Amp breaking up (in a bad way)at gig volume

[KennysFord]

Hey Folks,
I just bought an old Crate BT350....yeah yeah I know.. but... i've been searching for one of these amps for the last two years plus after the one I had died. Believe me when I say the BT350 is a lovely sounding head and not to associated with a lot of the Crate products that get less than favorable comments.
Anyway, now that bits out the way........
These amps were built in the same Ampeg factory and on the same line with a lot of the same internals as the the SVT 3 type heads, the pre however is Crate's own. It's basically a valve pre into a 350 watt @4 ohm mosfet power section.

Ok, so I'm gigging the amp last night for the first time and at decent / loud volume the sound would go into really bad distortion and break. Turn the amp down and it went away. I've tried the amp this morning at loud-home volume and it's working fine. It seems it's an issue when the head is being pushed.
Any ideas folks, I'd be grateful for any pointers.
Thanks in advance.

Edited April 18, 2014 by kennyrodg

[StraightSix]

What cabs were you using...?

[Guest]

Hi Bud,
I was using my pair of Bergantino AE112's, 4 ohm load.

[StraightSix]

Were you using the Low switch on the Crate...?

[6v6]

By "[color=#282828][font=helvetica, arial, sans-serif][size=4]bad distortion and break" do you mean the sound cut out completely?[/size][/font][/color]

[color=#282828][font=helvetica, arial, sans-serif][size=4]If so then I'd check all the speaker leads and connections, wiggle the connectors, you could have a bad connection particularly if it's jack not speakon.[/size][/font][/color]

[font="helvetica, arial, sans-serif"][color="#282828"]Likewise check the input cable and wiggle all the pots and switches looking for a bad connection.[/color][/font]

[color=#282828][font=helvetica, arial, sans-serif][size=4]After that it's open it up, replace the preamp valve, then use chopsticks to carefully probe for bad connections in internal wiring and components (don't do this unless you're comfortable working on open mains appliances, it can be lethal to take care!)[/size][/font][/color]

[Guest]

Hi Guys,
StraightSix,
Yeah, the Low Boost was enabled at the time. Is this something that's happened with you on this particular head ??

6v6,
Pretty sure it's not the valve as I'd taken the one that was working fine in my SVT7 pro.
The issue came to light when the power amp was pushed, it wasn't on the pre side as I tried that at various levels.
It happened when the master was at 12 or above, (graphic eq level was at 80%).

I've been using the amp all week at home (master at 10 or below ) with a single Berg 12 and it's been spot on working fine.......damn fine sounding amp this !!

Thanks for the comments on this guys btw.

[StraightSix]

Drop the graphic to 50% and turn off the Low Boost - adjust everything else to taste and let us know how it sounds at gigging volume.

[Guest]

Any chance of a clue as to what your thinking it might be ?
I'd have to try and find somewhere to take my gear to set it up and play it loud, I can't do it a gig sound check as we're usually pushed for time.
Cheers.

[StraightSix]

I'm thinking you may be running out of steam from the amp or maybe the speakers by using too much low EQ.

The Low Boost switch is adding 8db at 20hz which is way low for live bass and no bass cabs that I know of can even handle 20hz...also, where on the scale is the 40hz graphic slider...?

Have you tried the amp with different cabs...?

Manual is here: [url="http://www.crateamps.com/pdf/manuals/BT350_OM.pdf"]http://www.crateamps.com/pdf/manuals/BT350_OM.pdf[/url]

[Guest]

Cheers Bud,
Mmmm not sure about this.
I had the 40hz slider boosted by two notches max, Bass at 12 oclock on the knob and a slight bump in the mids. The Bergs weren't running out of steam or farting at all but as yet I've not tried it with any other cabs.
The limiter was engaged but even then I think I had more volume on tap, there's loud and crazy loud, I reckon I was at "creeping into loud" territory.
It wasn't an amp clipping sound either, more an intermittent loss of signal.
Of to the tech with it I think, see what can be found.

[Guest]

Just a little update.
I got the head back from the tech today and he thinks it was the speaker output jack that was faulty. He's retro fitted a speakon connector in it's place, fitted nice new fat wires to the speakon, the original ones were puny. He's fitted a bit of cushioning under the transformer, found and sorted two solder joints that were slightly suspect, fitted four new feet and given the old girl a full service.
£50 all in and I'm a happy bunny again.
Really looking forward to gigging this head now, it nails the tone of my SVT7pro and has a bit more heft due to a nice lump of metal on the inside. A two year search for a suitable replacement has "hopefully" borne fruit.

Edited May 4, 2014 by kennyrodg