Here's an Audio Engineering Society J-horn for 12, 15 or 18 inch driver, similar to the Fane.

I'm posting this one here because it's out of my private stash (not on-line) and the book is way out of print now.

If you look closely at the response curves the main difference as the diameter goes up is you get that extra bit just above 50Hz, but at the expense of some top end roll-off.  I'm considering a pair of these with 12-inch drivers, and maybe a low-reach tweeter horn in each for use with synth/keys.


Circuits for the Musician 300 series appear to be available here;

www.audio-circuit.dk/schematics_o-r.php

re: Peavey Musician screaming

Q: Do any of the controls have any influence, louder, softer, change tone or pitch?

Yeah, "buildable" is certainly a word, and not a bad concept if you want to actually finish something and use it. 

Ah, so you found my Siamese.  The amp just happened to be what was around at that time and it has been driven by all sorts of things since it doesn't really have an amp of its own.  It's nominally a couple of hundred watt 15-inch Etone driver but normally gets driven with about 50 watts (and I dread to think what would happen to the back wall if I drove it with 200 watts).

Like most of my stuff this was build mostly out of scrounge, the cloth covering and corners were bought but most of the rest were scraps gathered from here and there.  I did an earlier, smaller Mid-Ranger that was built entirely from wood that had been pile up to burn in a bonfire, warped ply and the like.

A criminal amount of good ply &c gets thrown out at building sites as "offcuts" or used formwork that has a bit of cement residue on one side, and for a bit of dumpster diving after quitting time, and a bit of cleaning, you can have all the materials you need to build guitar speaker cabs - leaves more money to spend on the actual driver(s).

While I'm not unhappy with the Siamese W-bin I'm now keen to try one of the Fane J-horns which I think may give just as good results with less building effort (and weight).

Any box with knobs you can get for $40 has to be worth serious consideration - all the better if it's actually working.  :dbtu:  If it doesn't suit your needs, or you can't adapt it, you can always flog it again (to JM  :cheesy: ).

http://OzValveAmps.org/cabinets.htm#fane
Get 01-11, and 34-41 bass horns.

attach: Fane-rear-J-15

1. okay, this suggests that there isn't actually anything wrong and it is working as designed, just not to your satisfaction.

2. no it wouldn't be dramatic, roughly a doubling of gain. (820 / 470 = 1.7 times)

3.

Quote from:
so i just went straight for a jumper wire.

Yikes!  Oh well, okay, so now you know what it will do with the preamp first stage pedal-to-the-metal.  8|

Just guessing on the numbers you gave I'd say that distortion due to overload will start with the "gain" control flat out with a gain-limiting resistor of about 330 ohms (orange/orange/brown), so if you want a bit of crunch right up the top end of the gain control I'd go for something like a 220 ohm (red/red/brown).

I assume the "467" was from your ohmmeter (maybe with your fingers in parallel?) and it will be a nominal 470 ohms (yellow/violet/brown).  Holding the meter probes onto the resistor lead with your fingers works up to a few k ohms, but above that you start to get errors due to you body resistance being about 20k, and not constant at that either, so you can only hold one end.

The high pitched whine may be the oscillation I was worried may happen with very high gain, but it could be that it is external electrical crud (light dimmer, electric drill or blender, &c&c) and you can now hear it because the amp has a whole heap more front end gain to amplify it (and it may be reduced or eliminated when the amp is reassembled).

Yes, well, the pot sets the first stage gain and the resistor limits how high that gain can go, so replacing the limiting resistance with a bit of wire seriously supercharges the first stage.  Now it's a matter of tweeking the value of that resistor until you get the result you want, or at least can live with.

I have a large box full of printed circuit boards ripped out of sundry stuff.  The cases are generally useless and just take up space, but you can get 10 or 20 PCB in a small cardboard box, and whenever you are short of a cap, LED, resistor, or even transistor you can hunt one down and recover it.

Learning how to read the resistor colour code on sight is very helpful, but you are normally only dealing with about a dozen values and their multipliers.  Get a colour copy of a resistor cheat-sheet and pin it up above your soldering iron, and pretty soon you'll be picking up resistors and seeing their values without looking them up.

It's one of Murphy's very many Laws, you'll need tomorrow what you threw out yesterday.

Have we now moved closer to what you originally wanted?

I'll just remark that (apart from any specific problem with this particular build) the Baxandall tone control is almost universal in modern Hi-Fi's, stereos, and ghetto blasters, but is the least favored tonestack by guitarists who prefer Jones and "Jones-like" Fender and Marshall passive tonestacks.

{I don't think JM was actually trying to be funny about conductive Soy Sauce    }

"Your best service instrument are your eyes".

