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Post by DarKnight on Aug 28, 2007 7:53:38 GMT -5
Name says it all... Are those things sold for cars any use from guitar amplification perspective... Just having in mind that building preamps (and effects and so on) is a bit easier and safer than doodling around with power stage without adequate education and/or knowledge... Safety is... I know that separate power amps for guitars do excist, but is that the only way around?
Dark
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Post by ranchtooth on Aug 28, 2007 19:57:16 GMT -5
Sure they could be of some use... if you like CRAPPY TONE!
Meaning those high powered, solid state hi-fi jobs will leave you with brittle, harsh, sterile... etc. Thats all speculation though... someone could (and should) always try to make it work...
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Post by DarKnight on Aug 29, 2007 3:20:18 GMT -5
Anyhow I was looking for solid state in the first place... Just interested because rather low price.. but again... are they suited... I dunno... Had also in mind that using such a thing would easily give chance to make module-type preamp-section and effects... and after that I could assign different preamps and effects to eg. two channels in the amp.. and send two different sounds to eg. 4x12 (or maybe 2x10 + 2x12 :  cab.. so that another channels runs first pair and another the other...  just doodling with ideas.. not sure if it would work at all... more opinions please and thanks tooth!  Dark |
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Post by RJB on Aug 29, 2007 11:35:09 GMT -5
Couple of points.
Most car power amps, at least the inexpensive ones, are not designed for hi fidelity. Most distort, and not in a pleasing way, when pushed beyond loud conversation levels.
Also a little electric theory for you. Power = Voltage X Current. Lets say a 100W/channel power amp. Thats 200W. If you can get a 75% efficiency you're doing good. So it takes 275W to make 200W of audio. 275W/12V= 23A! You're average house oulet can supply only 15-20A, and that was average, on music peaks you would be drawing in excess of 30A. You will need to drag around a car battery. Even the "brute force" supplies I've seen top out at 20A/12V.
If the plan is for something more in the 20-30W/channel range, then it might work. But again not with the cleanest sound. A better bet might be a low power PA power amp.
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Post by DarKnight on Aug 29, 2007 11:42:56 GMT -5
I think my question about using car amp is solved. Thanks... Anyhow about alternatives.. is there no other way than buying power amp for guitar(except making one by yourself)? Dark |
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Post by sumgai on Aug 29, 2007 11:54:50 GMT -5
DarK, Yes, your idea has merit. Separating the two main sections of an amplifier is not a bad idea at all. Cost, weight, ability to modify one without harming the other, all of these are good considerations. Remember, in the very early days of hi-fi, just after WWII, most gear was made in just this fashion. It made sense to most people, engineers and listeners both, that if you wanted to produce the highest quality (and if you wanted to listen to the highest quality), you built and bought specifically designed gear for each part of the signal chain. The tuner might have been a Marantz, the preamp might have been a Fisher, and the power amp was probably a Macintosh. It wasn't until the very late 50's or the early 60's that "combo" amplifiers starting coming out. And for the record, it's no coincidence that this the same time that stereo came to the public in a big way. It was getting too expensive to buy (and find a suitable location for) at least 5, possibly 6 different pieces of audio equipment. Hence, the move towards putting all of it on one chassis, in one housing. As soon as that caught on, the separate-piece industry contracted a terrible case of lead poisoning. If you want such things nowadays, you'd better bring two checkbooks to the table, one just isn't gonna be enough.  Enough history.  The short answer is, from the viewpoint of a hobbyist (and as you note, safety), it makes sense to re-use a piece of gear from somewhere else, particularly if one's wallet is a concern. Just be sure to read all the information you can about what the outputs are (what impedance it can handle at how many watts), and what the inputs expect to see (how many volts at what impedance). If you can make your preamp feed the power amp properly, then you should have a good setup for a very low cost. And don't skimp on the speakers, they'll affect your tone just as much as the power amp, perhaps more. As you build and test and experiment, use good speakers that work well in other guitar amplifiers, or you may be disappointed in what you're hearing.  BTW, ranchy, talk to ux4484 about his new FM212R head, see what he has to say about solid state amps. Might surprise ya......  HTH sumgai |
