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Quote from: smsuryan on October 17, 2010, 04:00:55 PMare solid states less expensive to make compared to tube amps?...you dont need tubes obviously and i dont know about the pt and the ot, if theyre are in solid states...

For the most part I'd say yes, but there's a lot of maybes. The chassis, speakers, pots, power transformer, power supply caps, and other items that they share stay the same, but you don't (usually) need an output transformer or tubes. The output transistors are a few bucks each on average, and you can get just about any chip amp for less than $10US. I suppose most tube amps don't use a large heatsink, but that's not too bad as cost goes, especially if you salvage them from something else. That, and you don't have to worry about the tubes wearing out. The real benefit in my mind is avoiding the high voltages inherent in tube circuits.

Quote from: smsuryan on October 17, 2010, 04:00:55 PMwhere do i start studying how to make ss amps?  books?  this site of course...

Books, books, and more books. If you're search savvy you can find almost everything available online in pdf form. I recommend starting with Teemuk's 'Solid State Guitar Amplifiers' pdf, it covers just about everything and it's free!

Quote from: smsuryan on October 17, 2010, 04:00:55 PMi used to work for a living assembling and soldering curcuit boards so i know some basics about grounding and soldering and a little schematics...
also look at this board....it came from my central air unit, had to get it replaced...anything useable on it?  or should i just 86 the thing?  thanks...thats all the questions i can think of now...

If it were me I'd salvage pretty much everything there, maybe even the microcontrollers if I could find datasheets for them. When salvaging, especially appliance boards, keep an eye out for conformal coatings. It's a (usually) polyurethane coating that covers the solder side of the board to protect it from moisture, but desoldering through it will release some nasty smoke that's guaranteed to give you a headache and make a mess. Most of them glow under UV light for easy inspection. You can scrape them off or remove them with chemicals, but that's usually where I draw the line unless there's parts I really want.
You never know what will come in handy.

Hope that helps.

It's going to be tough finding an exact match, as there have been huge improvements in semiconductor manufacture in the last 35 years or so. Still, it'll be a lot less headache than trying to use two transistors.

It does depend on the application. The most common use I can think of for such a transistor is as part of the input differential amplifier. Back then these transistors were the best way to get high input impedance in an amplifier. A good clue would be if you have two of them in your circuit, and they're near each other or perhaps even thermally coupled with a zip tie or small heatsink.

It's very likely that a darlington like this is part of an amplifier that has an overall negative feedback, so the absolute Hfe isn't likely to be important. If it's part of a differential amp configuration then what's really important is the difference in the Hfe between the two transistors (which is why they are sometimes thermally linked). In short, if you have to replace one of a differential pair then replace both.

Fairchild's MPSA14 and it's close relatives (everything marked 'sourced by process 5') are all fairly good matches. Here's a link to the Fairchild parametric search that should show you the relevant parts. The current handling and breakdown voltages are all better than the D16P1 thanks to modern technology, and this is good. The 2N5308 is a match for Vsat, which could be relevant if it's used for switching, but that's pretty unlikely in an amp. Any of these should work just fine in the signal stages of a guitar amp with very little or no noticeable difference in sound, though you never know.

More info on the application would help to be sure, but assuming it's part of a differential I'd try any two of the MPSA14 family and see how it sounds. I'd order ten or twenty, just to have them handy, but I'm weird. They're fairly cheap after all. As Enzo said, double check the pinout when you install it! You'll have plenty of lead length to match the board holes, just be sure they're all in the right spot.

Quote from: bry melvin on October 14, 2010, 03:02:58 PMalthough I try to avoid them. NTE has a cross referenced part  I would carefully compare data sheets befor using it though.

I understand, I hate them too. They're reliably double the price of other parts, and I've seen it much, much worse. It's not so bad on signal transistors, but analog ICs and TO3 transistor prices make me gag.

Hope that helps, I've had a bit too much coffee today. 

There are a bunch of things to try without involving fancy equipment. Solder wick will make the biggest difference, and liquid flux helps a lot too. If you don't need to salvage the chip it's much easier, you can just cut all the pins. In the end, the screwdriver and soldering iron method is fastest.

If you've got the free time, the IPC has solder and rework training videos available. They're the primary standards association for electronics assembly worldwide, so if you can operate at their standards you're officially a pro (if you get the certificate). Not everyone can stand watching workplace training videos, but there's a lot of good information there. They naturally assume you have all the high end stuff, but the theory carries over.

Hope that helps.

Quote from: Electron Tornado on October 07, 2010, 09:38:00 PM
Thanks, DJ,

I did understand which pots did what, but the fourth connection on the vol pots had me scratching my head.

Ah, no worries. I babble on quite often.