Most of the time I like to open gear up for a look-see and dust out with brush (and vac if required).  This gives you an idea of what you are dealing with, and you will often notice the cause of the problem (e.g. a large cap has ripped its solder joint(s) free of the board) before you even do any power up testing.  Similarly, fried emitter resistors in the power amp will point you to dead transistors, and so on.

An internal pic or two would be good since I can't see anything on the net, and must assume it's one of those "everything on a PCB" types.

Quote from: peters0306
Actually, by pushing on them just a touch the thing plays loud and clean

Very good sign. :tu:  This strongly suggests you have a fractured solder joint or crack in a PCB trace right there somewhere.  This commonly occurs with largish electro caps that really require some physical support such as being glued down and/or tied down with cable ties.  This kind of break can range from the grossly obvious to very fine hairline cracks you can only see with a powerful magnifier.

It's at this point you may discover why some repairs are more expensive than others; that to get to the solder side of the PCB you have to unship every control and socket from the front panel.

Manufacturers love this style because it makes the amp cheap to build, while techs hate it because it makes amps difficult, time consuming, and therefore expensive, to repair.   :trouble

It's not like the series-pass element is getting hottest when the fan is stopped, so there is a degree of self-regulation here if the series-pass element is also exposed to the fan (and why would you not?).

PWM is all very sexy and all, but not around low level audio.  With any sort of controller there are potentially large voltage swings, possible control "chatter", and the need to keep anything like this right out of the audio path.  This more than justifies the use of a linear controller.

I cut my teeth on Tamla-Motown the first time around (I'm still gigging this stuff in my 60's).

400 Watt Columbian bass rig.  Yes, very impressive.

So is this;



...but you would be nuts to try and learn to drive in one.

Quote from: http://www.construyasuvideorockola.com/proyect_amp_mono_400w_1.php
IMPORTANT: This project is not for beginners. The voltage and current management are quite high, not counting the cost of components. For this reason you should have good knowledge and experience in electronics assembly projects of this magnitude. If you have no experience in the assembly of electronic projects, we recommend starting with a simple amplifier, such as the 40W amplifier. Otherwise any mistake can cost you money. {my emph.}

To be blunt, these amps are for advanced builders only. The preamps, sure, but the main amps are serious engineering.

It also has to be said that these are adaptions of stereo amps to guitar service, and as such are not intended to deliver their rated output continuously as is required of stage gear.

There is nothing wrong with the idea of getting high power by running several lower power amps in parallel, in fact there is a lot to be said for it, but how ever you do it you have to deal with some very serious questions of component capacity and sufficient cooling.

The power transformers, big as they are, are only for intermittent output at these power levels.  Rack amps designed for concert use have power transformers twice this size for the same power, and look more like welders than amplifiers.

The multi-amp method has a couple of real advantages; one is that lower powered amp modules make use of more commonly available components, thus they are cheaper and easier to build and to repair, and they also give you diversity in that if one amp blows up at a gig you still have the other(s), all your performance eggs are not in one basket.

As a keyboard player who uses a homebrew Twin-50, and as a soundie who has used multiple amps, I can tell you this diversity has saved the show on more then once occasion.  Even the classic Acoustic 360/361 used a single preamp, but independent power modules in each W-bin - and I would strongly suggest to you that they knew what they were doing going this way.

A speaker in a direct-radiator cab is about 3% efficient in converting electricity into sound.  In a J- or W-bin that jumps to 25 to 30% efficient; in other words it makes 50 watts sound like 500 watts - without having to use a genuine 500 watt driver.  Bill's "Siamese", one of his earlier designs I modified a bit, has ample slap thanks to having tweeters, but I wouldn't call it "mid-range" by any means, going down flat to the low-E on a four string bass it makes your guts shake.

Photos much better, thanks.  You really only need to work out the first bit, first two controls or three transistors from the input ('tho having an entire tracing to work from and offer others is helpful with any problems down the track, and to others struggling).

"10/16" will be 10uF/16V, but the value nor the voltage rating are critical here, anything within 2:1 will be fine.

Reading 1. is inconsistent with reading 2. but your comment explains that; "k" = "kilo" = x1000.

Reading 2. is as it should be.

Any of those caps will do, it's mainly a matter of what will physically fit.  I'd select the 22uF/10V on the grounds of voltage first, then the 10uF/35V on grounds of value, then 4.7/25 on voltage.  Just watch you get the polarity right - the black stripe means the negative lead and will almost certainly go to the 820 ohm resistor+pot.

