Hi folks, I'm still insisting on using my recently purchased Crest CA-18, 1000 Wpc class H amp for driving the (sub) woofers in my large home system.
Fan noise is the issue, as discussed on other threads.
Looking for opinions of my proposed solution; simply wire the fans in series and connect to the fan driver of one channel.
I do not want to make any mods to the amp that are not reversible. The amp will only be driven hard on brief occasions. Both channels will be driven more or less equally, so my guess is that there should be no problem having fan speed governed by sensors of only one channel. Will there be consequences of having the fan driver for the other channel not seeing a load?
If the amp is driven hard for any longer period, and temps rise, wouldn't the fan speed control compensate (to some extent) for the reduced air speed from series connection of the fans?
Fan noise is the issue, as discussed on other threads.
Looking for opinions of my proposed solution; simply wire the fans in series and connect to the fan driver of one channel.
I do not want to make any mods to the amp that are not reversible. The amp will only be driven hard on brief occasions. Both channels will be driven more or less equally, so my guess is that there should be no problem having fan speed governed by sensors of only one channel. Will there be consequences of having the fan driver for the other channel not seeing a load?
If the amp is driven hard for any longer period, and temps rise, wouldn't the fan speed control compensate (to some extent) for the reduced air speed from series connection of the fans?
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The other responder seems to be trying to sell you an amp, instead of the one you have already.
At the 1.5 Vpp average I run my PA amp at, the fan doesn't run. It is a CS800s, and if the heat sink is cold the fan doesn't run. I'm a bit hearing damaged, a USAR vet, and I played symphonic bands, so I like my casual listening about 70-80 db anyway with peaks to 100 or more on percussion hits.
If your music is loud enough, you won't hear the fan.
You didn't post a schematic. I've been diy up DC motor fan control circuits for organ amps with a 2n7000 fet, a resistor, a 14000 ohm cold NTC resistor. NTC resistor on the heat sink, the fet switches at about 4 v, the supply is 24, so if the resistor is picked right, the fan switches on if the heat sink warms up a little. I use a hair dryer for test. These fans are DC fans out of PCAT power supplies, dead ones.
If your fan is AC driven, to leave it off you have to install a DC supply that you can attach to line neutral, to use a triac to switch on the fan with the fet and a resistor. The triac gate will trigger on DC, but the fet won't take AC. Suitable DC supplies are wall transformers available at most charity resale shops for $1.
Plain triac fan switch circuits require a much more powerful NTC sensor. Triac gates typically require 50ma or more to make the gate trip it on. Peavey used bimetal snap on switches to the triac gate for the AC fan control, but these are hard to buy in small quantities. The triac switches to neutral of course, with the AC to one lead on any time the power switch is on.
You can also put the power amp under the couch, like I did one, where the fans are inaudible. Requires a little longer leads.
At the 1.5 Vpp average I run my PA amp at, the fan doesn't run. It is a CS800s, and if the heat sink is cold the fan doesn't run. I'm a bit hearing damaged, a USAR vet, and I played symphonic bands, so I like my casual listening about 70-80 db anyway with peaks to 100 or more on percussion hits.
If your music is loud enough, you won't hear the fan.
You didn't post a schematic. I've been diy up DC motor fan control circuits for organ amps with a 2n7000 fet, a resistor, a 14000 ohm cold NTC resistor. NTC resistor on the heat sink, the fet switches at about 4 v, the supply is 24, so if the resistor is picked right, the fan switches on if the heat sink warms up a little. I use a hair dryer for test. These fans are DC fans out of PCAT power supplies, dead ones.
If your fan is AC driven, to leave it off you have to install a DC supply that you can attach to line neutral, to use a triac to switch on the fan with the fet and a resistor. The triac gate will trigger on DC, but the fet won't take AC. Suitable DC supplies are wall transformers available at most charity resale shops for $1.
Plain triac fan switch circuits require a much more powerful NTC sensor. Triac gates typically require 50ma or more to make the gate trip it on. Peavey used bimetal snap on switches to the triac gate for the AC fan control, but these are hard to buy in small quantities. The triac switches to neutral of course, with the AC to one lead on any time the power switch is on.
You can also put the power amp under the couch, like I did one, where the fans are inaudible. Requires a little longer leads.
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Lets play a "dangerous" game 🙂, you said it would only be driven hard for short periods! I suspect its probably over engineered for your situation. On the wild assumption it has thermal overload protection ( in case of fan failure for example) then simply disconnect the fan/s altogether!! possibly try to orientate it so natural convection works best and hopefully the thermal mass of the heatsinks will absorb the peaks in your demand such that the thermal overload protection never kicks in (it may be worth reading the manual etc to see if it claims to have some). ok ready for being shouted down now 🙂
Hi and thanks indianajo
, The fans are 24 V DC and there is a speed control for each of the two fans already. Sorry, should have mentioned this. The fan noise was definitely not a design criteria for an amp that delivers 1000 W per C into 8 ohms.