Quote from: J M Fahey on October 08, 2010, 07:34:54 PMBefore you advance too far, let me remind you that TDA2009 and 2005 are *similar* but *not* the same . . .

Good call, I didn't even look at that side of the schematic.  :duh

Quote from: Electron Tornado on October 07, 2010, 05:37:42 PM
JM,

I took a look at the datasheet for the TDA2005 and it has basically the same circuit as the TDA2003. However, I have a question regarding the potentiometers, P3 and P4, from the TDA2005 figure 27. Those look like volume controls, but I don't understand why the schematic shows 4 connections. (Same situation exists in the TDA2003 schematic.)

Thanks again for your help.

The center pin is a loudness tap, basically just a wire that usually sits at 40% or 50% of the full resistance. At a certain point on the volume control it starts boosting the low end to make the signal sound louder. If that seems like a crazy thing to do, keep in mind that the common application for this chip was car stereo.

I'll try and go over the whole input, someone correct me if I go astray. P1/P2 are tone controls for each channel (oddly separate, in practice they're likely ganged), P3/P4 are volume (also likely ganged in normal use), and P5 is the balance. The mildly complex RC networks sprinkled everywhere are designed to set the response of the tone and loudness controls. You could use LTSpice to simulate from the input to the 0.22uF DC blocking cap and get an excellent idea of the workings. In short, all that mess is effectively just a tone stack and balance control, and you can replace it with a simple balance/volume system for use with a guitar.

Attached a screen cap of Figure 27 so nobody has to go looking for the sheet.

Hope that helps.

Quote from: GuitarLord66 on September 27, 2010, 11:20:37 AMAs you can see it came out a hell of a lot better, but I have one problem, a lot of the pots are scratchy when I turn them, how can I clean pots? other than that the amp is awesome and has currently replaced my Peavey Bandit 112 as my main amp

Nice work, that looks really good!

There's a couple of ways you can go with the pots. They do wear out over time, so even if you get them nice and clean they may still be really noisy. Ideally you'd replace them, but that can be a lot of work, especially if they're soldered into a board instead of free wired. If you just want to clean them and see how it goes you can use 90% isopropyl alcohol (rubbing alcohol), or a professional cleaner like CRC CO (much easier to get in AU than Deoxit, check Dick Smith or Jaycar). The further you take apart the pot the better the job you can do. I usually desolder them and open them up if possible, then I can clean the resistance strip directly. Be sure not to leave any lint behind, and don't remove too much material from the resistance strip. See 'The Secret Life of Pots' for some details on large pot construction, those are probably constructed in a similar manner in a plastic case. It's possible that they can't be opened, and also possible that they're sealed. If so you'll have to replace them.

Hope that helps.

I found the schematic and service notes for the non-blues Cube 15-30. This thing is a computer moonlighting as an amp! I'm not sure if this is the one you have, but it's got at least 3 rather large ICs in it where the blues version is more or less analog.
Looks like the audio pots are 10K B taper (linear).
I tried attaching but they were too large. I had to host them at a free site, and there's a download limit. If it maxes out before you get these just send me a pm and I'll email them or re-host it.

Hope that helps.


http://rapidshare.com/files/421165140/Roland_Cube_15-30.zip

Now updata successed into the AMPIX collection:
http://www.ampix.org/albums/userpics/10520/Cube_15_-_30_Service_Notes.pdf
http://www.ampix.org/albums/userpics/10520/Cube_15_-_30_Schematics.pdf

I saw your request in another thread, so I thought I'd try adding more here.

For all caps-
If it's bulging, burnt, or leaking goo, then it's bad. Always remove and replace such caps, as they're dead or dying and just waiting for the right time to take a bunch of stuff with them!

Most multimeters will be able to tell you if a cap has failed as a short circuit. The larger the cap the lower it's resistance when it's good, but it should always be at least a couple megaohms (1000KΩ). For example, I just measured some 2200uF 35V electrolytics that are brand new, and they measure 4.3M/37M depending on the polarity of the ohmmeter. I then measured several small 10nF (0.01uF) polyester caps and they're so high they don't register on my meter (40M max). A cap that's failed short will probably be 1K or less, perhaps even just an ohm or so.

The actual capacitance value is usually pretty unimportant unless the cap is part of a (very, very high) precision filter. Capacitor tolerances are horrid, rarely better than 5% in small values and soaring to -40%/+100% in most electrolytics. Guitar tone stack filters usually use caps with a tolerance of 10%, which is pretty standard for non-electrolytic caps in the nF to uF range. This sloppy tolerance stuff is worrisome, but don't lose any sleep over it. Consider that everything you've ever used uses caps with these tolerances, and it all (probably) works ok! This means that you can usually use a multimeter cap tester to see if the cap is anywhere near it's listed tolerance. I use a lot of salvaged parts and my rule is to toss any cap that's more than about 30% off, but I do test all salvage parts before I assemble them into something. Even for relatively precise filters it's more important that two caps are close to each other than close to a fixed value.

