Sunday, October 18, 2009

Damn it

In an attempt to discover what was wrong with my bass amp I further destroyed it. At least before it worked like 60% of the time. Now it's completely fucked.

I set it up to take some voltage readings yesterday. About 5 minutes after I plugged it and turned it on two resistors flamed out. I quickly unplugged it and drained the caps. I poured over the schematic trying to find out what had caused the burnout. Both of the resistors are close in the signal path but not in serial. It seems like if those two components burned out that other resistors should have burned out as well.

The Q13 driver looked suspect in the whole thing so I popped it out to test it. Under one set of testing this transistor indeed looks bad, but under another set of testing (that makes more sense to me) it seemed fine. I decided just to put the driver back in and maybe ship the amp off. Apparently when I de-soldered the driver to test it, the small metal pad that attaches it to the circuit board came loose as well.

This has all gotten quite a bit beyond me. I don't trust myself (especially with the erroneous driver testing) to actually sort this all out. I still can't even figure out why just plugging the amp in and turning it on caused catastrophic failure. And I certainly don't have the money right now to get it fixed. It's a $65 bench fee just to look at it, and on Ebay you can get a new one for $200. It's a shitty amp, but even shitty is better than nothing.

Wednesday, October 14, 2009

Unexpected bullshit. Usually the bull at least eats first.

I went to play my little tweed amp today. That's what I built it for. I played it two days ago, so it wasn't too weird to think I would be able to play it today. No dice. It's just been sitting there, but now it has a crazy hum with no input. Now on top of my bass amp being in pieces I have to take apart the tweed as well. It's troubleshooting week here at the Vernon household.

I know I always promise pictures, but this time I will actually try to post some.

In my tweed the first two filter caps became ungrounded. That's a problem. If I re-ground them that should fix the problem.
*end update*

*another update*
Grounding those caps indeed fixed the problem. The wire coming from both of those caps had come loose from the 'star ground' point back behind the fuse holder and light bulb holder. It is a pain in the ass to get to that grounding point without desoldering 5 other things. Instead I pulled the grounding wire forward and grounded it to another point which I had available. It doesn't look as pretty but it works and is FAR more serviceable.

To diagnose the problem I started testing voltages throughout the amp. Some voltages were a little low compared to the last time I tested the amp out, but all voltages were well within spec of the Fender drawing. From that I assumed no components, tubes, or transformers had gone bad mysteriously. Next I started testing continuity throughout the amp. I am ALWAYS fooled by the positive lead going to the speaker jack being shorted to ground. I do not understand why this is the case. Someone needs to explain it to me. After fooling around with the speaker jack with no progress I started back tracking from that point looking for continuity to ground. Low and behold I found the two caps not grounding out. I gave a little tug to the grounding wire and found it to be loose.
*end update*

Saturday, October 10, 2009

New part. Same old problem.

Well I put in the new relay. The good news is that the relay works. I didn't make the problem worse, and the amp actually seems to be working a little better but still not fixed. I'm going to dive in, perhaps this afternoon, with my multimeter to try and track down the actual problem. I will probably find out it's something expensive to fix, and then not fix it. Good times.

Thursday, October 8, 2009

A new post. A new oppurtunity to electrocute myself

My Ampeg (i.e. Crate) SVT-350H bass amp has been on the fritz for several years. I took it to Musical Instrument Repair on Highland in Memphis twice (that I can remember) each time to be told "There's nothing wrong with it." I hate that place. Never go there. I think it was those experiences that really made me want to learn about the inards of my amps et. al.

Several years ago I had a friend rig the fan so that it runs all the time at high speed instead of the stock "run when a little temperature diode that sucks overheats." The fan wouldn't run and the amp would overheat and shut down. So that's fixed. Fan always runs. It's a loud fan and kind of annoying but at least nothing cookc inside.

I've read online that the fan not running is a problem with this amp build (which is also used for the B2 I think). It's possible that the overheating burned something out, but at times the amp works perfectly. I'm hedging my bets against something being burnt.

There is a relay (the K1 relay) that stops the amp from popping the speakers on power up. I think this relay is causing the problems. I bought a replacement from Mouser for about $17 w/ S&H. I'll wire it in when it shows up tomorrow and see how things go.

I'm a little disappointed in myself with this project. I could really dive in with my multimeter and try to actually hunt down the problem for sure instead of just replaceing the thing I think is broken and hoping for a good outcome. I'm still worried I don't know enough to not electrocute myself I guess. I'd rather run the safe route, but I learn a whole lot less in the process. Eh.

Sunday, March 1, 2009

A summary of mistakes

I made a whole lot of mistakes when I was putting this amp together. The amp still doesn't work, and I wonder if one of these early mistakes has something to do with that.