My goal is to design a system that can delivery 120 db + when required but I want sit in the listening area and not know that the system is on, if there is no signal. Thank you for your time, regarding the control suggestions, but I was hoping for a simple 'quick-fix' to tone down the existing fan system.
colossusfan; Your strategy appeals to my lazy side! I already have a manual switch for external fans on my Phase Linear 700, which will be replaced by the Crest CA-18.
I think I might just insert a switch in the fans lines and manually switch on the fans, when it's 'Pink Floyd' time! I did not occur to me that the amp might be just fine with no fans. I have some experimenting to do.
Thanks guys, Peter in Canada
, The fans are 24 V DC and there is a speed control for each of the two fans already. Sorry, should have mentioned this. The fan noise was definitely not a design criteria for an amp that delivers 1000 W per C into 8 ohms.
My goal is to design a system that can delivery 120 db + when required but I want sit in the listening area and not know that the system is on, if there is no signal. Thank you for your time, regarding the control suggestions, but I was hoping for a simple 'quick-fix' to tone down the existing fan system.
colossusfan; Your strategy appeals to my lazy side! I already have a manual switch for external fans on my Phase Linear 700, which will be replaced by the Crest CA-18.
I think I might just insert a switch in the fans lines and manually switch on the fans, when it's 'Pink Floyd' time! I did not occur to me that the amp might be just fine with no fans. I have some experimenting to do.
Thanks guys, Peter in Canada
I think you should use 50 w power amplifier.
But need the best quality.
Greater horn the power needed to smaller, not bigger. On the sensitivity of reference.
But need the best quality.
Greater horn the power needed to smaller, not bigger. On the sensitivity of reference.
Hi,
I'm surprised, that nobody recommended to simply change the fans to a low speed version. This will keep You on the safe side, and easy to fallback in case of selling the amplifier. The price of the new fans will be not a big issue, I guess.
Sajti
I'm surprised, that nobody recommended to simply change the fans to a low speed version. This will keep You on the safe side, and easy to fallback in case of selling the amplifier. The price of the new fans will be not a big issue, I guess.
Sajti
I'd look for seriously quiet fans. Then build a dedicated fan run circuit which initially kicks them into rotating at maybe a few volts below their operating voltage, once running the voltage can be reduced - a bit of experimentation will be required here.
I've got 12V fans running almost noislessly at 5V.
I've got 12V fans running almost noislessly at 5V.
You can also get fans with built in temperature sensor so they speed up as required. Look at computer quiet fans.
It would be good idea, however the Crest 8001 has it's own fan speed regulator.
Sajti
You have to mount the amp vertically in order to do this. This may or may not be an option, but works with many amplifiers. You'll need to remove the grills and filters to get as much convection as possible. With no convection at all (normal orientation and no fan) it will overheat. It may take hours but it will, just with normal idle bias.
I would opt for slowing the fans down. Way down. Possibly installing a different type. It takes only a VERY small amount of air flow for forced cooling to equal convection and that can be done silently. Remove the grills and filters here too as they add noise due to turbulence and you won't be pushing enough air to build dust bunnies.
Thanks so much folks;
I really thought it would be so clever to simply wire the fans in series. Is there any downside to this, that I am overlooking?
Topic for a different forum, but I have done this with other DC fans (for my fireplace heating system); Fans switched from parallel to series for a simple Hi/Lo control.
I would check to see that the fans are not running so slow as to risk stalling.
I do not want to 'drag out' the issue, but isn't that what HI-Fi is all about?
I appreciate the advice about 'no fans'. My Phase Linears operate fine with no fans, but the transformer and output transistors are outside of the chassis. I want the Crest in my rack, so vertical mounting is not an option for me, (makes sense thought)
I really thought it would be so clever to simply wire the fans in series. Is there any downside to this, that I am overlooking?
Topic for a different forum, but I have done this with other DC fans (for my fireplace heating system); Fans switched from parallel to series for a simple Hi/Lo control.
I would check to see that the fans are not running so slow as to risk stalling.
I do not want to 'drag out' the issue, but isn't that what HI-Fi is all about?
I appreciate the advice about 'no fans'. My Phase Linears operate fine with no fans, but the transformer and output transistors are outside of the chassis. I want the Crest in my rack, so vertical mounting is not an option for me, (makes sense thought)
That is not the greater risk.
It is the NOT starting risk.
And this is much worse if a high source impedance is used to control speed. eg use a resistor to create an operating voltage that gives an acceptable speed will result in a much lower voltage when trying to start that motor, due to high start up current. That is when it won't start.
Pass and probably others, have shown a start up circuit that gives the motor a kick and then reduces to the slower running current.
Yeah, putting both fans on one sensor assumes no-one will trip/yank on the speaker wire and short the output to ground. Of course, the one shorted would be the one without a sensor. Dogs, servicemen, yourself in the wee dark hours, might pull a speaker cord. I've done it (to a tube amp, no problem with those). With the temperature sensor, you have an hour or more to notice that the channel is silent and correct the problem. With that channel sensor disabled, you have five or ten minutes before output transistors melt, unless the amp has it's own speaker over current protection circuits.
