Simple modification of Roksan Caspian

[analog_sa]

but I will endeavour to post some pictures of my pet cat

Sounds good. I love cats.

I am going to try adding 4x 10,000uf to really beef it up, and we'll see what that does for the bass...

It will likely turn it into a not very powerful subwoofer amp. Adding capacitance certainly changes the sound and i remember well how in the 80s all the american mags were coming up with monstrous capacitance banks projects; the authors, likely eligible for deaf disability payments, all claimed tremendous improvements in all areas. All areas bellow 100Hz, that is Adding capacitance above a sensible limit, in particular to a class AB amp is very likely going to destroy the subjective dynamics, especially microdynamics; dull the timbre and also put excessive strain on both transformer and diodes. It will probably also increase the diodes switching noise. And your cat won't appreciate it.

peter

 

[SimontY]

2 nights ago I added 2x10,000uf 63v Samwha, as I suggested I might. Rectifiers/transistors are ok so far, but I haven't added that much capacitance or played it for a party - in this house?!? ...not happening

I looked for results with a very open mind, and the knowledge that my Caspian "will likely turn it into a not very powerful subwoofer amp" ( analog_sa)

Before 'warming up/system bedding in/caps running in' the amp sounded unfamiliar, different but not necessarily improved or unpleasant. Hints of extra richness came through from the start, accompanied by some apparent loss of clarity in the mid/top-ranges.

Extended listening shows, I believe, a good sound improvement in overall musicality (rock, electronic, dance listened to mostly). Bass is very impressive, as predicted - it's richer, deeper, and less hard, sounds really effortless. And loud is lots of fun - it just gets louder - much better!

The idea that this sort of modding would make no difference made me wonder if people had tried much and actually listened, not starting an argument here - just saying I know what I heard. And the suggestion that adding much more capacitance would make it a low-power sub amp make me chuckle - this is utter nonsense in my case - and it's very powerful!! (with 91db speakers and a healthy sub, in a small room ) I reccommend trying cheap caps to rump up the reservoir storage to anyone with a less than mega-buck amp.

Thanks for reading.


-Simon

 

[SimontY]

ooh, almost forgot

He is called Leo, and doesn't give a flying feck about hi-fi...

 

[tbla]

good to hear about your succes....and you really didn't add that much capitance (shouldn't add more)

now, go for the rectifiers......
http://www.schuro.de/Daten/IR/hfa08tb60.pdf

 

[SimontY]

Hi tbla,

Those rectifiers look like some nice beasts, but they are 'TO-220AC' package. How could I connect them? Or even better, is there an alternative in the normal diode package? (sorry, I don't know what it's called...)


-Simon

 

[analog_sa]

Simon

I am really glad that you like it - there is absolutely no reason why we should share the same sound preferences - we probably don't listen to the same music either and all this is a question of taste. What is certain, though is that your ears function well
There should be no prob replacing your diodes with TO 220, you might have to extend the pins slightly.

peter

 

[Luke]

Hi tbla,

Those rectifiers look like some nice beasts, but they are 'TO-220AC' package. How could I connect them? Or even better, is there an alternative in the normal diode package? (sorry, I don't know what it's called...)

Hi Simon,

if your not sure about making bridges out of discrete diodes, try going to http://www.percyaudio.com/ and download his catalog, have a look at his IXYS bridges, they are allready made up for you and only have to replace your existing ones. If you can spare the cash try getting a couple of Nichion KGs and replace all your caps with 2 nice 10000 uF caps. I think cap quality may do more than actual amount (unless your building class A monsters
) This way you have a higher quality cap and about 30% more capacitance.
BTW If you can pull that off, your almost ready to build a gainclone

 

[tbla]

hi simon,

the biggest problem is actually stripping the hole amp apart once more......but you'll get used to it

you could cut the original diodes legs and solder the new ones on to them.....BE CAREFULL its high voltage - so do it proberly...!

go for it !!!

 

[SimontY]

Thanks Peter,

Glad you're happy now, I am too

I actually ordered four of those large caps, but decided to try two first, I won't bother with the other two as I'm quite happy with the result... still plenty of other ways to improve/tailor my sound I'm sure!

re: the diodes, which I am now quite interested in:
Farnell sell axial/DO-204AR Schottky types up to 9A@45v at 2.45ukp each - seems pricey, but if they're really good then 10 pounds or so will be good price for the upgrade, for the four.

