Crate b150 preamp distorting

[lucid77]

I'm kinda new to working on amps, but have built many small Ic based amps. My bass head is distorting when the volume on my instrument is more than half way. Plugged into the return of the loop, this problem goes away. I have schematics and can do some troubleshooting on my own, but don't know exactly what I might be looking for. Traded out instruments and cords and cabinet and still get the same result. Can anyone guide me in the right direction? Please?

[J M Fahey]

I'm kinda new to working on amps, but have built many small Ic based amps. My bass head is distorting when the volume on my instrument is more than half way. Plugged into the return of the loop, this problem goes away. I have schematics and can do some troubleshooting on my own, but don't know exactly what I might be looking for. Traded out instruments and cords and cabinet and still get the same result. Can anyone guide me in the right direction? Please?

Maybe you don't actually have a problem.

1) you don't mention the amp settings, but most (as in 99%) of amps distort past halfway volume.

2) if you plug your instrument on loop return, that point is much less sensitive and so very hard to distort.

We don't know either what bass you do  have.

Please post the schematic .

I suggest you set bass controls to full/10 (but tell us what it is), set EQ controls to 5 , master volume if any to 10, volume/gain control to 1 and play ... does it distort? 

a) if it distorts, slowly nlower Bass volume control until it does not.

b) if not, slowly rise volume until it does.

Post results.

[Roly]

Service manual from our old friends here;
http://elektrotanya.com/crate_b150_bass_combo_sm.pdf/download.html

{wait 30 secs until "processing" changes to "Get Manual"}

[J M Fahey]

Nice amp, very 80's design, much more complex than it needs to, looks like it was meant to be the brand flagship, with its dual effects loop, fully adjustable compressor/limiter (expecting the average musician to properly adjust threshold and attack is a bit too much), etc.

The first preamp stage is variable gain type, so very hard to overload, even by hot pickups; I guess we simply have SS power amp buzzy clipping (or master set too low, which allows preamp clipping).

Proper way to setup this amp is to set tonen controls to desired values (also avoid being too extreme with Graphic EQ settings) , Master on 10, start rising preamp volume until power amp clips (should be wall shaking loud by then) and kill the distortion by proper setting pf Limiter Threshold.

Modern amps (even by Crate/Ampeg)  have a factory preset Limiter to simplify Musician's life.

So in a nutshell I think this Crate amp has not defects, but setup is somewhat more complex than with others.

[lucid77]

Great! Maybe I just had the settings all wacked out. I am playing on a Mexican fender jazz bass for testing. Now I am plugging into the 0db jack and everything seems fine. However, -15db jack plays fine on the same settings and then will cut volume every couple seconds. Doesn't loose volume all together, but definitely cuts quite a bit. Is this normal?

[J M Fahey]

Very probably just dirty/worn jack or cracked solder, both jacks "are the same" and interconnected by just 2 resistors, as simple as can be.

[Roly]

 :dbtu:


Hi lucid77, welcome.

-15db jack plays fine on the same settings and then will cut volume every couple seconds. Doesn't loose volume all together, but definitely cuts quite a bit. Is this normal?

"Normal" in the sense that this is typical of how plastic sockets fail, particularly PCB mounting ones (which they mostly are these days).

Unlike the older metal chassis mount type, somebody trips over a guitar lead (seems to happen at least once every practice I've attended) and the sudden wrench is transmitted by the socket to the solder connections where it is mounted on the board, and they crack.  You may find that if you push the plug from side to side or up and down that you can turn your signal on and off at will.

This will almost certainly be a cracked solder joint under the socket.  If you get the board out and look at the solder side while moving the socket it is very likely you will see some movement in the joints (bright light, lens).  Sometimes the copper tracks break and he entire joint moves, but if you can see the socket tag(s) moving inside the solder joint then a touch with the iron and some fresh solder normally does the job (until the next time).

This is a very common generic problem with a lot of modern amps, stomps, and synths where plastic sockets are used.


Cleaning sockets
One way to clean a socket is to use a (smoking) pipe cleaner (with plastic twill) folded double and dipped in some metho (o.n.o.) and worked in and out while also slowly rotating.  I've made it a habit as part of my gig prep to give my sockets a going over and found it does help to minimise on-stage problems and stuffing about (which is never good look).

[phatt]

Maybe check the limiter threshold,, if set too high it will limit volume and may even distort.
Same with the Attack,, set hard and fast will make the signal sound weak and might even muff each note.
If the Led is lighting up and staying for every note then the limiter is likely set too high and fast.

Maybe re-read J M Fahey's post as He has covered most of this already. :tu:
If you are new to Music Equipment it can be confusing when faced with a panel of knobs.
Oh yes and be aware that some pickups have quite high output and you may find the low input socket will give better results.

Phil.