar preamp with a pair of 12AX7's a few years ago, basically a Marshall circuit up to the Master Volume knob. I used it to torture my HiFi amp designs. I got one of those $20 class D amp boards from China and wired the two together. Didn't sound as bad as I expected, in fact it sounded good until you hit the "D" amp hard enough to make it clip. It's in a box somewhere. I'll post a picture when I find it.
It may not fit this thread, but might have merit in another thread. I will post pictures of mine when it's done, but it has stalled again...too many projects, and I need to find the guitar preamp. It's part of the plan. Tube guitar preamp, stereo tube power amp, Windows 7 PC with audio in - out and MIDI, Overloud TH3 amp simulator, Peavey ReValver, multiple software keyboard instruments, and a DAW, all in one box.
I'm not sure where it fits since it's sort of a one box fits all kinda thing.
Doctors did not bother to mention the condition to me and I had to find out about it all on my own. A number of diseases can cause the condition and it tends to start in the extremities, part of the reason I mentioned it. Really glad we can rule that one out.
I hope to put a limiter on it before the max output is hit. Thought of doing one with a Marshall preamp also, no shortages of amps around my place. Had another come back home today. A SE Champ with bass and treble controls or just tone for a Tweed flavor. Gave it to my brother to use and he gave it back saying he will not have time to use it. Not having it was the prompt for me to make the current 12AQ5 amp. It even has a hole drilled for a reverb pot. Happy its back home.
I hope to put a limiter on it before the max output is hit. Thought of doing one with a Marshall preamp also, no shortages of amps around my place. Had another come back home today. A SE Champ with bass and treble controls or just tone for a Tweed flavor. Gave it to my brother to use and he gave it back saying he will not have time to use it. Not having it was the prompt for me to make the current 12AQ5 amp. It even has a hole drilled for a reverb pot. Happy its back home.
I sold or gave away all my guitar amps before leaving Florida. Now that I'm 1200 miles away, I doubt that I'll ever see them again.
The only one I really miss was a commercial product from the 1960's, an "Ultraflex" made by the "Audio Crafters Guild." The same amp was sold as "Panaramic" and "Magnatone." It had one preamp split to two different power amps. The "balance" was set by the Ultraflex knob. The two power amps had similar schematics, each with a pair of 7591's, but different component values, different OPT's, and each powered its own speaker. The amp with the bigger OPT fed a 12 or 15 inch speaker, and the amp with the smaller OPT fed a 6 or 8 inch speaker. It had a unique bluesy tone that I have never heard from any other amp. It was totally original, even the tubes, and worked perfectly.
I gave it to another forum member who had a dead version of the same amp. He didn't know that I had one until he came to my house to pick up some tubes and transformers that I was giving away. He saw it and told me about his, and asked if it was for sale.....maybe he could make one good one from the two. He was freaked when I turned it on and started playing it. I gave it and a Crown CE2000 (one dead channel) to him. The live channel in the Crown was strong enough to scatter the cone in one of those 80's vintage BSR coffee table downfiring subwoofers when I plugged my bass guitar into it!
I had to work on a project for a friend in Florida today. I will be going there for a vacation in a couple of weeks. Since I dragged my drill press out of its hiding place, I started working on a chassis for Amp 1.5. Maybe I will finally make a box for it, but it needs a chassis first.
I bought a chassis for it from Mouser back in January. I got it out of its box today. Apparently Hammond finds it perfectly acceptable to put a deep scratch through the white protective plastic into the aluminum, then put the sticker and shrink wrap over it and sell it anyway. The shrink wrap was not damaged, so the scratch was there first.
The only one I really miss was a commercial product from the 1960's, an "Ultraflex" made by the "Audio Crafters Guild." The same amp was sold as "Panaramic" and "Magnatone." It had one preamp split to two different power amps. The "balance" was set by the Ultraflex knob. The two power amps had similar schematics, each with a pair of 7591's, but different component values, different OPT's, and each powered its own speaker. The amp with the bigger OPT fed a 12 or 15 inch speaker, and the amp with the smaller OPT fed a 6 or 8 inch speaker. It had a unique bluesy tone that I have never heard from any other amp. It was totally original, even the tubes, and worked perfectly.
