DBX BX-3 faulty switch?

kwape

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Just bought this amp with pre. Problem I'm having is in Front speaker B switch. (This unit has front a & B, rear A& B). The right speaker is giving me trouble and keeps going out. I thought this was possibly the pre amp at first, deoxit everything, didn't help. Issue is specific to operating front speaker B. Sometimes a few represses of that switch will get it back. I tried to deoxit on the speaker switch but they are small, connect directly to a circuit, and difficult to gain access. Is there somewhere else is should be looking?
 
I have two of these amps--please download the manual to find out all that they can do...

As for a specific speaker cutting out--most likely one of four possibles--the switch (and yes they are tiny and hard to get to), the volume pot for that channel, the speaker relays that you hear engage on power up, or a cracked solder joint going to that set of speaker jacks. Since it is intermittent on only one speaker on one channel, I would start with the speaker jacks and work my way forward--could be just dirt or a loose/cracked connection right there at the back panel.
 
thank you I'll put that on the list of things to do. It sounds great as it is and yes I have the MKI version and preamp. I'm thinking of swapping the op amps out on that first.
 
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thank you I'll put that on the list of things to do. It sounds great as it is and yes I have the MKI version and preamp. I'm thinking of swapping the op amps out on that first.


Be careful on the op amps, but as long as they have good decoupling and the feedback loop is proper, you should be able to see what op amps you like best in it.
For sure start a thread for the pre.
 
Need New Relays

I've removed and cleaned the relays. It's a little better but not fixed. It's an intermitted problem where the left or right side will drop out. Now this is occurring with multiple speakers sections. I'm 99% sure it's the relays. I'm just going to replace them. I've cleaned 2 of the 4 relays. Too difficult to get to, take apart, clean and reassemble just to have them still ****in up.


Looks like the #s are 02 1D024 IBX relay. Anyone know suitable replacements?

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Question On BTL Wiring

ok viewing the manual off hifiengine.com

http://www.hifiengine.com/manual_library/dbx/bx3.shtml


MKI MKII, not sure if there is a difference in user manuals for this BTL setup.

Anyways I wired for BTL 2 channel mode.
R speaker - on R Rear + terminal
R speaker + on L Front + terminal

L Speaker - on L Rear + terminal
L Speaker + on L Front + Terminal

switch on 2 ch. (BTL)
2-6ohm selected

at my bench I was using some cheap Aiwa 6 ohm speakers.

Ran for maybe 2 mins. Amp got warm quickly, didn't have the volume cranked. But stated hearing some buzzig/amp noise and immediately shut it down. Hooked it back up without the channels bridged and is fine.

I'm new to separates so this is all new to me, ie bridging channels. Is it normal for it to heat up that quiclkly? is the manual correct for both MK versions? Didn't seem right to me and I can't risk blowing up my best stuff.
 
Bridging should have the amp act just like normal if set up correctly, did you make sure all the amp sections were adjusted to spec?
 
I've set the bias to 3mv and zero'd dc offset. Bias was low on a couple sections.

Running in BTL, using 8 ohm speakers this time. After about 2 mins the channels drop out and just start buzzing. WTF



update: I pm'd the previous owner it is a MKII amp.

I thought it was certainly a relay issue, now I can't be sure. From what I'm hearing it could be a cracked solder joint. Says it didn't have the intermitted issue before sending it out. That's going to suck trying to find. Still I will install new relays

more concerned about this BTL.

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As you can see I have it wired as shown on the back of the amp for BTL mode and as in the manual. After about 2 mins the music goes out, starts buzzing and shuts down. Or if I turn the volume up near 12:00 it will happen right away. Anyone know what could be causing this?
 
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Well it's not a MKII.
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It says it here and in front, and there are cosmetic differences.
I would pull out the amp boards and look at joints and components. Could just be a loose connector, or it could be a lot of little transistors. But probably not.
 
I've removed and cleaned the relays. It's a little better but not fixed. It's an intermitted problem where the left or right side will drop out. Now this is occurring with multiple speakers sections. I'm 99% sure it's the relays. I'm just going to replace them. I've cleaned 2 of the 4 relays. Too difficult to get to, take apart, clean and reassemble just to have them still ****in up.

