March Audio P451 Purifi 1ET400A Mono Blocks

[Casey Leedom]

Awesome about the 12V Triggers on the P451s @March Audio!

Casey

 

[March Audio]

Damn..... I wish I would've known that before I bought my P451's!

Oh well, who cares about 12W idle when you have these babies in your system!

Hi @Sparky

If you need trigger functionality we can swap out the control board. An additional hole will need to be machined in the case for the input socket.

 

[Sparky]

Hi @Sparky

If you need trigger functionality we can swap out the control board. An additional hole will need to be machined in the case for the input socket.

Is this something I could do myself or is it a RTB?
In either case, what would be the cost?
Also, would the trigger input override the power button on the front?
I use REW quite a bit and shut the monoblocks down while testing subs you see so I need that functionality to still be available.

Mike.

 

[ironhorse128]

@March Audio

Thanks for your reply.

I was not aware that there is a standby feature with the P451. That would be very helpful. How does it work? Just kicks in after 30 minutes of no signal? Is the standby feature part of the purifi board or did March Audio implement it?

12v trigger is definitely a highly appreciated feature. But automatic standby is also nice to have

 

[March Audio]

@March Audio

Thanks for your reply.

I was not aware that there is a standby feature with the P451. That would be very helpful. How does it work? Just kicks in after 30 minutes of no signal? Is the standby feature part of the purifi board or did March Audio implement it?

12v trigger is definitely a highly appreciated feature. But automatic standby is also nice to have

It's not automatic . It's operated by the piezo front panel touch switch. It puts the main psu into low power standby mode.

We use a piezo switch for a couple of reasons. It has no mechanical moving parts. Long term its more reliable. I have had normal push button switches fail on other amps. Also for aesthetics and operational "feel".

I'm not keen on signal operated devices. Don't want anything else in the signal path and concerns about accurate operation, ie being on and off when genuinely intended.

 

[March Audio]

Is this something I could do myself or is it a RTB?
In either case, what would be the cost?
Also, would the trigger input override the power button on the front?
I use REW quite a bit and shut the monoblocks down while testing subs you see so I need that functionality to still be available.

Mike.

Hi Mike

It's not complex to swap the control board but I would be more comfortable if it was returned for us to change. I will PM.

 

[AudioSceptic]

Damn..... I wish I would've known that before I bought my P451's!

Oh well, who cares about 12W idle when you have these babies in your system!

Are they situated such that you can't easily switch them off, or disconnect them from the mains? If so, have you considered using a smart plug like the Meross <https://amzn.to/3bn5lLb>? I have the version with built-in energy monitor so I can not only switch things on/off on a schedule (or on demand from phone app or using Alexa), but also see how many watts are being used.

[Edit] March Audio, would there be a problem with just switching off the mains, as opposed to a "controlled" power off/on?

 

[Andy Chapman]

The amplifier is fully balanced input. Balanced inputs are fully compatible with single ended RCA, however for best performance you have to follow correct implementation of the conversion from one to the other.

The correct way to do this is not to have RCA sockets on the amp itself. You should only terminate the balanced screen at the far (source) end like this:

In balanced connections the shield is a 3rd separate wire from the signal conductors. So if wired as above those noise currents don't flow in the signal conductors, even if the source is single ended RCA, and you maintain most of the benefit of balanced connections. If you put the RCA socket on the amp the noise currents still flow in the cable shield.

I must compliment you on a nice Class D implementation. Thanks also for the reasoning on driving a balanced input from an RCA unbalanced output.

I am however, a little worried by the way the 4-pin connector is wired at the circular amplifier on your diagram.

With balanced signals, it is only the voltage difference between the hot and cold wires (XLR pins 2,3) that are of interest to an amplifier's input. The screen is only there to provide RF screening.

Your diagram shows the screen of the internal balanced signal cable rightly grounded to chassis at the XLR connector end. However, the screen is then also connected via the top left pin of the 4-pin amplifier connector to ground via the top right pin of the connector.

Also, the 1ET400A module is grounded to chassis by its heat-sink fixing screws.

Thus there seem to be rather too many chassis connections for optimum noise performance here.

I suggest that the 4-pin connector only really needs two pins to carry the hot and cold signals. The screen and ground connections are unnecessary and actually undesirable.

 

[March Audio]

I must compliment you on a nice Class D implementation. Thanks also for the reasoning on driving a balanced input from an RCA unbalanced output.

I am however, a little worried by the way the 4-pin connector is wired at the circular amplifier on your diagram.

With balanced signals, it is only the voltage difference between the hot and cold wires (XLR pins 2,3) that are of interest to an amplifier's input. The screen is only there to provide RF screening.

Your diagram shows the screen of the internal balanced signal cable rightly grounded to chassis at the XLR connector end. However, the screen is then also connected via the top left pin of the 4-pin amplifier connector to ground via the top right pin of the connector.

Also, the 1ET400A module is grounded to chassis by its heat-sink fixing screws.

Thus there seem to be rather too many chassis connections for optimum noise performance here.

I suggest that the 4-pin connector only really needs two pins to carry the hot and cold signals. The screen and ground connections are unnecessary and actually undesirable.

Hi @Andy Chapman

Thanks for the kind words.