I gave it to another forum member who had a dead version of the same amp. He didn't know that I had one until he came to my house to pick up some tubes and transformers that I was giving away. He saw it and told me about his, and asked if it was for sale.....maybe he could make one good one from the two. He was freaked when I turned it on and started playing it. I gave it and a Crown CE2000 (one dead channel) to him. The live channel in the Crown was strong enough to scatter the cone in one of those 80's vintage BSR coffee table downfiring subwoofers when I plugged my bass guitar into it!
I had to work on a project for a friend in Florida today. I will be going there for a vacation in a couple of weeks. Since I dragged my drill press out of its hiding place, I started working on a chassis for Amp 1.5. Maybe I will finally make a box for it, but it needs a chassis first.
I bought a chassis for it from Mouser back in January. I got it out of its box today. Apparently Hammond finds it perfectly acceptable to put a deep scratch through the white protective plastic into the aluminum, then put the sticker and shrink wrap over it and sell it anyway. The shrink wrap was not damaged, so the scratch was there first.
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I spent much of the afternoon drilling, cutting, and filing a couple of pieces of metal. One was for a project I have to take to Florida in a couple of weeks, the other was for a once abandoned project. Guess which one I finished.
All the parts are mounted, maybe tomorrow I'll wire it up and plug it in.
All the parts are mounted, maybe tomorrow I'll wire it up and plug it in.
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That's really unacceptable.
Hammond stuff isn't exactly inexpensive, either. Paying through the nose for pre-damaged hardware is a bit much!I hope either Hammond or Mouser makes it right for you.
-Gnobuddy
A few days ago I mentioned my DIY guitar amp wasn't sounding right. One of the symptoms was dull-sounding cleans.
Shortly after that, I found I'd accidentally ended up with a 1 meg gate stopper resistor on the LND 150 (MOSFET) phase splitter. It was supposed to be part of the bias network, but later I changed my mind, rewired the biasing arrangement, and forgot to change the resistor.
I also had a conjunctive filter on the output transformer primary. I removed that as well.
I tested by plugging one of my guitars straight into the power amp section (no preamp). Excellent, the power amp now sounds good, at least for clean tones at low level. I'm guessing that conjunctive filter was a bit too aggressive.
Time to re-connect the preamp, one bit at a time. So I connected up just the input stage (a triode that's part of a 6JW8), and a 500k log pot to act as a gain control.
Guess what, the clean tones became dull again. Evidently the source impedance of the 500k pot, along with the capacitance of a foot or so of coax cable, was enough to filter out the high treble.
Now that, I wasn't expecting. It seems as though I see 1M and 500k pots all over the place in guitar amp schematics, even inside the guitar itself.
I've certainly heard the volume pots in the guitar cause treble loss, but that's with a 15 foot guitar cable's capacitance to deal with.
I didn't expect that less than 15 inches of shielded cable would cause audible treble loss, though!
-Gnobuddy
Shortly after that, I found I'd accidentally ended up with a 1 meg gate stopper resistor on the LND 150 (MOSFET) phase splitter. It was supposed to be part of the bias network, but later I changed my mind, rewired the biasing arrangement, and forgot to change the resistor.
I also had a conjunctive filter on the output transformer primary. I removed that as well.
I tested by plugging one of my guitars straight into the power amp section (no preamp). Excellent, the power amp now sounds good, at least for clean tones at low level. I'm guessing that conjunctive filter was a bit too aggressive.
Time to re-connect the preamp, one bit at a time. So I connected up just the input stage (a triode that's part of a 6JW8), and a 500k log pot to act as a gain control.
Guess what, the clean tones became dull again. Evidently the source impedance of the 500k pot, along with the capacitance of a foot or so of coax cable, was enough to filter out the high treble.
Now that, I wasn't expecting. It seems as though I see 1M and 500k pots all over the place in guitar amp schematics, even inside the guitar itself.
I've certainly heard the volume pots in the guitar cause treble loss, but that's with a 15 foot guitar cable's capacitance to deal with.
I didn't expect that less than 15 inches of shielded cable would cause audible treble loss, though!
-Gnobuddy
Been a bit absent from this for a while now, but still been tinkering.
Actually have mine all completed! (ish) I ended up sticking with the 12W6 in the output and ran the B+ rail up around the 250 mark for the 6SL7 on the input stage. I'm planning on turning it up to the 300 mark next time I get the thing open, just enjoying playing for now
OPT and PT are both EDCOR units. Fantastic construction and if you can plan out the timing, the wait time isn't terribly bad. WGS was my go-to for the 10" 'Veteran 20' speaker that's sitting in the donation chassis. Holy cow when a guy cranks up the volume knob it gets nice and loud, especially for a "4W" output.
