I have an Ampeg SVT-3Pro head with an SVT-410HLF (4ohm) cab and i've been running it in parallel with a SVT-15E (8ohm). I was told by a tech at a music store that i should be fine with the ohm load, but I'm still skeptical. Is this safe to run this combo through my SVT-3pro?
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Impedance
- Thread starter flowing421
- Start date
billfitzmaurice
Commercial User
- Sep 15, 2004
- 16,860
- 278
- 76
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- Owner, Bill Fitzmaurice Loudspeaker Design
In theory, no. In practice, maybe. If you've been doing so with no ill effects, overheating especially, you're probably OK.
I had never noticed any overheating or anything affecting performance or sound. I had my rig in storage or a few months and then moved states. I moved into an apartment where i couldn't crank up the amp. At low volumes i noticed a slight tube like distortion coming from the amp even after i turned the tube gain down. I can't get it clean like i had before. I tried changing my preamp tubes (3x 12AX7) but i haven't changed the driver tube (1x 12AX7 & 1x 12AU7). Got any advice why i'm getting the hum?
billfitzmaurice
Commercial User
- Sep 15, 2004
- 16,860
- 278
- 76
- Disclosures
- Owner, Bill Fitzmaurice Loudspeaker Design
True, but if I sold amps I'd build them to handle 2 ohms but advertise them to handle 4. You can't idiot proof everything (no offense intended to the OP) but you can try.
If you are playing at quite low volumes, it is probably OK, but it can go POOF! if you turn it up. There is a reason for the rating.
If I'm reading the schematic correctly (and it matches your version of the amp), there's some current limiting in the MOSFET output driver stage, sensing the current through two of the output transistors (one on the + side, one on the - side), and limiting the signal to all of them if the current is excessive.
Depending on how that limit is set, you might not blow up the amp, but you'll get less power out of it (maximum allowed current is reached at a lower voltage). If you're not driving it hard, you're probably going to be okay. Still, it's not a really good idea to load the amp beyond the design limits!
If it's noticeable at low volume but not higher volume, there's a good chance it's crossover distortion that would be fixed by adjusting the bias.
