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#61
8th September 2011
Old 8th September 2011
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So can I take the generality from this thread that matching the 6k8 resistors on the way in as tightly as possible will improve the pre's noise performance noticeably?

I am tempted to measure the ones in situ in my desk to see if I can improve them if so.........

Also, while I'm asking hopeful questions......could a rather broad sounding hiss (not hum, but not skinny either, full hush) be the channel electrolytics being worn out and letting power noise in? I ask 'channel' as I am getting this even when coming out of the insert, i.e. before any other bits, master, etc.....

Any pointers on either would be wildly appreciated. Sorry for slight hijack......
#62
8th September 2011
Old 8th September 2011
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Quote:
Originally Posted by rekloos View Post
Ur right, I should've been more specific....
Well, it does have a lot of scratchy pots, I'd say all of them have to b replaced. All faders need replaced, psu, and some of the knobs and fader (knobs??) as well.
Then, there's the question of things under the hood I dunno about but might need replaced....
Basically, i know a bit about soldering (did all the wiring in my studio) but not enough about electronics to take the whole project on my own. I figured jus do whatever simple stuff u can do and buy all the parts needed then take it to a local shop to finish it. But... is it even worth doing it? would the local guy charge more fir the parts or would it b the same ball park?
You're talking pretty much a full rebuild. It will be costly in parts and time. If you have a Mk 1 desk with 90mm faders then that will take a lot of hunting to find new ones. if you have a Mk 2 or Mk 3 then you're in better shapre with 100mm faders. Other pots need to be physically compatible since they also hold the PCB to the panel. Allow $2-3 per pot if you go for Alpha or similar replacements.

A new PSU will set you back around $200, give or take.

If you pay someone to do the work you'll find their time more costly than the parts. A lot more.

Ultimately the yes/no answer depends on you: how much you have already invested in your board, how much more are you prepared to invest (both time and money), what you hope to achieve by the end of it. Sometimes the answer is to walk away.

In my case its a hobby, so time is not an issue. And I'm an electronics engineer and I like to tinker around with analogue electronics - for me, the journey is the point, and at the end a half-decent analogue desk to mix my home-made synthesizers.

Cheers,
Neil
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#63
8th September 2011
Old 8th September 2011
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Quote:
Originally Posted by Karloff70 View Post
So can I take the generality from this thread that matching the 6k8 resistors on the way in as tightly as possible will improve the pre's noise performance noticeably?
It will improve the rejection of PSU noise (mostly 100/120Hz buzz) when phantom power is turned on. If you don't use it then there will be marginal noise improvement.

Quote:
Originally Posted by Karloff70 View Post
I am tempted to measure the ones in situ in my desk to see if I can improve them if so.........
If they are wildly out then 0.1% resistors are a quick and cheap option.

Quote:
Originally Posted by Karloff70 View Post
Also, while I'm asking hopeful questions......could a rather broad sounding hiss (not hum, but not skinny either, full hush) be the channel electrolytics being worn out and letting power noise in? I ask 'channel' as I am getting this even when coming out of the insert, i.e. before any other bits, master, etc.....
At what pre-amp gain is this? Sounds more like thermal noise. Given the age its most likely the resistors are carbon film. Metal film would be lower noise.
#64
8th September 2011
Old 8th September 2011
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Quote:
Originally Posted by neil.johnson View Post
It will improve the rejection of PSU noise (mostly 100/120Hz buzz) when phantom power is turned on. If you don't use it then there will be marginal noise improvement.



If they are wildly out then 0.1% resistors are a quick and cheap option.



At what pre-amp gain is this? Sounds more like thermal noise. Given the age its most likely the resistors are carbon film. Metal film would be lower noise.
Ok, I don't really use the board's phantom, only a separate AKG 6-way box, so bugger the 6k8's.....

It's at all gains, just obviously comes up with more. Seems to track the gain in a linear fashion, i.e. end result at high-ish gain is lots of the shite......

