Repair Amplifier Boston Acoustics VR-975 (Tower Speaker Containing Powered Subwoofer)

[geogherkins]

Anyone know of an electronics shop that can fix this at reasonable price?

Boston Acoustics VR-975 circa 1994? Subwoofer amplifier board blows 1amp fuse. I've removed the amplifier board from the tower speaker. This is an integrated amplifier driving a subwoofer speaker with a highpass filter for the signal for the midrange and tweeter... No obvious popped capacitors, burned components or visual damage. Attaching photo. I looked locally, nobody wants to touch it. I've got a search running on eBay waiting for a set to go up for sale (for parts), but none in the last month or so.


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Positives: Great sounding speaker, integrated powered subwoofer with deep bass response. Pairs well with the remaining Lynnfield VR series for home theater.
Negatives: No longer produced for sale. Subwoofer driver and Subwoofer radiator cones use a foam surround. This will deteriorate after ~10 years and must be replaced with after-market parts. Simple repair. Butyl rubber surrounds on midrange woofer cones. VR tweeter shared with the other VR series. The subwoofer amplifier board is now blowing fuses with no visually obvious damaged components on the amplifier board.
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[lovinthehd]

You could just use another amp with some dsp for the hpf you want....something like a Crown XLS amp has such. Do some actual bi-amping!

 

[geogherkins]

Interesting idea, I do have an unused amplifier, so could pass the DSP low-pass subwoofer signal from my AVR to that amplifier, and then connect the subwoofer directly. Similarly, woofer/mid/tweeter in the tower would need to be connected to the AVR output (set to speaker size: small). In both cases would need to rig up some speaker wire terminals. This is not ideal, I'd prefer to have the original amplier repaired.

Anyone have some ideas for a reputable amplifier repair over the Internet? I can Google search, of course, but really need someone with first hand experience, if possible. Thanks.

 

[lovinthehd]

No personal experience but in a discussion on ASR about maintenance of some older gear this outfit was mentioned by one guy who uses them if needed, altho he does much of his own work in general.... https://quirkaudio.com/ The last local guy I used I know has retired and closed his shop.....

 

[TLS Guy]

Interesting idea, I do have an unused amplifier, so could pass the DSP low-pass subwoofer signal from my AVR to that amplifier, and then connect the subwoofer directly. Similarly, woofer/mid/tweeter in the tower would need to be connected to the AVR output (set to speaker size: small). In both cases would need to rig up some speaker wire terminals. This is not ideal, I'd prefer to have the original amplier repaired.

Anyone have some ideas for a reputable amplifier repair over the Internet? I can Google search, of course, but really need someone with first hand experience, if possible. Thanks.

Unfortunately I fear that is the end of the road for those speakers.

You can not drive them from the sub output of a receiver. The bass unit is an ABR servo system. It is a 10" woofer and 12" ABR, with some type of sensor in the driver monitoring cone excursion.

I can not find the specs of the crossover to the mids, which are 4.5" units. So the crossover will be well above the range of a receiver sub output most likely.

I have looked for a circuit or service manual and come up empty. You will never service a unit like that without a detailed circuit at the minimum.

In addition that board will almost certainly have custom ICs which you can bet will be NLA.

I have to say the odds of getting that amp and crossover up and running is remote.

I think it is time to go speaker shopping. In addition if you do engage a service tech, you will have to pay him for his time, even if he can fix it or not. I think this will be money flushed down the drain. Time to move on.

 

[Jd1619]

Interesting idea, I do have an unused amplifier, so could pass the DSP low-pass subwoofer signal from my AVR to that amplifier, and then connect the subwoofer directly. Similarly, woofer/mid/tweeter in the tower would need to be connected to the AVR output (set to speaker size: small). In both cases would need to rig up some speaker wire terminals. This is not ideal, I'd prefer to have the original amplier repaired.

Anyone have some ideas for a reputable amplifier repair over the Internet? I can Google search, of course, but really need someone with first hand experience, if possible. Thanks.

Any luck with having your amp repaired, I have the same issue.

 

[Hobstar]

So, not sure where you are with your repair but I have a very similar issue with my VR970s. I was able to connect with a transformer manufacturer and sent them pictures of the transformer. They confirmed that they didn't have an exact match but proposed two alternatives that would give basically the same spec power, just slightly larger. They are sending me a quote and I will test it one one before buying the other one.

