Hunoz, The hum problem is related to the layout which is on a 60cmx60cm board, with lots of long wires running all over for power and ground, etc.
While layout on a PCB may be more difficult than p-p in some regards, it is an interesting approach which I would like to try. From reading about other PCB layouts, using twisted pair above the board for filament/heater wiring seems to alleviate heater relateed issues and would simplify the layout.
Home made PCBs are cheap to produce. Single qauantity PCBs are expensive but moderate volume drives the cost down rapidly.
While layout on a PCB may be more difficult than p-p in some regards, it is an interesting approach which I would like to try. From reading about other PCB layouts, using twisted pair above the board for filament/heater wiring seems to alleviate heater relateed issues and would simplify the layout.
Home made PCBs are cheap to produce. Single qauantity PCBs are expensive but moderate volume drives the cost down rapidly.
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Some Marshall lead amps have three gain stages using 12AX7's which have a Mu of 100. The gain of each stage is about 50 due to loading by the next stage. The total maximum gain of the gain stages is 50 cubed which is 125,000. The tone stack has a typical loss factor of 10 for a total maximum gain of 12,500. The actual gain is lower due to partially bypassed cathodes and resistive summing losses.
This challenge precludes the use of 12AX7's due to cost. I can find several types of low cost dual triodes in good supply with a Mu in the 35 to 55 range. I developed a gain stage that uses a mosfet buffer to remove the effects of loading. I measured gains of 22 to 40 depending on the tube used and the available plate supply voltage. I decided to use 4 gain stages since it is far easier to remove a stage on a PC board design than it is to add it. This amp is currently using tubes with a Mu of 50 which give a stage gain of 33. The total maximum gain is 33 to the 4th power.......1,185,921....What was I thinking! I was thinking 33 cubed is only 36,000 which falls short of Marshall Stack fed with a stomp box and cranked to 11 teritory. Still, taking gain out is easy. More experiments this weekend.
I do many things in my full time job as an electrical engineer. One of them is designing PC boards. Ordinarilly I would not commit a design to PCB layout until it was working in some form of prototype. AMP1.0 became AMP1.1 all on perf board. AMP1.3 is coming with one more tube. No PCB exists for that one yet and it is simple enough for PTP wiring.
I was away from my lab for 2 weeks due to a death in the familly. I knew that there would be a lot of dead time so I took a laptop and laid out a few boards with nothing more than ideas behind them. AMP2.0 was one of them. I finished it on the plane back to Florida. I will make all of my amps on PC boards, but the builder is free to make their own amp as they see fit.
The PC board in the picture was cooked up at home. It cost me about $10 which was not counted, but the amp will still come in at less than $100 if I counted the $10. Amp2.0 will likely be AMP2.4 or 2.5 before I am happy with it. I'm guessing more parts will come out of it than will go in. Especially those $0.88 mosfets.
Building an amp for $100 and selling an amp in kit form for $100 are two very different things. I have been selling electronic kits for about 35 years. For a small business to break even considering all the rolled up costs, NOT counting your time, you need to be able to buy all the parts for about half of what you sell the kit for. The shipping involved in getting the parts to you is the biggest expense, and packaging them in kit form is next.
Curiosity will eventually convince me to see what these little guitar amps will sound like when hooked up to some high efficiency HiFi speakers. I will keep it away from the FH3's since I could probably blow them. There are some cheap guitar speakers out there, especially on Ebay.
I
I don't watch much, but that will likely change when my wife returns home. I cancelled cable TV about a year ago. She wasn't here to object. I saved about $900 during that year and spent it ALL on this project.
I bought my "starter house" 33 years ago close to where I work. I still live there. My commute time has gone up though. It now takes me 10 minutes to get home in afternoon rush hour. At least 3 of those are wasted just getting out of the parking lot.
PC board design for tube amps is not trivial especially with the high gain of a guitar amp. A good PC board design can be completely hum free. The same techniques needed for clean PTP tube amp design are used, only you are restricted to two dimensions. Once the design is perfected it is REPEATABLE, over and over by builders of all skill levels. I have proven that with my HiFi amp boards. Some people have chosen to copy my SSE design using PTP wiring. At least one of them sent me an email saying the design sucked because it hummed a lot. Gee, no ones's does. Remember what I said, It has to be simple enough that "even a drummer could build it."
It is likely that one or two of my guitar amp designs from this challenge will become Tubelab products. There will be more that don't fit the $100 cost requirements.
Again, the cost for the boards is prohibitive for purchases less than 50 pieces using an American PC board house. I hesitate sending any of my PC board designs to a offshore PC board house for fear of seeing them on Ebay before I could finish the kit. Depending on the size of the board it will add $15 to $25 to the cost to build the amp.