The power supply issues I was having were remedied by putting some real skookum capacitors in there, along with a 5H hammond inductor. What had been taking a while for me to resolve was how I wanted to feed the filaments. Being an oddball myself, I've got a 12V and 6V tube that drew different currents so there was no easy way to get the damn things wired up (so i thought...hint...foreshadowing). In the process I tried several variations of DC supply; rectified non-regulated, rectified regulated, rectified with drop resistors.......and every single one of them got noisier than an SOB when they were placed *in* the chassis, not just sitting on my bench. So what did I end up doing? Just so happened to find the right power resistor to drop out the voltage (still no clue why i had a 40Ohm power resistor floating around) and yup.....the real simple AC with a dropping resistor ended up being the best option.
Still no tone circuit in it but I'm just wanting to enjoy playing it at the moment. Everything is in the cab and you can actually tote it around....not a mess of wires on the table (CRAZY!). It's got pretty good touch sensitivity, takes pedals really well and for being what it is, about 75-80% of what I could ever want. The "cleans" can get semi-loud before breakup and when it does start to breakup, its real nice and tubey with a little bit of bite on it. A light eq-booster type pedal on the front end helps drive the first stage into a little more distortion for some great bluesey sounds. I was thinking about lowing the gain on the first stage to try and use the full range of the volume pot but I'm going to wait as the tonestack's going to take some out for me.
Buddy of mine here in town has a real nice attenuator unit with a line out so we're going to try and get some line recordings along with stealing a mic from someone to get ambient recordings.
Actually have mine all completed! (ish)
I ended up sticking with the 12W6 in the output and ran the B+ rail up around the 250 mark for the 6SL7 on the input stage. I'm planning on turning it up to the 300 mark next time I get the thing open, just enjoying playing for now OPT and PT are both EDCOR units. Fantastic construction and if you can plan out the timing, the wait time isn't terribly bad. WGS was my go-to for the 10" 'Veteran 20' speaker that's sitting in the donation chassis. Holy cow when a guy cranks up the volume knob it gets nice and loud, especially for a "4W" output.
The power supply issues I was having were remedied by putting some real skookum capacitors in there, along with a 5H hammond inductor. What had been taking a while for me to resolve was how I wanted to feed the filaments. Being an oddball myself, I've got a 12V and 6V tube that drew different currents so there was no easy way to get the damn things wired up (so i thought...hint...foreshadowing). In the process I tried several variations of DC supply; rectified non-regulated, rectified regulated, rectified with drop resistors.......and every single one of them got noisier than an SOB when they were placed *in* the chassis, not just sitting on my bench. So what did I end up doing? Just so happened to find the right power resistor to drop out the voltage (still no clue why i had a 40Ohm power resistor floating around
) and yup.....the real simple AC with a dropping resistor ended up being the best option. Still no tone circuit in it but I'm just wanting to enjoy playing it at the moment. Everything is in the cab and you can actually tote it around....not a mess of wires on the table (CRAZY!). It's got pretty good touch sensitivity, takes pedals really well and for being what it is, about 75-80% of what I could ever want. The "cleans" can get semi-loud before breakup and when it does start to breakup, its real nice and tubey with a little bit of bite on it. A light eq-booster type pedal on the front end helps drive the first stage into a little more distortion for some great bluesey sounds. I was thinking about lowing the gain on the first stage to try and use the full range of the volume pot but I'm going to wait as the tonestack's going to take some out for me.
Buddy of mine here in town has a real nice attenuator unit with a line out so we're going to try and get some line recordings along with stealing a mic from someone to get ambient recordings.
I never thought about it, so I looked up the Heathkit power supply, and yes, the cover is exactly the right size.....and I was at the Dayton hamfest a couple of weeks ago. There was probably at least one of those old supplies lurking in a box somewhere in the acres of junk to be searched through in "the biggest hamfest in the world."
I didn't even think to look for one, but I did get a 32 input Mackie mixing console for $200....."It works" , yea right, everything here works, but for $200 I can fix it.
I will probably make a traditional wood box for it. Compared to making the metal chassis, the box is the easy part.
I bought two of these boxes a while ago when I had to order about $200 worth of parts for several projects. They have been in the Mouser box since then. I was pretty angry when I first saw the gash three days ago, but after thinking about it for a while, I came to the realization that their scratch would probably just be one of several that would be present after I was done drilling, filing, and hacking at it with a Dremel tool (IEC socket). I was right.
