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DIY Purifi Amp builds

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JimB

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Thanks very much for your reply Jim. That clears up the wiring. I’ll be using the Neutrik SpeakON at the Purifi end (and only for that amp), and standard pair of banana plugs at each speaker end.

Just curious why the 4-pole version per channel of the Purifi modules seems to be the more popular option here? Is there a slight measured advantage (lower impedance?) over the 2 pole, or is it slightly more mechanically reliable?

I’m using a Quad Artera Play+, which is a combination dac/cd/pre-amp, bought to cut down on the clutter. It can output up to 8Vrms via it’s balanced outputs. I assume therefore it might be advantageous to bypass the input stage on the Purifi for a tad more transparency, by moving the pre-gain jumpers as detailed in the manual?
The speakON socket in the Ghent case is offered, and is 4-pole, because Purifi chose it for themselves. I'm not aware of any other case kits for the EVAL1 with speakONs, so no other basis for it to be considered popular.

You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
 
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You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
Hi,

How will be required output in Vrms for into 6 ohms (and/or 4 ohms) ?

Also, if one have the source's max output at 5.55Vrms (0.035 ohms) and it will ONLY be used to drive the tweeter, will it be enough to bypass the buffer ?
 
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The speakON socket in the Ghent case is offered, and is 4-pole, because Purifi chose it for themselves. I'm not aware of any other case kits for the EVAL1 with speakONs, so no other basis for it to be considered popular.

You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
Thanks again Jim. My speakers are 6 ohms and I don’t play at particularly loud levels so will give it a try, and report back in due course.
 

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Assembled the EVAL1/SMPS1200A400 in the Ghent case with Ghent harness and it was straight forward and easy having followed this thread. The case and harness fit perfectly (provided mains inlet was a bit tight fit) and all screws were provided.

Will leave it running for some time to settle in before giving it some serious listen.

There is one issue, thought, that I would like to consult the forum‘s experience on rather than finding out by trial and error myself. I have a tube pre-amp (Linear Tube Audio Microzotl MZ2, that does double duty as a headphone amp and pre-amp) that will feed the Purifi. I am very careful to switch the tube amp on before the Purifi and then off after it, as I am concerned with DC leakage into the Purifi and speakers. Now I would prefer to keep the Purifi permanently on, while turning the tube preamp on only when I need it. Does anyone already have any experience how sensitive the Purifi is to DC leaks/spikes?
 

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Assembled the EVAL1/SMPS1200A400 in the Ghent case with Ghent harness and it was straight forward and easy having followed this thread. The case and harness fit perfectly (provide mains inlet was a bit tight fit) and all screws were provided.

Will leave it running for some time to settle in before giving it some serious listening.

There is one issue, thought, that I would like to consult the forum‘s experience on rather than finding out by trial an error myself. I have a tube pre-amp (Linear Tube Audio Microzotl Z2, that does double duty as a headphone amp and pre-amp) that will feed the Purifi. I am very careful to switch the tube amp on before the Purifi and then off after it, as I am concerned with DC leakage into the Purifi and speakers. Now I would prefer to keep the Purifi permanently on, while turning the tube preamp on only when I need it. Does anyone already have any experience how sensitive the Purifi is to DC leaks/spikes?
Its not "sensitive" but it is dc coupled. It will pass it through.

If your pre sends out dc spikes at switch on/off they will be amplified and sent to the speakers.

BTW there is no need to keep the purifi on permanently for "performance" reasons.
 

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Thanks for the quick reply. I would like to leave it on for convenience reasons and I could then also let the rest of my family use the system without having to worry about switching things on an off in the right order.

I seem to recall having read somewhere in this or another forum that a lot of d-amp modules (hypex) are sent in for repairs to them because of dc spikes from tube pre-amps. The tube amp manufacturer also cautions about this in the manual. That‘s why I am a little concerned and would rather not try myself.
 
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JimB

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Thanks for the quick reply. I would like to leave it on for convenience reasons and I could then also let the rest of my family use the system without having to worry about switching things on an off in the right order.

I seem to recall having read somewhere in this or another forum that a lot of d-amp modules (hypex) are sent in for repairs to them because of dc spikes from tube pre-amps. The tube amp manufacturer also cautions about this in the manual. That‘s why I am a little concerned and would rather not try myself.
EDIT: I know nothing about your particular schematic, but a VT preamp could produce a very high voltage 'spike' at turn on.

Would you plan to keep both the preamp and the amp on at all times? If so, you can time the initial power on and they can need do nothing that would produce a transient. BTW, I suspect the turn off transient would be less if the amp mute fast enough at power off. that would depend on the decay of the supplies in the preamp.
 
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FBU

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As I mentioned, the VT pre is a Linear Tube Audio MZ2. In order to prolong tube life and be a bit environmentally conscious, I would not like to run it 24/7. I believe the Purifi uses much less idling, so that would acceptable.
 

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The speakON socket in the Ghent case is offered, and is 4-pole, because Purifi chose it for themselves. I'm not aware of any other case kits for the EVAL1 with speakONs, so no other basis for it to be considered popular.