It's really tricky to test the value of a cap in circuit, I'd avoid that if at all possible because you really have to know about the rest of the circuit to be sure you're not getting a bad reading (which is very likely to nearly certain for most situations). What Enzo described above is really the best way, see if the cap is doing it's job when it's working with the rest of the circuit. Keep in mind that it's dangerous to test a live circuit, so please use caution and ask if you're not sure about the proper safety procedures. No one here will think less of anyone asking about safety, and we'd all be glad to point anyone asking to good resources.

Example: AC coupling or DC blocking cap
The purpose of one of these is to remove the DC offset of a signal before it's sent to the next stage (see here for details). Using a scope you probe the 'input' side and see a DC offset, which might be very small. Probing the 'output' side should show a reduction in the DC offset, usually setting it to zero. If you're still getting a DC offset on the output side then the cap's not doing it's job, time for a replacement! If you've grounded your probe and you get very little or no signal on the 'output' side then it's possible that the cap's failed open.

Example: Power Supply Filter cap
These are for shaping the 'bouncing ball' rectified AC from the transformer into a flat DC supply (see this ST appnote for details). Keep in mind that the goal is usually not to completely eradicate ripple, but reduce it to a manageable level. Load is a factor as well, and you may have to test a power supply under load to see the worst case ripple in the supply. It's possible to calculate the expected ripple, though a rough guess is usually good enough. The best way to see ripple on a supply is with a scope (just probe the rail AC coupled) but if you're familiar with your multimeter (i.e. it's true RMS or you can do the necessary correction) you can get a fair idea of the magnitude of the ripple by testing the AC voltage. Anything over a couple of volts is probably suspect, but it really depends on the supply and the load. If you're seeing more than five volts of ripple then it's fairly likely that at least one filter cap is bad.

As Enzo says, it's usually done this way because it's faster and caps are relatively cheap. There are other factors with caps that come into play when designing circuits, like ESR, but I'd argue that it's not worth worrying too much about if you're simply fixing and not modifying or creating. An aged electrolytic with high ESR will be slow to charge and discharge and behave poorly as a filter cap, but you don't need an ESR tester to see this if you can probe for ripple.

I'm no pro, but I hope that helps some. Caps are a confusing mess sometimes, but at least they're not inductors.  :duh

Quote from: 86warlock on September 12, 2010, 09:56:17 PM
Thanks for the note. I removed to volume pot today and tested it out of circut. Its a 10K linear pot and tests 8K turned all the way to the right and 16 Ohm rolles all the way back, Shouldn't it be ) Ohms to 10K Ohms? Thanks for the help!

In a perfect world yes, but this is a fairly common spread. Poor original tolerance and age may have taken that last 2K, which is important for your low volume operation.

However!

A linear pot you say? You might get the fine control at low volume you're after by simply replacing it with a log pot! The downside is that if there's something truly wrong you're just treating the symptoms instead of finding a cure. It's not uncommon for amp manufacturers to use a linear volume pot as a marketing strategy, as it sounds louder at low volume implying more total power (Dude, this thing is loud at 2, imagine 10!). If this is the case then you are actually treating the problem, at least in my opinion. Has it always been this way? If so, it's a good sign that there's probably nothing wrong that wasn't built in.

If you have a log pot handy you can test it. Ideally you should use a 10k log, but anything up to around 100k should be fine, and you could go higher. If you have a lot of choice, try a 20k. No log pots handy? You can get really close with a linear pot and a resistor. The main issues with the creative substitution of pots involve loading the circuit, but without a schematic it's hard to say if this will be an issue. This loading won't usually hurt anything at audio signal levels other than to potentially add non-linearity or distortion to the signal, and this is not often a concern with a guitar amp. Essentially, you probably won't hurt anything by experimenting (unless you have an accident or do something silly) and you can judge by your own ear to see if there's an undesirable change in tone.

The one thing to watch out for is the giant, high power pots or rheostats used to attenuate the high power output on some amps. I've seen them in schematics for older tube amps, but who knows, there may be some solid state amps that do this too. These aren't too common in my limited experience, and are easy to spot by their size. They're intended to serve as a volume control for large amps that want a low power mode for studio use while still overdriving the amp's power stage, and dissipate several to tens of watts as heat. I wouldn't suggest experimenting with one of these unless you're sure of what you're doing, as there's a lot of power flying around.

See The Secret Life of Pots for details on tapers and simulating them with a linear pot.

If in doubt, there's no harm in waiting until one of the pros stops by, I'm just a new guy.

Too much coffee, I hope I didn't ramble too much!