Indeed this board (Raindirk Concord) is full to the brim with carbon resistors.......you think they're the culprits of this fuzzy seanoise?
#65
8th September 2011
Old 8th September 2011
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Quote:
Originally Posted by Karloff70 View Post
Indeed this board (Raindirk Concord) is full to the brim with carbon resistors.......you think they're the culprits of this fuzzy seanoise?
Difficult to say. I don't know of your desk, haven't seen the schematic. there might be a fault in the desk or the PSU, or something else. At the very least get a good tech to look it over first just in case there is something wrong with it. I'd hazard a guess it was not designed to sound noisy ... or your expectations of a vintage desk are a little too high!!

Cheers,
Neil
#66
8th September 2011
Old 8th September 2011
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Quote:
Originally Posted by neil.johnson View Post
Difficult to say. I don't know of your desk, haven't seen the schematic. there might be a fault in the desk or the PSU, or something else. At the very least get a good tech to look it over first just in case there is something wrong with it. I'd hazard a guess it was not designed to sound noisy ... or your expectations of a vintage desk are a little too high!!

Cheers,
Neil
It's defiinitely not designed this noisy. No Raindirk is.

It's going home to its maker, Cyril Jones, asap....only he's busy on a big LN desk and until he's got it out the door I'm in the queue.....trying to find out what I can beforehand, but like you say, he'll soon tell me when he's had a look, as it's his baby.

Thank you very much anyway though!! Thread hijack over....
#67
8th September 2011
Old 8th September 2011
  #67
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Quote:
Originally Posted by neil.johnson View Post
You're talking pretty much a full rebuild. It will be costly in parts and time. If you have a Mk 1 desk with 90mm faders then that will take a lot of hunting to find new ones. if you have a Mk 2 or Mk 3 then you're in better shapre with 100mm faders. Other pots need to be physically compatible since they also hold the PCB to the panel. Allow $2-3 per pot if you go for Alpha or similar replacements.

A new PSU will set you back around $200, give or take.

If you pay someone to do the work you'll find their time more costly than the parts. A lot more.

Ultimately the yes/no answer depends on you: how much you have already invested in your board, how much more are you prepared to invest (both time and money), what you hope to achieve by the end of it. Sometimes the answer is to walk away.

In my case its a hobby, so time is not an issue. And I'm an electronics engineer and I like to tinker around with analogue electronics - for me, the journey is the point, and at the end a half-decent analogue desk to mix my home-made synthesizers.

Cheers,
Neil
good points there Neil....
this is a MKII Board with 24Ch and I paid 500 for it, I use it mainly for running multi ch from computer plus some keys and drum machines. basically I run everything thru and record back in daw but I want smooth noiseless control of faders/knobs. I like the sound, layout, and routing capabilities which is why I want to stick with it but it sounds like it migt b xpensive but.... maybe I find another for 6-700 in a better shape... I guess I could a little more if it's really good shape.
maybe I'll try to get an estimate locally see if it's worth it.

I do wonder about something, if I assign one of the channels to a bus I hear a sligh drop in volume, the more buses gets assign the more it drops- is that normal? is it related to the psu?
#68
18th September 2011
Old 18th September 2011
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Sorry for the late reply...holiday

Quote:
Originally Posted by rekloos View Post
good points there Neil....
this is a MKII Board with 24Ch and I paid 500 for it, I use it mainly for running multi ch from computer plus some keys and drum machines. basically I run everything thru and record back in daw but I want smooth noiseless control of faders/knobs. I like the sound, layout, and routing capabilities which is why I want to stick with it but it sounds like it migt b xpensive but.... maybe I find another for 6-700 in a better shape... I guess I could a little more if it's really good shape.
maybe I'll try to get an estimate locally see if it's worth it.
The size of the desk, compared to modern mixers, is very attractive - so much more spaced out, not squeezed together. Gives it a hint of professional feel to it. The downside is the monolithic design, so getting to any one board means turning the entire mixer over and cutting it out. The most cost- and time-effective (or just cost if you're paying someone to do it ) approach is to do all the fixes at the same time. Especially given the busses comprise soldered links rather than a more service-friendly busboard.

