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cps 150 failure Consoles
Old 13th February 2013
  #61
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Hi
I would like an explanation of WHY increasing the FILTER caps on a REGULATED power supply such as this will do anything for [better, tighter, & cleaner low mid and bass response ] since the capacitors in question are BEFORE the regulator.
There will be practically NO audio signal variations detectable on the 'output' side of the regulator before cap change and after changing there will still be no audio signal variations on the output of the regulator.
Use diagrams, MEASUREMENTS and logical argument to quantify any 'perceived' change in the above mentioned 'affects'.

The 'supposed' differences could possibly be observed when changing capacitors on a badly designed and built audio power amplifier.
Matt S
Old 13th February 2013
  #62
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Matt, this power supply is under powering the board in the first place, it’s a known issue.
1. The board draws more watts than the power supply can give causing excessive heat and failure. Parts are changed for more robust parts.
2. The stock rectifiers are too lightweight to handle the heat and fail fast. They are changed for much more robust parts and heat sinking.
3. The phantom power voltage regulator resistor is also modified to handle more power as per the modified schematic and value is doubled.
4. The stock filter caps are supercaps and fail badly causing excessive hum and heat in the supply and eventual catastrophic failure. They are only 4700 uf each which is only good if they stay at that value, which they don’t. Non-supercaps that are double the value and voltage and lower ESR provide a better reservoir, eliminate ripple better, and eliminate the hum and extend the life of the supply.
5. PLUS you get a chance to get in there and tweak the voltage better.

All that heat and hum being eliminated, it is a more robust supply and with a better reservoir and less ripple current, it makes less noise, and doesn’t deplete the reservoir as easily as the underpowered supply may have. This would be heard as cleaner tighter bass and tighter low mids since those are the sounds which deplete the reservoir faster when they accumulate causing the failure. They are also a known problem with this board because of the supply’s stock deficiencies.
Old 13th February 2013
  #63
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Hi
What I was asking for was a measure of the amount of SIGNAL that appears at the output of the power supply. This is done by using an AC meter capacitively coupled to the power supply output pins and measure anything that is not 'DC' while the desk is idling with no signal and when there is audio going on.
I am not necessarily disputing some of the other claims but at the end of the day if there is no audio peturbation at the output of the power supply then some of the other claims are spurious to the exact topic.
I have just measured the output impedance of an old supply I threw together 25 years ago using similar regulators and the output impdance measures about 20 milliohms although this rises somewhat above about 2 KHz as there are no 'output' capacitors. It is certainly 'flat from 2KHz down to DC.
Matt S
Old 13th February 2013
  #64
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Even when taxed to the boiling point?
The power supply that comes stock was spec’d for duty when most mics to be used were dynamics, thus not taxing the supply’s phantom power or pushing faster active slew rates and wider dynamic ranges. When you load it up with a bunch of condenser mics and monitor returns, subgroups comped and maxed out, auxes all working and shortly you get a cooked supply.
Would that cause anomalies in that area?
Old 13th February 2013
  #65
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Hi
A mic taking phantom power would typically add an extra 'load' on the supply of 0.33 Watts, typically it would be rather less as I am assuming a thirsty mic.
If you shorted the phantom power (pins 2 and 3 on the XLRs) to ground then it would only be 0.67 Watts per input.
Whilst it would not be good for overall longevity of the supply, the regulator chips would be working properly at 70 or more Centigrade. The specification sheets say rather more but you then get into issues of burning operatives fingers and thermal cycling. The transformers are usually rated to around 90 Centigrade (as a 'withstanding' level, not suggested operating level) but capacitors as we all know will suffer from long term high temperature operation.
I have just been measuring some 800b input modules which I presume will be similar to other soundcraft units (similar number of chips) and the 'normal' no signal current draw is 29 milliamps which rises to 36 milliamps when driving a 600 Ohm load on the direct output, and 32 milliamps when driving a, more usual, 10K load. This was with the signal just short of clipping (+21dBu).

