I recently picked up a broken NAD C315BEE which just needs a fairly straightforward cap replacement. But as others have noted the standby power on this integrated amp is fairly outrageous at 20W. I'm trying to understand where this comes from.
The transformer has three secondaries. An 8VAC winding is rectified and regulated to 5V for the microcontroller circuit. This rail is always on but it is low power.
There is a 25VAC secondary winding which is rectified and then regulated to produce the +/-17V rails. This regulator is turned off by the microcontroller when in standby.
There is a 35VAC secondary winding which is rectified and filtered to produce the +/- 45V rails. These rails are ON even in standby and the power amp circuit output transistor bias is probably drawing the current.
However, the between the 25VAC bridge rectifier and the 35VAC bridge rectifier there are two light bulbs (!). Are these part of some power boost circuit? It looks like even in standby these bulbs have ~10VDC across them. Is this really the source of the standby power draw?
The transformer has three secondaries. An 8VAC winding is rectified and regulated to 5V for the microcontroller circuit. This rail is always on but it is low power.
There is a 25VAC secondary winding which is rectified and then regulated to produce the +/-17V rails. This regulator is turned off by the microcontroller when in standby.
There is a 35VAC secondary winding which is rectified and filtered to produce the +/- 45V rails. These rails are ON even in standby and the power amp circuit output transistor bias is probably drawing the current.
However, the between the 25VAC bridge rectifier and the 35VAC bridge rectifier there are two light bulbs (!). Are these part of some power boost circuit? It looks like even in standby these bulbs have ~10VDC across them. Is this really the source of the standby power draw?
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"Ballast Lamps " which I do know about in the tube radio world.
Crude but its cheap and works -low current -low resistance ,
high current- much higher resistance.
Not a "high tech" current limiter and not ideal for various reasons in a high quality audio amplifier .
Nobody has answered this so far but if anybody thinks its something else then say so ?
Obviously it depends on the specification of the lamps as to their "operating range " .
Crude but its cheap and works -low current -low resistance ,
high current- much higher resistance.
Not a "high tech" current limiter and not ideal for various reasons in a high quality audio amplifier .
Nobody has answered this so far but if anybody thinks its something else then say so ?
Obviously it depends on the specification of the lamps as to their "operating range " .
Some of the older NAD amps I've worked on used a DPDT switch to select which transformer secondary taps to use for generating the high current output power rail. The "4 OHM" switch setting used a slightly lower voltage than the "8 OHM" setting if I recall correctly. Maybe these bulbs were a cheap way to eliminate that switch and implement an "auto" selection mode.
The lamps are contained in metal cans bolted to the chassis. There is a sticker warning not to touch the cans until the power has been off for 5 minutes.
I've got the cover off and leaving it in standby. Something dissipating 20W should be pretty obvious but so far haven't found it.
Side note: the 10,000uF 50V filter caps on the +/-45V rail are totally gone, bloated, ready to pop!
The lamps are contained in metal cans bolted to the chassis. There is a sticker warning not to touch the cans until the power has been off for 5 minutes.
I've got the cover off and leaving it in standby. Something dissipating 20W should be pretty obvious but so far haven't found it.
Side note: the 10,000uF 50V filter caps on the +/-45V rail are totally gone, bloated, ready to pop!
It might be 20W apparent power, not real power. So you won't necessarily find power being dissipated, but
as I understand it you are normally charged for apparant power. Transformers under no output load will be
quite reactive and could easily account for this.
as I understand it you are normally charged for apparant power. Transformers under no output load will be
quite reactive and could easily account for this.
Drawing the transformer center tap secondary winding another way and showing the dual bridge rectifiers connected via lamps. Even if no current is drawn by the rest of the amplifier from the +V/-V rails, these two lamps would have ~10VDC across them all the time. In this amp the transformer is energized even in standby.
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It seems that 20W in standby is considered normal for this amplifier.
The simple answer is switch it off at the wall, but if you wanted to be more adventurous, from a cursory glance at the service manual, the standby circuit only requires +5vdc.
