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Destroyer x Amplifier DX HDII version.

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#24
Hi Harry

I am not sure, but I believe those resistors are larger than the 7mm pitch of standard 1/4W metalfoil resistors. The witdth should not be a problem, as few resistors are "blocked in", alll resistors on the board are 7mm pitch, except the 3 power resistors which were spaced for non inductive R's, the 2 47R resistors at the diff pair also allows for 9mm pitch and input resistor is a 5mm 1/8W jobby (space constraints). In fact I mounted my input cap and this resistor "offboard" in my unit to allow for larger input caps... you can simply solder a 180R resistor to the positive pin of the input RCA socket...

To keep size of PCB (cost) and inductances low, I had to minimise traces, and in the process, component sizes....

Trust me, there is not a single "audiophile" component in my box, and it sounds better than anything, I have had the honour to listen to... Small caps are all 5mm pitch... you ca fit a mica cap in the space provided for the Cdom cap... I did this in mine...

If you'd like to start stocking up, you will need 20 x 100nf caps if you also want to bypas elcos... else you will need 12 of those caps for the 2 channels....(I can provide these at a cost of about $2 as they cost me only about 9 south african rand + VAT) Same type as provided with the Twisted pair Kits, not sure ofthe brand... they are little yellow caps, they work well.

I can also provide the resistors at about the same cost... there are about 50 resistors between the 2 channels...

Welcome to the new faces, we are at 13 sets (26 boards) after just one weekend...
 
#25
Hi,
0.28inch (7mm) is very small.
The normal minimum pitch for low watt resistors is 0.35inch (8.9mm). Most PCBs use 0.4inch or more for minimum resistor pitch.

When space is available I always recommend at least dual pitch for as many caps as possible. But you are excused when PCB space is scarce.
 
#26
I have seen the larger resistors RS sells a .333W unit in this size..., but 7mm pitch worked just fine... legs take a standard 90degree corner straight down the hole... with no unnessecary leads.. The issue is to not go to a larger PCB size... without going for miniature parts...

I have constructed 2 units with no construction problems up to now.. did get the idea to provide holes for a BG or other NP elco type input caps though...

I know there are those who believe in "audiophile" parts, but Carlos made me experience for myself that topology means more in the big scheme of things... I still believe in nice input caps though (big fan of Ampohm brand), but without fast swapping AB, I will not be able to say wich one I am listening to...

I didn't have any more nice large film caps to aid in comparison listening, will get a few diffirent ones of e-bay again... and I like my chipamp best with the ampohm jobbies... so I settled for cheap hitano non-polar 10uf cap to get the amp boxed again, and the livingroom cleaned up.....I would never have believed this cheap cap can sound so "good"
 
#27
I'm interrested too

Hi Nordic,

count me in for a stereo channel... (a PCB pair, right?)

I would be interrested to get as many parts as possible from you too to build it, if you have surplus to sell...

(I'm living in a country of very little DIY offerings... even for some chips like LM3875 or audio transistors I have to order overseas...)

I'm contactable at david_winarso at yahoo dot com

Thanks,
---
David
 
#30
Wonderfull and welcome on board, sorry for not posting today... busy with my first SMD project... boy 0805 is alot smaller than I thought.... but, I have a large supply on a dead PC motherboard...
Only have to buy 2 values to complete the boards... I guess 1M and 470k, is not all that popular on PCs.. Maybe I should just get 1M and paralell 2 for 470k...


Managed to reduce my Pedja Rogic buffer to 3 x 4 cm...yep it will fit in a matchbox...but, I am dead tired now...

The group buy looks more or less like a sure thing at this point in time... I will let it run on till Friday, if noone objects, before finalising costs...

David we will sort you out partswise.... Let me know if you can get large electrolytics though say from 2200u to 10000uf under 25mm diameter, 50V.

Also if you can get 2sc5200 and 2sa1943 localy... else we will have to get you some off ebay... my regular suorce, sell fake ones... I can get real ones localy at good prices through the official distributor... but need to take a whole tube... will only happen if more people need those...


Welcome Greg... father of the DX amp layout...!!!!!!
 
#31
Let me know if you can get large electrolytics though say from 2200u to 10000uf under 25mm diameter, 50V.
Click to expand...
Hi,
I can find upto 4700uF 63V in 25mm diameter.
I have not been able to find any 4700uF 50V as small as this, possibly due to the low profile high diameter that seems to be more common at this voltage.
To find any decent uF for smoothing and high local decoupling at under 25mm will be an achievement.
Any sources out there?
 
#32
Just a quick scan through RS Components catalog.

Panasonic TSUP 50V 4700 stock no. 3396865
Phycomp 50V 4700 sn. 4406777 both pretty expensive
enter 38 zar in usd, or whatever your currency is, in google

Looking at the datasheet TSUP is available in 10000uf 25 x 50, panasonic parts no. ECOS1HP103C. Not sure where one would source that...

I settled for jamicon 4700uf which I think were about 22mm...
Local price about ZAR14 + 14% VAT.

A 2200uf cap has a ripple current rateing of about 2A a 4700u 3A...

The output pair's caps I took out the spades and used over 30mm 10000uf caps there, but this is way overkill I believe...

I doubt any diffirence would exist if I used the 4700ufs all around.. especialy not with driving 8 ohm loads...

I think Carlos is useing even less...
The original DX specified 47uf... On Graham Maynard's advice I upped this to 10000uf on the output, with amazeing results.... so that concept... and the capacitors stayed with me...

P.S. 50VDC cap has 63VDC surge rateing.

I would say a reasonable supply voltage would be between 24 and 38VDC so there is the chance... that if you operate at the smaller scale, that you could even use say 35VDC caps

The board is at the limit for half a eurocard, and I am seriously thinking in hindsight, we might need to go for a 2oz copper thickness for the guys running 4ohm speakers.
 
#33
Nordic,

For those traces which would really benefit with the additional copper thickness: What about using the "standard" copper and remove the solder mask from the traces that need an increase in capacity? Would the solder overlay be an acceptable, effective way to increase current carrying capacity?
 
#34
I'm pretty sure a solder layer is more than adequate, and you do have a fairly good idea there... I was looking into the wall of how will people get more current through there with the silkscreen on... Then I typed some number into a trace calculator... and it suggested I'd be OK provided I went for the ticker copper....

Your way sounds wonderfull... Into 8 ohm loads, this is not a worry....

P.S. no wonder I had such a battle with the SMDs last night... turns out they were 0603... only realised this when I picked up the remaining values in 0806 from the shop... these look much easier to cope with... allthough according to my multimeter I did OK last night...
 
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