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Post by ranchtooth on Aug 29, 2007 12:28:04 GMT -5
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Post by DarKnight on Aug 29, 2007 12:54:12 GMT -5
Thanks sumgai! I'm going to cut corners (money wise) where ever it doesn't significantly affect the outcome (ie. tone)... Partly cos I'm not Uncle Scrooge... and partly it is just pure curiosity how stuff works... ;D AND of course I'm hunting the perfect tone and also versatility... I'm so modest...  So I'll "just" take some time and find out what goes to where and how much... But I've been a bit puzzled about size of the preamp... Would it work if I built something like stompbox... Like these, or these, or these. And then use them as a preamp? Or should I build something specified for that certain power amp I'm having? Somehow all documents surrounding DIY amps feel awkward and don't be very specific (or then I'm just too uneducated - prolly yes) and leave lots of things in the mist and clouds... So if there is some sort of "easy" way to explain what is required from the preamp... I'd appreciate it... Dark |
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Post by sumgai on Aug 29, 2007 13:40:42 GMT -5
DarK, The "standard" is that for a power amp to put out its full capability, it usually needs 1½ to 2 volts RMS at about 600 ohms (or greater). In many sub-industries, like musical intruments and car audio, that standard may not apply, but it's still a good starting point. I personally would not "put it all" on the floor. That's convenient, true, but it's also putting the whole ball of wax in harm's way - what if someone trips and steps down - hard- on the box....... what if some drunk pukes on the stage right in front of you....... (don't laugh, I've watched it happen  )....... what if the batteries go bad right in the middle of a song.......... what if, what if, what if.......... Long story short, I'd keep the box up off the floor, or at the least, in the back area of the stage. Plus, that's one less chord going out front, and snaking around under your feet. (I'm refering to a power cord, if you're not using batteries.) As for those runoffgroove circuits you linked, I don't consider them to be proper pre-amp circuits. They are one-trick ponies that are truly stompbox material - they do an effect, such as overdrive or distortion, and that's about it. No tone stack means you're stuck with whatever tone they put out, and in my mind, that's not very useful. But that is just me, your mileage may vary.  HTH sumgai |
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Post by sumgai on Aug 29, 2007 13:57:58 GMT -5
RJB, Methinks your math needs more cowbell, in this case the cowbell being defined as where to put the decimal point! You show "275W/12V= 23A", and that's correct, but then you relate it to household wiring. If I'm not mistaken, there's nowhere on this planet that uses 12v on the electrical grid to feed customer's homes - they're all at least 100v, and up to 240v in some cases! That brings your equation, in the USofA, to 275W/12 0V = 2 .3A, also a correct calculation, and highly likely to be more applicable for most home-dwellers, I'm sure you'll agree. Equally to the point, if 275W could blow a circuit breaker rated at 20 amps, then how the hell would we ever get more than one or two 100 watt light bulbs on the same circuit?  But all that was a matter of mistyping an equation, I'm sure. Your "Get out of jail free" card gets you off the hook on that one. Sadly though, you truly do need to hit the books again when it comes to that bit about power efficiency. I'll let you mull that over before dissecting it further......... Say, would you like to try for what's behind Door #2, Monty?  HTH sumgai |
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Post by DarKnight on Aug 29, 2007 14:09:23 GMT -5
Sorry sumgai I should have been more precise too... I ment that I'd pick up stomp box DESIGNS and put them in encasing which would be rigid and prolly as "head" or integrated to speaker box... And I'd go with cords.. batteries make me mad. ;D So I wouldn't put those on the floor as pedals... :S So are my thoughts totally crazy if I plan to build some "real" preamp... clean... and make it perform well on that purpose.. and then add runoffgroove stomps which can be assigned on different chains.. and I thought their tonemender-circuit would make great tone control... before and after the effects (maybe one in the middle)... but would I then need all those components in those circuits? basicly I have one amp (preamp) on the top of the chain and then signal goes forward towards the power amp... Of course overdrive/distortion circuits would need their own amplification to produce such an effect.. but eg. the tonemender circuit would not necessarily require it's amplification/buffer whatever? Lots to discuss here... My mouth has diarrhea... ;D I hope I didn't forget anything...