The reason I say that the signal will not appear at the power suppy is that for this possible 7 milliamps 'signal' current at the module amplifier stage, if you ignore the various supply rail decoupling capacitors, it would generate a 0.329 volt 'signal' on the IC supply rail pins (47 Ohm rail fuse resistors typical). If you then consider the attenuation of 47 Ohms to 20 milliohms this would give a 'signal' appearing on the output of the supply of 0.014 millivolts.
This is about equivalent of -94dB. Remember I suggested this is the case with no rail capacitors on each channel, so the real influence will be rather less.
Although some of my numbers may be inaccurate you have to consider the general validity as for a significant AUDIO signal to appear at the supply unit terminals, and to have amplifier circuits that were susceptable to this interference, the overal mixer would tend to simply be a massive 'mono' mix of all signals that are going on inside the desk which is clearly not the case. From this, it is taken that as there is no 'massive signal' going on at the power supply, therefore change in the filter caps (which are of course on the 'other side' of the regulators will have no significant effect on the audio.
The fact that if they are fitted as standard with 85 degree caps and normally run at 60 degrees or more then their life will be curtailed which is quite predictable. If you took the longevity to be double the life for each reduction of 10 Centigrade, a 2000 hour life would be around 8 to 10 thousand hours, around a year. Of course capacitors are not usually 'dead' after this lifetime rating but a percentage reduction from their original value.
Matt S
Old 13th February 2013
  #66
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hymenoptera's Avatar
 

the resistor R32 in my CPS-150 is cracked and sorta scortched looking. PSU works just fine, buzzes a lot, but everything on the board seemed to work when tested (except all the VU meter lamps were out).

I might consider replacing R32 with same but 1/2w [sic - see below] before setup and install this spring.

Great thread, thanks for the info, everyone!

edit: I meant 2 watt, thanks for the correction, Matt

Last edited by hymenoptera; 16th February 2013 at 05:57 PM.. Reason: brain fart
Old 13th February 2013
  #67
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Hi
As R32 (specified as 2K7) dissipates 0.85 Watts continually it must be at LEAST a 1 Watt rated part. Since the cost of resistors is so low compared to time wasted making the exchange I would use at least a 2 Watt part.
Personally I would have taken the 'bottom' end of this resistor to ground and then provided another resistor as a 'dropper' for the LED. This would reduce the risk of the phantom going 'high' if the LED fails or the 2 extra connections involved in the LED get broken for any reason (kicked faceplate for example). An alternative scheme would be a 2V7 zener diode in parallel with the LED such that if the LED fails it would only go half a volt or thereabouts more than the nominal 48. The specifications for microphones is generally 48 Volts with a 52 Volt maximum so this would be perfectly safe.
Matt S
Old 13th February 2013
  #68
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Hi
Not that anyone cares but with a module putting out +20dBu into 600 Ohm load the 'audio' measured at the power supply terminals is -76dBu 10Hz to 60KHz or more. Pretty much what I predicted earlier.
Matt S
Old 13th February 2013
  #69
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Matt, as I understand it, the reason that the rectifiers fail is because they are under rated.
The reason the filtercaps fail which is either at the same time as the rectifiers or later is, they’re worn out.
There isn’t enough draw at the under rated power supply for the rails to see audio at the power supply, but, because the board is known to draw more watts than the power supply is rated for at the rails would that account for anomalies in the mids and lows?
I’m not sure if you’re saying that’s the case or not, I’m just glad you’re posting at all.

I personally wasn’t speaking at any point about the audio level at the power supply specifically. i was only speaking about the draw of the board versus the supplies known ability/inability to supply enough power on demand and still staying hum free.
Old 13th February 2013
  #70
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Hi
There are a couple of separate themes going on with these things.
The supply in one respect is perfectly adequate in that it valiantly produces low impedance DC which will be unaffected by the ESR or whatever of the caps, transformer or rectifiers up to the point where 'ripple' is encroaching on the 'drop out' voltage of the regulators.
It would not really matter if you had a 1000 Amp lead acid battery supplying the regulator or a weedy little transformer/rect/cap arrangement that was at the point of exploding, the desk would 'see' the same source of power.
A separate issue is the reported 'death wish' aspect of the supply which it is claimed that they overheat, which may well be due to inappropriately rated capacitors and lack of heatsinking on the rectifiers.
The 'problem' with power supplies is mostly down to heat and the way it is disposed of. If you design a supply for say 5 Amps, it will have parts rated to achieve that, but if it is to cope with a wide range of mains voltages, lt will probably have to dissipate considerable waste heat when the mains is high. Any 5 Amp supply must be able to give more than this in the short term and so there is a tendency in this 'specmanship' world to overstate what it can sensibly produce. So a 5 Amp unit may be good for 7 Amps short term so you may label this as such.
Having measured current consumption with and without signal, the increase of around 7 milliamps per full driven output circuit is NOT a 'massive power drain' as typically for real world useable audio it will only be increasing by a couple of milliamps per output circuit, the remainder of the 'internal' circuits being largely 'constant current'.
Matt S
Old 13th February 2013
  #71
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memphisindie's Avatar
 

