I'm wondering if anyone has any recommendations for a good practice amp.
. . . electrical modification practice, that is. 8|
I've been looking at various second hand websites, and I've discovering that one can buy any number of entry lever guitar amps dirt cheap (<$20 US). I was thinking it would be fun/educational to pry one of these open and try to make some changes to it. Is there any particular amp(s) that stand out as being commonly modified to improve the sound a little? Not necessarily improve the sound, but make it somewhat at least noticeably different (e.g., doing something to reduce the hum). I figured I could work on my circuit skills, and worst case scenario I bought a bin of parts useful for twenty bucks.
Your thoughts?
Good idea :dbtu:
Since most go for that price, and knowing what you want them for, I'd choose a "known brand" one, say Peavey/Fender/Crate/etc. instead of mystery ones , simply because schematics are easier to find and they will use standard parts, say TDA2030 , TL072 , etc. for which datasheets are easy to find.
While data on First Act, Esteban, etc. are impossible to find.
I agree with Juan, look at one you can find a schematic for.
However, for the most part, inside those small amps, things are pretty much the same. Most of them use a TDA2030-2040-2050 type power amp. Most have one or maybe two op amp ICs. So the brand and model don;t matter a lot.
There is one specific model which I have already seen under a hundred brands (not kidding), it´s always the same with: jack input - distortion pushbutton - treble - bass - headphone out and the telltale " 6"/6.5" speaker " and they are usually labelled 10W.
It´s the typical amp which comes bundled with the cheapest guitar.
Hey!! I even saw one of these paired with a "Metallica guitar" and Kirk Hammett himself pushing it !!
(http://www.mygear.com/img/item_pictures/large/30865.jpg)
Never had the schematic but I´m certain they have 1 dual Op Amp, a TDA2030 , basically the same as the next higher 15W version, and they spec them as 10W simply not to cut on sales on the 15 watters, which typically have heavier 8" speakers (and a few even 10").
I imagine a huge factory churning just these for anybody who wants them.
Well if Metallica uses it, it must be good, right? :cheesy:
Yeah, I've seen a lot of those types around recently. Pretty much exactly what I was looking for. Though I did see someone selling a beat up Marshall 15DFX for $20, which I used to own and really liked (I sold it to help pay for my wedding), so that one has had my eye for a couple of days now. It's a really nice day today though, so I might go out and see what all the yard sale people have to offer.
I posted an ad on Craig's list looking for broken solid state amps just for this purpose. I specified that I would pay no more than $25.
I got two replies right away...one was an old Heathkit TA-16 and the other was an 80's era Yamaha B-115 bass amp. I paid $20 for each, no cabinets or speakers, just the chassis and electronics. Both have been good "practice" amps and the Yamaha will be re-appropriated into a guitar power amp soon.
Point being, try CL if you can...you may find some gems for cheap.
Cool !!!
You got more than you bargained for, much better than typical beginner´s amps.
The TA16 is a classic oldschool discrete amp and one was repaired here (or in MEF) short ago, search for the thread.
The Yamaha is a killer "real" amp and chassis/heatsink/transformer are worth way more than $20 ... even better bargain if you actually repair it original.
As of the Marshall, it´s a very good sounding amp , so if you have spare $20 ... go for it.
And then stop, or your home will look like mine: impossible to walk through because of towering mountains of junk which *may* be repaired ;)
.......... someday :(
JM: that thread about the TA-16 was by BrianS, (not the OP of this thread) so he already fixed the amp in that thread :).
http://www.ssguitar.com/index.php?topic=3511.0
The price of a second hand amp (or just about anything actually) is simply demolished by a fault, yet in most cases the faults are minor and easily fixed. The vast majority of "trove" amps I've been given/roadside hard rubbish/dumpster diving/tip scrounge have gone to new homes and not one in ten has turned out to be really worthless junk.
The Yamaha in particular looks like a real find.
Yamaha B-100-115 service manual;
http://elektrotanya.com/yamaha_b100-115.pdf/download.html (http://elektrotanya.com/yamaha_b100-115.pdf/download.html)
QuoteI was actually going to start "repurposing" this amp yesterday, but after staring at the chassis...for what seemed like hours...trying to figure out how to re-cut and re-bend it, or just remove everything and try to make a new chassis, I decided that I will just refurbish the amp and build a new cabinet for it.
So yesterday I purchased a "Tiny Giant" amp kit. Not nearly as nice or as powerful as the Yamaha would have been, but hopefully it will suit my needs (power amp for a Tech 21 Fly Rig 5).
Why rehouse the 100W Yamaha?
You trying to fit it in a pedalboard or even worse, your guitarcase, like in the Flyrig ad? :o
Don´t think so. 8)
And the Tiny "Giant" is really ... tiny .... and does not even have its own power supply which when added will also add its own space needs and weight.
And anyway you´ll also need a speaker cabinet (no pedalboard sized ones that I know of) , so I guess the least bulky/heavy yet loud usable anywhere solution would be to build some kind of "combo" or powered cabinet housing, say, a good 12" speaker or 2 x 10" ones and the Yamaha chassis inside.