To easily make pictures from a digital camera forum friendly I use Irfanview. It's free and very useful. Download here.

Here's a short, somewhat half-assed tutorial that assumes some familiarity with computers:

• Copy your pictures to your computer somewhere where you can find them.
• Open with Irfanview. The view controls are under View>Display Options (Window mode), spend a little time getting familiar with them until you can see what you're doing. It often defaults to 1:1, which can be much larger than your monitor (and confusing). The "Fit Images to Window" option is probably what you'll want to proceed with.
• Draw a box around the important parts of the picture and use Edit>Crop Selection (Ctrl + Y). If you framed the shot perfectly then feel free to skip this step, but it can save a lot of space if you just want to show something specific. Don't remove so much that the photo's not useful!
• At this point I usually use Image>Auto Correct Colors (Shift + U). This can help legibility with pictures that have bright borders cropped out. Skip this if it makes it look worse.
• Time to resize. The settings on your camera and the cropping you've done will determine the original size, and it's usually huge. Use Image>Resize/Resample (Ctrl + R). This will open up a box that allows you many ways to choose the final size. Always make sure the "Preserve Aspect Ratio" is checked, as this keeps the image from distorting. I usually just set it to 25% of normal size, but I'm used to how large my pictures come out. You can use the drop down box in the upper right for quick selection, 800x600 should work ok. Using the "Apply sharpen" check box is recommended, as is setting the "Size method" to Resample on the slowest filter (high quality).
• Almost done, use File>Save for Web. This will optimize the picture to take up as little space as possible while still trying to retain detail. All you have to do here is hit the big Save button and it will save a finished copy.
• Double check your new skinny picture by opening it Irfanview. Can you see enough detail when you zoom in to make you happy? Often you don't need much detail to get a point across, so don't sweat it unless you're looking to convey something specific.

Irfanview has all kinds of other options and abilities, and it's definitely worth the investment in time to learn the program if you work with digital images.

Hope that helps

Quote from: J M Fahey on September 06, 2010, 05:07:17 PM

Quotea dead HT rail fuse probably means a short in the power amp, likely dead output transformers.

Am I missing something here?  xP
Which HT rail?
Which output transformer?
And even if that Kustom did use one, it would be almost last in a looooooooong list of things to check.

Gah, I've had transformers on the brain lately, I meant to say transistors.  :duh
Also, I should probably have said DC power rail instead of HT rail.

Man, I've really got to take a break from reading about tube amps, I'm confusing more than just myself!  xP

I dug around to find some schematics, you can probably piece most of it together from here.
You can use the block diagrams to get specific board numbers, they're listed separately in the PC section below.

K200-1
No signal from the power amp. I'd check and see if you're getting any output from the preamp board. This might just be a loose connection or dirty switching jack.

K150-2
This sounds more serious. Which fuses? An AC line fuse could mean a dead transformer, where a dead HT rail DC power rail fuse probably means a short in the power amp, likely dead output transformers transistors. (brain fart)

Ungrounded plug
This is one for the pros. I'd strongly advise converting these amps to grounded plugs, but I'm not 100% certain about how to do that with the way the power is set up so I'm giving no advice. It'd be much, much safer to use (for the guitarist and the tech) if converted.

I'm just the new guy, but the pros will want to know more, so I figured I'd help get you started.

The picture is definitely a bit fuzzy, it's a bad scanning job. I've found it's way faster and easier for me on those to squint than try anything fancy with graphics programs.

Definitely keep us posted.

I love the smell of new parts.

Somehow I totally missed this thread earlier. If you ever want to talk tech stuff and happen to be up in Omaha let me know. Not too many folks around here seem to be into electronics.

Keep us posted, I'm slowly working on a 3886 build here too, though I'm only after about 40W.

Good photos, is always nice to have pictures to work with.  :tu:

I went to Crate's site and they've got the manual for download, which contains a schematic. The last page has the power section, and the diodes in question are D6 through D9. The band on the diode case is the cathode, and goes to the more negative side of the connection in normal operation. The schematic symbol points in the direction of the cathode, and the short line at the end of the triangle is on the same end as the band on the case. That should help you sort out the orientation, just trace the circuit and double check as you go.

Those look to indeed be the rectifier diodes, which they specify as 1N5392 (datasheet). These are available for something like $0.03 to $0.07US from various distributors like Digikey and Mouser. Essentially any diode with similar ratings should work, the important specs are 100_Vrrm and 1.5_IF(AV). These can handle about 30% more continuous and peak current than a 1N400X series diode, so those should not be used.

With some creative wiring and a little space you could use a chassis mount rectifier (about $5US) to replace all four diodes. This is what I would do, though many would say this is overkill.

This should sort out the diodes, cross your fingers and hope nothing else got roasted.

Hope that helps.