Swordfishy/ASPEN FETZILLA power amp

[audiorasp]

Hi Hugh,

Add 4 boards to the list for me.

Thanks,
George

[AndrewT]

Originally Posted by JKC

..........at 50W into 8ohm impedance will produce 3.5A peak current.......................100W into 4ohm impedance load ........peak current of 7A which is quite high. Because of non-linearity of the speakers you should be expecting that kind of situation on a transient basis.

Your transient peak currents to the speakers when driven to nearly max Vout, could be much higher than the resistor load predicts. Expect at least two times higher and probably design for 3times higher.
A recent paper suggested that all three speakers tested at ~5times higher when worst music conditions met with worst reactive conditions.

[AKSA]

Welcome to our little project, George! Now at 58 boards and building!

2+P JoMo Adelaide SA Australia
2+P Ian Finch Coffs Harbour NSW Australia
2+P Gennaji Hyderabad India
2 Ken Lewis LA USA
2 Ron Russell Kent UK
2+P John Kenny Dublin Ireland
2+P Francis Morrin Dublin Ireland
2+P Vitalica Bucharest Romania
2+P Erik Deinum Groningen Netherlands
2+P Keith Correa ? India
2 Igor Polyakov California (city?) USA
2 Steve (aka SRH) Whangarei New Zealand
2+P George (aka JKC) Calgary Canada
2+P Anthony Mills Gold Coast Australia
2+P Dinesh (aka Chlorofille) Christchurch New Zealand
2+P Colin S. (?) (city?) NSW Australia
2 Chris Powell Sydney Australia
2+P Danny (?) Lierde Belgium
2 Sonnya (?) City (?) Denmark
4+P Jozua Cape Town South Africa
2 JT (? aka Sandyhooker) City (?) Arizona USA
2+P Nicola City (?) Vincenza Italy
2+P Sparkey (Brian ?) Melbourne Australia
2+P Chalkandtalk (?) City (?) NW England UK
4+P Woody1911a1 (?) Marblehead , MA USA
4+P George Cherhit Sacramento CA USA

We have one week to Greg returning from Europe, and two days or so after that I will pull the lever on the board manufacture.

Cheers,

Hugh

[AKSA]

Folks,

Here is the advantage to taking your time with the pcb layout; insurance against mistakes, and refinement.

I have added the output inductor and 10R resistor to the output buss. This saves time as the inductor can be soldered directly to the pcb.

Cheers,

Hugh

[srh]

Hi Hugh, would it be a good idea to have the take off point for L1 to be at the midpoint of the R19,R20 trace?
Cheers,
Steve.

[sonnya]

Source resistor recommendation:

http://www.ohmite.com/catalog/pdf/10_series.pdf

or:

http://www.ohmite.com/catalog/pdf/20_series.pdf

The 10 series is noninductive below 0.25R, but the largest value available is 0.15R

The 10 and 20 series can handle 5 times rated wattage in 5 second.

[AKSA]

Steve,

That would be optimum, but what is important is that the feedback is taken from the midpoint. A good compromise would be to thicken the track between the fb takeoff and the left side of L1.

Thanks for the tip.

Nice resistor, Sonnya, thank you. Planned resistance is 0.15R, in fact. The 25 5W series will fit fine; the default size is the stock sandcast ceramic which is not a wonderful component but is at least ubiquitous. I really think 10W at 47.2mm long is too large, however.

Hugh

[sonnya]

Okay, here is the links to digikey.com

Digi-Key - 15FR150E-ND (Manufacturer - 15FR150E)

and

Digi-Key - 25JR15E-ND (Manufacturer - 25JR15E)

The 15FR150E is 2mm shorter and noninductive

[AKSA]

Sonnya,

Thank you, that helps a lot!

Steve,

Something like this?

Cheers,

Hugh

[sonnya]

Hi Hugh.

what is the pitch on the source resistor in your design? You will need at least 30mm or 1181mil > 1200mil.