Torching FST ribbons on RM40's

brj · « **Reply #40 on:** 27 Oct 2017, 04:57 am »

Scotty, I won't lay odds, but I certainly don't disagree with you, as the scenario you describe is certainly plausible. I just haven't heard of many amps developing such a tendency over time, vs. those that are simply more prone to it as a function of their design. Then again, at 14 years, you're approaching the 15 year mark that most people quote as the lifetime for electrolytic caps. (Though that's based on an assumed operating temp.) I wonder what caps the Bryston has tucked under the hood...

Perhaps I missed it, but what speaker cables are being used? (Curious as to how capacitive they are.)

jules · « **Reply #41 on:** 27 Oct 2017, 10:08 am »

A couple of thoughts ...

Seems like it could be heat related if it's taken an hour of running before the blow ups and ...

Wondering if it's something as basic as a poor ground connection, probably somewhere in the amp but possibly before that.

The fact that the problem occurs simultaneously in both channels would seem to limit the options.

Jules

LosGatosSTI · « **Reply #42 on:** 27 Oct 2017, 05:25 pm »

I have Harmonic Technology 6N Single Crystal Copper PRO-9 + from 2003.

fredgarvin · « **Reply #43 on:** 27 Oct 2017, 06:17 pm »

I had a similar issue with RM1's, two tweeters failed on one side, a couple weeks apart. The second time I took it apart and found the Lpad was actually melted. I replaced it and a few weeks later it melted again. I sold the speakers and put something else in while I looked for more VMPS. Yep. The tweeter failed. That's when I finally realized it was the amp.

Leaked DC, sporadically.

Tyson · « **Reply #44 on:** 27 Oct 2017, 06:47 pm »

Quote from: fredgarvin on 27 Oct 2017, 06:17 pm

Leaked DC, sporadically.

This! It is almost certainly this. OP needs to send the amp to bryston and let them load test it and run it on the bench. Everything else is just fumbling around in the dark.

LosGatosSTI · « **Reply #45 on:** 27 Oct 2017, 07:08 pm »

Thanks Fred,

How did you verify that it was the amp leaking DC sporadically as I would love to know how to do this? The measurements I have taken of the amp did not reveal any DC issues (during the few minutes with the Fluke connected to each channel) with it while unhooked or while connected to the Sunfire processor and playing the same Oppo SACD material. Speakers were not connected during these measurements. I guess I would need some sort of data logging multimeter and would need some load on the amp.

It is not a quick, simple or low cost task to crate up an 80lb amp and send it to Canada although that may be the only thing left to do here aside from replacing the ribbons yet again and installing new caps in the tweeter portion of the crossover.

LosGatosSTI · « **Reply #46 on:** 27 Oct 2017, 07:11 pm »

I agree Tyson but I am really dreading the thought of subjecting a pristine Bryston amp to UPS shot put team. I bought the amp new and it doesn't have a scratch on it...although now it may be a death machine to tweeters.

Tyson · « **Reply #47 on:** 27 Oct 2017, 07:14 pm »

Quote from: LosGatosSTI on 27 Oct 2017, 07:11 pm

I agree Tyson but I am really dreading the thought of subjecting a pristine Bryston amp to UPS shot put team. I bought the amp new and it doesn't have a scratch on it...although now it may be a death machine to tweeters.

Did you consider it might have been damaged already, on the inside, and that's why it's doing this? Not from shipping, but just from age. Caps, especially electrolytic caps used in power supplies, absolutely need to be replaced after a decade or so, or bad things can start to happen. The other thing is that solder joints can come loose if they weren't 100% soldered properly. On/Off cycles and heat up and cool down cycles can exacerbate that, too. As some one who builds some DIY stuff, ask me how I know that! Hah

Personally I've had better luck with the USPS than with UPS or Fedex. At least double box, and triple box is even better. Don't use peanuts or other packing material that can shift.

WGH · « **Reply #48 on:** 28 Oct 2017, 02:01 am »

Quote from: Tyson on 27 Oct 2017, 07:14 pm

At least double box, and triple box is even better. Don't use peanuts or other packing material that can shift.

If you read the fine print, all electronics need to be double boxed or insurance will be declined.

jules · « **Reply #49 on:** 28 Oct 2017, 04:18 am »

Might be worth a chat to Bryston Scott. If you're DIY inclined you could possibly replace the PS caps along with the output coupling cap [upgrade possible] and at the same time look for any failing soldered joints, which as Tyson says, can happen easily where there's lots of heating and cooling [= PS board particularly]. That would save you the trauma of USPS though sending the amp away is probably the best option.

*Scotty* · « **Reply #50 on:** 28 Oct 2017, 06:21 am »

If you are going ship the amp back to Bryston you will want to double box the amplifier. I would recommend a box with about 1 inch larger dimensions than the amp on 4 sides and 2inches larger on the front and the back sides, additionally you will want a total 2inches thickness of styrofoam at the front of the amp to protect the handles and at least 1.5inch thickness at the back to protect the binding posts. You put the amp into a plastic garbage sack first to help reduce the chance of scratching finish.
You will need to purchase a quantity of 1 inch thick white bead board sufficient to enable you to put a layer between the amp and the box on all sides. You are going to then repeat the process with a box big enough fit the first box inside it with about 1 inch to spare on all sides more than that is okay. You then put a layer of styrofoam board into the space between the first box and the second box. By having a total space between the amp and the outside of the package roughly equivalent to about 2 inches on all sides, the amp is less likely to be damaged by sharp object puncturing the box.
The complete package will be quite a bit larger than the amp on its own. In as much as your weighs in at 103lbs., you really don't have choice about whether you go to extremes in packing the amp to insure that it arrives alive at both ends of its trip. Bryston may also be able to ship you a box they consider adequate for shipping the amp to and from the factory.
This is the product you want or equivalent from some other source. see link. https://www.lowes.com/pd/Common-1-in-x-4-ft-x-8-ft-Actual-0-9375-in-x-3-875-ft-x-7-875-ft-Expanded-Polystyrene-Foam-Board-Insulation/3365576
Scotty

