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Fixing active speakers (Samson Rubicon r5a)
Fixing active speakers (Samson Rubicon r5a)
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Old 16th October 2017, 08:16 AM   #1
swever is offline swever
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Join Date: Oct 2017
Question Fixing active speakers (Samson Rubicon r5a)

Hello everybody!

First time poster here. My name is Alex, I am from Saint-Petersburg, Russia. I have been building and modifying guitar effect pedals and amplifiers for a couple if years, so I can hold an iron but not much more than that haha.

Anyway, let me get onto the subject. I've got this pair or Samson Rubicon r5a that I bought used about a year ago. The speakers were made in 2011 or 2012. There was two issues with them one of which I've just addressed - (extremely) scratchy volume pots with (extremely) steep operation near the minimum. It was not easy to balance the level between the two and I had to keep the source volume very low because the volume would go from nada to LOUD. So I changed the b10k pots to a10k's and it's perfect now.

The second issue is that there is a very noticeable background noise. It sound to me like mains hum but I am not 100% sure about that. I have a gut feeling that it has to do with the power section, perhaps the trasformer or the filtering caps. The caps look intact though.

Here's some gutshots I've just taken and a schematic for higher models of the same line that I found in the webs. Mine seems to be a bit different, at least some values are different. There is also a sample of the hum I recorded.

I noticed that the character of the hum is slightly different in the two speakers. I think it's only the woofer that hums in one of them, whereas in the other both the woofer and ribbon tweeter do. The latter is the most annoying, its audible even at very low volume settings and can even be heard over quiet parts.

Lastly, is it okay for this things to get seriously hot? After a couple of hours the metal plates on the back (that also serve as heat sinks for the poweramp ic's) get literally burning hot. Any advice on how I can go about fixing that? Should I start with replacing the power filter capacitors?

Ps I was not sure which forum this belongs to, so posted here.
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Old 16th October 2017, 09:06 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Location: The Jurassic Coast, England. GB
That looks like the Rockit 5 or 8, as sold in the EU.
I have one with a 100Hz permanent hum. The two smaller capacitors could do with being changed, that will help a bit but if you take a voltage reading on the output pin on the TDA2052 or across the HF wires with no load connected, you will find there is a DC level on it, causing the hum.
Replacing the two 1000uF 25V caps and the TDA2052 will stop the DC on the speaker and the hum will go.
TDA2052 is obsolete and there is no substitute, you may have to trust a fleabay source!
Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk
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Old 16th October 2017, 02:37 PM   #3
swever is offline swever
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Join Date: Oct 2017
Thanks for the reply, Jon!

I just now realised that I forgot to mention that the hum goes louder as I increase the volume with the volume control. Could that mean that the noise is coming from somewhere before the volume control – the preamp stage?

You mentioned that it could be the 2052. May I ask why do you suggest it's this chip? If I understand the schematic correctly the 2052 only drives the twitter, and there is a TDA7294 that feeds the woofer. Please correct me if I am mistaken.
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Old 16th October 2017, 04:35 PM   #4
turk 182 is offline turk 182  Canada
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the R5a takes a balanced 1/4 inch connection if your patch to it is unbalanced you may be creating a ground loop...
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