Whoa, it works.

Turns out I had the female power jack wired up (in)correctly. A while ago, I was playing with it on a breadboard before putting the amp together and had figured out the pin out with a DMM. When I went to solder it in, I didn't remember how I had it connected, so I followed a picture I found online. Who knew, the internet can be wrong.

Obviously, I haven't had much time to play with it yet. It gets surprisingly loud.

I think the 500K pot for the pre-amp gain is way too much for my needs. Turning it all the way up with the output volume maxed creates a rumbly/buzzy sound.

Switching the power amp gain switch to max (200X) gives a metal sound, while the other two settings (20X and ~52X gain) are just sort of clean and louder clean. Which I guess makes sense and is probably more useful than not.

The top boost/bright switch doesn't really seem to make much of a noticeable difference to my ear.

All in all, I think it sounds pretty good considering it's sitting unenclosed on a desktop connected to a speaker without a cabinet. Especially considering I didn't electrocute myself, start a fire, or blow up anything. There is quite a bit of extra room on the board, so I would still like to add some sort of tone control (because why not). I also would still like to add an extra diode to get asymmetrical clipping (not sure how to fit this in).

Fun project. Definitely learned a bit. Not sure if this really solves my goal of a super clean amp. Sort of interested in trying to put together an amp with the LM833 Roly mentioned earlier.

Anyways, I'm rambling. I need to get the speaker housed and find something to fit the amp into.

I'll say it again, because I can't say it enough. Thanks for all the help.

 :lmao: I was only kidding about no one asking about the project.

Thanks for the info on the crimps.

I did forget to mention that I switched out the battery for a DC jack and am using a wall wart for power. Don't know how I forgot to mention that.

So the wall wart is rated for 12V and is putting out 12.3V according to my DMM. So I guess it's working.

I'll have a look at the rest tomorrow and try to figure out how to measure/check what you asked for.

Thanks for the help.

I thought I did a pretty good job with this (I was even a little proud of my work), so it's definitely frustrating that the amp isn't working. Anyways, below are the pictures of the work in progress. Hopefully the pictures don't break my thread again.

Broke the tracks.



Added the jumpers.



Added the op-amp sockets.



Added the resistors and diodes.



Film caps.



Electrolytics.



The backside.



Op-amps installed.



All the pots, switches, and jacks connected.

Well, I'm a little bummed that no one checked in to see if I ever made any progress with this.

I did finally make some progress. I even have some play by play pictures. Unfortunately, the amp doesn't seem to work, so I need some (explicit) help figuring out what's wrong. I imagine it's something simple that I'm overlooking, but who knows.

When I plug the amp in, nothing explodes or gets hot, but the LED fails to light up. There is absolutely no signal being put out to the speaker.

The only intentional modification I made was Roly's suggestion of buffing up the capacitor's to 2200uF/16V (to replace the 470uF) and the 100uF/16V (to replace the 47uF). The only other peculiarity is I have the speaker connected via alligator clips since I don't currently have a cabinet to plug into. Probably not ideal, but it's what I've got. Speaking of which, what are the little crimp connectors called that you use to connect speaker wires to the speaker terminals?

So if someone can explain what I need to do to troubleshoot, I'd appreciate it. Pictures to follow.

Edit: Weird. At least on my computer, my pics seemed to keep this last page from loading correctly. I'll post links to the photos for now.

As I said, I need to get some pics of the cabinet up, so here are some blurry pics of the pieces still in their frames. Note that there is protective paper on the pieces which hides the grain of the bamboo.

http://imgur.com/ULqVVOL
http://imgur.com/NvNVSfH

All in all, pretty happy with how it turned out. I had a chance to dry fit the pieces, and everything lines up about as well as I would have managed with a saw and router. The only booboo is the front panels. I think some gremlins invaded my design software; they are about 1/16" short on one side. I think some creative gluing to the short end will make the mistake unnoticeable though.