You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
I asked Kim Nordtrop Madsen of Purifi Audio about this b/c I'm thinking about pairing my Purifi with an Octo DAC 8 Pro and having Octo set the RMS voltage to higher than the standard 4v RMS on the two outputs I'll be connecting to the Purifi, and the reply was:

"If you look in the 1ET400 datasheet table 4 on page 8, section : Audio Inputs & Outputs, you can see that 9.6Vrms is needed for 1% THD with +/-65V supply voltage. " Goes on to say that rounding up to 10Vrms would be the reasonable course here. So if you order the Octo, tell Pavel 10Vrms on outputs 1-2.
 

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Just another way to express it, from Neurochrome buffer design doc:


Gain Configuration
The default gain of the Input Buffer is 13.2 dB. The gain of the Purifi 1ET400A is 12.8 dB. Thus, when used with the Purifi 1ET400A, the total amplifier gain is 26.0 dB, which is the THX standard.”
 
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Hi everyone,

I am new here and in the process of buying a complete new system. The speakers I have selected after listening to 20+ different floor standers are the Klipsch RP-8000f, and based on a whole lot of research I have also settled for a Purifi amp with the EVAL1 buffer which I still need to order. I am really struggling with how to drive the amp without losing the benefits of it (low noise, clean and excellent SQ).

My main concerns are volume control, balanced input (or not) and avoiding blowing up my speakers because of the input Voltage/gain of the EVAL1 input buffer. As you all know the Purifi EVAL1 power amp has max volume at an input Voltage of 1.5V. Ideally, one would hook the amp up to a balanced XLR DAC for a fully balanced connection but I wouldn't rely on just the volume control of a balanced DAC as I am reading online that some DACs sometimes revert to 100% volume after a power outage for example. That would blow my new speakers/ears (and amp?) and is an unacceptable risk. I would therefore need to add a passive volume control (like this JBL Nano Patch+) which may or may not add distortion/noise. How have you guys solved this problem? It also just seems silly to use a balanced DAC with a 4V RMS output to then limit that gain before it goes into another gain stage (EVAL1) and then into the Purifi modules.

An alternative is to go with an unbalanced DAC and use a modified RCA to balanced XLR cable (like the one from March Audio) just because that opens up a whole lot more DACs (at lower prices, such as the E30) to choose from, do you see any issues with that approach? However, if you then add a passive inline attenuator such as the Schiit Sys passive preamp (which adds noise at reduced volume) to make sure that the E30 can run at a higher volume (with lower distortion, right?) and for the aforementioned speaker/amp safety reason, won't you lose all the benefits of using the March Audio 'balanced' RCA to XLR cable? With this setup [E30 DAC - RCA to Schiit Sys - March Audio 'balanced' RCA/XLR to Purifi EVAL1 amp] there would be an unbalanced RCA connection from the DAC to the Schiit, followed by the 'balanced' RCA/XLR connection to the amp.

Furthermore, does the EVAL1 contain the necessary RF filters to stop the issues as recently raised by March Audio in this Purifi thread?

Apologies for all the text, but how can I best drive a Purifi EVAL1 power amp and how do you guys drive the amp? I just want to hook it up via Toslink and computer via USB whilst having remote volume control without running the risk of blowing up my speakers and ears!

Cheers
 

March Audio

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Hi everyone,

I am new here and in the process of buying a complete new system. The speakers I have selected after listening to 20+ different floor standers are the Klipsch RP-8000f, and based on a whole lot of research I have also settled for a Purifi amp with the EVAL1 buffer which I still need to order. I am really struggling with how to drive the amp without losing the benefits of it (low noise, clean and excellent SQ).

My main concerns are volume control, balanced input (or not) and avoiding blowing up my speakers because of the input Voltage/gain of the EVAL1 input buffer. As you all know the Purifi EVAL1 power amp has max volume at an input Voltage of 1.5V. Ideally, one would hook the amp up to a balanced XLR DAC for a fully balanced connection but I wouldn't rely on just the volume control of a balanced DAC as I am reading online that some DACs sometimes revert to 100% volume after a power outage for example. That would blow my new speakers/ears (and amp?) and is an unacceptable risk. I would therefore need to add a passive volume control (like this JBL Nano Patch+) which may or may not add distortion/noise. How have you guys solved this problem? It also just seems silly to use a balanced DAC with a 4V RMS output to then limit that gain before it goes into another gain stage (EVAL1) and then into the Purifi modules.

An alternative is to go with an unbalanced DAC and use a modified RCA to balanced XLR cable (like the one from March Audio) just because that opens up a whole lot more DACs (at lower prices, such as the E30) to choose from, do you see any issues with that approach? However, if you then add a passive inline attenuator such as the Schiit Sys passive preamp (which adds noise at reduced volume) to make sure that the E30 can run at a higher volume (with lower distortion, right?) and for the aforementioned speaker/amp safety reason, won't you lose all the benefits of using the March Audio 'balanced' RCA to XLR cable? With this setup [E30 DAC - RCA to Schiit Sys - March Audio 'balanced' RCA/XLR to Purifi EVAL1 amp] there would be an unbalanced RCA connection from the DAC to the Schiit, followed by the 'balanced' RCA/XLR connection to the amp.