Tyson · « **Reply #51 on:** 28 Oct 2017, 03:43 pm »

Another option is to contact Bryston and have them send you the box/packing material that they use for their amps currently, then just use that.

jules · « **Reply #52 on:** 29 Oct 2017, 11:59 pm »

Thinking about this, I'd suggest that before you do anything else, you need to be sure if the caps in your crossover have zero or infinite resistance. In the unlikely but not impossible event [given the apparent scorching around the terminals of the large caps] that they are zero resistance, then all the drivers in your speaker could be operating full range. The tweeters would be the first to throw in the towel under this load but the mids wouldn't be too happy either.

You could also find that the fault that is the root cause of your problems, is quite simple to fix. So it might be worth going to a reputable local person just to check for stuff like dry soldered joints near the PS.

Please tell us how it works out.

LosGatosSTI · « **Reply #53 on:** 31 Oct 2017, 08:27 pm »

Thank you guys for all the detailed packing and shipping instructions. I will call Bryston and see what they suggest and see if they will send me the packing matarial. I am working with Sonic Craft to get some new caps for the tweeters.

Anything else that I need to buy or install to protect and upgrade the sound for the tweeters at this time?

jules · « **Reply #54 on:** 31 Oct 2017, 09:37 pm »

Your Bryston amp will use output coupling caps. Basically they're the last component in the chain before the signal leaves the amp and they're there with the vital role of stopping any DC getting through. Given they're in the signal line, coupling caps also influence sound quality significantly. I'd suggest you should be replacing those caps in your amp. I don't know what Bryston use but a high quality 1uF film cap with a cap of the same brand and 1/100th of the value of the main cap and in parallel to it, will do the trick. At least you can ask Bryston to check the existing caps for damage.

Hope it all works out well for you Scott

john1970 · « **Reply #55 on:** 1 Nov 2017, 02:28 pm »

Hi Scott,

Contact Bryston or a local Bryston dealer to order a new box from Bryston:

"In the event of a defect or malfunction, contact Bryston repair centers for return authorization. Products must be returned using original packaging material only."

http://www.bryston.com/pages/warranty.html

I once had RM40 speakers that had a X-over issue with a Bryston 4B SST2. Eight years ago switched to different speakers and had no issues since which makes me think it could be the crossover. I would check out the X-over very carefully as well. Good luck.

raindance · « **Reply #56 on:** 1 Nov 2017, 06:42 pm »

Your Bryston amp will use output coupling caps.

Really? Most solid state amps are direct coupled and use a servo circuit to ensure no DC offset. Some really strange advice here. I'd be looking at an oscillation issue, but that's just me.

HAL · « **Reply #57 on:** 1 Nov 2017, 07:00 pm »

Agree, did not see any coupling caps in the Bryston 6BSST schematic. All direct coupled as most modern solid state amps.

jules · « **Reply #58 on:** 1 Nov 2017, 07:44 pm »

Quote

did not see any coupling caps in the Bryston 6BSST schematic

Thanks for the correction raindance and HAL. I admit I haven't seen the schematic.

LosGatosSTI · « **Reply #59 on:** 2 Nov 2017, 01:22 am »

Jeff from Sonic Craft among others have suggested Jupitor Copper Foil paper wax caps. Jeff's calculations with the Aurum cantus G2 taken into account specify the following from his email to me:

"By the numbers... The cap will increase 0.123uF in value. The coil would decrease 0.018mH in value.

However, I know he trended towards a smaller coil over time. I would have no problem with a 0.22-0.25mH coil, and a 1.5uF cap. The Jupiter Copper would be good, and so would the Mundorf Supreme Silver/Oil. Matching would not hurt, and you could request a low value (1.46-1.48uF)."

My Questions to you guys Below:

There are 600V 1.5 uF Jupiter caps and also 1.0 uF and 0.47 uF available on Sonic Craft site supposedly.

1) Would it be recommended to use TWO caps instead of single 1.5 uF to get to 1.47 uF for each matched pair of caps?

2) Are using two matched pairs better than using a single 1.5 uF cap?

3) What percentage of matching should I choose. this service is pretty cheap so I'm leaning towards the most critical matching possible of L3. (L1-factory tolerance 1% matching; L2-1/2 factory tolerance 1% matching; L3-1/4 factory tolerance 1/2% matching.)

Regarding coils Jeff has this to say:

This is not a bass circuit, and an air core should be used. SC is exiting the inductor/coil business, so I would not be able supply the coils.

1) Where should I shop for coils and which coil type and manufacturer should I buy?

3) What type or gauge wire should I get?

Also I need a foot or so of chassis wire. What type and gauge and composition of wire did Brian use? Refer to pics of small diameter red wire from TRT caps to binding post.

Thanks