Completed yet another Purifi-Neurochrome build. This time a 4 channel build to complement the previous 5 channel unit.
However, decided to go for my first customised case as I was getting bored with the previous builds plain fronts.
More pictures and notes here: purifi-the-4ch-build
This means I can now ditch the AVR and move onto a pre-processor to drive my 5.x.4 HT system. I may try to rebuild the 5 channel unit (which used a generic Modu-shop case) into a slimline one too, thermals permitting.
So far the base plates are transferring heat to the sides without any heat pipes etc.
Now for some movies
Andy, like you case. Any chance to share the files for the front panel? Or does Modushop have this already in place?
Also can you share the specs of the case, would like to start with a stereo setup and move later on to a 5 channel amp version.
The idea is to order 2 (one stereo and one 5 channel) back plates for the case, maybe already drilled.
We already have the file for the front panel, if Andy does not mind letting us use it for you too we are good to go
All okay with me, however, the front panel design needs a change in the positioning of the push switch as it is flush against the inside bracket. This requires some *customised* bracket work to get the nut on the switch I selected.
I would have fixed that in 5ch version I received yesterday, but wanted the switches aligned when the 4ch and 5ch units are stacked. So more bracket work
Will have a look at putting up some fixed versions on my blog page.
Posted the main part numbers and modified Front Panel Designer panels with some modifications for switch clearance.
purifi-the-5ch-rebuild
The designer software does have some limitations, but Gianluca has the extra instructions required.
Have fun !
I think the main benefit of a FET input OPA1656 op amp is the ability to use a higher impedance input signal, since the current noise is so low. The resistors on the FET input can be larger & still have reasonable effective input noise compared to the BJT input op amps like the OPA1612 & LM4562 which are better suited 1k ohm or less.
Attachments
I think it depends on the output impedance of your source. Bipolar input opamps generally have lower voltage noise, and while they are more susceptible to current noise with high source impedance, if you are using a DAC or preamp with a low output impedance, a bipolar input opamp may be preferable.
Are you using a a source impedance greater than 10K ohm for the input to the the Purifi Buffer? If the source impedance is closer to 1k ohms, the OPA1612 may be a better choice?
A compendium of blog posts on op amp design topics (page 26-28): https://www.ti.com/lit/pdf/slyt701
OPA1656 SoundPlus ultra-low noise and distortion, Burr-Brown audio operational amplifier
OPA1612 Dual sound-plus high-performance, JFET-input audio op amps