Matt,
You keep putting “massive power drain” in quotes as if someone stated that.
That is not the case.
The power supply was designed and spec’d, as stated by soundcraft’s own tech department, as, "underpowered for it’s application".
That is from Soundcraft’s tech department.
The revised schematic with the suggested upgraded parts is also from Soundcraft’s tech department.
Are you saying it works, or, are you stating why it doesn’t, though it’s a known problem even to Soundcraft’s tech department?
Every detail I’ve shared regarding the possible reasons why it may fail came from Soundcraft’s tech department, I’m not making it up myself.
And I’m not saying you are in any way wrong either.
I’d just like to get it clarified.
Old 15th February 2013
  #72
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alls i know is the thing started humming like a sum bitch a few weeks before the reftifiers crapped out. used it for one session after replacing the filter caps, rectifiers, and R32 so far so good the hum is gone. also, it did seem like the bass was tightened up, but i certainly won't attempt to quantify that perception.
Old 15th February 2013
  #73
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I get that, and I like Matt’s suggestions too, they seem like they would make the power even more stable and robust. He’s awfully smart at this stuff.
Old 16th February 2013
  #74
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hymenoptera's Avatar
 

Quote:
Originally Posted by Matt Syson View Post
Hi
As R32 (specified as 2K7) dissipates 0.85 Watts continually it must be at LEAST a 1 Watt rated part. Since the cost of resistors is so low compared to time wasted making the exchange I would use at least a 2 Watt part...
Matt S
right, I meant 2w, thanks for that
Old 17th February 2013
  #75
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Ike Zimbel's Avatar
 

Old 1st April 2013
  #76
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Band_Master,
Thanks for postin the link to Mouser.....I used it to order the upgrade/fix items.

I'm a bit of a novice, but I figure I'll either understand when I have the pieces in my hand & refer to your pic, or I'll axe more kweschuns.
and thanks to all the posters before.....this thread rox.
Old 5th July 2013
  #77
Gear Nut
I've just received a Soundcraft Delta DLX 24-4-2 with a loud, buzzing CPS150 power supply. Quite annoying.

Is this HDD15-5-A+G Condor / SL Power a good alternative to the Power One HDD-15-5-AG?

I'll be giving it straight to my tech to turn into a working supply.
p.s. I don't require phantom power.

Thank you.
Old 7th July 2013
  #78
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memphisindie's Avatar
 

Quote:
Originally Posted by jimelectric View Post
I've just received a Soundcraft Delta DLX 24-4-2 with a loud, buzzing CPS150 power supply. Quite annoying.

Is this HDD15-5-A+G Condor / SL Power a good alternative to the Power One HDD-15-5-AG?

I'll be giving it straight to my tech to turn into a working supply.
p.s. I don't require phantom power.

Thank you.
They are all 15 volt + & - 5 amp supplies, that’s 150 watts. No improvement.
NO.
They are all underpowered. You need 300 watt supplies capable of 17 ? 18 + & - volts if you want a supply that will last and provide enough power to clean up the bottom end. 8 amps.
Old 7th July 2013
  #79
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Quote:
Originally Posted by memphisindie View Post
...All that heat and hum being eliminated, it is a more robust supply and with a better reservoir and less ripple current, it makes less noise, and doesn’t deplete the reservoir as easily as the underpowered supply may have. This would be heard as cleaner tighter bass and tighter low mids since those are the sounds which deplete the reservoir faster when they accumulate causing the failure...
I question this. We technical types know that with a power amp driving a loudspeaker, a wimpy power supply can cause "sagging" when there's a lot of low frequency demand. This is because loudspeakers need lots of power to produce high SPL's at low frequencies. If a power amp is too small, bass problems are often the first thing you notice. (You have big cone excursions and large amounts of air to move when loud bass sounds are reproduced!)