Well, Mr. Fahey, I'll take you up on your offer. I think I've already zeroed in on the most readily available and best bang for your buck, but I'd still like to hear opinions from the pros. Anyways, some data sheets, in no particular order:

Eminence Patriot 820H http://www.eminence.com/pdf/820H.pdf
Eminence Alpha 8A http://www.eminence.com/pdf/Alpha_8A.pdf
Jensen Mod 8-20 http://www.jensentone.com/printpdf/45 *The Jensen links are a little flakey. I had to save the link as a PDF to view the files correctly.
Jensen C8R http://www.jensentone.com/printpdf/30
Jensen P8R http://www.jensentone.com/printpdf/14
Celestion Eight 15 http://celestion.com/productpdf.php?id=8
WGS G8C http://wgs4.com/g8c
Weber Speakers (various 8" clones?) https://taweber.powweb.com/weber/ They have all kinds of variations, but no specs. They also offer reconeing of vintage speakers via their eBay store, if an 8" ever pops up. Maybe someone here knows some of the intricacies of their speakers?

They all look pretty similar spec-wise, although the Jensen's seem to be a little low in sensitivity relative to the others. Given its current price, my pick would be the Celestion Eight 15 ($29 shipped), but I welcome someone telling me why I should opt for something else.

Apologies Roly, I misunderstood. I thought you meant to take the sensitivity and power ratings and come up with some magic ratio. At least I was correct in assuming that sensitivity was important.

There aren't many 8" speakers with (relatively?) high sensitivity. Hence why I was looking out of the box at the 8MRA? I imagine it still produces at 82.41Hz, just not as loudly. I don't know if that's a good thing, a bad thing, or just something outside the norm. I wouldn't step on a bassists toes if I played in a band. Is the frequency rating really that important?

If I stick strictly with "high" sensitivity "guitar" speakers, really the most readily available speakers are the Eminence 820H, WGS G8C and Celestion Eight 15.

Anyways, I realize I'm doing lots of typing with very little building. Time to take some pictures of the cabinet pieces.

So, just to make sure I'm understanding you exactly, I want both dB and W to be as big as possible when selecting a speaker?

I'll use an example. So that Eminence speaker I saw comes in a couple of flavors. They are (with specs in the order sensitivity, power rating, usable frequency):

Eminence Alpha 8A: 94dB, 125W, 58Hz - 5kHz
Eminence Alpha 8MRA: 100.9dB, 125W, 400Hz - 4.8kHz
Eminence Beta 8A: 95.1dB, 225W, 78Hz - 4.5kHz

Again these are only examples, but your selection would be the Alpha 8MRA or Beta 8A due to the higher sensitivity and power rating?

Thanks for clarifying.

Just wanted to thank everyone again for the help and to add a bit of an update to this. I have a box of components but haven't had time to actually do anything with them yet. Hopefully I'll get some time in the near future to do some finger burning.

However, I did get a chance to get/make parts for a speaker cabinet. My living space just doesn't allow me to do any cutting or sawing of anything anymore, so I decided to go the laser cutting service route. I haven't had time to glue and screw the parts up yet, but I think it will turn into a cool little cabinet. At the very least, it will be unique.

Unfortunately, the service I used doesn't cut 1/2" ply any longer (no service seems to) so I had to go with 1/4" bamboo and lots of bracing. I know it's not standard, but I'm really having a lot of fun working this project out and seeing what comes of it. At least I hope something comes of it.

I designed the cab to sort of kind of look like an 8" tweed champ. There were a lot of ways I could have gone with the design, but I just wanted something simple and relatively cost effective. Not sure about finish yet, but the bamboo looks pretty cool, so I'm contemplating doing some type of wipe on finish. This cab is never going to see heavy duty use on the road, so it shouldn't be a problem. I'll have to get some pictures put up of the pieces when I get a chance.

So the above is a long way of bringing me to my next question, which I think is a fairly important one. Any suggestions for 8" speakers or are there any specs I should pay particular attention to? Speaker specs are a bit dizzying and as expected, every hobbyist seems to have their own idea about which speakers are great. One speaker that looked kind of interesting (although it looks like it's a not a true guitar speaker) is the Eminence Alpha 8A. I even found some clips of some guy using it as a guitar speaker. Anyways, I'm digressing. Any helpful hints?