Furthermore, does the EVAL1 contain the necessary RF filters to stop the issues as recently raised by March Audio in this Purifi thread?

Apologies for all the text, but how can I best drive a Purifi EVAL1 power amp and how do you guys drive the amp? I just want to hook it up via Toslink and computer via USB whilst having remote volume control without running the risk of blowing up my speakers and ears!

Cheers
The eval 1 has GBW limiting and filtering built in, so should be OK, although I confess I havent tried a test with it to see if intermodulation occurs.

The eval 1 has +14dB gain. The 1ET400 requires about 9.6 volts to get it to rated power (1% THD). This equates to an input of 1.9 volts rms not 1.5.

Its quite happy being driven from a 4 v dac output, I do this all the time, you just turn the volume down :)
 
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The eval 1 has GBW limiting and filtering built in, so should be OK, although I confess I havent tried a test with it to see if intermodulation occurs.

The eval 1 has +14dB gain. The 1ET400 requires about 9.6 volts to get it to rated power (1% THD). This equates to an input of 1.9 volts rms not 1.5.

Its quite happy being driven from a 4 v dac output, I do this all the time, you just turn the volume down :)
Appreciate your response! The only issue I have with using a 4V RMS balanced DAC is what would happen if the DAC somehow goes up to 100% volume? Some people on this forum have said that their DAC (e.g. SMSL SU-8) can default to 100% after a power failure overnight for example. Would that not damage the amp/buffer and/or blow my speakers?

Also I don't know if this is an issue, but isn't it better to run a DAC as close to its highest volume as possible to minimise distortion and noise?
 

March Audio

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Appreciate your response! The only issue I have with using a 4V RMS balanced DAC is what would happen if the DAC somehow goes up to 100% volume? Some people on this forum have said that their DAC (e.g. SMSL SU-8) can default to 100% after a power failure overnight for example. Would that not damage the amp/buffer and/or blow my speakers?

Also I don't know if this is an issue, but isn't it better to run a DAC as close to its highest volume as possible to minimise distortion and noise?
Well I have left analogue volume controls up high and blasted myself ;)

It's not difficult to check volume before you press play.

Buy a dac that doesn't have faulty firmware. You can test its behaviour with power outages and send it back if it defaults to max.

I use Roon and its volume control. It has volume limit settings and in thecyears I have been using it not one uncommaded volume excursion.

Ok, analogue v digital volume.

With an analogue volume control when you turn it down both the inherent dac output noise and the signal (the music) both go down in level. You maintain the signal to noise ratio until such point that the amplifier noise dominates (your dac will be less noisy than your amp).

With digital volume the noise level stays the same as you turn the volume down, just the music signal reduces so your signal to noise level reduces.

This is a genuine theoretical disadvantage. However back in the real world most dacs have such low noise levels that you wont hear any noise so its actually irrelevant. I would caveat that by mentioning that if you have some crazy sensitive speakers above 100dB/w/m then you may start to hear noise.

As mentioned the RME dac overcomes this with a hybrid stepped analog and digital volume.

Also you do require some headroom to cope with quiet recordings that don't go up to 0dBFS, so that extra 6dB from 2 to 4 volts isn't a problem.
 

hyperknot

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I recommend you buy the very reasonably priced Soncoz DACs.
- the cheap QXD1 always starts from volume 0 after a power down, and
- the more expensive SGD1 properly remembers volume level for each inputs separately

Basically these would protect you from accidental 100% volume situations.
 
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Well I have left analogue volume controls up high and blasted myself ;)

It's not difficult to check volume before you press play.

Buy a dac that doesn't have faulty firmware. You can test its behaviour with power outages and send it back if it defaults to max.

I use Roon and its volume control. It has volume limit settings and in thecyears I have been using it not one uncommaded volume excursion.

Ok, analogue v digital volume.

With an analogue volume control when you turn it down both the inherent dac output noise and the signal (the music) both go down in level. You maintain the signal to noise ratio until such point that the amplifier noise dominates (your dac will be less noisy than your amp).

With digital volume the noise level stays the same as you turn the volume down, just the music signal reduces so your signal to noise level reduces.

This is a genuine theoretical disadvantage. However back in the real world most dacs have such low noise levels that you wont hear any noise so its actually irrelevant. I would caveat that by mentioning that if you have some crazy sensitive speakers above 100dB/w/m then you may start to hear noise.

As mentioned the RME dac overcomes this with a hybrid stepped analog and digital volume.

Also you do require some headroom to cope with quiet recordings that don't go up to 0dBFS, so that extra 6dB from 2 to 4 volts isn't a problem.
Hah I also nearly gave myself (and my neighbours) a heart attack once or twice with one of those volume mishaps myself :D

Good point on headroom with regards to quiet recordings, so a 2V or 4V DAC without adding a passive/analog attenuator could be alright. Is there a danger of damaging the amp if it is fed a 4V RMS full volume signal if something were to go wrong or would it just clip excessively?
 
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