F5 power amplifier

[daviddsailor]

Originally Posted by AndrewT

David,
have you fused the main power rails between amp and smoothing?

No, I don't have any fuses in the DC path/s. Only a 2A fuse in the 240VAC line.

Regards, David.

[Geofd]

Originally Posted by Geofd

Seems like my "very hot" is equal to Papas "Bloody Hot". I will have to test some forced cooling options as we have a youg kid in the house.
My comment was more to the issue of how I am amazed that these 2 small devices can create so much heat and still keep the smoke in.
Thanks for the pointers - maybe when I am done I can post the reults ( convection and forced cooling) to help any future new constructors , as I have noticed that heat sinking is a common cause of questions.

And for the F5 turbo seems like we are going to need some serious heat sinks for that one.

OK, I have tried some experiments with forced cooling - with a fan attached I can run one F5 channel on the heat sink at 34 degres C or both F5 modules on the same heat sink, the heat sink is 42 degrees C (with convection it was 54 degrees C with only one channel)

The fan I am using is a 24 volt unit with a 35CFM rating (with a 41dBA noise rating - very nosiey, but all I had at hand to test) - I am running it at 19V from an old switch mode laptop power supply (yes they do have uses) (I am having trouble downloading the derating table for reduced voltage - so cant really say what the CFM is at present , but it is less than 35 CFM)

I have the amp setup as per instructons, the supply voltage is +/- 23.5 Volts, for R11 and R12 the voltage is between 0.59 and .6, giving an offset voltage at the output at less than 2mV

Also I have used a fully encapsulated transformer (Noratel brand), it is rated at 225Va (I will 1 per channel) but at present I am running both channels off one transformer just to check for hum under heavy current load (and it is easier for testing, less wires every where), there is absolutely no hum - these appear to be a great solution for heavy current draw applications - under these conditions it is quite warm, about 43 degrees C

Other adventures - maybe this will help othes who make dumb mistakes like me - ie connect the power supply round the wrong way ( moral to the story is dont rush to test the amp , take your time and check and check again)- lots of glowing resistors ( R11 and 12 anyway) toasted Q3, Q4, Q1 and Q2. What really suprised me is that it also cooked P1 and P2 - check these as if you power up again with these cooked - what I mean is the wiper point was open circuit ad so I got the 5K which gives a high bias current and so R11 and R12 start to glow again and let out smoke.

[Nelson Pass]

Originally Posted by daviddsailor

Only difference in builds is that this time I used some self adhesive heat sink washers. Grey looking like normal washers but very soft and squishy. Anyone had trouble with these? I'm now using the normal grey washers and amps are OK (so far!).

What did you use the first time?

[daviddsailor]

Nelson

The previous two F5 builds have used the standard grey flexible heat transfer washers. They look like they may be some sort of fabric covered in grey (silicon?) material. I have used them on other projects and never had a problem.

One other change is that I did a triple plait with the pos/neg/earth DC leads between the PS rails and the F5 PCB. I seem to remember now that this might not be the best way of running these wires.

Thank you for your interest in helping me.

[regiregi22]

Originally Posted by c_door

Thanks Regi.
Were you able to find the 47.000 PEH169 anywhere ?

I managed to get my PEH200 from Elfa. You are comparing two capacitors with a whole of different specs, thats why you see big differences between PEH200 and PEH169. You have to compare capacitors with same capacitance and voltage rating, otherwise it is useless.

IMHO, I would go with 47.000uF PEH200 better than 22.000uF PEH169

[c_door]

Originally Posted by regiregi22

I managed to get my PEH200 from Elfa. You are comparing two capacitors with a whole of different specs, thats why you see big differences between PEH200 and PEH169. You have to compare capacitors with same capacitance and voltage rating, otherwise it is useless.

IMHO, I would go with 47.000uF PEH200 better than 22.000uF PEH169

Thanks a lot for the info Regiregi, I'll follow your suggestion.
I didn't know the Elfa Distrelec dealer, very interesting.
ciao, have a nice day. Carlo.

[jameshillj]

The 44,000uF of Rifa caps per rail is going to produce a massive turn-on current surge - also, 15,000/40v caps will do quite well in the basic CRC but still need a Soft Start/ CL60 limiter cct -

Not much difference in the sound of the peh200 and peh169 for the same uF value - best with fast, soft recovery diodes and avoid the common block bridges (sound is quite hard, rough with these caps) - the combination of 0.1R, 15,000uF, 0.1R, 15000uF (RCRC) is a fairly well known configuration (extra series resistor after diodes - no ceramic wirewounds)

The threaded stubs on the case is for cooling the capacitor case on a heatsink - can just cut them off, insulate the case and use capacitor clamps - best mounted vertical - Not the easiest cap to use but very fast, "punchie", bright cap, slow to break-in & very long life ...

... my 2 cents

[regiregi22]

Originally Posted by jameshillj

The 44,000uF of Rifa caps per rail is going to produce a massive turn-on current surge - also, 15,000/40v caps will do quite well in the basic CRC but still need a Soft Start/ CL60 limiter cct -

I used a softstart board, but slow blow fuses should do the trick.

[c_door]

Originally Posted by jameshillj

Not much difference in the sound of the peh200 and peh169 for the same uF value - best with fast, soft recovery diodes and avoid the common block bridges (sound is quite hard, rough with these caps)

Thanks jh. An IXYS FRED bridge like this, you mean ?
http://www.partsconnexion.com/product4794.html

[jameshillj]

Yeah Regi, SoftStart and Slow fuse, just fine - I was quite surprised at the Rifa charge/discharge rates - not written directly in the specs.

IXYS bridges okay - there's some diodes specifically built for the job - fast, soft recovery - ON versions like MSRF1560, can't remember the Phillips equiv - don't be put off by the relatively slow Trr (about 50nS) - those Rifa caps are a bit harder to please than most.

Can balance the sound of the amp a lot with carbon, etc (softer) Fet gate stopper resistors and metal ox in the RCRC (suggest you avoid the common Nichrome ones) without losing the "grunt" and "speed" - most other power supply caps not so critical altho some of the BHCs need some care also to bring out the exc. mids/tops (ie. the DNM versions 4 pole & slit foils)

I did try a balance with Sikorels for the ripple cap and the Rifas as the power cap (ie 0.1R, Siemens 10,000uF, 0.12R, Rifa 15,000uF) with the BYV diodes (on heatsinks) for PHY-HP based speakers & copper spkr wires - rather good result.