From past experience, finding exact replacements for dbx parts can be problematic at best. Maybe you can find a generic relay to do the same switching. Luck wit dat. But ...

Before you do that, maybe explain "cleaning"? If you just popped the caps and spritzed cleaner at the contacts, that's seldom adequate. I use a piece of card stock soaked in D5, and drag that back and forth while putting slight pressure on the fingers. Do that until you can see some shine on the contact areas. If they're really bad, maybe a light pass or two with some 3-4k grit hobby paper, but careful as the coatings are really thin.

If your switches are anything like a lot of dbx stuff, those are a real PITA to clean. Here's a good write up on what all's involved.

http://www.tapeheads.net/showthread.php?t=13426

I've got a dbx 200 on the shelf right now that's intermittent. I cleaned and refurbed one a while back and swore never again. Considering pulling each switch off the board on this one, forming a sleeve from some flexible forming "clay" I use for plastic repairs, and letting them soak in D5 for a while.
 
you're right it's an MKI, previous owner thought it was MKII. I'll pull the boards and look at them.

for cleaning the relay I used strips of paper folded up and soak with deoxit to clean them. They did not seem dirty and it did not help
I only cleaned 2 of the 4 speaker relays, one that I cleaned still didn't help much. What about the big power relay?

I'll try cleaning the switches again too.


this is ****ing weird
 
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I've pulled the relays again, all 4 speaker relays and power relay. This time I was more aggressive cleaning them. I was able to remove some oxidation on the contacts applying some pressure and using paper. Also I deox'd the **** out of the speaker selector switches. You can get some internal access via the underside of them. Also deoxit was used on the rear mode & impedance switches.

Reset the bias down to 2mv after warmed up. Was a little high from my last setting, about 4.7mv warmed up. I noticed the amp was getting warm and fan was turning on. I definitely need to change these bias pots, they are the worst pos I've dealt with. I would imagine vibration could be enough to knock them off setting, 25 turn pots would solve this. Also, when the amp got warm, I would here a humming sound coming from the amp itself, not the speakers. Not sure what that means (the cooling fan was on at the time and the amp was bridged). Bias was a little high and I've since lowered it. But at the time, if I shut the amp down or let it cool for a min or two that humming sound would stop. Not sure if it was coming from the transformer or what. The fan runs quiet and is not from the fan running.

I haven't tested in btl mode yet, but so far the issues I was having seem to be eliminated. I think the problems I was having were from dirty switches and relay problems.
 
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Fun having three projects going at once, eh? :D


holy shit not really. This amp was supposed to be plug and play. Removing and cleaning these relays is 2+ hours per side. There is no "easy" access on this beast.

I should demand a discount!!! hahaha
 
holy shit not really. This amp was supposed to be plug and play. Removing and cleaning these relays is 2+ hours per side. There is no "easy" access on this beast.

I should demand a discount!!! hahaha

Sorry for all your issues. I didn't ever have it in BTL mode and it worked great for me without issues. Best of luck with it.

(I did give you a discount :))

Rick
 
I know I was being sarcastic.


shipping something that big and heavy takes a toll. you got it here without a scratch on it. maybe a little impact and vibration issues, a little maintenance. but you can't buy this equipment without having some capability to work on them, or know someone who does. :)
 
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The toroid hums a little on mine. I think it's normal.

I checked the bias when it was really warmed up, and at idle. Was a little high being around 4.7mv. I re-set it down to 2mv (2-4mv in manual) and that has alleviated the humming I was hearing from the amp.

Also I've ran it in btl for a couple hours and everything been working properly. All of this issues I was having were from the relays and switches it seems.

I monitored the temp and was getting 110-121F (44-50C) on heat sinks, fan operatonal. This was over a 2 hour period in bridged mode and playing rather loud.

If anything was wrong I think it would show. best part; only had to press each speaker switch once:D

so if anyone buys one of these amps and has these weird ass problems, check the relays and switches. I'm done here :)
thanks guys
 
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