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Tips on SVS 13-Ultra 750W BASH Subwoofer Amp Failures (+ Checks Before you Buy)
(Updated to include SVS PC13-Ultra Replacement Amp Info.)

  I have an older 750W BASH Amp PC13-Ultra, bought used with an Amp problem in Dec. 2010 very cheap. (No label on the Amp to check the mfg date, and turned out to be a PC13-Ultra not a 12".) Without a label with S/N, no way to check if any warranty was left. Original BASH 750W Amp no longer made/no mfr repair. (A SVS Sledge 1000D replacement Amp at that time was $599.)

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 PB13/PC13 ultras. I've seen some from as far back as 2002 era still working as well as 2 PB12/Ultra2's with BASH 1000W Amp. 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.)


Update on PC13-Ultra Replacement Amps   [- or skip to BASH Amp Repairs -]
In early 2020 I found out that Sledge 1000D replacement Amps are no longer available from SVS. And now confirmed the (Bluetooth Controlled) SVS 13-Ultra 1200D Amplifier Upgrade ($399.99) will not fit most PC13-Ultras that shipped with BASH Amps, due to Port Tube contact. See updated notes below about Port Tube changes made in later builds of BASH Amp PC13-Ultras.
(One BASH Amp PC13 owner made a thick Spacer to allow the 1200D Amp to fit.)
If your PC13 shipped with a BASH Amp, verify you have clearance for the 1200D Amp in your PC13 before buying, as there are currently no other SVS replacement Amps for the PC13-Ultra (Cylinder model). If in doubt, contact SVS Support first. (They have excellent customer support.)

FYI: In late Oct. 2020, I asked Ed Mullen at SVS about the 1200D fit issue with PC13s, as IIRC there may have been a change in port tube location from the early builds of the PC13 (Cylinder) model. He said the 1200D Amp doesn't fit most of the original BASH Amp PC13's unless you make a spacer (he suggested 3/4" or 1" thick baltic birch). He also confirmed there was a PC13 Port Tube location change in later builds, to avoid contact with the Sledge 1000D Amps. (See update/notes below - some rare BASH Amp PC13s were built with the Port Tube change.) I had no fit issues with a 1000D Amp in my originally BASH Amp PC13, but it may have been a later production with the Port Tube change. Note my PC13 was made with a strip of foam tape on a Port Tube in an area where the Amp may make contact. (On Oct. 24, 2020 I removed the Sledge 1000D Amp from my PC13 (after 7+ years of use), and saw no evidence of contact on the foam tape, and felt no interference reinstalling it. I must have one of the rare BASH PC13s with the Port Tube change.)

More Info on 1200D Amp Fit Issues in PC13-Ultra
I saw a 2nd BASH PC13 owner report on the 1200D Amp upgrade, who after making a thick spacer, tried the 1200D Amp before installing the spacer. He said it fit OK. SVS's Ed Mullen replied with more info on the Port Tube orientation change (rare in an original BASH Amp PC13).

"The vast majority of PC13-Ultras with the BASH amps have major port interference with the 1200D. We did make a running change to the port orientation in anticipation of migrating to the Sledge STA-1000D. There weren't many PC13-Ultras made with the revised port orientation but still with the BASH Amp - you must have gotten one of those rare subs...
Regardless, all PC13-Ultra customers with BASH amps get the same advice - expect port interference unless a spacer is used - because that is the reality with nearly all of the BASH-equipped PC13-Ultras."
PC13 owners considering the 1200D Amp upgrade should check for possible interference. The owner reporting it fit said the 1200D Amp's depth into the subwoofer (from the Amp mating surface) was 64mm (2.52 inches), and that he had 15mm clearance from that (79mm - 3.11"). That 2.52 inch depth for the 1200D surprised me (I expected a higher number), so I measured my original 750W BASH Amp's component heights from the Amp flange gasket surface. (Gasket is about 1/16" thick.)

My 750W BASH Amp Component Heights above the Flange Gasket
(Right/Left is relative to viewing from front face of the BASH Amp)

    750W BASH Amp Measurements
    (Height from Amp Flange Gasket)
  • Lower left side Heat Sink - 2.675"
  • Lower right side Capacitors - 2.875"
  • Circuit board at the top - 2.625"
I wish I had a 1200D Amp to measure, since my original BASH Amp measurements are higher than the 64mm noted by the 1200D owner. (Which doesn't make sense, as the 1200D was supposed to be deeper than the BASH, causing interference with PC13s made before Port Tube position change for 1000D Amp clearance.) If I get access to a 1200D Amp, I'll post an update here.

The Sledge 1000D Amp fit OK in my original BASH Amp PC13 (and it's still working). But next time I remove it, I'll check the distance from the Amp mating surface to the Port Tubes in my PC13. (I may also have a rare original BASH Amp PC13 with the relocated Port Tubes.)


(Original comments on the 750W BASH SVS 13-Ultra Amps follow.)

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
  1. Ensure Subwoofer and Receiver are OFF, no active input to the Sub.
  2. Set the Subwoofer's "Auto/On" Toggle Switch to the ON (not "Auto") position
  3. Power the BASH SVS subwoofer On (A/C power switch)
  4. 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 to remove stuck plate Amps 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)
(A photo below shows where the broken piece of TH1 landed.)

A wider view of TH1 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.

Photo shows a piece of the Thermistor on top of driver magnet

(Note piece of gray foam tape on the left Port Tube.)


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 2 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:

750W BASH Amp on PC13 Ultra
(Using larger screw to remove a 'stuck' plate Amp.)

Of course the screw doesn't have to be as long as this one. It was just one I had on hand.
TIP: A little silicone lube on the gasket area may make future removals easier.
(To the right in picture is an upside-down PB12/Ultra 2 after a driver reinstall.)


  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.

  The later "13-Ultra" series 1KW (RMS) "Sledge" 1000D 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 1000D 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. My PC13 is in a corner.)

  I wish I could afford enough quality sealed subs and Amp power for flat response for any content. That's the ideal 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. I prefer the PC13 over the Box models since it has a small footprint (appx 16.6" diameter, 47" tall), 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. (Both have Sealed/16Hz/20Hz tunes, dual PEQ, room size compensation, etc. - although the PB13 has a bit more output down low than the PC13 (due to cabinet volume), but not a factor in my room.)
(Update - SVS now has a PC-4000 model with improved Sledge 1200D Amp, a Remote Control + Bluetooth iOS/Android App support, and retains the variable tuning. No baseplate like the PC13 (which I liked), but I'm glad they kept a Cylinder model in the lineup.)

I know there are more powerful subs available, but I'm happy with the PC13 Ultra. (Currently in a very small room which is ideal for a sealed sub, but I want the ported option in case that ever changes, as I can't afford to add more subs. In the small room I'm using the 16Hz mode with room gain compensation. I used Ed's (SVS) PEQ tweaks for a bit more mid-bass 'slam', and later fixed a huge mid-bass null by adjusting the Sub distance in the AVR.)

SVS 13-Ultra Subwoofers 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.

Unfortunately their Ultras are now priced out of my budget, and in that price range there are other great Internet Direct options like the JTR Captivator models, Rythmik, and Power Sound Audio; although they don't offer all the perks of SVS. (Power Sound Audio's policy is close - great customer service from 'Tom V.", one of the original SVS founders.) Good options if don't DIY.


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