Should be available at XRK's audio shop on Etsy:
https://www.etsy.com/listing/758183821/alpha-nirvana-39w-se-class-a-amp-pcb-one
https://www.etsy.com/listing/758183821/alpha-nirvana-39w-se-class-a-amp-pcb-one
It depends what bias current you're running - and what your room temperature is. I have my AN 4Rs (2.5a) in the Modushop 5RU Dissipante case - so each heatsink is 300 x 210 x 40.
After half an hour ... the heatsinks get too hot to touch comfortably.
Am I right in thinking that increasing the bias current improves the sound? I saw in the diagram that the bias current is 1.65A.
Andy has adapted his AN's primarily to drive 4ohm speakers. The 4ohm version runs a lower psu voltage but higher bias current.
The main design is meant for an 8ohm speaker load with 1.7A bias current. Really depends on what speakers you intend to drive with Alpha Nirvana.
The main design is meant for an 8ohm speaker load with 1.7A bias current. Really depends on what speakers you intend to drive with Alpha Nirvana.
I plan to use it with Elac Debut 6.2 speakers which have 6 ohm impedance. Does that mean I need to set the bias current to a mid-range value between 2.5A and 1.65A = 2.07A?
@Yurid
To make life simple, just stick with the AN39 8 ohm version as detailed on the 1st post of this thread. You’ll be fine. I’ve played with speakers having a 6 ohm impedance and the AN39 8 ohm version works great. If you want to increase the bias current… you can, but I doubt much of a difference will come especially since the Debut 6.2’s impedance and phase curves are benign.
Best,
Anand.
To make life simple, just stick with the AN39 8 ohm version as detailed on the 1st post of this thread. You’ll be fine. I’ve played with speakers having a 6 ohm impedance and the AN39 8 ohm version works great. If you want to increase the bias current… you can, but I doubt much of a difference will come especially since the Debut 6.2’s impedance and phase curves are benign.
Best,
Anand.
Hi Yurid,
As Anand already proposed, the AN39 8ohm version will play fine on your speakers.
I have also built the AN39 8ohm, with my 4ohm 93db speakers they play very good.
The 4ohm version is for the extremes: so that it can give enough current when playing loud(large voltage swings) on low sensitive 4ohm speakers.
When you have those three variables: playing loud, low sensitive speakers and 4ohm speakers, then you can opt for the 4ohm version.
The only thing I did for better 4ohm compatibility is a change in the feedback resistor, I used 1800R instead of 825R:
it lowers gain and FFT on 1800R with 4ohm load is the same as 825R with 8ohm load.
I'm using the Hifi2000 chassis 4U-400 with the 10mm front panel,
my amp is biased at 1.8A, that is about 90W heat/channel.
The heatsinks are 18-20°C above room temperature.
Two tips to make it better at heat transfer:
As Anand already proposed, the AN39 8ohm version will play fine on your speakers.
I have also built the AN39 8ohm, with my 4ohm 93db speakers they play very good.
The 4ohm version is for the extremes: so that it can give enough current when playing loud(large voltage swings) on low sensitive 4ohm speakers.
When you have those three variables: playing loud, low sensitive speakers and 4ohm speakers, then you can opt for the 4ohm version.
The only thing I did for better 4ohm compatibility is a change in the feedback resistor, I used 1800R instead of 825R:
it lowers gain and FFT on 1800R with 4ohm load is the same as 825R with 8ohm load.
I'm using the Hifi2000 chassis 4U-400 with the 10mm front panel,
my amp is biased at 1.8A, that is about 90W heat/channel.
The heatsinks are 18-20°C above room temperature.
Two tips to make it better at heat transfer:
- use Ceramic Alumina Al2O3 pads
- include the front panel as heatsink by putting some paste between front panel and heatsinks,
this way I've installed my mosfets 1-2cm closer to the front, instead of the middle of each heatsink
@danny_66 Thank you for your advice. I am planning to use aluminum case of 310x260x70 size for monoblock.
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I am using a 350x150x50mm Conrad heat sinks and with our current MidWest temps they are hardly warm even after couple of hours of music. But during the summers they get hot to touch but still manageable. I usually run my amp without top plate and I have a wooden front panel instead of aluminum as its DIY chassis. I would also prefer to go with aluminum front panel say 10mm which also gives additional cooling especially if the bolts are tightened up and also putting some thermal glue in between the sinks and the panel. May not be required but I did try that option gives better heat dissipation and also even.
Yes, one channel = two mosfets (P+N) with +25v and -25v rails = 2x 25v x 1.8A = 90W
I guess a good idea and I believe you will be keeping the toroidal + psu external chassis? So each sink will manage a single mosfet and I think good enough to try and also cost wise much better than big chassis.
This chassis is way too small for the heat AN39 creates!
For the stock 8ohm build each channel dissipates almost 100w.
A good example size is the Modushop 4U 400mm chassis.
I plan to use a 600W switching power supply in the same case, not a linear power supply.
Then I think too small internal space to hold the SMPS and the amp board on top which might also induce hum/hiss issues with grounding.