However the line inputs of devices connected to consoles don't behave like loudspeakers, and power supply demand for preamps, line drivers, EQ's etc. in a console is not frequency dependent. (Actually one could argue that opamp circuits "work hardest" when amplifying the highest frequencies...though in the real world, I don't think this would ever show up as a increased current on the outputs of a console power supply.)

When a console power supply is pushed beyond its ability the first symptom is usually hum...often followed by sudden failure.

If someone can offer a good explanation to the contrary (especially one backed up by test results) I'd like hear it, but IMO this "weak bass" thing is just a myth that comes up from time to time on audio forums. I have serviced hundreds of consoles and console power supplies of every description over 35 years and never observed anything like this.
Old 7th July 2013
  #80
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Hi
Thank you David.
This 'you need a monster power supply to run a mixer' is complete nonsense and a few minutes pondering Ohms law would tell you why.
Any functioning power supply for a desk will have a low output impedance. Even a humble LM317 manages around 50 milliohms. (The power cable from supply to desk will probably have a greater impedance).
Now consider the amplifier circuits in a desk, usually fed with 10 Ohms or more per module.
At 'short circuit' load this could pull 1.5 Amps (quickly followed by smoke and flames).(you don't need massive current rating).
Your realistic load could be 600 Ohms if you are a traditionalist pulling a modest 25 milliamps.
Practically all 'AC' (signal) current is provided by the various capacitors on the power rails inside the mixer, DOWNWIND of the 10 Ohm 'rail resistors' so only a small fraction of this alternating signal appears on the 'PSU' side of the resistors and when considered as an attenuator you are in the region of 10 Ohms down to the milliohms of the supply itself.
Further reasoning says that IF the various audio circuits were so lousy that they were affected by fluctuations on their supply rails and it WAS due to some mythical failing of the power supply (which could be swapped for a different unit) THEN all output signals would be verging on a mammoth 'mono' mix of every signal in the desk (which clearly it isn't).
Diverting to the issue of power amplifiers, 'sagging' of the supply rails under heavy load does not normally cause alteration in gain in a competently designed amplifier as the negative feedback defines the gain pretty rigorously. VALVE amplifiers employing minimal or 'no' negative feedback WILL suffer alterations in gain however this is a long way from an mixer full of ICs.
Incidentally, although Power One or equivalent supplies may appear attractive, they do lack the 'tracking' facility in that if one rail fails the other will not shut down, a feature of most of Soundcrafts supplies.
Matt S

Last edited by Matt Syson; 7th July 2013 at 09:35 PM.. Reason: spelling
Old 7th July 2013
  #81
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Quote:
Originally Posted by David Kulka View Post
I question this. We technical types know that with a power amp driving a loudspeaker, a wimpy power supply can cause "sagging" when there's a lot of low frequency demand. This is because loudspeakers need lots of power to produce high SPL's at low frequencies. If a power amp is too small, bass problems are often the first thing you notice. (You have big cone excursions and large amounts of air to move when loud bass sounds are reproduced!)

However the line inputs of devices connected to consoles don't behave like loudspeakers, and power supply demand for preamps, line drivers, EQ's etc. in a console is not frequency dependent. (Actually one could argue that opamp circuits "work hardest" when amplifying the highest frequencies...though in the real world, I don't think this would ever show up as a increased current on the outputs of a console power supply.)

When a console power supply is pushed beyond its ability the first symptom is usually hum...often followed by sudden failure.

If someone can offer a good explanation to the contrary (especially one backed up by test results) I'd like hear it, but IMO this "weak bass" thing is just a myth that comes up from time to time on audio forums. I have serviced hundreds of consoles and console power supplies of every description over 35 years and never observed anything like this.
Soundcraft told me that’s what happens because the CPS 150 is underrated for the jobs it was put into service for, causing problems including foggy mids, mid bass, and low end.

Did you ever test for that specifically?

What we know:
He had a CPS 150.
He said it as humming. As per your post, you know that they don’t do when the filter caps are new and the rectifiers are robust enough and the rails are adjusted properly.
His was already humming.

He didn’t state that he was only using line inputs, only that he wasn’t using phantom power.