The diagram is only a generic one I use to demonstrate the idea of using RCA with balanced inputs. For reference it's taken directly from Hypex data sheets. In other words from Bruno Putzeys the designer of those modules and the Purifi module.

In the P451, and all our other amps, the xlr socket has sharp pins that penetrate into the chassis connecting the external cable screen (pin1) to the chassis as close as possible to entry. This is what the diagram denotes. BTW the 4th wire on that square connector is actually specific to the Hypex nc400 and is used to turn the module on.

The screen from our buffer amp board connects to the input RF filter board on the back of the xlr socket however it does not connect to pin1. It connects to a link wire which connects to the chassis at a different point. This is correct implementation.

Also note our buffer amp is fully differential.

This post shows measurements of our implementation compared to the Purifi reference board. Whilst it is ultimatly limited by the measurement system it shows the P451 to actually have lower noise at low frequencies than the Purifi. No sign of 50Hz or harmonics of mains noise.

https://www.audiosciencereview.com/...-purifi-1et400a-mono-blocks.10138/post-278712


Hope that helps

 

[March Audio]

Are they situated such that you can't easily switch them off, or disconnect them from the mains? If so, have you considered using a smart plug like the Meross <https://amzn.to/3bn5lLb>? I have the version with built-in energy monitor so I can not only switch things on/off on a schedule (or on demand from phone app or using Alexa), but also see how many watts are being used.

[Edit] March Audio, would there be a problem with just switching off the mains, as opposed to a "controlled" power off/on?

Hi

Only problem is it wouldn't work . The amps at mains power application default to standby.

 

[AudioSceptic]

Hi

Only problem is it wouldn't work . The amps at mains power application default to standby.

Thanks, but I thought that Sparky just wanted to avoid leaving them on (in standby) when not in use, and wasn't bothered about using the touch switch.

 

[Sparky]

Thanks, but I thought that Sparky just wanted to avoid leaving them on (in standby) when not in use, and wasn't bothered about using the touch switch.

Yeah, it would be a nice feature to run a trigger to my preamp but it's not the end of the world.
I generally leave them on to be honest.

I'll probably start switching them off manually as Alan suggests as I don't like the sound of reducing the life expectancy!

 

[March Audio]

Yeah, it would be a nice feature to run a trigger to my preamp but it's not the end of the world.
I generally leave them on to be honest.

I'll probably start switching them off manually as Alan suggests as I don't like the sound of reducing the life expectancy!

@Sparky It's difficult to predict life of caps, it depends on several factors, temperature, ripple current etc. It certainly doesn't mean they will life any time soon if permanantly left on. Even then it doesn't mean the device stops working. Life is typically considered a 20% reduction in value, not total failure, but other effects include increased esr so performance may get affected. This is the case for any electrolytic cap, in any bit of equipment, although some are higher quality than others

It's really a case of the potential of seeing negative effects after maybe 6 to 8 years or 16+ years.

So the effect is unpredictable, but there is a simple precaution which will also save you a small amount of beer money. The difference between 12 watts fully on and 0.2 watts in standby.

 

[March Audio]

Thanks, but I thought that Sparky just wanted to avoid leaving them on (in standby) when not in use, and wasn't bothered about using the touch switch.

It's absolutely fine to be left in the standby state. I would only be concerned about permanantly "fully on"

 

[ironhorse128]

@March Audio
Thanks for the clarifications on standby and power buttons. Your efforts around here in the forum are much appreciated.

 

[Sparky]

@March Audio

Hi Alan. Is it ok to use "smart plugs" to control the power on/off state of these monoblocks?
I have bought a few for around the house including to control my audio set up and I am basically leaving the monoblocks powered on.
They obviously lose power when the "smart plug" cuts the power and, when I reactivate the plugs, the monoblocks return to their original powered on state.

Basically, my question is, can the monoblock circuitry be harmed by a sudden loss in power like this or, a sudden re-energisation back to their powered on state.

Mike.

 

[March Audio]

@March Audio

Hi Alan. Is it ok to use "smart plugs" to control the power on/off state of these monoblocks?
I have bought a few for around the house including to control my audio set up and I am basically leaving the monoblocks powered on.
They obviously lose power when the "smart plug" cuts the power and, when I reactivate the plugs, the monoblocks return to their original powered on state.

Basically, my question is, can the monoblock circuitry be harmed by a sudden loss in power like this or, a sudden re-energisation back to their powered on state.

Mike.

Hi Mike

No its not a problem, won't cause any harm.

BTW the newer versions of the control board default to off.

 

[TimoJ]

BTW the newer versions of the control board default to off.

Is there a jumper to change this default to on? How do you handle trigger voltage vs. the front panel switch, can you still power off the amp with the touch switch even when 12V trigger voltage is present?

 

[Sparky]

Hi Mike

No its not a problem, won't cause any harm.

BTW the newer versions of the control board default to off.

Thanks a lot bud. Really appreciate that. I actually prefer that they stay in the last state as it suits my situation better.

 

[March Audio]

Is there a jumper to change this default to on? How do you handle trigger voltage vs. the front panel switch, can you still power off the amp with the touch switch even when 12V trigger voltage is present?

No its fixed. Trigger on state will over ride the front panel switch.