DIY Purifi Amp builds

[TimoJ]

When my EVAL1 is powered on, there's a quiet "click" or "snap" sound coming from speakers right before the amp starts to play. (I'm not talking about the relay of the power supply).
AC power is switched fully on/off, I'm not using standby to power off. I have AmpOn and Fatal wires connected. I haven't yet tested if AmpOn is causing this and if the same happens also with the AmpOn wire disconnected and using just backpanel switch. Or is this a normal "feature"?

 

[mocenigo]

When my EVAL1 is powered on, there's a quiet "click" or "snap" sound coming from speakers right before the amp starts to play. (I'm not talking about the relay of the power supply).
AC power is switched fully on/off, I'm not using standby to power off. I have AmpOn and Fatal wires connected. I haven't yet tested if AmpOn is causing this and if the same happens also with the AmpOn wire disconnected and using just backpanel switch. Or is this a normal "feature"?

A quiet click is absolutely normal. This happens because the amp has some DC at the output - in the order of a few mV, which is ridiculously low, but audible if your speakers are sufficiently sensitive (I got the impression that Bruno Putzeys listens on bricks, from what he writes).

Also a soft sound at power down is normal, which can sound like an very very short “whoosh”, because when the supply on the gate driver sinks the amp starts doing this sound and that supply will probably lower a bit before the undervoltage protection kicks in and shuts outputs off.

 

[JimB]

A quiet click is absolutely normal. This happens because the amp has some DC at the output - in the order of a few mV, which is ridiculously low, but audible if your speakers are sufficiently sensitive (I got the impression that Bruno Putzeys listens on bricks, from what he writes).

Also a soft sound at power down is normal, which can sound like an very very short “whoosh”, because when the supply on the gate driver sinks the amp starts doing this sound and that supply will probably lower a bit before the undervoltage protection kicks in and shuts outputs off.

Yes, and it should not be a problem, normally.
https://www.audiosciencereview.com/...y-purifi-amp-builds.10478/page-25#post-336085

@TimoJ, you can check the DC offset level of your channels if you are concerned (a DC voltmeter reading on the output) when you turn it on, with no music playing.

 

[JimB]

... However, I wired the ERROR output of EVAL1 to the DC ERROR input

Would you like to SHOW your connection details for this? It is hidden in the (otherwise very nice) photos.

 

[TimoJ]

See if you can increase the signal to noise ratio of the preceding stage

I switched preceding stage from MiniDSP DDRC-88A to Monoprice HTP-1 and enabled EVAL1's buffer again: very little noise, 2-3 inches from the tweeter I can hear only quiet hissing. Major difference to the MiniDSP unit, with buffer enabled I heard it's noise 3-4 feet from the speakers...

 

[JimM]

I connected /fatal J3-3 to the J4 IDC breakout SMPS DC Error pin-10, seems to work ok. I also played around with buffer, no buffer in EVAL1 and DAC gain, went back to no buffer and 0 db on dac gain, will just have to watch volume level when switching sources. I could tell a difference when the EVAL1 buffer was in and preferred the no buffer the presentation was just clearer.
JimM

 

[JimB]

... I also played around with buffer, no buffer in EVAL1 and DAC gain, went back to no buffer ... I could tell a difference when the EVAL1 buffer was in and preferred the no buffer the presentation was just clearer.
JimM

With the buffer active, could you detect any noise from your speakers?

 

[JimM]

No, but these speakers are a 3 way dynamic with around 86db sensitivity. And the current configuration is the maximum gain from the DAC and no buffer from the EVAL1. With the EVAL1 buffer in and -10db from the DAC the relative over all gain is about the same level as the above configuration. The third configuration was EVAL1 with buffer in and DAC -20 db but there was just not enough gain in all cases. In every configuration I have played with, this amp is one of the quietest I have. My other speakers are maggies 1.7 with around 84 db sensitivity which are even more immune to noise. The only time I have noticed any hiss or noise is from my phono- preamp which are tubes and then only with MC, with transformer step up and even then you have to stick your head in the speaker and have amp way above normal listening levels. But I live in a remote area with good AC power and no industry to pollute the AC so I normally do not have problems with ground loops or other nastiest that I have had in large cities as in Dallas, TX. In the past I have owned horns with around 90 to 100db sensitivity both multi way and single driver and have never had a noise problem to speak of.
JimM

 

[mocenigo]

No, but these speakers are a 3 way dynamic with around 86db sensitivity.