As such you could possibly use a small transformer or switch mode supply for the +5vdc supply, and tap the "standby" line with a small driver which turns on a 5v relay to energise the main transformer.
As it stands it seems to energise the +-17V rails by turning on Q306. It may be better again to add some kind of delay circuit to turn these rails on after the mains transformer has had time to stabilise.
The same standby line appears to be used by the protection circuit.
There is of course a chance that something in the protection circuit will not like this scheme and cause it to go into protection, or some other strangeness.
Be easy enough to test by isolating the 5v line and powering it externally, with the main transformer off, and see that the orange LED comes on, then measure the standby line. Turn power on from the standby pushbutton and observe the standby line to get an idea of what's needed (probably just a transistor to drive a relay). Then power up the main transformer and see if it performs as expected.
The simple answer is switch it off at the wall, but if you wanted to be more adventurous, from a cursory glance at the service manual, the standby circuit only requires +5vdc.
As such you could possibly use a small transformer or switch mode supply for the +5vdc supply, and tap the "standby" line with a small driver which turns on a 5v relay to energise the main transformer.
As it stands it seems to energise the +-17V rails by turning on Q306. It may be better again to add some kind of delay circuit to turn these rails on after the mains transformer has had time to stabilise.
The same standby line appears to be used by the protection circuit.
There is of course a chance that something in the protection circuit will not like this scheme and cause it to go into protection, or some other strangeness.
Be easy enough to test by isolating the 5v line and powering it externally, with the main transformer off, and see that the orange LED comes on, then measure the standby line. Turn power on from the standby pushbutton and observe the standby line to get an idea of what's needed (probably just a transistor to drive a relay). Then power up the main transformer and see if it performs as expected.
Yes, the 20W in standby is real power and is normal for this amplifier. That's a bit obscene. I think this model was on the market for a few years until some green directive on standby power kicked in and it was redesigned as the C316BEE.
The C316BEE redesigned amplifier uses a scheme similar to what you describe to get the standby power down. The 5V rail is generated by a small transformer that is always on. A small relay kills the power to the main transformer primary when in standby mode. It was kind of kludged in and something similar could be done with the C315BEE too.
You're right, there is probably some interplay between Standby going low and the protection circuit releasing. When I get the replacement 10,000uF filter caps installed I'll poke around and determine how picky that microcontroller software is about startup sequencing. Making a little board with a transformer and small solid state relay would be fun.
The C316BEE redesigned amplifier uses a scheme similar to what you describe to get the standby power down. The 5V rail is generated by a small transformer that is always on. A small relay kills the power to the main transformer primary when in standby mode. It was kind of kludged in and something similar could be done with the C315BEE too.
You're right, there is probably some interplay between Standby going low and the protection circuit releasing. When I get the replacement 10,000uF filter caps installed I'll poke around and determine how picky that microcontroller software is about startup sequencing. Making a little board with a transformer and small solid state relay would be fun.
In the case the existing microcontroller is "picky" you could always spin up your own standby circuit (a microcontroller seems overkill but could actually be the cheapest and easiest way these days) to intercept the existing standby switch and sequence the main power relay some time before triggering the "standby" switch input on the built in controller... standbyception
FWIW, these NAD amps did come with remote control and also interconnects to other NAD equipment.
So yea, the 20W (in my case of a C325BEE it's 13W measured) is for this remote control + interconnect capability.
So yea, the 20W (in my case of a C325BEE it's 13W measured) is for this remote control + interconnect capability.
Ubergeeknz's suggestion of intercepting the standby signal and using that to energize the main power before generating the "fake" button press is a neat idea for getting the standby power down, but it does prevent the remote from waking up the unit.
The two signals in question are STANDBY and PROTECTION. The microcontroller monitors the button and controls STANDBY, which when low turns on the +/-17V rails. The micro monitors the PROTECTION signal and uses that to control the red/green LED on the front panel.
