fender pro 400 combo heats up

SAMEEE · #1 09-03-2011, 08:19 AM

Hi - Help - bought a Fender 400 pro 2x10 combo
I own the single 15" and 4x10 matching extension cabinets
When I plug either or of these 8ohm beauties into this 4ohm combo .......the transformer really heats up ( after a gig )
worse with the 4x10 than the 15" .........
I also tried just the 400 pro head and 2 - 15" bassman single 8 ohm 15's ............same thing
Should this rig in either situation get so hot its almost untouchable after 4 hours ?

ButtUglyJeff · #2 09-03-2011, 09:01 AM

Have you taken the back off yet? I had a 250 and I believe they have bulbs to displace load. Maybe you could check for that?

**B-string** · #3 09-03-2011, 10:16 AM

Is the fan OK? Able to run at full speed?

rumblethump · #4 09-03-2011, 10:48 AM

Are you running the internal speakers with the extension cabs?
If so you are running at 2.67 ohms and I think that amp is 4ohm minimum. That WILL cause the amp to over heat.

RickenBoogie · #5 09-03-2011, 11:24 AM

+1 min impedance is 4 ohms, and most likely, internal 210 is already 4 ohms. Adding ext cabs may be running the amp under it's minimum, and thereby causing the heat.

fettbass · #6 09-03-2011, 11:32 AM

From the manual:

PARALLEL SPEAKER OUTPUTS -
WARNING: In order to maintain the rated load impedance,
disconnect the internal speaker (400 Pro) before
connecting external speakers.

NOTE: Safety Agencies in some countries have requirements
that prohibit a rating of less than 4-ohms for this product.
However, internal testing and consumer feedback have shown
this product to function reliably with various external speaker
enclosures. Fender® will warranty this product under normal
usage conditions with external speaker enclosures.

So I guess that means you shouldn't connect extension cabinets while running the internal speakers, but you technically can.

**B-string** · #7 09-03-2011, 11:34 AM

Its a 2 ohm min amp. According to Fender (350 watts at 4 ohm, 500 watts at 2 ohms).

fettbass · #8 09-03-2011, 11:40 AM

The specs do say 2 Ohms for the standalone head, which I assume is the same as the one used in the combo, maybe fender ran into different regulations with the combo vs the head? Either way, the manual for the combo does state that they can't rate it below 4 ohms officially, but you should be fine to run it to the same tolerances as the standalone head. I had a Bassman 250, and it would get pretty hot after gigs, off just the internal speakers. I assume that's just a fender thing. One of the reasons I switched to Genz Benz !

agedhorse · #9 09-03-2011, 01:18 PM

I suggest calling Fender technical support and asking them directly. The number is 480.596.9690 and ask for technical support for your amp. If they don't have the answer they many transfer you to the service dept. but one way or another they will help you out.

BassmanPaul · #10 09-03-2011, 01:52 PM

As a point, the lower impedance an output stage is driving the hotter the amp will get. For my comfort level, a heatsink should still be cool enough to handle with out too much discomfort.

agedhorse · #11 09-04-2011, 03:21 PM

Quote:

Originally Posted by BassmanPaul

As a point, the lower impedance an output stage is driving the hotter the amp will get. For my comfort level, a heatsink should still be cool enough to handle with out too much discomfort.

As long as the design is solid and the SOA thermal derating curves are followed, heatsinks can SAFELY be hotter than you can handle. Modern semiconductor temperature limits are well over 220 deg F.

Hot to our hand is different than hot to a semiconductor.

Son of Bovril · #12 09-05-2011, 03:31 AM

I also was under the impression that the 400Pro could run safely at 2ohms but that may be incorrect...?

I played the same 410 and 115 with the MB1200 poweramp and TBP-1 preamp supplied by the sound company on fri at a gig and it sounded great to me

although sadly that has no relevance to this thread.

Amps do get hot and some use the chassis to help dissipate the heat (SWR comes to mind) is the fan working properly and is the amp performing properly sound wise? maybe try giving the head more ventilation or running a fan blowing on it to help cool it

BassmanPaul · #13 09-05-2011, 12:05 PM

Quote:

Originally Posted by agedhorse

As long as the design is solid and the SOA thermal derating curves are followed, heatsinks can SAFELY be hotter than you can handle. Modern semiconductor temperature limits are well over 220 deg F.

Hot to our hand is different than hot to a semiconductor.

Agreed BUT my preference is to run them cooler. That said nowadays I don't have to design for anything but own pleasure. If the sinks were hotter than I like I'd go for a fan.