Dark
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Post by RJB on Aug 30, 2007 12:05:27 GMT -5
Sumgai Sorry for the confusion. I guess I took too many shortcuts in my discussion. you relate it to household wiring. If I'm not mistaken, there's nowhere on this planet that uses 12v The comparison was trying to show type of heavy wiring that was needed. Equally to the point, if 275W could blow a circuit breaker rated at 20 amps, then how the hell would we ever get more than one or two 100 watt light bulbs on the same circuit? This was kind of 2 fold. Again partly to show the kind of currents that would be needed, and that if you could find a 300W 12Vdc supply it would need special mains service just to run it. You are right in that you theoretically can get 1800W out of standard household wiring. I guess the main thing I was trying to show was that a 12Vdc based poweramp system would draw about 10x the current from it's supply. And therefore require much heavier wiring. And that also due to inefficiencies in AC-DC power supplies for higher currents (only about 60% efficiency through a standard power transformer) and inefficiences in current based power amps one could end up not being able to power the system convieniently. It would help keep the studio warm on those chilly nights though. I should have also included an example of a proper 120Vac based poweramp solution like this that would be a lot more cost effective. Sadly though, you truly do need to hit the books again when it comes to that bit about power efficiency. Can I just dust off my EE degree? I was typing quickly at lunch and jumped quickly and incompletely when comparing apples/oranges/grapes. And you were right in calling me out before the confusion just any further. Ron I'm open to any other criticism |
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Post by sumgai on Aug 31, 2007 3:17:48 GMT -5
Ron, No other criticism necessary! For a moment there, I thought I'd gone overboard, but truly, it was my mistake to turn your 12v of DC into 120v of AC. You were, of course, correct insofar as the unit in question is intended to draw 12vDC from a battery/mechanical power source within a vehicle, not directly from household current. That'll teach me to think that what looks like a simple typo ain't necessarily so!  ;D Actually, I was all set to delve into another topic when I made that myopic mistake. If you'll allow me to pick up the gauntlet once again, I'd like to remind you that Dark will need to convert his household power down to 12vDC. That conversion will lower the voltage, and at the same time, raise the amperage. Ohm's law sort of guarantees this, no? So, a 10 to 1 step down for voltage means a 1 to 10 step up for the amperage, and that brings us back to my original estimate of 2½ amps of household current will be needed in order to feed the amp's "habit" of consuming upwards of 25 amps, at 12vDC. Through a conversion of this nature, the only constant is the product of the voltage times the amperage, aka VA (also known as wattage, to the layman). All of which leads me to believe that DarK can safely hook up his "home-brew" amplifier to his household wiring, with the properly sized fuse, of course. ~!~!~!~!~!~ DarK, And with the appropriately heavy transformer, too! Hope you've been eating your Wheaties! ;D sumgai p.s. In case you didn't know, DarK is in Finland, so he'll need to use 220/240 vAC for his calculations. |
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Post by JohnH on Aug 31, 2007 8:00:21 GMT -5
Id like to add a comment about those Runnoffgroove circuits. I think the general direction they take of using JFETs to emulate tube circuits has alot going for it.
Ive tried one or two of their specific designs, and then I just started experimenting with the ideas. I use three JFET stages and a tone stack followed by a buffer, with various other tone shaping along the way, and I get into very nice overdrive territory, which I feed into a clean amp.
I have this set up as stomp box, but I had thought of building a two channel version, as a preamp. It has enough output to drive a power amp directly.
Its a great avenue for experimenting
cheers
John
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Post by DarKnight on Aug 31, 2007 12:52:55 GMT -5
Thanks again for the info! ;D I definitely need some sort of transformer for that car amp... Prolly that won't be a huge ( ) problem... But another thing that I had in mind was that for some extra safety... would it be wise to add automatic fuse + residual-current device (household wiring stuff) before that transformer? Probably that is not my business to build and don't know is it even allowed by our laws... but if that was build properly by someone - would it make it safer? Opinions? Safety is an issue and I'll prolly doodle around with that amp a lot if it is built someday... so I want to be sure that I don't fry my macnuggets (or anything else) while doodling... Dark Edit: just checked and found out that I can get residual-current device rather cheap which is ment to be used in normal power cords... so I'll prolly go for that, but sake of interest... would there still be any worth build such an encasing from rcd ment for household wiring... (and maybe accompany an autofuse) |
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Post by RJB on Sept 4, 2007 12:13:40 GMT -5
Expensive switchers run about 90% effecient, brute supplies about 65-70%. So actaully about 4 amps. I had some confusion about an old project where in a brute supply I ran into a 20A limit for output current, but alas on further review, it was a 24V supply  . Either way for the cost of a hefty power supply and car power amp, a better quality dedicated "PA" or bass amp could be purchased. Now for a portable system to literally take on the road??!! DarKnight: With regard to safetly, most comercially available power supplies use some form of transformer in ther power conversion. This provides some protection/isolation between the power mains and the user. The RCD that you mention (I believe) is called a GFI, ground fault interrupter, here in the states. One of those is ALWAYS a good idea for any mains conneted guitar gear. Mine is actually the wall outlet itself. As far as an enclosure is concerned. I've seen people use electrician "Work boxes" as inline junction boxes as well as standard "hobby" boxes. The rule of thumb would be, it should be closed, no place for curious fingers, and you need to maintain a ground/earth connection from the mains to the box (if metal) to the power supply to the power amp. |
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cab.. so that another channels runs first pair and another the other... 
just doodling with ideas.. not sure if it would work at all... more opinions please and thanks tooth! 
The short answer is, from the viewpoint of a hobbyist (and as you note, safety), it makes sense to re-use a piece of gear from somewhere else, particularly if one's wallet is a concern. Just be sure to read all the information you can about what the outputs are (what impedance it can handle at how many watts), and what the inputs expect to see (how many volts at what impedance). If you can make your preamp feed the power amp properly, then you should have a good setup for a very low cost.
So I'll "just" take some time and find out what goes to where and how much... But I've been a bit puzzled about size of the preamp... Would it work if I built something like stompbox... Like 
.