What this bit of the circuit does is change the voltage gain of the first preamp stage, and the 820 ohm resistor sets a minimum resistance which sets a maximum gain.  By reducing this resistor you allow the stage to go to a higher gain, more crunch.

If you carry this to extremes (such as putting in a wire link instead of any resistor) the gain will go to a very high value.  This may work but the amp may also become unstable with so much gain, and oscillate at high gain settings.

Something for you to experiment with.

Try and find some sort of old electronic junk, radios, Hi-Fi amps, whatever, you can recover components from.  Anyone who is into electronics has a well stocked "junk" box (although the class of the junk varies quite a bit).  It is just shocking how many perfectly good components go to landfill every day. I haunt my local rubbish transfer station and tip shop, garage sales, op-shops (thrift stores), roadside hard rubbish collections, &c&c.

Keep us posted on how you get on.   :tu:

I think JM is being kind.  I'm an experienced builder and I would have a long hard think before attempting a build of this class.  Just re-creating an Acoustic 361 at the (genuine) 160 watt level took the best part of a year.

I'd also suggest that while brute force is popular with bass guitarists, my own experience strongly suggests that cunning beats brute force every time.  I have built some horn-loaded speakers for bass and found that they can more than deliver in a moderately sized, powered, and priced package.

I can vouch for the fact that this guy's designs are not hyped but realistic, and deliver what is claimed;

http://www.billfitzmaurice.com/

The Fane back-loaded J-horn design looks good too.

The basic point is not watts but dB_SPL, and when you discover that you can get more dB with 50 watts and a good horn, you are going to wonder about others flogging 8x10's with 500 watts for fewer dB Front of House.

The normal value for a fixed bleeder is to allow 1k ohm per volt, so for around 300 volts use 280k or 330k.  The power rating;

P = E * I;  300V * 1mA = 300mW or a bit over 1/4 watt, so use half or one watt resistor.

Quote from: guitarfreak666
how i could put a 3band tonestack in this amp?

Perhaps the most important aspect is to drill enough holes for all the controls you are going to need before you start any actual assembly or wiring.  If you intend to tweek a lot then add a few extra tagstrips scattered around, but always try to do all your metalwork before you start mounting any components.

First build the basic amp and get it going, then you can have endless fun trying different tonestacks, etc.  It's a good rule only to make one change at a time and see what effect that has, any more at once and it quickly gets confusing.

Quote from: guitarfreak666
i cant find a transformator with 215 on primary, if i use a 230, what value of resistor should i use to drop the voltage?

I think you mean secondary, the rectifier/amp side.  The primary is the mains side.

The DC voltage is found by multiplying the secondary voltage by the rectification factor, root(2) or 1.414.

Originally;
215 * 1.414 = 304.01 (which has been rounded on the circuit to 305V)

If you use a 230V secondary the new HT voltage will be;

230 * 1.414 = 325.22, or about 20 volts more.

The valve databook gives typical conditions for push-pull EL84's on 300V as an idle of 2x 36mA, or 72mA, which we can round up to 80mA for the entire amp.  We therefore want to lose 20 volts at a current of 80ma.  Ohms Law;

R = E / I;  20V  / 0.08A = 250 ohms (available values either 220 or 270 ohms)

Power dissipation;

P = E * I; 20 * 0.08 = 1.6 watts.  I'd use a 5 watt ceramic wirewound so it has ample reserve for full drive.

The overvoltage is, however, only (230/215) * 100 = 107 or 7 percent which I personally wouldn't worry about if it were my build.

I agree that running first double triode in parallel is a waste, so see the attached circuit for a minimalist two stage preamp.

Preamp notes: the first 1Meg resistor could be changed for a pot, but there is no need to use both a pot and a fixed resistor; this only lowers the input resistance and loads the guitar pickup making it less lively.

The stage coupling caps are shown as 5nF but these can be tweeked up for a fatter sound or down for a thinner more trebly sound.  These need to be rated for the HT voltage (300V) or greater.

The 25uF cathode bypass caps are fairly nominal in value, and can be rated anywhere between about 5 volts and 25 volts.

The 1Meg on the grid of the second stage can also be changed for a pot if a more conventional "gain" control is desired, the "volume" then becoming the "master volume".

Any tonestack can be inserted after either of the stage coupling caps (5nF or whatever).

In any case I would increase the value of the main volume control from 500k to 1Meg, and include a 100pF "top coupling" cap as shown to maintain brightness at lower volume settings.

Extra HT decoupling is required in the form of a 1k 1 watt resistor and another high voltage electro (33uF 450V).  Neither the value nor the voltage is critical and anything more than say 10uF and 320 volts will do.

This amp generally provides almost endless scope for tweeking and mods, but get a basic version going first, then start playing.

