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Old 28th May 2007, 03:14 PM   #1
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Default Bass amp from salvaged parts?

Hi everyone,

I'm a new guy, that is, both new to the forum and new to building amps (though I have done some repairs before.) Sorry this will be kind of a long post, but I'm hoping to ask the right questions so I can learn something from those with experience in these things.

I have a bunch of parts, mostly salvaged from an old Yamaha electronic organ (probably early 70s): two 30-watt solid-state amps, a bunch of potentiometers and switches, one 15" (8 ohm) woofer, and... one 25" x 35" (really!) woofer with a styrofoam cone. Irregularly shaped, kind of like a giant pancake! So I'm looking at this stuff and thinking, I can't trash this - I have to try to come up with a bass combo amp (or two) from the parts.

Unfortunately I don't have a schematic and I don't think one will be available for the old organ. And I didn't get to see how the thing was originally set up. So I have a bunch of questions which I'll list below -- any help at all will be greatly appreciated.

1) For starters, Is building a bass amp with the giant woofer a stupid idea? (i.e., is bigger not really better?)

2) Would the amps even be appropriate for a bass combo? They were originally designed to handle a pretty wide frequency range, coming from an organ. Am I asking for trouble by trying to make them into one-trick ponies?

3) Speaking of frequency ranges, what about building a bi-amped cab with BOTH the giant "pancake" woofer and the 15"? Say, if I added a crossover to send only the really low frequencies to the pancake woofer? What is the frequency output of a standard 4-string bass anyway?

OK, I have lots more questions but that's a good start. This post has gone on long enough anyway! Again I welcome any comments, including "that's the dumbest idea ever", if it really is.

thanks in advance for advice-
Scott B.

PS I can post pics no problem if that might help.
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Old 28th May 2007, 07:24 PM   #2
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i guess you mean for bass guitar?
If so i prefer useing 4 x 10" and 1 x 15" woofers for bass.. Dont really need anything bigger than a 15"
I will say though that you will have to overbuild the amplifier and the woofers will have to be very hardy (i tend to use car subwoofers in my cabs) as bass is pretty stressfull on both and things can easily self destruct if you play hard!
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Old 28th May 2007, 07:50 PM   #3
teemuk is offline teemuk  Finland
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1) Building bass amplifier with giant woofer is definitely not a stupid idea. You need a large cone area to generate the low frequencies. Speakers with small cones can't do this - even when you use many of them.
2) 30 watts is way too low output power for a bass amplifier unless you plan to use it only at your bedroom. If the power ratings for the speakers are in the same range (30W) they are pretty useless for the application as well. Sorry.
3) In general, bi-amping is a good idea but...

...I remember reading from somewhere that those Yamaha flat panel ("pancake") speakers were not very sturdy and blew often. Fender tried them in Bantam Bass amplifier but it wasn't very successfull. Besides, replacements are likely very, very difficult to acquire. I know that flat panel technology is sometimes used in domestic HiFi applications but the fact that those speakers never became popular in PA or instrument use should tell something about the technology.
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Old 28th May 2007, 08:25 PM   #4
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on anothernote if you dont mind a bit of work you might be able to salvage the components from the 30Watt amps and depending what they are they might be suitable to build a more powerfull amp suitable for what you want.. I'm sure that for a start if you find out what the output transistors in those amps are then someone may be able to suggest some schematics you could try...
The other option is to shove them on ebay and get yoruself a large PA amplifier that has a blown channel, disconect the blown channel (just take fuses out) and use the good channel for bass through a suitable speaker cabinate (or build it into a combo amp) I have used such amplifiers with homemade preamplifiers before for bass and they seem to work pretty well (actually thats what i have at the moment for bass)
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Old 29th May 2007, 02:31 AM   #5
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1) Your collection of parts is a very good start and building a bass (guitar) amp from these is not at all a stupid idea ... although that bigg honker styrofoam cone may not last long under heavy use and its, well, probably not very road worthy.

2) 30 Watts may be plenty considering you have two amps. One for each of your 15" speakers or some combination of the speakers you have plus others.

3) As teemuk suggests, 2) above would effectively be a "bi-amp" setup.

Keep all the hardware ... as you probably know, Yahama has a good rep for decent quality parts and subassemblies ... Yamaha has been making electric music machines for decades.

Check out the power supply carefully ... all decent amps begin and end with power supply design. Find out: how big the main fuses are and the DC output voltage ~= power supply power available, etc.

Do try to find the original schematic or a service manual.

The real expensive parts: the cabinet, the power supply, the heat sinks, the control panel, etc ... can be recovered and reused. The basic amps' (the circuit boards) may not be too useful or may turn out to be a real time and money saver. I would say that this would make a very nice "practice" amp for guitar with added provisions for active or passive crossovers for use with a bass ... Got pictures?

Go for it! ...
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Old 29th May 2007, 05:17 AM   #6
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Awesome, guys, thanks a million for your advice. I'll post some pics tomorrow of the different components. Stay tuned...
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Old 29th May 2007, 11:31 PM   #7
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Default Yamaha salvage pics (1)

Hey again - got some pics of the components I salvaged. Let's see if I can get them up for viewing. This first shot should show both of the SS amps side-by-side. They're nearly identical; one is labeled D3016, one is D3018. I suspect they were a bi-amp arrangement for the separate Rotary and Stationary channels on the organ. OK here goes...
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File Type: gif bothamps.gif (41.1 KB, 108 views)
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Old 29th May 2007, 11:31 PM   #8
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Default Yamaha salvage pics (5)

Next up is the amp without the power cord; but I believe it picks up power via the Molex connector from the other amp. It's labeled D3016.
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File Type: gif d3016.gif (27.5 KB, 94 views)
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Old 29th May 2007, 11:31 PM   #9
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Default Yamaha salvage pics (6)

Then we have a shot of the D3016 from below, up under the chassis...
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File Type: gif d3016-bottom.gif (34.0 KB, 93 views)
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Old 29th May 2007, 11:31 PM   #10
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Default Yamaha salvage pics (7)

Finally a shot of the nifty little spring reverb unit that also came out of the Yamaha Electone E3. It's really simple, just signal + ground soldered in on one side (helpfully marked, "In"!), then signal and ground back out on the other (marked, you guessed it, "Out.")

I'll post a shot of the crazy "pancake" woofer tomorrow - accidentally left it behind.

So anyway, there's the stuff. Does it look like I'm right, that these amps must have run side-by-side for independent 30W channels? If so, I'm thinking maybe I can rig a bass amp with a Straight and a Reverb channel (using the little spring unit.) Or (now I'm going to really show my ignorance) is it possible to run the amps like in series, to get more than 30W of output power?

Thanks in advance for any thoughts.
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File Type: gif springreverb.gif (17.7 KB, 89 views)
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