If you can convince them that you are a legitimite business AES has a wholesale division called CE distribution. The same transformer is $15.95 through them. I have one and will try it.
No that box contains a Jensen 8 inch Alnico speaker. I bought two of the Ebay 12 inch Eminences. I am building the boxes for them now. They should finished enough to be usable but not covered in next weeks wood shop class.
I paid $125 for mine at ACE music store. I got my daughter a Mexican Squire for $99 at SAM ASH music and it played better. She pawned it without telling me.
Pawn shops are another option for guitars that are not highly sought after. Bring along someone who can play to weed out the unplayable junk with warped necks.
The Mexican and Korean Fender Strats are sold as Squier Stratocasters. The country of origin is usually on the headstock. The bodies are dipped in a "plasticizer" which covers the cheap wood and deadens the tone somewhat, but they are reasonably good guitars for the price. The Chinese Fenders "strats" are called Starcasters and can be found at Sams Club and Best Buy. I have never heard anything good about them, but haven't played one either.
For a couple of years I had a contract EE position that was 5 miles from home, took 20 minutes on average to get there, now I have a different contract position that is much further removed, but really shouldn't take more than 45 minutes, it's all highway except for a few miles..
I'm probably going to just cruise CL from time to time looking for a bargain guitar, I'm partial to some of the cheaper Parkers, (although they are heavy) the Telecaster and a couple of Strats.
I think the possibility exists with some scrounging at hamfests and flea markets to get some of the parts for cheap - obviously not always going to be the case that someone could replicate that success..
Anyone considered sub-minis? 6021 and some others still show up comparatively cheap from time to time, and would save the cost of a socket. Might not be a good choice in a $100 project I suppose.. I do have a bunch of them.. I'm sure there are some cheap compactrons that would serve well, but future supplies might be an issue.
I'm probably going to just cruise CL from time to time looking for a bargain guitar, I'm partial to some of the cheaper Parkers, (although they are heavy) the Telecaster and a couple of Strats.
I think the possibility exists with some scrounging at hamfests and flea markets to get some of the parts for cheap - obviously not always going to be the case that someone could replicate that success..
Anyone considered sub-minis? 6021 and some others still show up comparatively cheap from time to time, and would save the cost of a socket. Might not be a good choice in a $100 project I suppose.. I do have a bunch of them.. I'm sure there are some cheap compactrons that would serve well, but future supplies might be an issue.
Wavebourne is using Russian sub-minis in his amp. I have a big box full of these and some were dual triodes......They will fit into an 8 pin round IC socket too.
There are some tasty looking compactrons out there. I think I could make a 75 watt guitar amp with $4 worth of tubes. I put them pretty far down on the to-do list since they are not popular outside the USA. One of the criteria for my amp designs is at least 1000 of all tubes in stock somewhere. So far that eliminates ALL dual triodes with a Mu of 100 and a price of $4 or less.
So far all of my designs use totally obscure tubes that are in large supply. I am now trending back toward mainstream. I have refrained from mentioning any tube numbers since there is always someone out there looking to grab them all up in hopes of making a buck later.
Ebay used to show the ID's of bidders on an auction. I had to give up buying tubes on Ebay because people would snipe them at the last minute thinking that I was making some cool project and they could sell them later for a profit. One such weasel had the stones to email me after he grabbed a big bunch of sweep tubes that I bid on and ask what I was building. I routinely place very low bids on tubes that I want to play with. I used to get Chinese 6L6GC's for $3, 6LW6's for $5, 5842's for $3 and I got at least 20 45's for under $10 each, some as low as $3. Not any more.
When I first moved here I was 3 miles from the TI plant. I started riding a bike to work and almosts got run over so I quit. Years later I did get hit riding a bike and gave it up completely. Ten years ago we moved to the current location and I'm 9 miles from my house to work, 7 of that is on the highway so it is a short commute.
Happened to me too. I used to ride a bike to work when I had to work weekends. I must go through one retirement community and past another. I also must cross three 6 lane roads populated with cell phone yacking, text messaging, makeup applying idiots.
About 10 years ago I was crossing one of said 6 lane roads in the crosswalk with the walk light illuminated. A senile citizen was stopped at the RED light in the left turn lane. As I approached his stopped car he decided to move forward into my path. I slammed into his car at about 10 MPH and landed on his hood as he was moving....into an intersection with traffic. He suddenly hit the brakes dumping me into the path of traffic. Fortunately I wasn't hit again and the car that came the closest to crushing me was occupied by a county cop.
