Mackie 824 mod (cloudy mid range)

[Spencerleehorton]

I would really like to attempt this mod as my 824's are suffering from cloud mids!!
Ive used them for years and not really noticed until now!! as i got some yamaha MSP5 and Harmen Karden sound sticks MK2.
the sound really bothers me now, maybe my ears have grown up recently?
cant afford to change the tweeters yet but i have made a hit list of what i'm hopefully going to attempt to do:

1. replace volume pot - R184 = 10k
2. replace electrolytic caps before and after volume pot x 4 - C37 and C14 =  47uf/25v
3. change opamps to lm4562 (£25) x 12 - should i snip the legs then solder to the snipped legs rather than try and unsolder and wreak the pcb?
4. PIO coupling cap for low amp (paper in oil) x 2 - is this C89 = 47uf/25v? or C100  = 10uf/50v? or is it something else?
5. polyproperlene for hi amp replaced x 2 - C18 or C26 = 750pf are these the correct ones?
6. PS caps for hi amp (power supply?) - C86 and C17 = 470uf/25v, C84 and C16 =  10,000uf/50v ?

bypassed all eq caps with polypropylene? can anyone explain this one?

added additional filer caps for PS (power supply) and snubbed them? errr?

I have the service manual schematic just need to verify each part number so i'm changing the correct thing, and it must be that i have the Chinese version rather than the USA version which it seems the USA versions use correct parts and don't suffer from this cloudy (lack) of mid range.

any help or info on this i would be very grateful thank you.

regards

Spence.

 

[living sounds]

Got a schematic?

I would very much advice against naively changing components this way. I wasted a lot of time myself in the same fashion...

The circuits are not designed for LM4562. Expensive coupling caps should not be necessary.  Additional surrounding circuitry, especially decoupling, attention to grounding and the PSU may be necessary to make other op amps or even the original ones work properly, let alone close to ideal specs. You need measuring equipment to verify your work.

 

[abbey road d enfer]

I would really like to attempt this mod as my 824's are suffering from lack of mids!!

90% of the sonic signature of a loudspeaker is in its transducers. No fancy caps can change that.
What you may try is use an EQ, preferrably a parametric one, and try to determine if the issue is only one of frequency response or something more indidious, like midrange distortion, diffraction issues or beam narrowing, against which not much can be done.
I would say, you're not happy with your 824's, sell them or use them for whatever ancillary purpose, and use something else for important duties.

 

[Chris_V]

From the original post, and if I believe the author's ears, I would say that the most important modifications are :
- Tweeter change
- Damping of the waveguide

Like abbey, I am really doubtful about the sonic influences of opamp and caps on this powered speakers.

 

[Spencerleehorton]

ok, well i'm always gonna bow down to your knowledge but ideally, yes i would buy a set of Adam AX7's and be done with it.
unfortunately with everything at the moment i'm not in that situation so would like to do something to rectify the muddy mid range.
without any mods i could just  as you say use a parametric EQ or i have spare returns on my GS3000 which i could EQ in a bit more of Mid range, i have tried this and it works pretty well.

I am speaking to Pat(khstudio) who has done many modifications on these monitors and to great results, so this is the original post i found.

https://groupdiy.com/index.php?topic=29597.msg378080#msg378080

he has mentioned some of what he has done wasnt worth doing, re the opamp, im not going to attempt anything with them!!!

whats your thoughts guys?

 

[Spencerleehorton]

if i cut about 250hz 2-3db and boost 2.5k about 1-2db they actually sound much better, so this must be where they suffer.

 

[warpie]

I had the impression that most 8" speakers suffer in the 200-300Hz region but I might be wrong.

 

[Spencerleehorton]

Could you explain - Damping of the waveguide?

 

[Spencerleehorton]

Well, i've taken the studio 1 out from my GS3000 and put it into the line in on two channels, then taken the tape out to the 824's, i used the EQ and cut at about 300hz and boosted at about 2khz and it cleans the monitors up nicely.
Need to do a few mixes now and see if any better, might take a while but i'm happier with the sound now, although the EQ through the desk does introduce more hiss obviously.
Time to save up for some Adam A7X now!!!