If the fan noise is that objectionable, I'd vote for putting a power resistor in series with each to slow them down, leaving both the sensors working in series. If you use a powerPTCR with too low resistance cold and the right resistance hot, then the fan would be sure to start but then slow down as the PTCR heated up. You determine the right resistance by trying various power resistors to figure out what running resistance you want hot (at full slow speed).
I"m running 24 vdc PCAT fans with a 9 v wall transformer on my wimpy heat sink dynakit ST120 amp. The fans start every time, and shed enough heat that the idle current on one channel went to 240 ma for a ~year without damaging anything (blown idle sense transistor). I don't find this fan noise objectionable back in the corner behind the record storage tower.
Thanks Andrew, for pointing out the risk of using a resistor in the fan circuit. It did not occur to me that the lower starting resistance of the fans would cause a greater initial voltage drop across a series resistor. I can see how this could cause a starting issue.
By having the fans, in series, would this not keep the voltage supply always balanced between the 2 fans? (Always half)?
This is proving a sub-section of Murphy's Law; "If things seem simple, you have obviously overlooked something"...
So the series fans idea still does not sit well with you?
Thanks indianajo; Regarding the risk of speaker shorting, etc, I having been running two Phase Linears in this Tri-amped system, so I am used to 'living on the edge', I would share my wife before I would let someone else operate my sound system! (Amanda, this is a joke.) The Amp is a Crest CA-18, the owner's manual claims short circuit or high heat sink temp will open the speaker relay on the offending channel. Also, they claim that the fans initially rev up and then slowed to a speed governed by heat sink temperature. My thinking was; Both channels will be driven more or less equally, and when temperatures increase, the amps own fan control circuit will increase the fan speed. I realize that series connect will limit the ultimate cooling capacity, but the listening room is (only) 24' x 36', I just wanted 1000 wpc for the massive head-room.
By having the fans, in series, would this not keep the voltage supply always balanced between the 2 fans? (Always half)?
This is proving a sub-section of Murphy's Law; "If things seem simple, you have obviously overlooked something"...
So the series fans idea still does not sit well with you?
Thanks indianajo; Regarding the risk of speaker shorting, etc, I having been running two Phase Linears in this Tri-amped system, so I am used to 'living on the edge', I would share my wife before I would let someone else operate my sound system! (Amanda, this is a joke.) The Amp is a Crest CA-18, the owner's manual claims short circuit or high heat sink temp will open the speaker relay on the offending channel. Also, they claim that the fans initially rev up and then slowed to a speed governed by heat sink temperature. My thinking was; Both channels will be driven more or less equally, and when temperatures increase, the amps own fan control circuit will increase the fan speed. I realize that series connect will limit the ultimate cooling capacity, but the listening room is (only) 24' x 36', I just wanted 1000 wpc for the massive head-room.
Fans in series also tend to have startup problems. Maybe not so much when they are new, but as the bearings age they need more kick to start them. The supply voltage is only shared if both are running. I've put two 120VAC fans in series and had one stall and the other run.
Hi Peter this is indeed turning into a saga 🙂 I think you said the fans are 24Vdc, that means they are brushless motors and will absolutely hate starting in series as the motors wont kick synchronously. You say you dont want to modify the amp to much or irreversibly, but it already has a speed control ?
Well anyway providing each with its own series resistor would work if it was from a constant supply and the starting problem can be assisted by putting an electrolytic across the resistor to provide the initial kick. But all this wont work if its being fed by a variable voltage or god forbid a PWM signal from a built in fan controller.
As you cannot mount it suitably for natural convection you are gonna have to push some air through it somehow, as someone suggested a lower power fan or experiment with some series resistance till it wont start.
Of course the other alternative is to avoid listening to quiet music, I find that quite effective 🙂 eventually your deafness will also increase to the point that you wont be able to hear the fans or your wife complaining 🙂
Thanks again, colossusfan, with four 15 amp circuit breakers dedicated to my audio rack, and possibly having to run a 12 or 10 gauge line for the Crest, my signal to wife ratio should be pretty good.
On that note, I should start another thread, but since I have rattled all the experts;
Is there quick or simple way to measure S/N ratio. When My ear is beside the subwoofer, I can hear a minor 'hash'. This is not my general practice (I gave up smokin that stuff years ago), but the 40 year Phase Linear 700 with original PCB, is dead quiet.
I bought the Crest because it has specs that are in my opinion, very HI FI. ( 115 db S/N, .03% THD, damping factor 800 etc.
I have a scope, could I measure the P to P noise voltage, and would that mean anything to anyone?
On that note, I should start another thread, but since I have rattled all the experts;
Is there quick or simple way to measure S/N ratio. When My ear is beside the subwoofer, I can hear a minor 'hash'. This is not my general practice (I gave up smokin that stuff years ago), but the 40 year Phase Linear 700 with original PCB, is dead quiet.
I bought the Crest because it has specs that are in my opinion, very HI FI. ( 115 db S/N, .03% THD, damping factor 800 etc.
I have a scope, could I measure the P to P noise voltage, and would that mean anything to anyone?
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