I am using a 30-0-30ac tranny with just bridge rectifiers. Each rail is measurring +45 -45vdc. This seems to be the max voltage the chip will take. Speakers are 96db 8ohm. The heatsinks 3"x 4" just get a little warm.
Some posters have been scared to take the DC voltage above 35vdc per rail, but this seems to be o.k ?
Some posters have been scared to take the DC voltage above 35vdc per rail, but this seems to be o.k ?
Puffin said:
The datasheet (where you should always look first for answers to these questions) says +/-42V is the absolute max rating with an input signal. Anytime you are operating near or outside that range you are taking a risk, simple as that.
BWRX. When you say "risk", do you mean :-
a) Risk of blowing the thing up
b) Risk of operating the over-voltage mechanism (reduction in sound quality or shut-off to avoid damage ?)
c) Risk of damaging speakers
Just beacuse the thing only gets warm, that is no indication that things are o.k ?
Your help is appreciated.
a) Risk of blowing the thing up
b) Risk of operating the over-voltage mechanism (reduction in sound quality or shut-off to avoid damage ?)
c) Risk of damaging speakers
Just beacuse the thing only gets warm, that is no indication that things are o.k ?
Your help is appreciated.
Based on a quick glance at the data sheet, it looks like your saving grace is the 8ohm load... coupled with the possibility that you're dropping a couple of volts under load.
I'm curious, what is your tranny VA rating and what are you using for supply filtering?
7/10
I'm curious, what is your tranny VA rating and what are you using for supply filtering?
7/10
Again, just have a look at the datasheet.
From page 3:
Absolute Maximum Ratings (Notes 1, 2)
Supply Voltage |V+| + |V−| (No Signal) 94V
Supply Voltage |V+| + |V−| (Input Signal) 84V
Operating Ratings (Notes 1, 2)
Temperature Range
TMIN ≤ TA ≤ TMAX −20C ≤ TA ≤ +85C
Supply Voltage |V+| + |V−| 20V to 84V
Note: Operation is guaranteed up to 84V, however, distortion may be introduced from the SPiKe Protection Circuitry when operating above 70V if proper thermal considerations are not taken into account. Refer to the Thermal Considerations section for more information. (See SPiKe Protection Response)
From page 4:
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance.
From page 3:
Absolute Maximum Ratings (Notes 1, 2)
Supply Voltage |V+| + |V−| (No Signal) 94V
Supply Voltage |V+| + |V−| (Input Signal) 84V
Operating Ratings (Notes 1, 2)
Temperature Range
TMIN ≤ TA ≤ TMAX −20C ≤ TA ≤ +85C
Supply Voltage |V+| + |V−| 20V to 84V
Note: Operation is guaranteed up to 84V, however, distortion may be introduced from the SPiKe Protection Circuitry when operating above 70V if proper thermal considerations are not taken into account. Refer to the Thermal Considerations section for more information. (See SPiKe Protection Response)
From page 4:
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance.
seventenths. VA rating 160. Only supply filtering is the 1,000uf caps on the chip. I am trying to copy the original Gaincard.
BWRX. Thanks for that. It seems then that sound quality may suffer if voltage is too high. The heat sink seems to be sufficent as it only gets warm. I am concerned not to blow my speakers up!
BWRX. Thanks for that. It seems then that sound quality may suffer if voltage is too high. The heat sink seems to be sufficent as it only gets warm. I am concerned not to blow my speakers up!
If you want to be sure, you should have the supply voltage within the limits, otherwise only time will tell if it is going to work.
Rip Lm3875...
Perhaps a more durable solution would be to add a few turns to the primary of the tranny, so that will decrease the secondary voltages...
Disclaimer : in the case your skills in electrical engineering are appropriate !
Perhaps a more durable solution would be to add a few turns to the primary of the tranny, so that will decrease the secondary voltages...
Disclaimer : in the case your skills in electrical engineering are appropriate !
You can also ADD a winding and connect it in series but with the wrong "polarity". This requires a toroid transformer.
Thanks all for your input. Not knowing enough about these things I am just concerned that any over voltage could mean that if the chip reacts, blows up etc, that it will take my speakers with it ?!
If the chip runs farly cool and I cannot hear any protection circuits cutting in, can I assume that it is working within it's limits and not under any stress ?
If the chip runs farly cool and I cannot hear any protection circuits cutting in, can I assume that it is working within it's limits and not under any stress ?
I'd say chances are it will be fine. You aren't running hugely above spec and manufacturers do tend to quote conservative figures for things like that to cover themselves.
I wouldn't like to say that the chip isn't under stress however, any chip running close to or at its absolute max is under stress. It shouldn't be an immediate problem but if you want the chip to keep on running for years why not add some turns to the primary winding (or remove some from the secondaries). It wouldn't take long, is essentially free and might save you the headached of a broken chip or worse
I wouldn't like to say that the chip isn't under stress however, any chip running close to or at its absolute max is under stress. It shouldn't be an immediate problem but if you want the chip to keep on running for years why not add some turns to the primary winding (or remove some from the secondaries). It wouldn't take long, is essentially free and might save you the headached of a broken chip or worse
CRC pwr supply and drop a few volts. Smaller caps before the resistors, larger ones after.
With that sensitive a speaker I doubt you will draw much current anyway.
With that sensitive a speaker I doubt you will draw much current anyway.
am just concerned that any over voltage could mean that if the chip reacts, blows up etc, that it will take my speakers with it ?!
This is my main concern. No one has commented ?
This is my main concern. No one has commented ?
I have never stressed the IC and observed hwat may happen but take into account that bab things can happen. I f had expensive speakers I would never have an amp like yours. I would have settled for 35 to 40 V DC max.
Anything connected to the amp could potentially be damaged if the chip goes, particularly the speakers. That' just a given.
I like the sound so much I might just have to live dangerously ?!
2nd Thoughts.......I'll use lower rated tranny's that I can take off another project. I had hoped to be able to avoid doing that, but commonsense seems to dictate that it could be costly to be lazy.
2nd Thoughts.......I'll use lower rated tranny's that I can take off another project. I had hoped to be able to avoid doing that, but commonsense seems to dictate that it could be costly to be lazy.
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