Update. In light of new information about the amp being counterfeit I have removed the link. The question around the preamp conundrum is still relevant regardless, so I don’t want to just delete the entire thread.
Hey guys
I'm building out my first DIY speaker system and hoping for some advice. These will be speakers for my workstation. I will be doing crossover and DSP on my Mac, using the Motu M4 hardware interface and CamillaDSP software.
One thing I am having a bit of trouble with is amplification. Im interested in one of the Purifi 1ET400A based amps (link removed) from China. It comes in 2 versions: one without a volume pot and one with (for a small premium). The no volume pot version was tested and the results were phenomenal. As I understand it though, poorly implemented volume control could negatively affect the sound quality, and I haven't found any test results for the version with the volume pot.
The problem is that right now I don't have a preamp in the signal path. Since the system is being run on software, with volume controlled digitally. I feel it would be foolish to just hook the speakers up to a pure amp - risking hurting them (along with eardrums) should something iffy happen with software volume control.
So how likely is it that the volume pot version of these amps is going to suck?
If I was sure it would just be fine, then that's perfect, my problem is solved. But if it's actually a dicey situation, should I instead find some preamps and opt for the pot-less variant? (I don't really want to add much more to the bill)
Hey guys
I'm building out my first DIY speaker system and hoping for some advice. These will be speakers for my workstation. I will be doing crossover and DSP on my Mac, using the Motu M4 hardware interface and CamillaDSP software.
One thing I am having a bit of trouble with is amplification. Im interested in one of the Purifi 1ET400A based amps (link removed) from China. It comes in 2 versions: one without a volume pot and one with (for a small premium). The no volume pot version was tested and the results were phenomenal. As I understand it though, poorly implemented volume control could negatively affect the sound quality, and I haven't found any test results for the version with the volume pot.
The problem is that right now I don't have a preamp in the signal path. Since the system is being run on software, with volume controlled digitally. I feel it would be foolish to just hook the speakers up to a pure amp - risking hurting them (along with eardrums) should something iffy happen with software volume control.
So how likely is it that the volume pot version of these amps is going to suck?
If I was sure it would just be fine, then that's perfect, my problem is solved. But if it's actually a dicey situation, should I instead find some preamps and opt for the pot-less variant? (I don't really want to add much more to the bill)
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Most volume controls suck, but you could always bypass or replace it, if it seems too bad.
It's unlikely that the measurements would be affected too much: a little less HF extension,
a little less channel separation, and some interchannel tracking error, esp at low settings.
A really good control would cost more than the amp, but would still have the above degradations.
I'd just get the amp with the volume control. A separate new preamp would have even more problems,
in addition to the above. Definitely a legitimate concern though.
It's unlikely that the measurements would be affected too much: a little less HF extension,
a little less channel separation, and some interchannel tracking error, esp at low settings.
A really good control would cost more than the amp, but would still have the above degradations.
I'd just get the amp with the volume control. A separate new preamp would have even more problems,
in addition to the above. Definitely a legitimate concern though.
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I don't have a potentiometer/preamp. I use NUC11 as a streamer and May DAC followed by Aleph J, finishing all off with Dynaudio speakers. However, the system I have is a simplistic approach, DC-coupled throughout (sans x-over capacitors), with a balanced input amp that has "only" 15dB of gain, which is more than I need for very loud sound reproduction. In my case, even if I accidentally push the digital (in software) volume slider to the max setting, it is still okay... the sound just gets unpleasantly loud.
However, in your case of a powerful amp, the above way of controlling the volume (or your way of controlling the volume in software) would be too dangerous... so I suggest a nice volume pot. From the days I played with all sorts of potentiometers/stepped attenuators, the one I liked the most was the TKD 2CP-2500 series.
Down the road, you may find that the pot you choose will never travel past let's say 13:00 hours... in which case you could replace the potentiometer with the voltage divider (2 high-quality resistors per channel) that will mimic the 13:00 setting. Or, you could modify the gain structure of your amp... and then use the software control to adjust the volume...because you do not want the additional hook-up wiring and wiper contact resistance in the signal path.
However, in your case of a powerful amp, the above way of controlling the volume (or your way of controlling the volume in software) would be too dangerous... so I suggest a nice volume pot. From the days I played with all sorts of potentiometers/stepped attenuators, the one I liked the most was the TKD 2CP-2500 series.
Down the road, you may find that the pot you choose will never travel past let's say 13:00 hours... in which case you could replace the potentiometer with the voltage divider (2 high-quality resistors per channel) that will mimic the 13:00 setting. Or, you could modify the gain structure of your amp... and then use the software control to adjust the volume...because you do not want the additional hook-up wiring and wiper contact resistance in the signal path.
Okay cool, thanks for these insights Extrem_Boky. This idea of replacing the pot with resistors is an interesting approach. If I understand correctly, one cheap-*** approach I could take is opt for the amp that includes the volume pot and use that to evaluate what my max volume is. Then later switch to high quality resistors which will have the welcome side effect of increased sound quality. I’m getting a little outside my comfort zone here, so forgive naïve questions - but would it be possible to implement some kind of hot swap resistor? In case I change up my speakers in the future and need to change the maximum output?
You can choose whatever you deem suitable... maybe even a DIL IC socket. Personally, I would always use short signal paths and the least amount of contact resistance points possible which usually means everything is soldered.
Just wanted to mention, in case you weren't aware that those amps are reverse engineered copies of Purifi, not originals. Also the price seems a bit on the high side seeing as on Taobao they're ~4000RMB (~570USD) although currently out of stock.
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why would you buy counterfeit amplifiers that infringe on our patents and trademarks? even at a high price ?
We are a small start up trying to make a sustainable business and we have invested huge amounts of resources in the research and development of our products.
best regards
Lars/Purifi
Hi Lars, I did not know these were counterfeit, I thought they were using the Purifi boards that are available for purchase and putting them together with a chassis / power supply / assembly etc
hi Neigh, thank you for replying. We are investigating how they got the modules. It is a big concern for us. Luckily there are many legit assemblers of purifi amps out there.
cheers Lars
cheers Lars