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hackernap advice thread

During the start-up transient, the resistor could briefly see as much as 50V. A 1 ohm part would pass 50A, so the instantaneous dissipation could reach 2,500W!!! Now all resistor constructions can withstand much higher powers for a short period, but that is a lot of stress.

Using a decent sized part means it will have enough mass to not heat up too far during the start-up pulse.
 
sam_cat said:
Hacker - Very tempted to give those mods a go... My 2nd amp is soldered, casework done but no wiring yet so at the right stage to easily desolder a few components and give it a try.. Easily lets me do an A vs B as well (A being standard BOM build and B being with the above mods)...

Mighty tempted..

Sam
Click to expand...

Very cool. I'd also be interested to know if there was a difference using caps with even better dielectrics but lower capacitance. Something like Wima MKP2 0.33uF/100V polyprops for example. They'd be a drop-in for C5-C9, C11 and C25, and they're pretty cheap, too. I'd be tempted to try those caps instead of the polyesters, but I'd also add that I've no idea if this will make the slightest bit of difference!

Let us know what you decide to try and how it sounds :)
 
I will give it a go, but I am no expert on these things... Let me know what you think would be the best caps to try in which positions and I will give it a go and report back :)
Not afraid of spending a few ££ if there is a good chance that it will improve things.. Considering the cost of the whole build ;)



Sam
 
I'm finally getting all the components together to make a start but I'm struggling to get hold of the 1/4W 26.7K 0.1% IRC Metal Film Resistors. Mouser haven't got them in stock until the end of December! Trying to search for alternative supplies on Google's a nightmare so does anyone have any idea where else I could obtain some (or even lend me some which I'll repay back when the backorder's completed)?
 
hacker said:
Those are the wrong way around - you want your front end to have a higher voltage than the output stage.

50VDC for output and 55VDC for the front end are perfect as long as that's DC voltage across the amp's power inputs and not the raw AC from your transformers!

Edit: I use 35-0-35 for the output stage, which gives approximately 50VDC. For the front end I use 40-0-40, which gives a raw 56VDC, which is dropped to about 50 - 51VDC after the amp's on-board VBE.
Click to expand...

Hi,
I used a 45-0-45 for the FE and adapted the VBE to drop the required 50-51v, at test points A and B.
For the output stage I have used a 36-0-36 which is giving 56-57v at test points D and E. I don't know why my transformer is giving out 6 or 7 volts more than your 35-0-35. Is this likely to cause problems? and what could I do about it, other than change the transformers?

BTW My amps are working great at the moment.
 
Tony, the value is actually supposed to be exactly 27k but the 26.7k was the closest I could easily find given the desire for 0.1% tolerance and low PPM. You want very good resistor for this part, where "good" is basically now noise (PPM); often the low-PPM resistors are also very tightly toleranced at 0.1% or better (lower). Something like this would work pretty well: http://www.mouser.com/ProductDetail...=sGAEpiMZZMtlubZbdhIBIAPQamuofg2KUpAtY8rg85U=. Some people go nuts with these parts (1k and 27k resistors in the feedback network, R13 and R6 on the amp board) and spend a fortune on fancy 0.01% 1ppm Vishay Bulk Foil resistors; I've never tried them.

Paul3, it's weird that your 36-0-36 is giving 56VDC. It should give roughly 36 * root 2, or 36 * 1.414 = 50.9V. It won't really matter, but the ideal is to have the front-end at a higher voltage. As you've noticed, it already sounds pretty good!
 
sam_cat said:
I will give it a go, but I am no expert on these things... Let me know what you think would be the best caps to try in which positions and I will give it a go and report back :)
Not afraid of spending a few ££ if there is a good chance that it will improve things.. Considering the cost of the whole build ;)
Click to expand...

I'd go with the polyprops - it'll probably even save you money given that you don't need to buy fancy electrolytics!
 
hacker said:
Tony, the value is actually supposed to be exactly 27k but the 26.7k was the closest I could easily find given the desire for 0.1% tolerance and low PPM. You want very good resistor for this part, where "good" is basically now noise (PPM); often the low-PPM resistors are also very tightly toleranced at 0.1% or better (lower). Something like this would work pretty well: http://www.mouser.com/ProductDetail...=sGAEpiMZZMtlubZbdhIBIAPQamuofg2KUpAtY8rg85U=. Some people go nuts with these parts (1k and 27k resistors in the feedback network, R13 and R6 on the amp board) and spend a fortune on fancy 0.01% 1ppm Vishay Bulk Foil resistors; I've never tried them.

Paul3, it's weird that your 36-0-36 is giving 56VDC. It should give roughly 36 * root 2, or 36 * 1.414 = 50.9V. It won't really matter, but the ideal is to have the front-end at a higher voltage. As you've noticed, it already sounds pretty good!
Click to expand...
He may have a 230V transformer and 240V mains, I get 245V mains in Hartlepool so I allways spec a 240 primary tranny.
I get 55v from a 35-0-35 transformer which has 230 primary.

Alan
 
Can anyone... or specifically those with a Canterbury Windings transformer, confirm the correct way to wire up a HN5/9. Or, is it as I have in the 1st photo, in terms of positions?

Also, can I just use any bolt for the main transistors so long as it fits, It will have ceramic insulators and paste of course.

Cheers

(NB: no boards are bolted yet)
IMG_0047.JPG

IMG_0045.JPG
 
Looking good!

Black and White to the Front End power boards(Bottom), and Red and Yellow to the Output power boards(Top). The order as laid out is the same as mine.



Lucaslucas said:
Can anyone... or specifically those with a Canterbury Windings transformer, confirm the correct way to wire up a HN5/9. Or, is it as I have in the 1st photo, in terms of positions?

Also, can I just use any bolt for the main transistors so long as it fits, It will have ceramic insulators and paste of course.

Cheers

(NB: no boards are bolted yet)
IMG_0047.JPG

IMG_0045.JPG
Click to expand...
 
Yes your wiring is correct the black and white ones are for the front end the odd single colour being the 0V in each case
Yes you can use any suitably sized bolt & nut

very nice job by the way ;)

Alan
 
A bit of inspiration from yours cobo:)!

In terms of which the individual cables, I guess it does it matter if right side white goes to right side of fe cap board or other and mirrored for other side? like the order I have in the photos,

I guessed from the thickness of the cable that the thinner BW is fe as only <0.7A and colour Outs is a lot thicker for <5A
 
I just wired mines up so they were mirrored on each channel. Never really gave it much thought. It was more of a neatness thing. They seem to work fine that way.

Lucaslucas said:
A bit of inspiration from yours cobo:)!

In terms of which the individual cables, I guess it does it matter if right side white goes to right side of fe cap board or other and mirrored for other side? like the order I have in the photos,

I guessed from the thickness of the cable that the thinner BW is fe as only <0.7A and colour Outs is a lot thicker for <5A
Click to expand...
 
I really want to try some of these mods, but the thought of tearing my build down to try it is daunting. I knew I should have waited.

Will wait and see how it goes with your builds before I give it a go. :)
 
Do wait, I will list out the mods and get everything checked & ordered friday.. I have a totally stock build I can compare it against. If the mods work well then that will be torn down for the same mods.. Plan is to end up bi-amped.

Sam
 
Thanks for the help.
Up to now Ive been worrying about all the technical things, but now just keen to hear how it sounds. If it doesn't just blow up that is..
 
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