Quote:
Originally Posted by rekloos View Post
I do wonder about something, if I assign one of the channels to a bus I hear a sligh drop in volume, the more buses gets assign the more it drops- is that normal? is it related to the psu?
Err, yes that's normal for this mixer. To keep costs down there is no buffer amp after the pan pot, so as you switch in more busses you put more load on the pan circuit and the signal level drops. A trifle annoying I agree, but there's 10dB available on the fader to help compensate.

Cheers,
Neil
#69
18th September 2011
Old 18th September 2011
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#70
18th September 2011
Old 18th September 2011
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Quote:
Originally Posted by MrMegaEli View Post
Would this work for the PSU? LNR SUP DBL OUT 12/15V CASE CC - HCC15-3-A
Quite possibly. Its the right voltage, and should be able to supply plenty enough current. If you want phantom power you'll need an additional supply, but I guess you know that already.

Cheers,
Neil
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19th September 2011
Old 19th September 2011
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#72
19th September 2011
Old 19th September 2011
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#73
19th September 2011
Old 19th September 2011
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Quote:
Originally Posted by MrMegaEli View Post
That supply has an output of 90 Watts. What does that have to do with powering the console?
It just states the maximum power it can deliver. The desk should consume less than that though - the original PSU was 30W.

Quote:
Originally Posted by MrMegaEli View Post
Will this work for the phantom power supply? JLM Audio Shop - 48v 15w 315mA SMPS
Ewww... SMPS. I personally wouldn't make that my first choice, but I'm happy to be proven wrong. Couldn't see a spec sheet for it or even a manufacturer and model number to chase so I can't say anything worthwhile about it. Might be worth a go if you can afford to waste $40 or so.
#74
19th September 2011
Old 19th September 2011
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#75
20th September 2011
Old 20th September 2011
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The PSU from Digikey looks like the right one. The mouser one says only 12V, not 15V, even though they have the same part#. I'll just get it from Digikey.

Neil, what phantom power supply would you recommended? (and why is switched mode bad?)
#76
20th September 2011
Old 20th September 2011
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Quote:
Originally Posted by MrMegaEli View Post
The PSU from Digikey looks like the right one. The mouser one says only 12V, not 15V, even though they have the same part#. I'll just get it from Digikey.
Best to get the manufacturer's part number and check their documentation for the correct answer.

Quote:
Originally Posted by MrMegaEli View Post
Neil, what phantom power supply would you recommended? (and why is switched mode bad?)
No idea which one to recommend. I'd start with hunting around on this board - I'm sure I've seen one or two recommendations from people in the know.

As for SMPS, they generate lots of high frequency noise, and require careful attention to design, build and integration to keep that noise away from the low-level audio.

Now, it may be that this particular SMPS has been designed to be very low noise in the audio band, which it is certainly possible to do. Or it could be a cheap noisy little sod. As there is almost zero technical information about it I can't say.

Cheers,
Neil
#77
20th September 2011
Old 20th September 2011
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Quote:
Originally Posted by neil.johnson View Post
Now, it may be that this particular SMPS has been designed to be very low noise in the audio band, which it is certainly possible to do. Or it could be a cheap noisy little sod. As there is almost zero technical information about it I can't say.
Being it's a JLM product I cannot fathom it being anything but totally pukka myself.....as far as I can tell Joe doesn't do "cheap and noisy" little sods.....
#78
20th September 2011
Old 20th September 2011
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Quote:
Originally Posted by Karloff70 View Post
Being it's a JLM product I cannot fathom it being anything but totally pukka myself.....as far as I can tell Joe doesn't do "cheap and noisy" little sods.....
Well, I guess for $39 it could be worth a go. But still, as I say, no specs so you're "buying blind".

