Crate BX-15 amp

[freze]

I need Crate BX-15 schematic.

Thanks

[J M Fahey]

Hi freze.
Nice and clean design.
Can't find it right now, but it's no big deal: a dual op amp preamp, with second half being the simplest 3 band EQ used on the equivalent Fender, with an extra pot and one extra resistor and capacitor to turn it into a "4 band equalizer", a very simple yet good Led/LDR opto compressor and a simple "datasheet application" TDA2030 15W amp.
I might draw it by heart, but please state what your problem is.
If it's blown, usually replacing the 2030 is all that's needed.
EDIT: maybe this helps
http://music-electronics-forum.com/t7931/

[freze]

Thanks Fahey,

but my problem is in volume pot, need swap. I'm search but not encountered this value.

Thanks

[J M Fahey]

Well, that's (relatively ) easy.
Post the codes printed on the pot, look everywhere becouse sometimes they are even on the front, hidden by the front panel, also post what the PCB says, sometims the value is printed there.
If you find nothing, there are two basic options:
1) the pot has its center pin grounded; a 22 (or 25) K linear will most probably do.
2) if one end is grounded, it's a regular volume control, a 25K to 100K log(logarithmic) will do.
You *may* use a linear here, but volume will rise too much at the beginning (0/2) and almost nothing at the end (above 5 or 6), but you will burn nothing, so in a pinch .....

[oc disorder]

I could be wrong (disclaimer) but usually the guitar series and the bass series
are very similar with the exception of the speaker and possibly some of the coupling
caps.Also the bass version has no distortion or reverb.
There is a schematic for the guitar version here :-
http://music-electronics-forum.com/t13839/
I'm sure you will find the values are similar.
The pots seem to be either 250K or 10 k with the midrange 500ohms lin.
As JM said the values are usually printed on the pot.
Loud Technologies should be able to supply the circuit.

[freze]

The pot model is CTS. Not clearly communicates the value. Only with code letters and numbers (deleted) in spaces in the rear. I will try to remove and disassemble to check the value. I'm afraid to change for different value and burns it.

[J M Fahey]

You'll burn nothing.
At worst the response will be funky.
Check and post which lug is grounded.

[dobrota]

If circuits for various Crate bass amps are similar, so there's 50k linear volume pot in Crate BX50.

[bea]

Please let me pick up this old thread. I need the schematics for my old crate bx-15 as well. Background: i want to modify it (improved deep bass performance). The Amp itself is already modded with a fane studio 8m speaker and the possibility to run a 2nd 8 ohm speaker in parallel (usualy an eminence beta 12) to the fane to make it usable in small gigs. The cabinet has been adopted as far as possible to the different speaker.

Now i want to understand the preamp/tone stack in order to be able to improve it a bit.

Beate

[J M Fahey]

Hi bea.
I think you already have the best 8" speaker in the world , *but* in a terribly small box and *very* underpowered, specially if you want to use it live.
Give it what it deserves:
Build a simple powered box, say 20" by 20" by 12/15" and mount there a simple chipamp, say a 50W LM3886, for which great kits are available, which solve 90% of your problems.
Tweaking bass controls will add nothing at all to final output, which is acoustically limited.
If any, it will make for fartier bass, with *less* usable volume.
At home you practice with the BX15 alone, in shows you place the powered box in the floor and put the little Crate on top, as if it were a head.
Good luck.
EDIT: you can build a similar powered box for the 12" Eminence, just make it 24" by 24" by 12/14"

[bea]

Hi,

a few thoughts on the concept based on my experience with the two speakers:

the studio 8 m has a Vas of only 7 l, meaning it will live happily in small enclosures. I ran it in several enclosures - vented 21 l, and a TML enclosure tuned to 60 Hz, and the crate after enlarging its enclosure (which is easy by placing the front panel to the formost posssible position and closing the upper gab by a piece of wood), also vented and of course the vent adapted to the speaker.
The Studio 8 m works well in all three enclosures . This can also be by the simulations i did earlier.
In practice, if using the studio 8 m as a fullrange speaker, great care must be taken not to overload it a deep frequencies: the 12 W RMS of the BX-12 are not a problem, but the 50 W You suggested will definitely - i slightly overloaded it with the 32 W of my ancient Echolette M40 tube PA. (You see, i have more powerful Amps at hand if i need them.)

Back to the circuitry of the BX-15: the block diagram given in the owner's manual shows a buffer, the tone stack and the power stage, and it is spoken of a limiter. Upon first impression, the chassis shows a (dual?) op-Amp, the integrated power amplifier and another integrated circuit i could not identify upon first sight.

If the specs of the BX-15 are correct, it has a severe design flaw which might be easy to correct: input impedance 25 kOhm which will severely hamper the tone of each passive instrument. If not just a typo in the owner's manual this is *far* to small and possibly easy to improve. My interest is simply to look for other small flaws like the impedance thing which if optimised would convert that little box into a really fine sounding low power amp.

Maybe You have a look at design of the input stage of it larger cousin BX-50 (which has a similar sound characteristic as the BX-15) You might get an impression of what i mean.

Beate

[J M Fahey]

Hi bea.
I *did* "lift" the BX15 schematic a long time ago; I'm not posting it because I never digitized it, and God knows where that old notebook is now.
Anyway I somewhat remember it by heart, and it's very similar to the BX50, minus the "enhancer/contour" and the master volume.
There's not much to modify on that minimalistic tone control; it's made out of a lowpass filter, two bandpass ones and a high pass one.
The bass to low mid crossover frequency is 15K+.1uF ; 100Hz; everything below that is controlled by the bass pot; everything above by the low mid one; the trick repeats for Hi mid and treble.
There's no specific LF frequency definition beyond that.
Anyway, the lower you want to go, the higher the excursion; much more so than by simple power drive.
I doubt the input impedance is 25K; as far as I remember they may have used a 22K or 25K series resistor, but definitely the Pin3 to ground resistor was at least 220K as shown.
I use 1M.
The opto limiter is simple and very good, I have used it sometimes.
It's the only way to add a limiter to a chipamp.
In my discrete poweramps I use an embedded one, but as a general purpose add-on one the Crate Opto has no peer.
I also use it on Piano amplifiers.
EDIT: that Studio8 speaker is much used in high power Pro Sound; if you made it flap or fart then maybe it was not loaded properly.
A reflex box tuned to the lowest frequency your bass will provide (say, 42 Hz) will ensure the excursion is *minimum* at that frequency.
Add a 40Hz highpass filter as a safety precaution, not for musical notes but for thumbing, tapping, slapping, etc.
Of course, you may leave it as-is and build the powered box for the Eminence.
It will definitely handle more than the 7.5W the BX15 will supply.

[bea]

Thanks for the info: You confirm what i was assuming.

Concerning the Studio 8 M: in a vented enclosure and possibly a TML as well, the 32 W of the old tube amp (ok, 40 on Music material and possibly even more if overdriven...) should lead to an excursion within the absolute limits of the speaker (10 mm Xmax), but it will pretty surely exceed its limits for clean tone.

I am fully aware that the 8m deserves a better amplifier, but the BX-15 deserves a better speaker than the original one as well. And i simply had the fane lying around for years.


BTW: i am currently doing a few simulations on the studio 8 M and come to the conclusion that it definitely needs a really small enclosure - in theory 5.5-8.3 l which of course is hard to achieve in practice. Of course with restrictions in power, but 15-20 Watts should be possible.

Beate