BH-420 Head, Bage Ends: Heat

[Count Bassie]

Howdy,
Played a large hall last night on a big stage with full FOH. I had my AMP BH-420 driving 2x Bag End S15-D cabs, DI from the amp to FOH.

By the end of the night my head was hot-hot-hot, especially over on the left side (facing it), near the input side. Also the magnets on my BE's were noticeably warm.

I'm a little concerned about this. Anyone have some light to shed?

Thanks.

[KPJ]

The amp casing serves as the heat sink for the AMP. I played an outdoor gig on a Labor Day weekend where the AMP was in direct sunlight for the first set. It was scalding hot but functioned without issue. I have never felt a speaker magnet after playing through it, but I imagine it would be hot as the majority of power sent to the speakers is dissapated as heat. I imagine it would be normal. Every AMP I've owned has felt hot when pushed.

[Count Bassie]

Originally Posted by KPJ

The amp casing serves as the heat sink for the AMP. I played an outdoor gig on a Labor Day weekend where the AMP was in direct sunlight for the first set. It was scalding hot but functioned without issue. I have never felt a speaker magnet after playing through it, but I imagine it would be hot as the majority of power sent to the speakers is dissapated as heat. I imagine it would be normal. Every AMP I've owned has felt hot when pushed.

Most of my concern has been about the speakers, but I can accept that for an answer and pretty much let it go. They weren't 'hot' per se, just warm. As I went to pick the cabs up the air by the large rear-port was warm, so I reached in to check it out...

I had that SWR SM400 for a bit, and it got hot also- and came with the same story about the chassis being the heat sink. Also the same guy being involved with design is a clue... And the heavy gauge steel the thing is made of backs it up as well!

Cool, thanks Kev.

[Beej]

I had this exact problem with my BH420 when I ran it with a single 4ohm Acme B2. My thread is here: Acme B2 makes my AMP BH420 hot Some good info in there. I found that when I rolled off the bass quite a bit, I could play that combination for a long time without the extra heat. I've since just used the post-pre out and run it into my power amp to drive the B2. Otherwise, I just run two 8ohm GK cabs instead with my AMP and don't have the heat issue.

Its strange that I've used the AMP extensively even with low loads like 2.67ohms for extended periods and it never became hot like it did powering the B2. I think James Hart has used his AMPs with Bag End cabs, so hopefully he'll chime in with his experience here too. If not, maybe PM him...

[Count Bassie]

Poweramp is a good idea- myself I'm just into simplicity nowadays. Modular and lo-frills is my current program; I have a couple integrated heads that have turned out to be nice to use, and I'm looking for another cab or two.

Seems that heat is part of the deal here though: Russ Allee designed this thing, and much of that design moved over to the early SWR stuff (SM400 Bass Amp/Toast-R-Oven), so I'm not really buggered out about it now. But if I could run it cooler I would... yeah maybe James'll be able to add to this.

Interesting about the 2.67 load though.

James?...

[Beej]

Yeah, I hear you on the simplicity thing. I really prefer to just use the AMP with a single 4ohm, which is why I bought the B2 in the first place. I didn't predict the heat issue, because I've owned this amp for 20 years and have never had a heat problem despite many various cabs used. It pains me to use the power amp, but it just sounds so good together. I don't have any problems with my GK stack even though its kind of a stupid combination - 1x15 and 4x10. It does sound pretty good though, but not as clear as the B2. Oh well, life is full of little sacrifices...

[Count Bassie]

All those years- just curious- did you typically run that head at 8 ohms, or 4? Your answer may well be almost obvious, but I just waht to be thorough...

[James Hart]

Originally Posted by Count Bassie

But if I could run it cooler I would... yeah maybe James'll be able to add to this.



James?...

Mine get hot when pushed. I've never had any failures, but I'd be lying if I said it didn't give me a few moments of concern during long mid summer, outdoor day gigs.

[Beej]

Count, in the beginning, most of the time I ran mine with a single 8ohm cab - usually at low volume gigs with an acoustic BG or cello, however occasionally I'd do funk or rock gigs that required more juice and then I'd do two cabs at 4ohms. In the last decade+, its been steady with two cabs at 4ohms, or one 4ohm cab with many different combos and never had the pronounced heat (excepting hot outdoor gigs like James said).

Way back when, a fellow bassist noted my AMP and said it can be run as low as 2ohms safely for short jaunts (and it says so in the manual too). He showed me how to daisy chain three cabs together to make 2.67ohms and I would do that at shows without FOH support just to increase the 'presence' I felt onstage. Plus I liked a giant in your face stack . I never made it a regular practice though and haven't done it for years.

[Count Bassie]

Well since my TE head has had to sit out for a while I'm having opportunity to use the AMP some more. There will be a few large outdoor gigs coming in a couple weeks, so the testimony is helpful, thanks James.

I am brought to remember that I do have the manual here on .pdf, and will have a look later on. Quite a little dynamo, this amp! Thanks guys.

[brianrost]

The A.M.P. power stage is designed so that if the temperature of the transistors gets too high, the voltage from the power supply is limited until they cool down. It's OK for the enclosure to get very warm, I'd only worry if the amp started to lose volume, indicating that the overheating protection had kicked in.

I've used mine on many outdoor gigs in summer sun and had zero problems after over 20 years.

[Count Bassie]

Originally Posted by brianrost

The A.M.P. power stage is designed so that if the temperature of the transistors gets too high, the voltage from the power supply is limited until they cool down. It's OK for the enclosure to get very warm, I'd only worry if the amp started to lose volume, indicating that the overheating protection had kicked in.

I've used mine on many outdoor gigs in summer sun and had zero problems after over 20 years.

And another testimonial to the durability and probably clever low-tech engineering of the AMP BH-420, using the case as a heat-sink and not over-killing a concept. I applaud it.

Fine, I'm pretty convinced I don't have to stress over the heating up of my amp after a couple hours of use.

Thanks again Brian, Beej, James and Kev! And thanks for not busting my chops about my spelling ("Bage Ends")!

[KPJ]

Originally Posted by Count Bassie

And thanks for not busting my chops about my spelling ("Bage Ends")!

Too easy!

[Count Bassie]

Originally Posted by KPJ

Too easy!

I was just practicing my Portuguese...