amplifier imbalance

[Bushbaby]

Thanks both
No, I don't think that I will push the amp that hard - it seems that half way or just over sounds excellent and is probably driving the speakers well too.

Thanks again.

[Diabolical Artificer]

One thing non of us thought about was the phase of the speakers, worth checking you have them plugged into the amp correctly, EG correct polarity. I'd still also check the amp, bung it on the bench, 0.5v 1khz sinewave in, a couple of 4r7 , 8r2 or 10r resistors as dummy loads even if small 1w they'll be ok for a flash test. This should be done with no signal IP as well to check for DC offset, after all the amps knocking on a bit.

Andy.

[Murphyv310]

Hi Andy.
Indeed, I certainly took it for granted Rob would be fully aware of speaker connections and correct phase!
Your other comments are again sensible things to do and of course if there is any DC Offset a ticking time bomb.

[Bushbaby]

I will check this and my other A&R A60 . I agree they are rather old.

[Diabolical Artificer]

"Indeed, I certainly took it for granted Rob would be fully aware of speaker connections and correct phase" Me too. Miss wiring is easily done as amplifier back panels are often hard to get to as are backs of speakers. Getting to mine requires hanging upside down with a torch fighting through months worth of cobwebs and spaghetti wiring.

[Bushbaby]

I've now got my system up and running with the old Mission 770s speakers which have had the crossover modified for the changes to the bass drivers and tweeters. Wow, these sound amazing and I am pleased to say that drum kit cymbals are reproduced extremely well. The system is well balanced and very neutral. There is the odd crack that I hear very infrequently from the speakers so could this be a connection issue somewhere??

The bad news is that they are huge speakers and being old and knocked about, the speaker veneers need to be cleaned up/marks removed/polished. I am now thinking that they are too big for such a small room.

Best Regards

Rob



   

[Diabolical Artificer]

Glad it's all sort of working, sounds like the amp needs a look at, it could be a dodgy resistor or leaky transistor or dry joint. If it were mine I'd have it open and give it a thorough visual inspection, your looking for cracks in resistors, look especially round places where it gets hot & maybe touch up some solder joints. Did you check the offset/DC on the OP Rob?

Those speakers look too high, I'd drop em down about half again at least, AFAIK 770's were meant to flour standing although the manual for the 770 Freedom says up on stands, against the wall but not touching, 1.5 - 2.5m apart, see - https://www.hifiengine.com/manual_librar...edom.shtml. As to size you can't have too big speakers, the bigger the better IMHO. The 770's aren't bad, the earlier ones had decent drivers - Seas tweeters and Peerless woofers, yours don't AFAIK. There are better speakers out there, the 770's lack mid and are a bit weak sounding to my ears. Someone's selling a load of decent speakers Rob over on UKVRR for a very good price a week ago.

Andy.

[Murphyv310]

Hi.
I'd reinforce what Andy says in all points. A slight crackle definitely needs to be investigated. Agree re the DC Offset, cracked components and dry joints.
Also acoustically and aesthetically the speakers are too high and again I agree half the height would be better, although for me on a personal viewpoint I prefer them on the floor.

[Bushbaby]

Thanks for your feedback Andy/Trevor.
The stands that these are current on are the ones for the Heybrooks HB2 2000's. I do have the original wood stands for these but they are in such poor condition I didn't want to put them out (they are mdf and covered in hammerite type silvery/grey metallic paint thats now very worn and looks ugly. I've just bought some very low wood stands (6" high) that should do the job with these are about the same height as the originals.
My speakers have SEAS 25TN tweeters and VIFA M 21 WJ-09-08 bass drivers which replaced the original speakers at some point in the past I which I believe are are a good selection to make and are sounding in the same instance to the original 770's from what I can remember.
I must admit that I can't seem to find any info on the Missions 770 'S' speakers which these models are?

Yes, I agree, I do now need to look at this amp but having 2 of these would it be wise to leave this one in 'temporary use' and look at the other to get that fully up and working?

Best Regards

Rob

[Mark Hennessy]

Stand-mount speakers should be elevated so that the "reference axis" is level with your ears when you are in the listening position.

The "reference axis" is usually the tweeter, but occasionally it might be the woofer (or midrange, in a 3 way system). The user manual will tell you.

If you move a measurement microphone up and down in front of a loudspeaker, you'll see really quite large differences in response, especially through the crossover region where the two drive units overlap. It does depend on how well the designer has done their job - and that's the hardest part of designing the crossover - but even with the best design, variations must exist. Simple physics.

The sorts of differences I'm talking about are several decibels. Remembering that people manage to convince themselves they can hear differences in cables that might only measure 0.01dB if you're lucky, it's surprising people are so unaware of this.

Of course, with completely different drive units and a modified crossover, who knows what this particular speaker is doing, but even so, I'd still start by assuming the tweeters should be level with your ears.

A stand-mount speaker placed on the floor will "honk" terribly at the bass end. Some might like that, and it's all personal choice at the end of the day, but rest assured the original designer would not have done that.

Having said all that, that room looks like a total nightmare acoustically - all that glass and a wooden floor will make for a very lively space. Of course it looks lovely, but a thick rug and some heavy curtains will do far more for the sound in that room than anything else. But I appreciate that can be easier said than done if trying to maintain domestic harmony!