I need professional help ...aka "The Dead Mixer Conundrum"

solo2racr

solo2racr

SUCK, SQUEEZE, BANG, BLOW
I've been using, essentially, Tweekheadz Rig #3 (albeit a bit better than what he suggests) for the last 5 years and my mixer's PSU just went out. It's a Soundcraft Spirit E8. No band here (just myself) so, this setup is just fine for my needs. I have been looking at different options and just not sure what to do. What I have come up with are....

1) Repair the PSU (a SMPS). Though, there is a FET that is no longer available and I would have to find it's replacement.

2) Build a new linear PSU. I have built a few guitar pedals and modded a couple amps so this wouldn't be a problem. May be cleaner power as well.

3) Replace the mixer. New ones are out of the budget at the moment so, looking at eBay. ( Mackie VLZ 1202 or 1402, Behringer Xenyx 1204 as suggested by Tweek, another Soundcraft Spirit E series, or maybe a Yamaha MG with the appropriate routing options)

4) DIY something. Get a 2 ch. mic pre and DIY the routing, A simple gain recovery stage on the monitor out and a few switches for signal routing. Mixers are overkill. All I really use are the mic/line preamps and some of the routing.

Sooo....on option 3, what mixer would have the better (I know, subjective) preamps? I'm not much on Behringer but, I can't ignore Tweek's suggestion either. I have only used a Mackie once and it was years ago. Soundcraft I know. Yamaha???? A total unknown.

Also, does option 4 have any merit? Tone controls are worthless. Aux send/return are almost worthless, though I can see the rare use of an outboard effect on rare occasion. It's pretty much, for me, just mic preamps, inserts out to the M-Audio 2496, in from the 2496 and the "tape out" to the monitors.

I have considered a USB interface and start, almost, anew. But I like the 2496 and it works fine.

Suggestions????? Opinions????? Come on, I know you have them! :thumbs up:
 
Well, if the budget is somewhere around $100-$150 as it seems from your post, I would not tackle anything DIY unless you are a serious scavenger and don't mind taking a potentially serious chunk of time to get it done. I mean, one rack chassis and a semi-decent transformer and your budget is gone before you've started.

I've used all of the mixer brands you mentioned, and I think the Soundcraft is probably your best bet for overall sound and quietness. I would suggest option 1.
 
Thanks for the response, John. Your right about the budget. For option 2, I can build it on stripboard and fit it into the space the original PSU occupied. On option 4, I was thinking not so much a 1 or 2u rack chassis but more like a mixer style platform. Nice wood sides, aluminum top, front & back and a ABS plastic removable bottom. It and the mic preamps would occupy the place where the Soundcraft did. Option 1 would be the cheapest and would retain the Soundcraft mixer. The down side is sourcing a P7NB60FP or it's equivalent. It's also possible that when the PSU failed that it also hurt other components on the main board.
 
Maybe you could hook up a basic supply (like a wall wart) just to test the board for damage, then build or repair the audio-quality one if viable.
 
Assuming you are using this system for recording only? Many audio interfaces available in the $150 range, I know you say you like the 2496, but ... other option is to find a 2-channel mic pre I guess. From my limited experience, I'd say stay away from the Behringer Xenyx - very noisy preamps when I tried one.
 
I use it for general playback as well. Music, DVDs, YouTube, etc. I looked at new interfaces in that price range and they will do what I need. But given that they are "All In One" for that price, I have to wonder about the quality of the preamps. Right now, I could spend that much on a 2ch. preamp alone I'm sure they would be better. With that, I could go straight out from the 2496 to the monitors and control volume from within the PC. But I do like a hardware fader control for the volume just in case I find something that is super loud.
 
JohnWatkins said:
Maybe you could hook up a basic supply (like a wall wart) just to test the board for damage, then build or repair the audio-quality one if viable.
Click to expand...

It would be a bit more involved than a wall wart. Just to test, it would need +15/-15 volts as well as 48vdc for phantom power.
 
What voltages and currents are required from the power supply?