My job is primarily recording and mixing, I’d loved to have stayed there and never learned anything about tech, but, unfortunately for your time, I had to pop the hood.
This is what I’ve found regarding this subject.
In consoles, monitor amps, direct boxes, and preamps, some devices sound thin, some sound thick.
I asked an industry approved genius tech who modified my gear I knew and worked with what/why the difference was. It was the topology, slew rates up to a point make a difference. I guess “sag” would make it even more noticeable.
Time domain smearing is why people like transformer “sound”, possibly slower sounds better in the end to many. (this pans out with clients)
Problem is, when you’re mixing a dense mix and trying not to EQ much you get some buildup in the mid bass and bass which sounds muddy and foggy into the upper mids. I’m guessing that faster slewing devices sounding less midbass and bass dense overall will provide some relief or preventative measure up to a point. Those CPS 150 supplies work for a while but go bad pretty fast, rectifiers first then filtercaps and both make them hum before they go. Though they have some protection built in, sometimes, when they go they take the whole board with them. It did mine.
I did get a new supply once the board was done. During the process I did get in touch with the tech department at SC and they sent a revised schematic with explanation for the changes and a letter. I already had a new supply of the type I stated, so, my modified supply sat dormant. Then I made an equipment swap and had the supply taken in the swap. I hooked it up on an unmodified board like mine and it sounded noticeably better. It still had the same character to the sound but, it was tighter on the low end, no fog in the mids, and just as sparkly on top.

If what you’re arguing amounts to that providing a slightly overqualified supply with more robust construction is either going to fail or a bad idea, you can talk to the hand.

If you’re arguing that the company acknowledged underspec’d supply with too low value filtercaps and rectifiers which is definitely going to fail and possibly kill everything in it’s path is a good idea, you can talk to the hand.

If you’re arguing that a CPS 150 stock spec with underrated filtercaps and under rated rectifiers which burns out early isn’t causing sag when it can’t deliver the power it’s called to and instead delivers hum, heat, exploding supercaps and a small fire where the rectifiers once were is even a passable substitution, I dunno, I’m not sure what you’re promoting.

(flame suit is now ON, go ahead and burn me up)
Old 8th July 2013
  #82
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Hi
The supply rails on a soundcraft desk (or any other for that matter) don't 'sag', at least when measured AT THE SUPPLY. The supply in this respect will be fine.
The CPS150 may be 'under rated' for the job but this takes several forms for which audio quality is only secondary.
First is that they might get overly hot. This is a design statement and for longevity it is usual to have things running as cool as possible. If they intended these units to run for say 4 years before significant heat related issues then it probably makes it.
Rectifier failure, usually related to switch on surge current (or insufficient heat sinking causing them to fail).
Capacitor rating, as 105 degree types are now widely used it is possible to argue that these should be used. Again a design choice.
Matt S
Old 8th July 2013
  #83
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memphisindie, I feel that you're putting quite a lot of words in my mouth. I was only saying that an under-rated (or under-performing) console power supply won't cause frequency response problems.

Those Soundcraft power supplies are known to be failure prone, and many threads have been posted about them here. A few people have brought them to me for repair and I have been surprised by their marginal build quality...which is putting it kindly. I'm sure they can benefit from updates, and if Soundcraft recommends certain measures, they are probably worth doing.

But the person at Soundcraft who told you the CPS 150 is "underrated...causing problems including foggy mids, mid bass, and low end" did not know what he was talking about, and probably did not have a lot of technical knowledge or experience. This is not so shocking...consider all the misinformation and nonsense claims that have been dished out at Guitar Center. (Maybe he got the idea from an old Gearslutz thread. )
Old 9th July 2013
  #84
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Quote:
Originally Posted by Matt Syson View Post
Hi
The supply rails on a soundcraft desk (or any other for that matter) don't 'sag', at least when measured AT THE SUPPLY. The supply in this respect will be fine.
The CPS150 may be 'under rated' for the job but this takes several forms for which audio quality is only secondary.
First is that they might get overly hot. This is a design statement and for longevity it is usual to have things running as cool as possible. If they intended these units to run for say 4 years before significant heat related issues then it probably makes it.
Rectifier failure, usually related to switch on surge current (or insufficient heat sinking causing them to fail).
Capacitor rating, as 105 degree types are now widely used it is possible to argue that these should be used. Again a design choice.
Matt S
I agree that in this instance the audio quality is secondary…until it becomes nonexistent, which it will become.
I don’t know if the still make the CPS150, but, the units I’ve seen are older and have "50 volt 4700 uf 85 degree supercaps" as the main filter caps and though I believe they are on the bleeding edge of useful, the rectifiers, even with their 3 second powerup, will fail first.
They do run hot, the rectifiers always have burned traces,


