|Tips on SVS Ultra 750W Bash Subwoofer AMP Failures (+ Checks Before you Buy)
I have an older (made in 2007 I think) 750W Bash amp PC13-Ultra, bought used with an amp problem in Dec. 2010 very cheap. (No label on Amp, but turned out to be a PC13 not a 12".) Without a label with S/N, no way to check if any warranty was left. Original amp no longer made/no mfr repair. (A new SVS Sledge 1000D replacement amp would have cost appx $600.)
The Bash Amp's failed part was a Thermistor that I believe is used as a startup/inrush current limiter. I've seen several SVS 750W Bash amps with similar failures in older PB13/PC13 Ultra subwoofers. Drivers checked OK with a meter and no apparent voice coil or other damage.
(BTW: I'm not referring to earlier/older Bash amps SVS used in other subwoofers before the 750W PC/PB13 ultras. I've seen some from as far back as 2002 era still working. And the 750W Bash amp's thermistor failures I've seen may be affected by usage (left on) or a specific manufacturer's lot/component used.)
Before buying a used SVS PB13/PC13 Ultra with Bash Amplifier, I'd do this test first:
SVS PC/PB-13 Ultra (750W) Bash Amp Thump Test
- Ensure Subwoofer and Receiver are OFF, no active input to the Sub.
- Set the Subwoofer's "Auto/On" Toggle Switch to the ON (not "Auto") position
- Power the Bash SVS subwoofer On (A/C power switch)
- IF any "Thump" is heard from the driver, the amp may have a failing thermistor. (If you're not experienced with electronics repair, have someone that is do this for you. Disconnect power and heed warning labels on Amp.)
The photos below show TH1 location. It may have cracks, discolored hot spots, etc.
I've seen an amp with cracked thermistor (1/3 missing - see photo below) still work, but with a slight thump on Power-Up. Eventually it will completely fail however, so if any 'thump' is heard at power-up (again with the Auto/On switch in ON position - the "Auto" setting can mask this problem), have the amp checked for damage to TH1.
(If the amp has already failed/has no output/sound, no LED, etc - check the fuse, located in a removable part of AC input socket. If it's blown, likely a new fuse will blow again. If fuses repeatedly blow, other components (not just the thermistor) may have also failed.)
BTW: In general I'd suggest using "Auto" mode rather than "On". And I would not leave the Bash amp on all the time. (Regardless of type, I turn off all my A/V electronics when not in use.)
Not sure if EU amps are different, but I've now seen this problem on 3 (USA/120V) SVS 750W Bash amps (used with their earlier PB13/PC13 Ultra Subs). All had what appeared to be the same OEM (Green Disc/unmarked) Thermistor failure. A replacement I've used in US SVS 750W Bash amps is Ametherm Part Number SL15 4R008-03. (IIRC, a post by Ed M. of SVS also listed this as a replacement P/N.) I need one now, but no local electronic parts dealers here have them. They're typically sold mail order for appx $1/ea or less (depending on Qty) plus shipping, for instance at Newark.
This isn't the only possible failure mode/component of course, just one I've seen several times and something to check before things get worse/before buying. (BTW: I've had several of these amps that almost seemed glued in, see below for a tip I've used.)
The PB13 Ultra Bash amp that failed shortly after sold by original owner (about 2.5yrs old) with "Auto/On" Switch set to ON would "Thump" (very deep/low frequency tone) so forcefully on that test it would rattle items in a small room. Eventually it failed, blowing the AC input power fuse at turn on. A working PC13 Bash amp developed a much lower level thump at power-up (not noticed if Auto/On switch in Auto position) and inspection of the amp's thermistor showed it had cracked and about 1/3 of it was missing. (See green disc in right side of image below. Others I've seen were intact but had cracks from stress/overheating.)
Cracked Thermistor (TH1) Example (SVS 750W Bash Amp, still working)
Other photos of failing TH1 thermistor in a 750W Ultra Bash Amp:
The photo below shows a larger view of that area of the 750W Bash Amp
The missing piece of the thermistor from the Bash amp above was found on top of the (downfiring) driver's magnet/motor - luckily it did not fall through the pole vent, which did not have a screen. That's something I wanted to add considering the cylinder's design: a down facing driver, vertical port tubes and open pole vent.
Tip for a 'Stuck' Subwoofer Plate Amplifier:
I've had several cases where after removing the mounting screws, the plate amp still would not budge. (2 older SVS 13-Ultra's and an SVS PB12/Ultra 2.) I've never tried a large suction cup but doubt it would work well on the surfaces I've seen with several 'stuck' subwoofer plate amps for repairs/replacements. (These were older SVS bash amps without a lot of flat open areas and a brushed surface.)