 

[TLS Guy]

So, not sure where you are with your repair but I have a very similar issue with my VR970s. I was able to connect with a transformer manufacturer and sent them pictures of the transformer. They confirmed that they didn't have an exact match but proposed two alternatives that would give basically the same spec power, just slightly larger. They are sending me a quote and I will test it one one before buying the other one.

How do you know that the transformer is the issue? It is very rare for a transformer to be the cause of a failure. If a transformer is dead, then usually something else took it down.

 

[Hobstar]

How do you know that the transformer is the issue? It is very rare for a transformer to be the cause of a failure. If a transformer is dead, then usually something else took it down.

I had a Circuit board tech look at it and they confirmed that the board is fine and that the transformer was producing unstable Power. They quoted me some crazy amount to fix it and I said I would do it myself.

 

[geogherkins]

...You cannot drive them from the sub output of a receiver.
... The bass unit is an ABR servo system. It is a 10" woofer and 12" ABR, with some type of sensor in the driver monitoring cone excursion.
... that board will almost certainly have custom ICs which you can bet will be NLA

Quite right about not driving the speaker from a sub output; that must be run to an amplifier. I am not quite that dull-witted.

I cannot find anything in my Boston Acoustics literature (which came with the VR975 tower speaker) describing the servo or custom tech design, though I suspect you are correct. The electronics include the ability to send a full spectrum amplified signal AND/OR a LFE (low frequency effects) subout unamplified signal. There are several IC chips visible in the photo, they maybe are performing some signal EQ management. This is all a bit complex for repair, I agree (not sure what "NLA" means - no longer available?). So, "servo" or just "custom" at least, the Boston Acoustics VR975 does have a passive ABR (auxiliary bass radiator). Which is 10" (not 12" as you describe) and an active large woofer speaker 12" diameter (not 10" as you describe). Presumably some part of the signal was inverted to pressurize the tower speaker box to push upon the passive radiator and improve the base response? Marvelous in its day! The VR970 and VR965 probably also have a similar design.

What I did do? I gave up on repair! But my budget does not allow a replacement, and I have arrived at a satisfactory solution. Audyssey EQ provides the needed room correction and LPF/HPF (low pass filter / high pass filter) needed for my new setup. I bypassed the old VR975 tower's amp and have connected the 12" subwoofer to an outboard amplifier (which is connected to the subout on the AVR Denon A100 receiver). I have two subouts SW1 and SW2 on the Denon. I also had an unused stereo amp (NAD 214), so it works out nicely to "bi-amp" the VR975 towers. The NAD 214 doesn't claim rated power, but I'm guessing 100 Watts per channel. Quite enough to drive the 12" woofer. Audyssey EQ attenuates SW1 and SW2 at -11db.

These VR975s are now dedicated subwoofers and the "Wide" channels in my 9.2 setup.

This is not a golden ear audiophile system; but plenty good enough for home theater, and to my aging ears, great sounding for music as well.

 

[wldock]

There's nothing like the smell of hot solder in the morning!

The snow is falling as I type and this is the time to knock out repairs. I'm off work today and I'm about to turn my desk into a repair bench and save some stuff from going into a landfill. I have a couple of Boston Acoustics VR960 amps, a HSU VTF-2 MK3 amp, and a Mirage Omni S8 amp. Here's the stockpile waiting to get on the bench:

One of my Boston's is blowing the fuse as well. I don't remember if the transformer was the fault as I checked them out years ago and never got back to them until now. I'll know real soon and I did purchase a third working backup. So, if it takes three to get two working, I'm ok with that.

Anyway, given that these amp are now 20+ years old, it makes sense to perform a shogun repair and replace all of the caps. Also, if the transformer is not the problem, then replacing the bad semiconductor devices is the next things. So far I've found the output bipolar and MOSFET transistors to be ok but did find some bad diodes. One of mine has a loud 60Hz hum and replacing the large filter caps did not resolve it.

So, a shop could figure out one of these pretty easy but they don't like to touch them. Many times plate amps are cheap and don't hold up well to heat when trying to remove and replace components. I don't know what someone would charge these days but there are many (search 'repair service') listing on eBay for plate amp repair.