After all the holes were made, and the white protective film peeled, there were a few scratches, including one ugly scratch I made when a drill bit danced a bit. Fortunately the ugly one is now mostly covered up by the power transformer, and the Hammond scratches are really not bad.
I put it aside and made the box for my other project, a "machine gun sound simulator" which is basically a specialized WAV file player using one of the Teensy boards I described earlier.
After that box was done, I started wiring up Amp 1.5, when I made Dumb Blonde Mistake #347. During the wire up, I realized that I wanted a speaker impedance switch, so I just grabbed the hand drill and drilled a 3/8 inch hole in the rear panel.....right into the power supply input cap. DOH!
Take board out, replace cap, but board back in, too late at night to finish it......Power up tonight.
The 6JW8 could have a Miller capacitance of up to 125 pF depending on actual gain. It's probably about 100 pF total input capacitance, plus your cable. See if the treble response changes with the gain pot setting.
I had a similar problem in a HiFi amp when I used a 250K pot. All was well when I changed to 50K.
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At least it wasn't plugged in at the time!
The 6JW8 triode is the source, feeding a little UHF pentode via the 500k pot. The signal chain is:
Guitar -> 6JW8 triode -> 500k pot -> short cable -> 6AG5 UHF pentode.
That's one of the reasons I was really surprised, teensy UHF pentodes are not supposed to have much input capacitance. The 6AG5 datasheet specifies only 6.6 pF.
It did, that was the give-away. Nice and crisp-sounding near full gain, nice and crisp near zero gain, dull in the middle. Aha!
Interesting! I routinely see higher pot values in guitar amp schematics. I guess many guitarists don't particularly want those crisp trebles.
I was planning to do the same thing you did (lower the pot value to reduce its Thevenin impedance), but I'll have to order some more Alpha pots. I don't have anything lower than 250k!
I'm also a bit concerned about loading down the previous triode stage and losing some gain due to the lowered pot value. Perhaps the small amount of gain loss won't be an issue, because ra is fairly low for the triode in the 6JW8, nominally only 20 k ohms.
The next hurdle is the ugly, blatty-sounding distortion that shows up every now and then. There is some unpleasant blocking distortion going on somewhere...I need to track it down.
-Gnobuddy
I wonder that the amp pot values reflect those in guitars as well as in amps (Fender gets an extra deal if they order 250k pots by the millions, rather than severa different values for different applications).In the guitar, there's the pickup impedance. The coil is really thin wire that adds up to a few thousand ohms DC, but it's the several henries inductance that (is one of the) causes the big problem of the highs being reduced into a low resistive load. The suggestions I've seen (for the volume pot in the guitar) are for a 250k volume pot for single coils, and 500k for humbuckers.
When the guitar's volume control is less than full, it does raise the impedance as seen into the guitar, and the cable capacitance cuts the treble (a lot more than at full volume). I keep my guitar volume control at full on and control the volume at the amp.
And yes, an active preamp in the guitar fixes this, but then you need a battery or an extra cable for power to the preamp.
It's a bunch of tradeoffs like anything. It's possible to do low-impedance/balanced pickups (there was a Les Paul Recording Guitar with an XLR output, surely a clean low-noise output, but I hear it didn't sell well), but the "problem" is they then have flat frequency response, a horrible thing for an electric guitar. The usual high-impedance pickups with their thin wire and lots of windings have enough capacitance that they self-resonate around 5 to 7 kHz. Lots of turns on pickups was surely done in the era of tubes to get a decent signal voltage output, and the defect of the pickup coil self-resonance became part of the electric guitar sound.
agreed. Some weeks ago I set up a pickup resonance tester using my laptop with ARTA. This showed that some of these "hot" pickups resonate below 3kHz, even in the absence of the loading cable . Other ones are above 5kHz, the highest one above 10kHz.
On my opinion a peak of 5kHz is fine for a real transparent fender tone, on the other hand 3kHz or less give a dull sound.
I hate this archaic hi-ohmic circuitry, my first mod to an electric guitar is an active buffer pre-amp.
On my opinion a peak of 5kHz is fine for a real transparent fender tone, on the other hand 3kHz or less give a dull sound.
I hate this archaic hi-ohmic circuitry, my first mod to an electric guitar is an active buffer pre-amp.
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