I always wondered how some guitarists were getting so much use out of their volume and tone knobs. Thanks for explaining the power stage sag.

I went back and compared your clip to the Bonamassa video, and I gotta say, I think you nailed the effect/sound/magic. Very, very cool. I want to build one but I think it's out of my league for now.

For what it's worth, I'm throwing in a vote for you to design some type of compressor circuit so everything is always dialed in just right.

Again, awesome job.

Quote from: Roly on January 07, 2015, 03:22:21 AM


The body sleeve effectively contacts at only two points, and with the common single hot spring, at only one point on the hot side, and this is a sphere against a plate, the contact area is a pinprick, yet we are expecting it to carry up to five amps.

This is what I've always found perplexing. The 1/4" jack just never seemed like a good way to transfer power. Although, it has worked for how long now?

I'm certainly not going to be touring with the cab or the amp anytime soon, but I was thinking I might as well attempt to do it right from the outset. Never thought about using XLR jacks. I'll look into them and see what I come up with.

Thanks.

Well, I'm now waiting for some parts to arrive so I figured I might as well asks some questions about "features" for the speaker cabinet.

Should I install dual, parallel input jacks for daisy chaining? Not sure I would ever use this, but since I have the option to do it, why not?

Again since I have the option to do it now, should I consider using those fancy speakon type jacks or should I just stick with 1/4" jacks? Always been a little perplexed by the use of 1/4" jacks, since they don't seem very robust.

Edit: Also, do must people roll their own speaker cable for connecting amp heads to cabinets? I can't seem to find inexpensive short lengths of cable for this use.

Thanks, and a belated Happy New Year to everyone.

I might hit a trash bin and see what old electronics someone has tossed. I know I've seen old routers and CD players from time to time.

I know I said I wouldn't approach this until after the amp was put together, but I've been mulling over how to put together a speaker cabinet. I thought I could find a broken down amp and scavenge it, but I haven't had any luck so far.

I don't have any access to any heavy duty power tools, so I was thinking of doing something out of the box and having some panels laser cut via online service. The standard seems to be 3/4" thick panels. Would 1/2" ply with some hardwood bracing/battens work and glue and screws, or would it not be rigid enough? It seems like it would be sufficient for my uses, but then again, I've never built a speaker cabinet before.

Thanks for the circuit, Roly. It helps clarify what we were talking about. I now see where the 2200 and 100uF caps for the power supply go. I can handle that mod.

I see that you mentioned VR4 and R5 are of dubious value. I already thought R5 was dubious. Is there a (simple) way to improve the use of VR4 as an attenuator?

I don't seem to have any orphaned 12V or 9V adapters sitting in my junk bin, so I guess I'm stuck buying new.

Thanks for holding my hand through the planning stages. Just wait until I start to actually build something.

Roly, I think what you mentioned last resonates the most. I'm just going to go for building it according to the circuit diagram. I can sort out capacitors, resistors, and whatever else if the amp doesn't turn out well when all is said and done. I do have some final questions.

1. You mentioned using an LM833 for the preamp. How is the LM833 compatible as a replacement for the TL071 if it is a dual op-amp? Just looking at the pin out, they don't look interchangeable.

2. Google cache to the rescue. I was able to find a more recent image of the mylk diagram (although I think it's the same as what I posted before). I've attached a picture of the diagram with what I've been calling a decoupling capacitor circled in red. It's shown as 1uF. Since the author suggests anything between 1uF and 10uF I'm going to wing it and do 4.7uF. It wouldn't be off by an order of magnitude, correct?

3. By regulated power supply, you mean something like this, correct? I'm going to give it a go without the added capacitance and see what comes of it. Ideally I'd like the amp to be idiot proof (and by idiot I mean me) in case I accidentally grab the wrong wall wart. For now, I should be able to handle not using the wrong wart.

Thanks again.