HTH

@bassetrox - I practiced my craft for a time deep in the Australian bush and I have a heap of "sundry critters in the works" stories; metal mesh over speaker ports and the like were standard defensive modifications.


Well it sounds like the speaker itself is intact.  Take note: the amplifier must not be driven without a load (speaker) connected or it will be damaged.  Until we have a better idea of what is wrong be very moderate with any drive during power on tests - if you can't hear anything don't turn it way up and fang it.

We await crisp internal pix.

{My guess now is that it doesn't have HT on the output stage for some reason}

Quote from: Paolo
In the photo's, there is also a polished metal plate behind where the reverb was, where some wires from the PCB are attched.  Any idea what this is?

In your pix 0844 the shiny plate behind the reverb position is the heatsink for the output stage; the two black blobs screwed to this are the two output transistors, the white goo under them is a thermal compound to better thermally couple the transistor cases to the heatsink, and the white blocks look like sockets that the transistors plug in to.  Note that the tabs on these transistors are connected to part of the circuit and are insulated from the heatsink by plastic washers on the screw and small wafers of mica or similar underneath.

Avoid touching the white goo because it sticks to everything like thick paint or ink, and also may be somewhat toxic to ingest.

Ideally heatsinks should be matte black, not bright and shiny, but at least this one looks of a reasonable size, which is more than can be said for a lot of small amps.

Yep, that's a pretty basic reverb "tank" (or "spingline"), but I have actually see ones out of ghetto-blasters that are much smaller and more downmarket than this one - at least it's metal.   

Attached is a circuit of an early Pignose which is likely to be very similar to the one you are seeking.

While this uses 2SA-series PNP germanium transistors I am inclined to think that the main factor in determining the tone would be the two transformers, driver and output.  While the transistors, similar ones, or even silicon NPN substitutes, I suspect that obtaining suitable transformers would be the main obstruction to cloning this circuit.

Nah, valves (toobes) don't just go silent like that, and the fact that they are lighting up and getting warm are both good signs.

*Utterly* silent suggests to me that the speaker circuit is open somewhere because you normally get *something*, a little residual hum or hiss.  And this is a worry because if you drive the amp with the load open circuit you can easily destroy the output transformer, and in this case that would mean the amp is a write-off.

So I would try testing the speaker, either by driving it with another amp, a multimeter, or even flashing a 1.5V or 9V battery across it should produce some sort of "blats".

The majority of amp problems (in fact all electronics problems) are due to dirty or corroded connections, and since this amp has been in storage for a long time, this is most likely what is wrong (unless of course rodents have eaten the speaker); it's a matter of finding what should be connected that now isn't, and the speaker plug and socket are a natural suspect.

I can't find a circuit/schematic so I'm flying blind, but a rear photo shows only one fuse and that will be for the mains, however there may well be another fuse internally for the High Tension (HT or B+) supply for the output valves.

This may have blown because the electrolytic filter capacitors in the power supply tend to "dry out" and go low resistance if not used for a long period, as here, and this protective fuse will blow at first power up, and very effectively silence the amp.

You can disconnect the amp from the mains and remove the chassis (after first removing the output valves), and see if there is an internal fuse to be seen.  If so and it has blown you can try replacing it with an identical one, but if that too blows then post and we can take it from there.

Taking a few crisp and well lit internal photographs and posting them to this thread will also be of assistance, as would a circuit/schematic if you can obtain one.

Replacing old filter caps is something that all amps need after about 20-30 years and done frequently by techs, but is also normally within the scope of anyone who is a bit handy and can solder properly.

HTH

Quote from: srussell2 on June 07, 2012, 10:12:54 AM
Morning all,

Looking at the schematic and using the diode test function on my meter, I get 0 volts from the base/collector and collector/emitter so I guess Q29 is shorted?

Yes; with it isolated you should read somewhere between "500" and "700" (mV) for a good device.  It should test as two diodes connected to the base, and infinity collector to emitter.

It is vitally important that you find all the damaged components before powering up (via a limiting lamp) or you will simply destroy the replacement components at well.

This particularly means the driver transistor associated with the dead transistor, and the output transistors partner to the other supply rail which possibly may now be open circuit rather than shorted.

If you can't be certain with the device still in circuit then you are going to have to disconnect it to be certain (and to replace it correctly, photos are handy for this).

You should also leave the speaker disconnected until you can see that the output (aka "half rail") is settling to within about 100mV of zero DC across the speaker terminals.  Anything more than about a tenth of volt out of balance needs to be investigated.

You also need to be very sure that you have corrected the original cause of the failure or you will be very rapidly back to square one.