The cop stayed until the local city cops showed up gave them a statement and left. He also gave me his card. After several city cops came and went the last cop standing gave ME a ticket for hitting the old man got on his Harley and left me and my busted bike on the side of the road.
Of course the ticket was dismissed. About 3 months later I get a call from the old guys insurance company. They are suing me for the $2000 in damages my body did to the Nissan Maxima!!!!! They wanted the name of my insurance company. I refused to comply since I was on a flipping bicycle. I went down to city hall and paid $20 for a copy of the accident report, which gave me the old guys name.....It suddenly became crystal clear. The 84 year old geezer was an ex city council member. It also clearly stated that the make of vehicle was Huffy.
Fortunately I had the county cops phone number and we convinced the old guys insurance company that I should be suing them, and that a certain city cop had lied on the accident report.
I got a new bike but rarely ride it unless I put it in the back of the Element and go far from city traffic. The city cop is still standing by the side of the road at least 1 morning a week with his motorcycle and laser gun.
Grimp,
A 60x60cm board is large and you would have long wires running if you used the full size of the board. Having said that there is nothing stopping you running the long wires in a way that would represent good layout techniques. As such hum issues would not be a major concern.
Trying to create a printed circuit board for an amp and succeed not having hum and/or feedback problems without several trials is just about impossible in my opinion. That should not stop you though trying!
Beside the usual maintenance work, I have primarily worked on amps where the amps had some sort of problem (many with hum issues and or excessive feedback) or the client wanted the sound of his/her amp changed. Amps with printed circuit boards make these sort of tasks very difficult! In some cases impossible without ripping the PCB out and rebuilding the amp! So, you have guessed I am not a fan of amps with PCBs! Yes, I know commercial realities dictate cutting cost. Using PCBs are one way for large companies to make a lot of amps for very little costs! PCBs have their place and benefits. I just do not think they are ideal for guitar amps!
Getting back to your hum issues: You have mentioned using twisted wires for the heaters. Do you know the cause of your hum? Are you running AC or DC heaters? Are you using center tapped heater supply? Have you considered lifting the heater below or preferably above ground? I am not trying to tell you how to suck eggs. In case they help, they are just friendly suggestions that you may have not thought of. If and when I am dealing with the same problem day after day, it tends to be something obvious that I just could not think of at the time. Even just telling a friend sometimes makes me realize the obvious.
Wondering, George concerning the high gain in your amp, if you've noticed the very large grid stoppers used in amps from Soldano? He seems to add a lot of gain, then waste some away. It seems to borrow from the Fender Bassman and Marshall amps in a similar way that the Mesa Boogie Dual Rect does. I've read that the very large grid stoppers are to avoid forward grid current even in the preamp tubes. Here's the Soldano Lead Overdrive (SLO100) clone schematics in a .zip file in case you've not seen them:
http://www.blueguitar.org/new/schem/soldano/slo100.zip
There's a SLO Clone forum where they have chassis, panels, circuit boards, transformers, etc:
www.slocloneforums.com • Frequently Asked Questions
There are things that I like about the design, and just a few things that I'd probably change or experiment with.
http://www.blueguitar.org/new/schem/soldano/slo100.zip
There's a SLO Clone forum where they have chassis, panels, circuit boards, transformers, etc:
www.slocloneforums.com • Frequently Asked Questions
There are things that I like about the design, and just a few things that I'd probably change or experiment with.
Fender 5F2-A Build
I built this kit recently which was US$55 shipped. The design is a slightly mod version of the Princeton that ProjectG5 did a few years ago. Not an original design - just a simple, good sounding classic design that could be built with widely available parts...
The kit came with cheapo Chinese 6N4 and 6P6P, and I swaped them with Sylvanta 12AX7 and Gold Lion 6V6GT, they sound sweet! The transformers are generously sized, the OPT does not even get warm after hours of playing (not cranked of course).
Jaz
I built this kit recently which was US$55 shipped. The design is a slightly mod version of the Princeton that ProjectG5 did a few years ago. Not an original design - just a simple, good sounding classic design that could be built with widely available parts...
The kit came with cheapo Chinese 6N4 and 6P6P, and I swaped them with Sylvanta 12AX7 and Gold Lion 6V6GT, they sound sweet! The transformers are generously sized, the OPT does not even get warm after hours of playing (not cranked of course).
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An externally hosted image should be here but it was not working when we last tested it.
Jaz
Thanks for the suggestions.
I am running AC Heaters.
I have tried center tap grounded and elevated Center tap with no effect.
I tried adding capacitance at the anode resistor of each stage to ground with almost no effect.
I tried turning off all lights, etc in the local area with no effect.
