| beckypumps |
Hi Folks
I am looking to replace the 4 40000 uf 75vdc capacitors in my old krell ksa 50, but I am having no joy searching the internet.
Do I have to use exactly the same spec of components. if not what can I use and where can I get them.
please go easy on my as mechanics is my trade not electronics, I do understand V=IxR if that helps.
The amp seems to have difficalty drive ,bias and offset all check out on my meter also it heats up as normal.
it sounds as if you are feeding it a signal with no bass and lots of treble.
Im realy stumped on this one and any help would be most welcome.
Kindest regards: |
|
|
| jaycee |
Are you absolutely sure this is the power supply capacitors ? This could be a problem with the capacitors in the feedback path.
As for the power supply capacitors, you can use any similarly sized capacitors that have 75V or better voltage rating, and a similar amount of capacitance. While i've not seen the KSA 50, Krell usually use screw terminal capacitors. 47000uF 80/100V should work provided they physically fit
edit: Apparently the KSA 50 has 50V power supply rails. If that's the case, 63V rated capacitors will be fine. |
|
|
| pinkmouse |
| Yes, the symptom of supply caps going bad is usually hum breakthrough and lack of response at the bottom end. Which version of the Krell is it? |
|
|
| beckypumps |
Thanks guys.
The amp is a ksa 50 mk1 very early ,it shares a lot of parts with the orijinal ksa 100 so I suppose krell just used components at hand to build the 50.
I have found a few caps rated about 47000 100vdc the same size and also a few at 37000 uf 63 vdc.
Their is no bottom end to the sound things went pear shaped ages ago when I attempted to adgust the bias and managed to snap of a roc cap 16v 1000uf next to the bias pot. so I replaced all 4 with black gate ones then set up the bias and off set .
I keep on telling my self that I should leave things alone, but I cant help it, i HAVE TO TAKE THINGS TO BITS ETC.
Im not 100% sure the caps are dead people are suggesting that they may be the problem as the amp is 20 years old.
Any thoughts? |
|
|
| jacco vermeulen |
Resetting bias and offset is not bad, more like common sense.
If you have a MKI, and the big cans are the original ones, you can be sure that they are causing it. Or near death.
+20 years and those temperatures is a killer combo.
Only question i have is whether you replaced the 16V caps between the feedback resistor and ground in the right position, +and - where they belong ? |
|
|
| beckypumps |
If I had the 16v caps the wrong way round could this be causing the problem.
The amp was fine before I started to fiddle with it, do caps sudenly give up of is it a gradual process.
sorry for the silly questions but if I dont ask I will never now.
Cheers |
|
|
| beckypumps |
| Sorry I forgot to add for pinkmouses benifit there is no hum just a lack of bass/lower mid |
|
|
| jacco vermeulen |
| quote: | Originally posted by beckypumps
If I had the 16v caps the wrong way round could this be causing the problem. |
Yep.
in practice there is less than 1 volt across the series 16v caps.
Hooking them up the wrong way need not kill them, but the effect is peculiar.
I would change the big ones just the same, there should be little left in them. |
|
|
| pinkmouse |
That's ok, a few of us have had a little practise with Krells around here! :)
BP, can you take a pic of the boards so we can see what you've done? |
|
|
| jacco vermeulen |
I've got a cunning plan !
Join the Krell thread and build new Krell clones, you'll be the first one with a finished Krell and the bestlooking chassis.:clown: |
|
|
| beckypumps |
Ive taken a pict of the board im just trying to work out how to down size it as the file size is to big.
I hate computers |
|
|
| pinkmouse |
Hmm, I don't see how they would make as much difference as you seem to note. What's your bias set to?
edit: just checked the pics on Lloyd's site, and your caps are the right way round. I don't suppose you might have damaged C9 or C12? |
|
|
| beckypumps |
I set the bias to 620 mv as per Loyds drawing.
The + should face the outer edges of the board and the - should face each other.
The black gate caps have a gold strip down one side which signifies + or- both gold strips are faceing each other. so they are mounted + - - + or - + + - either way you think that this wont cause the loss of bass? |
|
|
| Mark A. Gulbrandsen |
As classic audio gear goes it should be kept all original if you want to maintain its actual value. I am pretty convinced that the KSA-50 clone thread has actually increased the value of KSA-50's in general. If it were my amp I wold be getting the Krell replacement caps right from the factory... if they will sell them to you. They should actually say Krell on them. They were probably chstom made and will be expensive to get .......... It all depends on how original you want to keep it.
Mark |
|
|
| Mark A. Gulbrandsen |
A bit later KSA-50. The date code on them is 1984. These are either customs or at least re-branded.
Mark |
|
|
| clem_o |
| quote: | Originally posted by beckypumps
Thanks guys.
Their is no bottom end to the sound things went pear shaped ages ago when I attempted to adgust the bias and managed to snap of a roc cap 16v 1000uf next to |
Since the capacitors seem to be in the right direction, I am wondering if you ever tried any other amplifier, and if you can say that an alternative amp gave you in fact more bass? Just guessing, could be the loudspeaker surrounds are torn...
Cheers!
Clem |
|
|
| beckypumps |
Speakers are fine they are soundlab m3s also for test purposes im using townshend glastonburys with full range jordan drivers+ribbon tweeter. my main amps are ASL hurricans and I have a few integrated cheepies that all give out proper bass.
Some people are talking about the feedback loop. Im not 100% sure what this is but would prefer to change a inexpensive cap that 4 big ones.
could someone explain about the feedback caps in simple detail to me, I feel that im at the bottom of a steep learning curve here.
Also thanks for everybodys help so far.I have also posted this question on audio asylum diy page. |
|
|
| clem_o |
beckypumps,
The "feedback loop" is the connection from the amplifier output to its input stage, a way for the amplifier to correct any errors its output produces. From the KSA50 pdf, those components would be R12, R11 and C3. Try replacing C3; if its capacitance has dropped due to age/heating it could cause the symptoms you describe, as others have advised...
Cheers!
Clem |
|
|
| Dick West |
I have a pair of Krell 40,000 uF 75 WVDC caps here. They were made by Capacitor Technology but are also branded as KRELL IND.
I reformed them about 10 years ago and they checked out OK but have since been gathering dust on a shelf.
They are "free" if someone will pay postage and give me $10 to package them and get them to USPS. Any interest?
Dimensions 5 5/8" tall and 3" in diameter.
Dick |
|
|
| beckypumps |
I would like to thank everyone who gave me info on my old krell ksa 50 amp.It is now fixed and also I have found out it is a mk2.
The neg feedback loop was to blame. caps were ok but it had a poor earth.I should of checked continuity on both sids of the PCB!
This is a major achevment for me as im not electricaly trained. now then what can I take to bits next?
Kindest regards
Beckypumps |
|
|
| lgreen |
Congratulations!
Perhaps next you can "rip to bits" some more items as you say. Hmmm why don't you replace the output transistors? I believe the Krell shipped with MJ15003/4, you can update these to new modern Onsemi devices MJ21193/94 and perhaps it will sound better and more refined? Plus, the old devices were probably wearing out from all that heat and even replacing them with the same devices (which are still made) might be an improvement.
Just my suggestion. |
|
|
|
