Anyone have a service manual or schematic for an Event TR8 active speaker?

[MikeHunt79]

One of mine stopped working recently and I was hoping to fix it...

I've checked the trafo an it appears to be ok, it's giving 18V ac on the secondaries.

There are 2 heatsinked chips say LM3886 on them, so I guess this makes it's amplifier similar to the infamous gainclone?

There are also 2 what appear to be op-amp type chips, which I assume are the crossover/pre-amp part of the circuit...

Where would be the best place to start in finding what is wrong with this circuit?

[wxn]

I have the schematic for TR6 which is a very simple input/pot/subsonic/xo/amp design. I suppose it's not much different. Try to probe around with a scope, measure preamp supply rails (should be around +-15V) etc. Then report your findings

[MikeHunt79]

Originally posted by wxn
I have the schematic for TR6 which is a very simple input/pot/subsonic/xo/amp design. I suppose it's not much different. Try to probe around with a scope, measure preamp supply rails (should be around +-15V) etc. Then report your findings

If you could post (or e-mail me) the schematic of the TR6 board that would be great. My e-mail address is mike_hunt_79uk at yahoo.co.uk (change the at to @).

I'm getting around +-25V on the legs of the large smoothing caps. I cannot see any voltage regulators on the board tho, so I'm assuming the op-amps are running of +-25V? The LM3886's do get warm tho, so I'm assuming they are ok...

I'm assuming the switch is ok as the LED lights up and I get quiet hiss thru the speakers... but if it's a dual gang switch then I guess one of the gangs could not be working.

One more thing, if I do have a signal going into the board, I can hear it very faintly thru the speakers if I put my ear up to it... So I'm thinking the signal isn't quite making it to the LM3886's.

I haven't tried tracing the signal with a a scope yet, but I will do once I get more free time later on tonight with any luck.

I managed to grab a few pics, I'll post them up in case I'm missing anything obvious?

[wxn]

D5 and D6 are 15V zeners. Check your email

[MikeHunt79]

Thanks for send the schematic, it makes fixing things much easier.

It turns out the on/off switch wasn't switching the MUTE pin on the LM3886's, yet it was switching the LED on and off ok. They're on separate gangs so I guess one of the gangs in the switch has gone.

I'll try switching the MUTE pin with an external switch to see if this fixes things...

[wxn]

BTW, notice all the ceramic SMD caps in the signal path. I changed them all to nice film caps, the sound has improved, especially the highs. Which always sounded muted on these monitors.

[MikeHunt79]

Good idea, the treble definitely sounds like it could be improved (, I found this out today - see my mod )...

After shorting the mute pin switch gang to the LED gang, the amp is now giving out sound, but it's still pretty quiet, and reaches clipping very early... My zeners are giving out +-15v ok also, so once I get hold of a scope I'll have to trace my signal. I guess the LM3886's could have burned out, I've found the backplate and transformer can get pretty hot...

I figured it wouldn't hurt to remove the working PCB from the other speaker, as I'll be able to compare them and it would really help finding the problem with the non-working pcb.

I still wanted to listen to the speakers however, so I've gone for some external amplification. I made my own replacement backplates out of 4mm perspex and hot glued some 4 pole speakon jacks, then connected up the woofer and tweeter.

I used a 41Hz.com Amp9 amp which is 4 channels and a DCX2496 as a crossover I can still keep it bi-amped...

The sound quality has definitely improved, the treble or a lot more refined, but I still am going to try and fix the LM3886 PCB's tho, plus change the caps to see if I can get them to match the Amp9 for sound quality.

[wxn]

Originally posted by MikeHunt79
I've found the backplate and transformer can get pretty hot...

Which is weird. Seeing an almost non-existent heatsink and a seriously undersized transformer in a peace of "professional" equipment does make think..

[MikeHunt79]

Originally posted by wxn

Which is weird. Seeing an almost non-existent heatsink and a seriously undersized transformer in a peace of "professional" equipment does make think..

You're right, I guess the accountants must have stuck their oar in and tried to cut costs wherever they can... Usually pro stuff is built a little better...

It is a shame really as I'm always worried something might melt if I crank the volume... Still, at least with my current setup I can crank it all I want and the amp is ClassD so it carely gets warm...

Event did also make a TR8 XL which was basically the same as a TR8 with a more powerful amp and a toroid trafo. I've seen a photo of the back and it does have a bigger Alu plate but not anything resembling a proper heatsink...

[wxn]

Yeah well I'm in the process of redoing these speakers. I had a pair of 200W trafos, nice heatsinks, some spare LM3886 and willingness to redo everything from scratch, including filters and input section. I'll post pictures later