F5 power amplifier

[acold7dusta]

are the shorted input necessary for testing? i didn't see it anywhere in the guides, so i didn't do it.

 

[nigelwright7557]

are the shorted input necessary for testing? i didn't see it anywhere in the guides, so i didn't do it.

If the input is floating it might pick up mains hum and rf which might confuse readings.

 

[acold7dusta]

it won't cause damage without it though, correct?

 

[ichiban]

it won't cause damage without it though, correct?

True.

 

[bear]

pots read 0.3R, the fuse is fine, and my 0.47R resistor reads 0.5R. not sure why my other resistors are all now out of wack though...

Most, not all, DVMs have a small offset at very low resistance ranges... check to see if you get 0.00 with the leads connected or not.

_-_-bear

 

[acold7dusta]

Most, not all, DVMs have a small offset at very low resistance ranges... check to see if you get 0.00 with the leads connected or not.

_-_-bear

I get 0.2 ohms when they're connected directly. The 0.47R reads 0.7ohms uncorrected, and the pots read 0.3, which is 0.1 corrected

 

[acold7dusta]

here are my resistor values that are out of wack. This is for the left channel, and the right channel is similar (as well as my other boards)

R1&R2: 8.1R, 8.5R (10R)
R5-R8: 12.3R, 15.8, 7.2, 15.8 (100R)
R15&R16: 1.6K (2.2K SERIES 4.7K)
R17&18: 130R (1K)
R19&R20: 130R (150R, NOT TOO BAD)
R21&R22: 130R, 173R (22K!)

does anyone know what is going on with my amp? my other boards read the same numbers and that's why i bought new parts and boards because they read so much off.

The resistors were all normal before they were loaded (didnt check after they were mounted though)

readings were as the amp hooked up to the PSU, but not 120V wall power

 

[udailey]

You cant measure the value of a resistor once you put it in the board. It ends up being in series and parallel with other resistors. Maybe you put in a 1k resistor that goes to ground and elsewhere you put in another resistor of 100R that goes to ground and if you measure from both sides of the 1k you measure the value of a 100R in parallel with a 1k. That would be kind of simple but then you resistors in series somewhere between those two and others going to ground and it ends up a mess to measure while in circuit.
Like look at your R21 and R22. They must be parallel to a resistor that is close to 150R. Probably R19 and R20 but I am not looking at the schematic right now.
Uriah

 

[acold7dusta]

well that clears that confusion up thanks

 

[dantwomey]

I was looking around for caps for my F5 and came across this deal on FleaBay 200pcs 15000uf/25V Capacitor.
At about 63 cents a piece before shipping they're not a bad deal for those on a tight budget.

Regards,
Dan

 

[woodturner-fran]

The voltage rating on those caps is a bit tighter than I would like:. If there were 35v ones you'd be better off...


Fran

 

[udailey]

They would be good for something like the MiniAleph. Can you imagine 500,000uf for $21? Of course you still have over $100 of caps left over More Minis!!

 

[steve jones]

The voltage rating on those caps is a bit tighter than I would like:. If there were 35v ones you'd be better off...

25V rated caps in the stock F5 seems to be OK with Mr Pass.

 

[labjr]

25V rated caps in the stock F5 seems to be OK with Mr Pass.

Those are Panasonic Caps. I wouldn't trust every brand.

 

[HaflerFreak]

Looks like a '93 date code to me...

I got 10 of these (price break at 10) from Digikey:
Digi-Key - P6671-ND (Manufacturer - ECO-S1VA223EA)

 

[dantwomey]

Since I'm building four channels I'm looking for 16 of something. As usual, I think capacitor choices would cause much debate. Peter (the infamous one ;-) uses Jensen four-pole which are worth a small fortune. On the flip side of that coin we see some decent regular caps in the sub $10 range. I, just for the hell of it, may squander my kids inheritance ;-) and try Mundorf's Mlytic Audio Grade.

Regards,
Dan

 

[Tea-Bag]

Dan,
I would personally go for the 470000uf panasonic one's on Ebay.
2pcs Panasonic Radial Capacitors 47000uf 25v 85C - eBay (item 200449742234 end time Apr-12-10 09:54:46 PDT)
I've bought other stuff from this guy before. Quick service.
I use 4x 47000uf Panasonic's in my F5. Under load, the are 22.5v on V+, at least on mine.

 

[dantwomey]

Dan,
I would personally go for the 470000uf panasonic one's on Ebay.
2pcs Panasonic Radial Capacitors 47000uf 25v 85C - eBay (item 200449742234 end time Apr-12-10 09:54:46 PDT)
I've bought other stuff from this guy before. Quick service.
I use 4x 47000uf Panasonic's in my F5. Under load, the are 22.5v on V+, at least on mine.

Purchased. Hard to ignore good advice. They look like they fit on my PD universal PS boards.

Thanks for the advice.

Regards,
Dan

 

[cjkpkg]

OK,

Up and running...Peter's PSU, and F5 boards, Dale CMF50 and Panasonic resistors, PSU is 4X22,000 uF 35V caps with 4X panasonic .47, JFETs are Blues toshibas, and MOSFETS are IRFP244 and IRFP9240.

Lastly which may lead me to my answer is the xformer which is an antek 300VA 18V unit.

I am currently running R11/R12 at 800mv and the heatsinks are HOT but I can touch them for a good 15 sec before I need to let go. DC on the speaker terminals is minimal - 10mv at best. I am reading 5.25V across R3/R4 on both channels

I have all current limiters and thermistors installed.

While the amp is dead quiet and am disappointed at the power. Honestly my aleph mini seems to pack more punch - at an anemic 13.5V rail voltage.

The rails on the F5 are running 22.6V tonight.

Any ideas where to look next? I am already considering either A-purchase a duplicate xformer or buy the 400 or 600VA unit.

thoughts?

 

[labjr]

You power supply seems a little wimpy. Get the 600VA Antek. And add more capacitance too. Make sure the bias is where it should be.