dbx-Bx3 MkI restoration (noise and some channels not turning fully on)

[AshhBoy_]

Hi, first of all, I'd like to mention that I'm new to audio stuff and this forum.

My father bought a dbx-Bx3 power amp back in 1986 when he was living in Japan. Since it is the domestic version, it doesn't have an input selector for the mains voltage, nor a switch for the load impedance... The manual for this only exists in Japanese -sigh- even if I have it on hand (paper version but I could scan it if someone is interested).

The amp is still with us today and performs like a charm at higher volumes. However, it has a few issues that I am planning to fix and will document here:
- Relays seem to be cooked for all 8 outputs (4 relays, 1 per amp L+R). Since they engage, the contacts must be burnt and I've bought some new ones to replace them anyway. I noticed this by turning on the amp at a low volume, some speakers don't output anything, while others might make some funky noises. The temporary fix for this was to simply turn the volume up or/and engage/disengage the relay)
- The 6 front selector switches have problems (4 relays, 2 for the meters). Since they control LEDs that flicker, they might just need a good spray of D5... I've ordered some to replace them but 14weeks of delay...
- Lamps are out on both meters, the one behind the dbx logo was flickering a little yesterday... got some 14v 0.2 amps ones to replace them

I was wondering two things:
- Does the internal transformer have 2*110v coils that I could wire in series to plug the beast directly into my outlets (220/40 here in Europe)?
- Would a full recap be necessary (If yes I might take it to a shop since I don't want to mess too much with the values and stuff with limited knowledge)?

I'll be opening the amp in the next minutes, and add some photos of the insides to this post.

Thanks for your help, stay safe in these times

 

[AshhBoy_]

Update regarding the renovation which took me roughly 4-5 hours.

I'll pass on the opening procedure which is quite straight forward... I just had two major problems:
- Figuring out how to pull the two output boards while removing as little components and screws as possible was quite a challenge. Finally, I just unscrewed everything from the back panel and took it out (not the fan), while keeping it close enough in order to maintain the mains plug cables soldered and under little stress.
-I was unable to unscrew the lamps at first because of corrosion buildup and some yellow factory paint that must have been put there in order to ensure royalty of the after-sales department and warranty stuff. To resolve this I just poured a little D5 down the screw bases and gently cracked the paint (gently means it was extremely hard... had to use 2 sets of pliers). Replaced the bulbs with 'JKL standard mini screw-based 14V 0.2A E10' and glued their bases in place inside the isolating plastic thing as I wasn't comfortable with them going up and down towards the exposed metal surface.

Finally to the important part: the output boards and their relays.
The boards are directly mounted behind the back panel and they are populated in every possible direction on one side while the other is easily accessible when the back panel is out. Fortunately, it was quite easy to unsolder all four relays (boards are thick and made of real stuff unlike modern ones; they require a powerful iron to get the job done in good conditions). I used a manual solder pump to get the job done. And there when I finally pulled the relay came the surprise... They weren't original although the amp showed no signs of being previously opened and my dad didn't remember having it fixed. I noticed flux not cleaned during the previous job on the boards later on. The relays in place were some kind of cheap Chinese fake garbage, copies of Fujitsu stuff, with no brand on them and poor build quality and materials. I replaced them all with 'Omron relays DPST 24VDC 5A 21.8mA 1100ohm'. I had to bend the white clay resistor on one of the boards to get the relays in and out (forgot to bend it back in its place oops). Cleaned the boards and then got everything back together. Hope it will stay like so for as long as possible

Doing this, I solved all my issues with the amp, the meters are now illuminated with a delightful old-fashioned yellow shade. The output noise problems are now all gone and I am able to use this wonderful piece of ancient tech in the way it was intended: BTL-2Ch. The sound is profound, powerful and reactive on both lows and highs even at really low volumes. I'll add pictures to illustrate my process, including one from the old relay that I destroyed in order to study its wear and construction (no wonders why it wasn't working).

Still wondering if it is possible to rewire the transformer but it seems like it is sealed with some kind of foamy glue (I haven't tried to pull out the top cover).
I'll see if I try to open the front face to access the push-switches. For now, I just clicked on them a LOT which seems to have solved (mostly) the flickering issues with the LEDs, but not entirely on the green ones.

With hopes that this follow-up will help someone,
Ashh

 

[goodolpg]

Welcome to AK.
Can't help you with your technical (transformer) question.
Just wanted to say congrats on getting your amp up and running again.

 

[AshhBoy_]

Welcome to AK.
Can't help you with your technical (transformer) question.
Just wanted to say congrats on getting your amp up and running again.

Thanks! I'm still investigating but not sure if I really want to open it... Could damage/ruin the whole thing.

 

[Jiggz]

I understand this is an old thread. But I'm also experiencing the same noise coming from the rear speakers. And after reading your post I would like to take the route you took of replacing the output relays. Can you please post a link where you got the replacement relays? Thank you.

 

[ivandezande]

I understand this is an old thread. But I'm also experiencing the same noise coming from the rear speakers. And after reading your post I would like to take the route you took of replacing the output relays. Can you please post a link where you got the replacement relays? Thank you.

Dbx bx3 relays

So i have a question..i know that the bx3 amp has a known problem with the relays causing drop out at low volumes my question is are there improved relays out there to prevent it from happening again and also why does this amp have such a problem with them compared to other amps was it just a...

audiokarma.org

Just gotta search a little more....

 

[JimDeLely]

Has anyone replaced the 4 volume pots on the front of the BX-3 amp? And if so with what and your source, please.

Thanks