The protection circuit appears to be all hardware, no assistance from the micro, and monitors the temperature, power amp DC offset, and possibly the current flowing through the power amp output transistors. If everything is OK then PROTECTION is pulled low and the output relay is energized engaging the speakers. The protection circuit appears to be heavily dampened to reduce glitching and chatter; normally when coming out of standby the power LED is red for a good 2 seconds while the protection circuit is making up its mind.
I think it will probably be OK to install a small power supply to keep the +5V rail on all the time and use (inverted) STANDBY to control the main power through an SSR or relay.
The two signals in question are STANDBY and PROTECTION. The microcontroller monitors the button and controls STANDBY, which when low turns on the +/-17V rails. The micro monitors the PROTECTION signal and uses that to control the red/green LED on the front panel.
The protection circuit appears to be all hardware, no assistance from the micro, and monitors the temperature, power amp DC offset, and possibly the current flowing through the power amp output transistors. If everything is OK then PROTECTION is pulled low and the output relay is energized engaging the speakers. The protection circuit appears to be heavily dampened to reduce glitching and chatter; normally when coming out of standby the power LED is red for a good 2 seconds while the protection circuit is making up its mind.
I think it will probably be OK to install a small power supply to keep the +5V rail on all the time and use (inverted) STANDBY to control the main power through an SSR or relay.
Missed the remote control bit. Anyway if they made this mod on the C316BEE then it will probably work anyway, worth a shot
The "Power Envelope" 12V lamps wired across the rectifiers, are much the same in NAD 316BEE as they are in NAD 315BEE. I don't think that's the difference. It's more likely that power to the remote control circuits is now derived from a small 5V standby transformer, T61 (in AH and C variations of 316BEE), as is normal for many appliances. Then mains power to the audio power supplies is switched on via a relay under remote and front panel control.
However, the CCC variation of 316BEE doesn't appear to be much different to 315BEE. I think that means you can' t be certain what you have without checking the compliance label or at least inspecting what's inside, if you know what to look for.
However, the CCC variation of 316BEE doesn't appear to be much different to 315BEE. I think that means you can' t be certain what you have without checking the compliance label or at least inspecting what's inside, if you know what to look for.
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Those two light bulbs in the power supply are what NAD refers to as "PowerDrive-S" technology. In standby mode there is some current flowing through the bulbs, but it's not significant.
Most of the power in standby is consumed because the +45V and -45V rails are ON and bias current is flowing through the output transistors. So there's a warm heat sink right next to two big no-name 10,000uF 50V caps which are always under power. No suprise these units often show up on the used market "AS IS" with two bulging leaking filter caps.
I've got a solid state relay I'll be using to control the AC to the main transformer. This relay will be controlled by the microcontroller pin 15 (high when ON). I'll be installing a small 6.3VAC transformer which will be always on to provide the +5VDC for the microcontroller.
I also noticed that the C316BEE fixed these problems in the same way as I described. Except for the C316BEE CCC variant, which has the same power standby issue as the C315BEE. Why would NAD keep that inefficient design around? Are there customers using it as a feeble space heater in standby mode?
Most of the power in standby is consumed because the +45V and -45V rails are ON and bias current is flowing through the output transistors. So there's a warm heat sink right next to two big no-name 10,000uF 50V caps which are always under power. No suprise these units often show up on the used market "AS IS" with two bulging leaking filter caps.
I've got a solid state relay I'll be using to control the AC to the main transformer. This relay will be controlled by the microcontroller pin 15 (high when ON). I'll be installing a small 6.3VAC transformer which will be always on to provide the +5VDC for the microcontroller.
I also noticed that the C316BEE fixed these problems in the same way as I described. Except for the C316BEE CCC variant, which has the same power standby issue as the C315BEE. Why would NAD keep that inefficient design around? Are there customers using it as a feeble space heater in standby mode?
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"Why would NAD keep that inefficient design around? Are there customers using it as a feeble space heater in standby mode?"
A couple of bucks lower BOM
A couple of bucks lower BOM
No. Think about the rectifiers. They can't both pass current. The only flow is the idle of the power stage. (Which may indeed approach 20 real Watts.)