The hum is not that loud, I just don't like it.
Listen to the recordings linked to YouTube in post 750 and see if you can hear it.
Speaking of post 750, it has been 24 hrs and no one has commented on the demo.
Is it that bad?
Nice looking amp jazbo8, $55 is a very aggressive price. What was included?
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Grimp,
I checked out your circuit diagram at the time, but missed listening to the audio clips. Just did though. I like the clean, but am not much fan of the crunched sound of your amp. It is just my personal taste so others my love both! I hardly can hear the hum and only occasionally hear it. So, it is probably not much of an issue.
I have to say that I think your layout is most probably responsible and the cause of your hum issue. Based on the video clip, it would seem that the sections are intermingled rather than are in separate logical sections. You may not have any hum issues at all if you were to separate the sections on your board, like PSU, Power amp, PI, 3rd, 2nd, 1st preamp.
Jazbo8,
I would also like to know more about this amp. It may just be a cheap way to get started on a new amp project. I wonder if it could be ordered directly from China.
Princeton Kit
hunoz - I am pretty sure they do not ship overseas, but I can check for you to make sure if you are really interested...
Grimp - The kit came with everything, all the parts and the blue chassis you see, which is pretty small (300mmx140mmx40mm), the parts are mounted on three PCBs (no PTP wiring here) - the main board, the tonestack board and the effect send/return board. The parts are of average quality (what can you expect for $55?!) I am actually surprise at the size of the transformers, they are pretty heavy, I am not sure who makes them, but I think they got to cost something like $10 a piece.
Anyway, since I am just starting out with tube amp building, I thought this kit was a good beginner's project for me to start with, encouraged by the success of this relatively easy build, I am now ready for my next project, which will be the AX84 SEL, which I think could also be build for around $100, may be a bit less. Since there is no kit for the SEL in China, I will have to source all the parts myself, what fun...
Jaz
hunoz - I am pretty sure they do not ship overseas, but I can check for you to make sure if you are really interested...
Grimp - The kit came with everything, all the parts and the blue chassis you see, which is pretty small (300mmx140mmx40mm), the parts are mounted on three PCBs (no PTP wiring here) - the main board, the tonestack board and the effect send/return board. The parts are of average quality (what can you expect for $55?!) I am actually surprise at the size of the transformers, they are pretty heavy, I am not sure who makes them, but I think they got to cost something like $10 a piece.
Anyway, since I am just starting out with tube amp building, I thought this kit was a good beginner's project for me to start with, encouraged by the success of this relatively easy build, I am now ready for my next project, which will be the AX84 SEL, which I think could also be build for around $100, may be a bit less. Since there is no kit for the SEL in China, I will have to source all the parts myself, what fun
...Jaz
hunoz - I am pretty sure they do not ship overseas, but I can check for you to make sure if you are really interested...
Grimp - The kit came with everything, all the parts and the blue chassis you see, which is pretty small (300mmx140mmx40mm), the parts are mounted on three PCBs (no PTP wiring here) - the main board, the tonestack board and the effect send/return board. The parts are of average quality (what can you expect for $55?!) I am actually surprise at the size of the transformers, they are pretty heavy, I am not sure who makes them, but I think they got to cost something like $10 a piece.
Anyway, since I am just starting out with tube amp building, I thought this kit was a good beginner's project for me to start with, encouraged by the success of this relatively easy build, I am now ready for my next project, which will be the AX84 SEL, which I think could also be build for around $100, may be a bit less. Since there is no kit for the SEL in China, I will have to source all the parts myself, what fun
Jaz
Hi Jaz,
I am genuinely interested as the price of the transformers and chassis alone would make it worthwhile to get it. However, if they do not ship to Australia or it costs too much to ship it then it becomes a mute point. Hence I thought shipping from China may be the way to go.
Thanks in any case.
Andy
Very large grid stoppers in the preamp are used for three things.
As you suggested they prevent or minimize grid current. Last night I proved to myself that "farting out" can be generated entirely in the preamp. The large stopper creates a built in limiter and distortion generating effect.
A large grid stopper working against the Miller capacitance of the triode forms a low pass filter to roll of highs. This helps heep RF pickup to a minimum especially in the first stage, and helps control oscillation.
A large grid stopper should not waste much gain at reasonable signal levels and midrange frequencies since the grid should be a very high impedance.
Since this is a guitar amp, you can throw away gain by overloading stages if you have too much gain (this will increase distortion which if done properly is good), or use a resistive divider to control where the overdrive begins by scaling the output between stages.
Also you could use one section osf the ECC81 as a cathode follower to drive the output tube. This leaves you with three gain stages which should be fine.