Well, with 95Db speakers the amp noise (inputs connected to an off source, or inputs shorted) is barely audible in the immediate vicinity of my horns - and no noise from midwoofer and woofer at all. With 86Db speakers I would be extremely surprised if the Purifi had any background hiss at all, no matter how low (same for a NC400 or a good NC500 build).

 

[wineds]

Almost finished my build. Only issue is 12v trigger doesn't work. Actually my trigger from the dac08 pro is 5v. So I have ordered a Darlington based optocoupler which should fix that.

 

[hyperknot]

Almost finished my build. Only issue is 12v trigger doesn't work. Actually my trigger from the dac08 pro is 5v. So I have ordered a Darlington based optocoupler which should fix that.

What is that small box for?

 

[wineds]

What is that small box for?

It's a 12v power supply for standby and 12v trigger. Once I have verified everything is working I can post a full schematic if there is interest.

 

[al2002]

It's a 12v power supply for standby and 12v trigger. Once I have verified everything is working I can post a full schematic if there is interest.

Yes, please!

 

[hyperknot]

Sorry for the basic question but I see that everyone puts a lot of effort into these 12V trigger solution. Why is it needed?

I mean what would happen if I just:
- Use a mains switch to turn the amp on and off? Would it make any kind of click/pop?
- Leave the amp always on, 24/7? I've read it has quite a low idle consumption.

 

[JimM]

Turning the amp on/off with main switch is fine, there should be no pop on or off. Also in my opinion leaving it on all the time is also acceptable except when you will be gone for extended period of time. In the past and even now I have a phono peramp that is left on all the time, keeping voltage to the tube filaments. The reason I incorporated the 12v remote and front panel switch was a exercise to see how easy it was to do (refer to post 428) for a schematic for a simple opto interface. You should be able to use the +5vdc remote signal to trigger the opto circuit to turn the amp on. I leave my DAC and AMP on a lot of the time from morning to night as it takes about 30 minutes for every thing to get warmed up.
JimM

 

[JimM]

The above comments should have included, YOU MUST have proper fuses in AC line connection in case of a fault condition within the amp
JimM.

 

[ChrisPa]

Sorry for the basic question but I see that everyone puts a lot of effort into these 12V trigger solution. Why is it needed?

I mean what would happen if I just:
- Use a mains switch to turn the amp on and off? Would it make any kind of click/pop?
- Leave the amp always on, 24/7? I've read it has quite a low idle consumption.

Nothing untoward will happen

My nc400 mono blocks have been powered up for several years

 

[JimB]

Sorry for the basic question but I see that everyone puts a lot of effort into these 12V trigger solution. Why is it needed?

I mean what would happen if I just:
- Use a mains switch to turn the amp on and off? Would it make any kind of click/pop?
- Leave the amp always on, 24/7? I've read it has quite a low idle consumption.

I prefer not to have my equipment on all the time, AND to have the convenience of having it all go on, and off, together. An established method for this is the 12V trigger system, where one can switch a primary component on/off, and all other connected components will do likewise. There are external products one can buy to provide this functionality in case a component does not incorporate it. A couple examples have been given in earlier posts:

DLI (120VAC):
https://dlidirect.com/products/iot-power-relay

Audiophonics (240VAC):
https://www.audiophonics.fr/en/powe...v-230v-slave-power-supply-device-p-10661.html

 

[Count Arthur]

Some electronic components, capacitors in particular, have a finite life span, albeit a fairly long one. I prefer to switch my stuff off.

 

[mocenigo]

Some electronic components, capacitors in particular, have a finite life span, albeit a fairly long one. I prefer to switch my stuff off.

There may be reasons for which a specific audio component sounds better after it has been on for some time (it can be minutes, one hour, one day, whatever) and it may have to do with various factors, esp with the capacitors forming and reaching full performance (both have been measured) and thermal reasons. In my opinion these are badly designed components if they are build like that today, considering what today's technology can offer. The Soekris DAC1541 and my Purifi/Neurochrome amp build do not suffer from that. A slight hardness during the first minute or so, maybe 10 minutes after a long pause (for instance if I am away for more than 3 days and the system was switched off in the meantime). Whereas the NC500 build needed some burn in (subjectively at least, maybe it was me that had to adjust to the distortion free sound), the Purifi did not need that as well. SO I switch stuff off before going to bed.