What I found that worked on those amps was using a slightly larger screw in one of the amp's mounting holes and using a screwdriver, tighten it just enough to have a good 'bite' into the through hole. (See photo below.) I then use pliers on the screw head to pull it out/break the 'seal' on the amp. All these subs were over 5 years old - one more than 10 years old and the original gasket/seal was so tight it almost felt bonded on. (An alternate method: If you have a small flat head nail (smaller head diameter than the amplifier screw hole) - inserting the nail head into the hole and using the flat head shoulder as a lever may work, but I've personally not tried that.)
YMMV but carefully done, I've seen no damage and the original mounting screw head is large enough to cover any minor scrapes. Here's a pix using this method on a PC13 Ultra Bash amp:
Of course the screw doesn't have to be as long as this one. It was just one I had on hand.
(To the right in picture is an upside-down PB12/Ultra 2 I'd previously repaired.)
After seeing several SVS 750W Bash Amp failures like the above over the years, I'd want to inspect the amp before buying any older used PC/PB13 Ultra. IMO, a used Sledge amp Ultra is a better choice even if it costs a bit more. If it originally shipped with the Sledge amp, I'd also be more confident that the driver hasn't been abused as the Sledge amp has much better driver protection (limiter/compressor) than the Bash amp. I liked that the old amp's knobs and switches made it easy to see all settings at a glance (vs the small LCD screen with scrolling menu on the later amps), but I'd pick an Ultra with Sledge amp over the Bash every time.
Their current "Ultra" series 1KW (RMS) "Sledge" DSP amp is a much better design than the Bash and likely more reliable (lower parts count, DSP vs Analog design). But with the Sledge's different gain structure and lower input sensitivity, its amp "Volume" (Gain) setting will be much closer to max than the Bash amp for the same output levels. (Gain adjustment on Sledge amps is labeled "Volume".) And although many probably never use all its features, a combination of Room size Compensation (adjustable frequency and slope), variable port tunes (16Hz, 20Hz or Sealed) and Dual Parametric Equalizer (adjustable frequency, cut/boost, and Q) allow a VERY wide range of signal shaping. See SVS's Guide to Sledge DSP Amplifiers. (BTW: I've seen many posts from SB13 owners saying they switched because the PB13/PC13 was less "musical". To quote SVS' Ed Mullen, the PB13 in Sealed Mode is a 'textbook sealed sub' (plus benefit of larger enclosure) but I can't recall seeing any notes from those that said they switched to a sealed only model mention trying the PB/PC Ultra's sealed mode and any of the amp's PEQ (and other) options. SVS Sledge amp PDF user manuals are available for download at their website.)
Of course the room, Subwoofer location and listening position are major factors in how any model sounds/performs. And don't assume the best location will be the same for every model. (Ideally test data from Room EQ Wizard (REW) (or similar utility) is key to finding the best location for your specific room and setup. Most won't do that but at least experiment with placement even if you consider a 'sub crawl' impractical.)
I wish I could afford enough quality sealed subs and amp power for flat response for any content. That's the idea setup of course. (Despite comments that most movies don't have significant content below 20Hz.) But for a single sub, unless smaller size is a must, I prefer a model that offers both sealed and ported modes. This is why I'd never trade my PC13 for any other SVS model - it's adjustable (Sealed/16Hz/20Hz tunes, dual PEQ, room size compensation, etc.), has a small footprint (appx 16.6" diameter, 47" tall) and is light enough (appx 90lbs) to be moved (rolled on edge) without help. (And easily rotated to get at the amp, unlike the 155lb PB13 box model.)
Don't get me wrong, I'd love to have a SB13 Ultra but I'd not trade my PC13 Ultra for one. (Currently in a very small room which is ideal for a sealed sub, but want the ported options in case that ever changes as I can't afford to add more subs. In the small room I'm using sealed mode with room gain compensation. Ed (SVS) posted some PEQ tweaks for more 'mid-bass slam' if desired.)
SVS PB/PC Ultras are well engineered products, with a very beefy 13.5" driver (appx 55lbs and a cone that's stitched to the surround), full featured amplifiers with excellent driver protection, from a company with a history of good Customer Support and warranty - even if you're not the original owner. (They replaced a failed 750W Bash amp from a second owner PB13 Ultra that only had a few months of the original 3 year warranty left with a new ($599 list IIRC) 1KW Sledge amp. The only cost was shipping the failed amp back.) They now have a 5 year warranty, 45 day in-home trial, free shipping in CONUS and more - see their customer bill-of-rights for details.
(However I was sad to see some typical marketing speak on cables i.e. "SoundPath audio cables deliver a spacious soundstage, solid three-dimensional imaging, sparkling and airy highs...")
Unfortunately their Ultras are now priced far out of my budget, and in the $2K range there are other great Internet Direct options like the JTR Captivator models and Seaton Sound, although they don't offer all the perks of SVS. Power Sound Audio's policy comes close. (Nothing beats DIY for value however.)