There are some nice PSU kits from JLM Audio which provide + and - voltage rails, and +48V phantom. Joe also does a PSU which provide 2 + and - rails (can be different) and phantom.

What are your needs?

Paul
 
An easy cheap and above all, very safe way to build a +-0- 15v is to buy a pair of 22V SMPS wall rats and feed a 78/79 reg board (I am sure you can buy a PCB for those which makes it a doddle to build)

A 50V supply is harder to find but I managed it. You will need some extra filtering (LC for preff) on that.

But! Power supply fryups on that model of mixer are so well known that I feel sure someone will do a replacement/repair service.

Dave.
 
I took a look at the JLM kits. The AC/DC Ver2 kit would be more than enough. The schematics look like a straight forward linear PSU. $50.00 + shipping from AUS. + the cost of a tranny. Probably would add up to about $100.00. A new PSU from Soundcraft runs $150.00USD. I believe I can build one on strip board, including the tranny for less than $50.00. I would have to search the parts from Mouser to confirm that.

Finding parts to build a linear PSU is not a problem. And there are plenty of designs on the internet. The only part that I have not found is the FET used in the original SMPS. Rebuilding it would be the least expensive route, provided I can find that FET. Next in line, cost wise is to build one from scratch. I am going to borrow a friend of mine's variable PSU just to check out the rest of the mixer to be sure nothing else is fried on the main board.

Yea...I have read were the PSU is the weak point on the Soundcraft Spirit E series. I found a very in-depth blog about repairing the SMPS it comes with.

From I am reading here so far is to keep the Soundcraft and repair/replace the PSU.
 
solo2racr said:
I took a look at the JLM kits. The AC/DC Ver2 kit would be more than enough. The schematics look like a straight forward linear PSU. $50.00 + shipping from AUS. + the cost of a tranny. Probably would add up to about $100.00. A new PSU from Soundcraft runs $150.00USD. I believe I can build one on strip board, including the tranny for less than $50.00. I would have to search the parts from Mouser to confirm that.

Finding parts to build a linear PSU is not a problem. And there are plenty of designs on the internet. The only part that I have not found is the FET used in the original SMPS. Rebuilding it would be the least expensive route, provided I can find that FET. Next in line, cost wise is to build one from scratch. I am going to borrow a friend of mine's variable PSU just to check out the rest of the mixer to be sure nothing else is fried on the main board.

Yea...I have read were the PSU is the weak point on the Soundcraft Spirit E series. I found a very in-depth blog about repairing the SMPS it comes with.

From I am reading here so far is to keep the Soundcraft and repair/replace the PSU.
Click to expand...

Are there any readable markings on the FET? I would have thought the IRF830 suitable. It is rated at 500V, well above peak mains +10% (~358V ).

The Spirit does have a very good rep for its performance in virtually every other respect!

Dave.
 
The FET is by ST and is a P7NB60FP. I have searched high and low for one but to no avail. All I have found is a pulled (used) one on eBay. I suppose I could pull mine off the PCB and test it. It may very well be fine. Given the choice though, I would rather replace it with a new one or it's equivalent. But I can't even find what would be equivalent.
 
solo2racr said:
The FET is by ST and is a P7NB60FP. I have searched high and low for one but to no avail. All I have found is a pulled (used) one on eBay. I suppose I could pull mine off the PCB and test it. It may very well be fine. Given the choice though, I would rather replace it with a new one or it's equivalent. But I can't even find what would be equivalent.
Click to expand...

P7NB60FP | Transistor: unipolar, N-FET; 600V; 4.1A; 40W; TO220 | tht n channel transistors // TME

The IRF 840 is rated at "only" 500V but I think that is well good enough. It has a current rating of 5A and a dissipation of 125W.

My company uses the 830 in lots of circuits at up to 480V and the little buggers are VERY hard to kill!

Dave.
 
The IRF 840 looks like it may work. I simply don't know enough to tell. Looking at datasheets for both of them, I see that the IRF840 has a RDS (Resistance Drain-Source) of .85 ohms where as the P7NB60FP has a RDS of 1.2ohms max (typ 1.0 ohms). What difference this may make in the circuit and if it can be accounted for, I have no idea. As stated before, SMPS power supplies I know nothing about. Linear supplies I can deal with.