... Blimey, he sells NE5532AP for $5 each!!!! Definitely not cheap then!!
#79
20th September 2011
Old 20th September 2011
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I'll probably just look into a point to point 48V supply. Will look at the manufacture's spec sheet, since mouser has a better price.
#80
3rd October 2011
Old 3rd October 2011
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Replacement VU meters and bulbs

One little update. I've found the make and supply of the VU meters. They are made by a UK company called Anders Electronics. They are part number SQ10, and can be ordered in the UK from Rapid Electronics, Farnell and RS Components. Not sure about other countries.

Not sure about light bulbs just yet. Need to see one to check its dimensions. I'll email Anders anyway, but a quick look on Farnell brought up this possible item. Although I have no idea if this will fit or work.

Cheers,
Neil
#81
4th October 2011
Old 4th October 2011
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good work! I’m not sure if the lamps are out on mine, since I need to find a suitable 48VDC supply, so I can buy all my PSU parts
#82
4th October 2011
Old 4th October 2011
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Well, you only need the 48V supply if you're going to use phantom-powered mics. If not (or not yet) then you can skip that and just get the 15V supplies working. The lamps run off those, two bulbs in series.
#83
4th October 2011
Old 4th October 2011
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Skip the lamps, PITA and they will fail.

Use LED's instead. Available in pure white and incandescent colored white for that "olde time" look.

Just connect a 1n4001 diode in series and select a resistor to adjust briteness. 470~2.2k ohms is the usual range with 15 volt supplies.

Get the incandescent colored LED's from:

LED Lights, Bulbs & Accessories - SUPER BRIGHT LEDS

I sand them with 400 grit paper to difuse the light.

Install and never deal with it again.
#84
4th October 2011
Old 4th October 2011
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The Convicted
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#85
12th October 2011
Old 12th October 2011
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Completed mods

I cut my board down to an 8 channel front end.
The first 2 channels, I replaced the tl072 ICs with AD8512, machined sockets, and .1uf mono ceramics as bypasses.
On Channel one, I raised the value of all the caps and bypassed them with .1uf wima mkp caps.
The result on channel one is Much cleaner, its a big difference over the stock channels.
Channel 2 has upgrades ICs, but stock value caps. Its cleaner than stock, but not as clean as channel one.
The other 6 channels are stock but have panasonic FM and FC caps.

Im probubly going to do exactly what I did to channel 2 as channel one. And maybe replace the transistors with 2sa1084s, as I have some here.

IIf any one is intrested, Im going to sell this when Im done.
#86
13th October 2011
Old 13th October 2011
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MrMegaEli:

You might want to check the power supply before you order?

I purchased one for the same console MKIII (haven't had time to hook up yet) and it was this:
HDD15-5-AG

Maybe if you have a MKI, the power requirements are different. If so... ignore me.

http://www.mouser.com/ProductDetail/...JXX8DrdYIec%3D


#87
13th October 2011
Old 13th October 2011
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Hi,

The HCC15-3-AG is a 3A rated supply in a size CC case (238.25 x 123.70 x 83.31mm).

The HDD15-5-AG is a 5A rated supply in a size E case (355.60 x 123.70 x 89.66mm).

The original MPS8P power supply was rated at 1A, so both supplies would be suitable.

Neil
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13th October 2011
Old 13th October 2011
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The Convicted
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#89
14th October 2011
Old 14th October 2011
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Pics Of Board

Heres what the 8 channel Front end Looks like
Attached Thumbnails
Allen And Heath System 8 Modifications-img_1314.jpg   Allen And Heath System 8 Modifications-img_1315.jpg   Allen And Heath System 8 Modifications-img_1316.jpg  
#90
17th October 2011
Old 17th October 2011
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Nice work!

I have “The Convicted”s extra channels, knobs, buss and master sections, more than I need, and extra knobs, so I will extend the same offer to anyone else, you can have parts just pay for shipping.

Has anyone found suitable terminal blocks or other connections that would make removing and replacing channels easier than it presently is?

Maybe even DIN connectors? Molex? For the buss wiring, the connections to the XLRs, the connection to the faders. and other connections in the board.
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