The biggest/most-work-intensive-to-fix mistake I made was putting the tube sockets in wrong. The pins on each tube are numbered, so I assumed I could just put the sockets in whichever way I wanted (it can only go in two ways). I could then line the tubes up, decide which hole on the socket I wanted to line up with pin 1, and solder everything on. That's what I did. After sodlering everything I found out that things don't work that way at all. Each socket and tube have a registration tab of sorts. Each tube will only fit into the socket one way. I had wired the 5Y3GT one pin off and the 6V6 completely backwards with respect to the registration tab. To correct this problem I took a dremel tool and sanded off the registraion tab from the tubes. Without that tab the tubes go into the socket in anyway I want. The downside to this is that I would have to sand any future tubes the same way. Here are some pictures to document this mistake:

With all of the problems I'm having now I wonder if either the sanding or some part of incorrect tube installation is causing my OT problems. I don't have a tube tester to see if the 6V6 tube is screwed up. I went back and fixed the tube sockects and resoldered all connections to be in sync with the registraion tab.

Wednesday, February 25, 2009

Where there's smoke

While I feel slightly contrite for not updating this more often I am comforted in the knowledge that few, if any, read this blog. I guess my main hope is that if someone out there is trying to build a similar project that they will google-stumble their way here and find some helpful information.

A lot has happened since my last update. I will post later, perhaps this weekend, with more details and pictures of my progress up to this point.

A brief summary of events of the month: I soldered everything together, thought I was finished, turned on the amp, covered my ears to block out the extremely high db squealing from the amp, cursed, fixed a few things I screwed up, turned the amp back on, covered my nose to block the stench of the cloud of smoke emanating from the amp, cursed again, de-soldered most of the amp, fixed a whole lot of little things and a few big things I had screwed up, yanked out the burnt output transformer, and ordered a new output transformer. It arrives today.

As I mentioned before I'll go a bit more into depth in a later post in an effort to turn that paragraph of nonsense into possibly useful information.

Sunday, February 1, 2009


I found a clear image of what the wiring for the input jacks should look like:

I definitely would not have come up with this wiring scheme based on the layout and schematic I am using to build. It's strange to me to have everything wired to ground this way, but I guess if that's the way it's done who am I to argue. It sort of makes sense because the center switch is engaged when nothing is plugged in sending all hum to ground. On the other hand it seems like it would also send 'ground' from the unused jack through the hot tap of the jack that is being used. Maybe that resistor cancels that flow. I'm currently shrugging my shoulders.

Saturday, January 31, 2009

The missing piece(s)

Turns out these amp kits are a little more shoddy than I would have originally guessed. I'll admit I'm a bit more of a novice than I should be when starting a project like this, but the 'kit' certainly isn't helping.

A: It didn't come with step-by-step instructions. Lame but I'm sure I'll feel more accomplished with doing something worth while if I can make the thing work.

B: There are at least three MAJOR holes that have to be drilled in both the chassis and the cabinet. I'm really worried about the cabinet holes because the tweed looks so nice. I'm afraid I'm gonna screw it up by drilling. The two holes are absolutely necessary, so I'm baffled as to why these holes don't come pre-drilled. If I had to build the cabinet from scratch I'd understand, but it's like buying a case for a desktop computer with no drive bays cut into it.

C: The hardware that came in the kit is all over the place. By that I mean the bolts for mounting the tube sockets are too big to fit in the socket bolt holes, there are a lot of loose nuts that didn't come with matching bolts, there are several odd sized and non-paired bolts, the RCA jack is for a blackface amp and not a tweed amp, and the RCA male plug is 'vintage' and I can't figure out how to solder anything to it.

I was wrong about the tube socket bolts. They are a tight fit, but they do fit. The pre-amp tube shield bracket took a bit of prying and molding to screw in. All of the tube sockets are now installed.
***End Update***

There are some other smaller issues as well that I won't innumerate here. I did buy a few things from Mojo and Tube Depot to help out the cause. I got a nice blue jewel for the power light. I bought some speaker wire (to replace the speaker wire I quite stupidly screwed up). I bought the correct tweed RCA female jack and a workable RCA male jack. It's not 'vintage' but at end of the day if the RCA jack isn't vintage I don't really give a shit. I bought some safety glasses so that if a cap explodes it won't take my eyes with it. I also got a pre-amp tube shield. It came with a shield receiving socket base but no shield. Lame.

Today I'm gonna start soldering things to the fiber board. I might be getting a bit ahead of myself, but I'm chomping at the bit to get this thing put together.

***Another Update***
Everything is soldered (including one thing I didn't want to solder that I'll have to un-solder and then re-solder.) Also Yuengling Black & Tan is excellent.

Friday, January 23, 2009

It Begins

My call time today isn't until 12:00pm, so I took the extra time to sit down and start planning the layout for the Tweed Champ. There are still quite a few things I'm not sure about. The biggest question floating around is how to ground the whole thing.