Alternatively there are Schottky diodes as DO-220 which look nice, and can take more current. Or there is 15A T0-220AC for £1.79 - this one is 'ultra fast recovery'. Another option could be 'soft-recovery'/do-220/15A/400v.

Can anyone tell me which sort is most appropriate for upgrading an amp psu? Farnell have so much to choose from!

Cheers


-Simon

 

[SimontY]

Aha! More options and things to try, thanks chaps. I'd actually started writing that last reply several hours ago and left the room/house, so I'd not seen the previous 2 posts.

Percy audio sell some amazing stuff! Good to look at, though I don't like to order things from the States. Mind you, if I can think of enough things I can't get hold of here... I see what he says about the 'soft recovery' diodes - just what most amps need, I'm sure. I take it the t0-220 or silimar type packages are the ones commonly used for the serious diodes then...

"the biggest problem is actually stripping the whole amp apart once more" - dam right, it's a royal pain in the buttocks. I'm totally used to it with my cd player though - done it so many times to tweak/change things, but I've only just worked up the courage to fiddle with my amp, as it's so much more expensive!


-Simon

 

[analog_sa]

Dunno about the diodes you mention. They may well be good. If you'd rather play it safe i suggest the MUR860 which seem to be generally liked. I get them dirt cheap even in SA - about 50p.

cheers
peter

 

[millwood]

If you'd rather play it safe i suggest the MUR860 which seem to be generally liked. I get them dirt cheap even in SA - about 50p.

but do they sound good tho.?

 

[tbla]

it's one or the other.....go...!

 

[SimontY]

MUR860 diodes

MUR860 is 85 pence from Farnell, so about a dollar/euro or more with tax.

Looking at the datasheet, I see MUR820/40/60 are "designed for use in switched mode psus..." Is there significance in this design goal?

Also, what does 'soft-recovery' mean? Are they lower noise? MUR860 doesn't appear to be 'soft-recovery'.

Cheers,

-Simon

 

[SimontY]

Hmm, here is an interesting question for you all.

Has anyone tried bypassing diodes with film caps e.g. 22nf or 220nf, (which I have some of)?

Is this safe, and is it worthwhile? If so, I will try this before replacing the diodes, and see if there is any noticable difference to sound-q. I would position the caps across the tops of the diodes, the legs would just reach each of the diodes' legs.

Any thoughts?


-Simon

 

[tbla]

as i recall, the original diodes are allready bypassed by some caps - likely wima mks4...right now, don't touch them.....

personally i would go for the http://www.schuro.de/Daten/IR/hfa08tb60.pdf

 

[SimontY]

Thanks tbla, I searched Farnell for that part no. and found it, it's £3.06 - pricey, so I hope they're good I will order them soon I reckon...

Meanwhile I've shielded some caps and a chip in the amp - yeh, I know it shouldn't make much difference, but I like to do these things (worked in my cd player, I think)

Tbla, you seem to know the Caspian well I saw some caps, Wima I think, near the diodes and wondered if these were 'bypass' - I wouldn't know without turfing the board out!

Will keep y'all posted....


-Simon

 

[tbla]

....expensive...rs is a bit cheaper.

check these prices...http://www.schuro.de/preisl-dioden.htm

 

[SimontY]

Oh my word, they're one quarter the price!!!

Have you ever heard the phrase 'rip-off Britain'...? This is a perfect example. And I believe one needs a trade account to buy goods from RS here Oh well, it's only 4 I need, so it's not a huge amount in total.

BTW there are three voltage regulators with large heatsinks on them, are these likely to be critical? I think two are in the pre-amp section, so I guess they are very important. The sinks get incredibly got, even with the outer cover off - is it wise to apply some good thermal paste inbetween the reg. and sink? Or even to fix on a larger heatsink? I remember reading how they work better at lower temps... though my amp sounds better as it gets hotter - as they all (class a/b) seem to.


-Simon

 

[tbla]

yes, its a rip off - but schuro has some very good prices too.....

and you only need 4 of them so perhaps farnell is the way to go.

if you want to do anything else to your amp, i strongly advice you to get a service manual and study it closely.....