For minimum size you might even include the chassis in the back (top or bottom your choice) á la Tech 21 Power Engine but in a similar size yet *louder* pack.
How´s that?
Of course, if your hands itch with building the Tiny Giant, go ahead, it will be an excellent intermediate project before tacking the larger one :dbtu:
^Yo! Why was my post messed with? Just to be clear:
The above post (#9) was altered by someone (JM Fahey?). The only part that is attributable to me is the part that is quoted, which if memory serves was the original post.
As to the questions that have been inserted into MY post, I've answers for them, but I'm a little confused as to how this is all going down right now, so I think I'll wait to respond.
My guess is that Juan click "modify" instead of "quote" and didn't realize his mistake. I will wait and see what he says though before making any other changes.
¿¿¿¿¿¿¿¿¿ ?????????? :o :o :o
Don't understand, FWIW I *answered* a post in my own words, it's clear from the text itself; don't have the faintest idea why the answer is labelled or signed by Brian S.
Maybe it was "glued" and pasted covering Brian's post?
No clue.
Only thing I think *might* be related to it is that I often have 5 or 6 windows open, jump to a new one to answer (usually search for a schematic or picture, *might* have read a thread suggested as related) and pasted my answer in the wrong window.
*If* anybody has the original text (often sent in the post update notification by email) please post it here so we replace it.
I have no idea of what it said.
Sorry if I messed something :'(
EDIT: AFAIK I *quoted* Brian S , that's clear to see, and then continued with my own answer.
¿¿¿Maybe I clicked the Modify button instead of the Quote one which lives just by it???
But then why does the "quote" label and corresponding greyed rectangle appear around Brian's text?
Maybe joecool can check that .
Oh well, delights of fingertip driven netbook touchpads :(
Oh No harm done, Lets hope BrianS understands we are all human and even the best of us make mistakes. 8)
I once answered the wrong post with another post answer so the answer made no sense at all and to make it worse I went to bed and only realised my mistake a day or so later.
Oh boy that made me feel very stupid. :-[
I recall a friend who finally got his Dad to embrace the internet and when He recieved his first Email from Dad it was empty. ???
He then realized that Dear Dad had written the whole Email in the *Subject header* so took quite a while to read it all. :lmao:
I'm not much farther ahead sometimes, doubt I will ever fully grasp the internet and how all these software programs work. :loco
Phil.
"Man, woman, child, all up against the wall of technology."
As journalist say "if you have to chose between a conspiracy and a stuff-up go for the stuff-up every time, they are much easier to organise". :lmao:
To return to the OP; I don't know how much you can plan this sort of thing, ask your friends, keep your eyes open around second-hand/thrift/op-shops, garage sales, fêtes and fairs, hard rubbish collections, dumpster bins (particularly outside houses where people are moving out), recycling centres, the "tip shop" at your local dumps, and such. Some junk will come to you but mostly you have to ferret it out. Then tinker with what turns up - it's all grist.
I think most of the experienced techs here would agree that most of the time you can't get a circuit and have to fly by the seat of your pants, and that's an important skill to learn/acquire, but that only comes with practice and exposure to lots of gear. Also remember that many faults are "off-circuit", pot cleaning, broken socket connections, dirty contacts, etc.
"Your eyes are your best service instrument".
Yes.
People tend to service relatively expensive stuff, but discard without warning "cheap" stuff.
For good reason, considering average Tech bench hour rate or minimum charge is around U$60 in USA and reaches U$120 in expensive to live New York, a lot of stuff whose used proce falls below that is simply junked.
If you have at least basic troubleshooting skills you have nothing to lose checking such stuff yourself; I´d say 30 to 50% of the time is not an electronic problem but a "mechanical": bad/rusty/dirty jack, pot or switch.
In Buenos Aires there used to be a Tech which everybody nicknamed "the digital guy" because he accepted stuff which nobody else would touch with a 20 ft pole, (specially keyboards butalso Studio stuff) because of absolute lack of schematics, spare parts, etc.
This was over 20 years ago, where you could not ask for some PDF service manual over the Net.
He had a small rented office, with a front desk to receive stuff, and a back room Lab.
Once I got invited to that secret place, after swearing over 10 Bibles not to tell (at least inside Argentina ;) ) what I was about to see.
I expected a ton of NASA type gear, digital stream analyzers, the latest Scope money could buy, etc.
Fact is he had only an *analog* multimeter (with a slightly bent needle, a battle scar from some wrong scale measurement) , a good set of jeweller´s screwdrivers, torx bits, a couple cans of cleaners, degreasers, etc. , some cotton, isopropyl alcohol , a few spare fuses, a jeweler´s loupe ... and not much else.
I was *amazed*.
He told me: "I test-by-use and dissassemble stuff, pull and reseat flat ribbon connectors, pull, wipe clean and reset PCB edge connectors, clean and work end to end: pots, switches and jacks, flex and test MIDI cables, check for cracked solder, specially at external access points, etc. That alone solves 30/50% of problems. Besides, I check (with the bent needle meter) that power rails are available and reach all boards (+/-15 and +5V)".