Here is a picture of this morning's work.

With a few exceptions everything laid out fairly nicely. The orange drop caps' leads come out at strange angles (i.e. not from the edges), so they sit up off the board a little more than the other components.

The circled components are the ones with more major problems. Starting from the right, the bias resistor for the 12AX7 tube has leads that are too short to reach the eyelets on the fiberboard. This is a carbon comp resistors so I can't just head over to Radio Shack to get another one. I'm trying to decide if I will make a solder bridge to the leads or solder in a bit of wire to bridge the gap. I'm leaning towards a solder bridge.

The 470 1W resistor circled in the middle of the board (which serves as a bias for 6V6GT tube) also has leads which are slightly too short. It does reach the eyelets but just barely.

The 10K 2W resistor in the bottom left is the only metal film resistor in the circuit making it the only non-carbon comp resistor. I'm not 100% sure of the significance of this type of resistor in this position. I'll look into it. The problem with this resistor is that the component is actually longer than the distance between the eyelets laid out for it. The leads are bent in under the component.

Here is a photo of the Chassis:

The circled bit on the Chassis is a rubber gromit which protects the OT (output transformer) wires from the sharp metal edge of the cut hole. There was only one grommet included in the kit. I guess that means I need to track down another one. Hopefully Home Depot can help in this department.

That's all the time I have this morning. This weekend I'm going to see Rascal Flatts with the TV show I work on. My slit wrists might make it more difficult to work in the future, but I'm sure I'll find a way.

Wednesday, January 21, 2009

Everyday I learn there are 10 more things I don't know

I haven't been doing much more than reading and studying lately. The more I look into this project the more I realize I know just enough to kill myself. As an example I found articles about how to drain the filter caps which hold, even at rest, upwards of 320 VDC. Scary.

I did find a website that has a pictorial step by step construction of the 5F1 circuit. It's not a huge help, but seeing the different connections at least gives me an idea of how the whole thing is suppose to come out. Being the visual person that I am it's nice to have a picture to go along with the wiring diagram which, by the way, is the only piece of instruction that came with the amp kit.

Yesterday I wrote the company where I got the kit to ask them, among other things, about how to mount the Fiberboard and Insulation Board (pictures to come later). As it stands I think I have to drill two holes. It would seem to me that if you HAVE to drill these two holes that the boards would come pre-drilled as all the other necessary holes have been drilled on the board.

Other issues include the color coding on the AC power line not matching the schematic (also pictures to come later), and general lack of understand on how to properly ground everything. I still have a lot to learn.

*update* So the folks at home can learn along with me: I found a few handy articles in reference to the AC power wiring problem mentioned above.

Saturday, January 3, 2009

Signs of progress

Today I got tired of watching the Penguins lose. With Melissa gone and TV production on hiatus I have a lot of free time on my hands so I sat down to finally build a working version of a small solid state amp from a schematic in Make Magazine. The amp is centered around the LM386 chip readily and cheaply available at Radio Shack.

I built one of these about a year ago that worked to a limited degree. Looking back at that project I had mistakenly swapped the polarity on one of the caps causing unwanted yet interesting intermittent operation.

I thought that if I'm going to try and put together a more expensive project like the Fender Champ then I should probably practice soldering and schematic reading on a smaller project. Here are some pictures of the successful completion of the amp.

As you can see it's a pretty simple amp involving just a couple of components. The reason I failed at building it properly so many times can be chalked up to stupid mistakes. As an example on the working version, before it was working I thought I was finished and just about bashed my head through the wall when it didn't work. I then realized I had yet to solder the chip to voltage. Stupid.

Also forgive the soft focus of these pictures. My digital camera has no macro capabilities. Also, when not working I tend not to care too much about image quality as long as you can see the image well enough.

There aren't very many solder points thanks to the design of the PCB which has long connective rows. That made it a lot easier to tie everything to 'ground' which in this case is the negative terminal of the 9V power supply.

That's a shot of my 'workbench.' It's frustratingly small but gets the job done most of the time. Also note the rockin' Penguins rug adorning the floor.

My computer is woefully unable to record audio right now. When I fix that issue I will put up some audio from the amp.

This project was more about the 'making of'' than the final product, but the final product doesn't sound that bad at all. I could wire in a pot to control the gain if I really wanted to (which I don't). I was thinking that you could build another of these and couple them. You could get a bit more power out of the extra speakers, and you could have different gain settings for each amp. I've always liked mixing a bit of distorted in with any clean signal.

I've read online about people powering a 4x12 cab with this amp. I've got a cable wired to plug it into my 4x12, but my 4x12 is wired to be a 1x12 right now. I'm wanted a bit less volume when I play for my neighbors sake.

As a side note this amp was constructed while listening to the latest Big D and the Kids Table album 'Strictly Rude'