Quote:
Originally Posted by David Kulka View Post
memphisindie, I feel that you're putting quite a lot of words in my mouth. I was only saying that an under-rated (or under-performing) console power supply won't cause frequency response problems.

Those Soundcraft power supplies are known to be failure prone, and many threads have been posted about them here. A few people have brought them to me for repair and I have been surprised by their marginal build quality...which is putting it kindly. I'm sure they can benefit from updates, and if Soundcraft recommends certain measures, they are probably worth doing.

But the person at Soundcraft who told you the CPS 150 is "underrated...causing problems including foggy mids, mid bass, and low end" did not know what he was talking about, and probably did not have a lot of technical knowledge or experience. This is not so shocking...consider all the misinformation and nonsense claims that have been dished out at Guitar Center. (Maybe he got the idea from an old Gearslutz thread. )
Well, it is semantics regarding what the person at soundcraft stated about that supply.
What he said was:
“The biggest improvement you can make to this console is to upgrade the power supply. It will affect the sound of the board, most people report better (cleaner) sounding mids and low end, a punchier output.
The board was designed when few people had many condenser mics (thus the phantom design).”

I use a LOT of condenser mics, they took much longer than the rated 3 second to power up with the CPS150.
I think if a supply can’t pull as much power as the board consistently draws when used hard, heats up during normal use almost committing hari-kari, it’s probably going to be a problem for the audio.
Old 10th July 2013
  #85
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Quote:
Originally Posted by memphisindie View Post
What he said was:
“The biggest improvement you can make to this console is to upgrade the power supply. It will affect the sound of the board, most people report better (cleaner) sounding mids and low end, a punchier output.
The board was designed when few people had many condenser mics (thus the phantom design).”

I use a LOT of condenser mics, they took much longer than the rated 3 second to power up with the CPS150.
According to this logic, if you use fewer condenser mics the board will have better mids and low end and a "punchier" output? Think about it.
Old 10th July 2013
  #86
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Quote:
Originally Posted by mjrippe View Post
According to this logic, if you use fewer condenser mics the board will have better mids and low end and a "punchier" output? Think about it.
There it is, invest in more SM57’s!

No, you have a false dilemma there, a logical fallacy.

Even with no condenser mics the PS is still underrated.
The statement about the phantom design speaks ONLY to the phantom power regulator resistor in parallel with a trim pot still being too low a value and wattage rating to dissipate heat efficiently then it fails.
Old 10th July 2013
  #87
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Sorry, the way it was phrased made it seem like you were connecting the two. Next I expected to hear that bypassing the filter caps with Wimas gave you better top end ;-)
Old 10th July 2013
  #88
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Hi
The 'issue' about phantom failing to come up in less than 3 seconds has no relevence to anything really. Certainly a darn sight quicker than 'Musos' waking up!
I suspect the supply rail itself will come up pretty quickly but there may actually be some relation to the time it takes the mics themselves to 'wake up' and don't forget you are putting a MASSIVE overload into the mic pre circuit, a 'thump' of about +37dB into an input set to anything between +15 and +60dB gain. The 'thump' is of course common mode so will force the input transistors either fully on or fully off for the duration until the input capacitors have charged.
Nothing remarkable here.
If all the supply rails reach their 'nominal' set voltage and remain there with no significant mains related ripple or noise, and the output impedance is correctly low (as it almost always will be) then the supply itself is NOT strictly FAULTY.
The fact it may run hot is a different matter which is now related to long term reliability and could be the material of endless discussion with the accountants claiming one end of the spectrum and engineer / designers with an eye for reliability heading into many decades at the other.
Users should of course take responsibility and ensure their supplies are presented with cool, clean dry air, so those that stack them with other hot gear or stuff them in a cupboard can only have themselves to blame for premature failures.
Matt S
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