Just with that he repaired (and charged for) over 50% of the stuff .
For the rest, he tested them until he found which was the bad board, pulled it and had his beautiful girlfriend (an Airline hostess) bring it to USA to have the original Factory repair it for a fixed amount.
Of course, he charged double that.
And yes, way back then "good" stuff was still made in the USA (think UREI, Gain Brain, Mackie, Ashley, JBL, Eventide, Shure, Ampex, etc.) or had strong presence, specially servicing (Yamaha, Tascam, etc.)
Today that is impossible, because most stuff (Behringer, etc.) is disposable.
QuoteOh No harm done, Lets hope BrianS understands we are all human and even the best of us make mistakes
Indeed, and I do. I also
greatly appreciate the fact that guys like JM take the time to share their knowledge with everyone here.
I guess I did feel a bit insulted by the tone of the response, and that feeling was multiplied by the fact that the comments were placed directly into my post. ANYWAY...I'm over it. Again, my apologies to the OP for the thread derail...
Hey I like Brian already,,A group hug all round. <3)
Now what was that Q,,, oh yeah which amp to disect thing.
He is my little story.
Long before an old bugga like me even understood "press any key to continue"
Let alone internet I started pulling old transistor junk apart, no make that anything electrical I could lay my hands on that looked like it might make music.
I back engineered old radio grams by following the tracks on those old single sided boards. My first schematic drawing where close to unreadable but at least I understood what they meant.
I read heaps of old EA magazines I'd find at book stores and other like places.
My first breakthrough was a good friend who changed direction at Uni handed me a pile of Elec Eng books (those expensive ones university students have to pay for)
One was Art of Electronics and many others, some old including Valve equipment.
Much reading went on until things started to sink in.
** Please note I urge anyone wishing to learn this art to start at the basics like magnetism/rectification/ all the basic AC DC concepts as it will speed up the process a lot. (The net now makes that even easier) And please don't forget the most important one **SAFETY**
My rules of thumb are; Don't touch anything you can't outrun,,, and Never assume it's dead. :trouble
My next breakthrough was a chap handed me a copy of a basic El simulation program.
So between that and books and now the net I feel I'm at least much more able to pick out what might work and what is just another boring old fuzz box.
Ok I've melted quite a few perfectly good components in the past ~30 years and added to landfill with many disaster circuits I've built but it's par for the course of being a hobby geek trying to get your head around all the tecky stuff. :cheesy:
Coming from that perspective I see the fastest way to get ahead is a bread board, a couple of decent multimeters and simulation software.
In your particular situation *as J.M. Fahey noted* get those little Amps and just back engineer it then simulate to see what happens inside then start modding. ;)
Take the time to follow the tracks on the pcb note all the pins of transistors and chips, refer to data sheets for pinouts.
OK you maybe rolling your eyes by now and YES it will be slow at first but will go a long way to get in touch with circuit design and how to layout a board.
The beauty of sims for me is that I can change a value on the sim then look at how it effects the result (A visual plot on the screen) all in a few clicks of a mouse then do it on a working breadboard circuit and HEAR the resulting sound. That way you quickly learn to identify the sonic result of that visual graph or plot. This makes for a very fast process and negates the shed full of test gear to find the same result. (cheaper also) ;)
I've worn out 4 of those little bread boards making all sorts of music related circuits. So out of hundreds of failures I've designed about 4 I'm really proud of and most of those circuits are posted here on SS guitar.
One other point to make Which Jaun pointed out beautifully way back;
Once you start modding unknown pcb's it's easy to stuff up the pcb and render the whole thing useless and not repairable. (Hey I'm also guilty of that silly mistake)
You are far better off starting at the breadboard and *COPY* the Amp circuit you wish to understand then when you find the sweet spot transfer those changes to the original amp thereby lessening the chance of destroying the PCB.
The Pcb is the hardest part to replace and likely impossible to replace with some gear.
Phil.
Agree :)
For me "parts is parts" and can be bought over the counter (or by mail) at some place or another, or often substituted by some equivalent, but the PCB **is the amp** , it's what arranges all those individual part to be that particular amp and not other, and can not be bought anywhere.
In fact, once he finished the production run, not even the Manufacturer has them for his own use.
There are very few exceptions , counted with one hand's fingers, such as :
manufacturers of very expensive very high power , professionally abused amps (touring PA systems) such as Crown, which can send , say, Guns and Roses playing in Kuala Lumpur a couple stuffed power boards to replace those blown in Sydney 4 days earlier , or Marshall sending new production boards for DSL2000 to replace a bad batch of conductive boards or Hartke sending new boards (minus the outpuut transistors) to amps in warranty because for them that is cheaper than moving a heavy amp both ways, but those are the exceptions.
For *any* amp consider damaging the PCB beyond a couple pads or tracks a complete loss situation.