I am leaning toward building a linear PSU. Even though it would cost more, I think it may be a cleaner supply and I can deal with them if there should be a problem. I have a couple schematics right now and am looking to fit what I believe the better one onto strip board (veroboard).

I think I'll pull the P7NB60FP off the PCB and test it. If it checks out good, then go with repairing the original PSU. If it's bad, then build a linear PSU.
 
You can definitely build a PSU on perf board. I have done this many times. I would personally tend to use the adjustable lm3x7 devices which are generally credited with better noise performance than the 78xx/79xx fixed regs. The 3-pin adjustables are rated to 1.5amps with suitable heat sinking.

Something to consider: you can get JLM's power supplies as bare pcbs which you populate with your own parts. This would work out cheaper than the kit (with cheaper postage), and even cheaper if you already have parts on hand. It also reduces the likelihood of wiring mishaps. Just a thought.

But certainly, see if you can resurrect the SMPS.

Paul
 
Sol2, I know little in depth about switching supplies (other than hatred) but I have had to deal with them in another life fixing TVs and VCRs.

The higher R ds of the 840 will make it less efficient and run hotter, hardly a design improvement! It is very likely however that the original device has survived.I believe that the caps were the weak ness on that PSU (mainly because they were next to some high dissing' resistors IIRC!)

if you DO get it working I would also fit a wee, 50mm fan since the supply is only just not quite good enough. Or, leave the PSU outside in a nice "heatsinky" tin?

Dave.
 
I copied and pasted my OP over at the new recordingstudiocentral.com and Rick Levine over there turned me on to a new original (abeit updated) PSU from Fullcompass.com. $80.00 for a new one. That's about what it would cost to build a linear PSU from scratch. I am going to pull the FET and see if it is good or not. If it is, I can repair the original PSU for about $10.00 in parts. If it is bad, I may go this route as opposed to building a linear PSU myself.
 
At this point I would suggest you get an ASUS i7 Sandy Bridge laptop with an 8 channel converter. You can do on site recording and multitrack recording Get Adobe audition or Pro tools. We're talking about $2000 but you will be much more up to speed. Good Luck, Rod Norman

solo2racr said:
I've been using, essentially, Tweekheadz Rig #3 (albeit a bit better than what he suggests) for the last 5 years and my mixer's PSU just went out. It's a Soundcraft Spirit E8. No band here (just myself) so, this setup is just fine for my needs. I have been looking at different options and just not sure what to do. What I have come up with are....

1) Repair the PSU (a SMPS). Though, there is a FET that is no longer available and I would have to find it's replacement.

2) Build a new linear PSU. I have built a few guitar pedals and modded a couple amps so this wouldn't be a problem. May be cleaner power as well.

3) Replace the mixer. New ones are out of the budget at the moment so, looking at eBay. ( Mackie VLZ 1202 or 1402, Behringer Xenyx 1204 as suggested by Tweek, another Soundcraft Spirit E series, or maybe a Yamaha MG with the appropriate routing options)

4) DIY something. Get a 2 ch. mic pre and DIY the routing, A simple gain recovery stage on the monitor out and a few switches for signal routing. Mixers are overkill. All I really use are the mic/line preamps and some of the routing.

Sooo....on option 3, what mixer would have the better (I know, subjective) preamps? I'm not much on Behringer but, I can't ignore Tweek's suggestion either. I have only used a Mackie once and it was years ago. Soundcraft I know. Yamaha???? A total unknown.

Also, does option 4 have any merit? Tone controls are worthless. Aux send/return are almost worthless, though I can see the rare use of an outboard effect on rare occasion. It's pretty much, for me, just mic preamps, inserts out to the M-Audio 2496, in from the 2496 and the "tape out" to the monitors.

I have considered a USB interface and start, almost, anew. But I like the 2496 and it works fine.

Suggestions????? Opinions????? Come on, I know you have them! :thumbs up:
Click to expand...
 
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