Mark A. Gulbrandsen said:
I did not make the suggestion for exactly copying the Krell badge logo.
imo however, an improved KSA wouldnt be one without the sanded brass plate.
For me, its also what makes a Krell a Krell.
As the circuit is free for copying, i suppose it is ok to use the KSA50 typing, but leave the Krell name alone.
And the Krell transistor logo, that is what will be registered and copyrighted.
I am using 6 parallel devices, not wise to go without base resistors,imo, with 6 i dont think it will hinder performance.
The SA/SC devices have far better noise numbers than the MPSA's, besides better linearity.
Achieving low signal/noise of the VAS must have been an important factor for Mr. D.
Frankly, that he made the choice to use the 968/970/2238/2240 in the KSA50 in the early 80s was a surprise to me, no doubt he is a very good audio amplifier designer.
I had the chance to listen to the KSA50 back then, but not look inside.
Means i am also going for the 2SA968/2SC2238 instead of the MJE's, sort of keeps it a classic.
Member
Joined 2002
I wonder if i can use 50V rails ? yes no ?
I have 2 useless transofrmers right now @ 1kva that id like to build up with some thing..
I have 2 useless transofrmers right now @ 1kva that id like to build up with some thing..
jacco vermeulen said:
Its a shame Al went with the MPSA pin outs for the layout as I too will be using the SA/SC's.
I do understand why he did it though as they aren't easily available in some parts of the world.
Hi Guys,
I tried to locate this info along the +2000 posts, but didn't find it. Maybe some one can help me.
I'd like to more boards to my wiki current order, but i have 2 doubts:
1 - Do you know the price for any additional output board ?
2 - Could they work with Alpehs amps too ?
Thanks,
Loris
I tried to locate this info along the +2000 posts, but didn't find it. Maybe some one can help me.
I'd like to more boards to my wiki current order, but i have 2 doubts:
1 - Do you know the price for any additional output board ?
2 - Could they work with Alpehs amps too ?
Thanks,
Loris
should work fine...
I am using 85v rails and heading to 100, at this level there are some adjustments needed for the front end, but I don't think you will have any issues. The c2240 and a970 transistors are 'only' rated to 120v, so the max rail for these parts would be 60v, but other things would be too hot before this.
For the very high rails I have swapped all the small signal transistors to be MPSAx2 types, 300v parts, though the MPSAx3 types would work fine too.
Basically since you have the transformers your biggest 'problem' with 50v rails is heatsinks, assuming you want the full 8ohm class A output you will increase the idle current to about 2.5-3A, and dissipate ~275w per channel...
Re noisy transistors...so far the noise floor in the big krell is defined by the power supply hum. I will get the odds and ends needed to assemble a more substantial supply today, but with 'only' 10000uF per rail per channel and ~1A idle current there is about 0.25mv random noise and 3mv 120hz ripple...ie currently the signal to noise ratio, including hum is still approaching 90db, pretty darn good, excluding hum it is exceptional...and I'm not yet at the peak output of the amp...
Yup, ~600w into 4ohms, but right now I can't do full power tests for very long, my 'resistor pack' is nominally rated to 450w, it gets quite hot...I am planning to solder a bunch more of the packs together, since I want to do 2ohm tests...
Stuart
I am using 85v rails and heading to 100, at this level there are some adjustments needed for the front end, but I don't think you will have any issues. The c2240 and a970 transistors are 'only' rated to 120v, so the max rail for these parts would be 60v, but other things would be too hot before this.
For the very high rails I have swapped all the small signal transistors to be MPSAx2 types, 300v parts, though the MPSAx3 types would work fine too.
Basically since you have the transformers your biggest 'problem' with 50v rails is heatsinks, assuming you want the full 8ohm class A output you will increase the idle current to about 2.5-3A, and dissipate ~275w per channel...
Re noisy transistors...so far the noise floor in the big krell is defined by the power supply hum. I will get the odds and ends needed to assemble a more substantial supply today, but with 'only' 10000uF per rail per channel and ~1A idle current there is about 0.25mv random noise and 3mv 120hz ripple...ie currently the signal to noise ratio, including hum is still approaching 90db, pretty darn good, excluding hum it is exceptional...and I'm not yet at the peak output of the amp...
Yup, ~600w into 4ohms, but right now I can't do full power tests for very long, my 'resistor pack' is nominally rated to 450w, it gets quite hot...I am planning to solder a bunch more of the packs together, since I want to do 2ohm tests...
Stuart
2 - Could they work with Alpehs amps too ?
No2:
you can use the output boards for the Aleph5.
(unless you wish to leave one position on the board empty)
Only problem is where to put the parallelled output resistors ?
imo, using these for an Aleph is better than PTP.
But quality of the layout is of great importance too for Aleph amplifiers ( confirmed by Mr Pass also on this forum)
iiwy : wait for the universal Aleph boards Blues is developing.
(i happen to be the chosen European distributor stiff for those boards)
90dB is good, but the KSA50 is supposed to be the one for sensitive loudspeakers.
No2:
you can use the output boards for the Aleph5.
(unless you wish to leave one position on the board empty)
Only problem is where to put the parallelled output resistors ?
imo, using these for an Aleph is better than PTP.
But quality of the layout is of great importance too for Aleph amplifiers ( confirmed by Mr Pass also on this forum)
iiwy : wait for the universal Aleph boards Blues is developing.
(i happen to be the chosen European distributor stiff for those boards)
90dB is good, but the KSA50 is supposed to be the one for sensitive loudspeakers.
Hi,
you might be right about choosing 968/2238 due to noise but I think it much more likely HE chose to go 968 for the much higher Ft (above 100MHz from 75mA to 400mA) and good gain (hFE O >70 & Y>100).
However the SOAR plummets, already down to 12.5w by 40Vce making it unsuitable for higher voltage drive and particularly into low loads.
I have heard some say keep all the transistors at the same speed. I believe that a gradual reduction in speed from input to output with the outputs effectively the slowest is more likely to sound nice.
Unfortunately my thread asking for advice on this received very little response and no guidance.
you might be right about choosing 968/2238 due to noise but I think it much more likely HE chose to go 968 for the much higher Ft (above 100MHz from 75mA to 400mA) and good gain (hFE O >70 & Y>100).
However the SOAR plummets, already down to 12.5w by 40Vce making it unsuitable for higher voltage drive and particularly into low loads.
I have heard some say keep all the transistors at the same speed. I believe that a gradual reduction in speed from input to output with the outputs effectively the slowest is more likely to sound nice.
Unfortunately my thread asking for advice on this received very little response and no guidance.
Andrew,
that holds truth also for the 970/2240, check Hfe values for those compared to mpsa's.
(i did read your thread with great interest, thought it wiser not to post, only repeating my opinion)
(i am putting only 34vdc(25vac toroids) on the output)
Drivers already were MJE's, 15030/15031, right ?
Swapping those for the 15032/15033 should be an improovement
that holds truth also for the 970/2240, check Hfe values for those compared to mpsa's.
(i did read your thread with great interest, thought it wiser not to post, only repeating my opinion)
(i am putting only 34vdc(25vac toroids) on the output)
Drivers already were MJE's, 15030/15031, right ?
Swapping those for the 15032/15033 should be an improovement
AndrewT said:
I don't know if this applies to your comment but NP philosophy regarding rolloff that might be good to have in mind:
"When selecting values for input vs output rolloff, we greatly
favor the input rolloff frequency as being higher than the output
because you don't want to work the amp harder than you have
to at low frequencies."
Actually installing theSA/SC devices in this board will be very easy. All one needs is a tiny piece of teflon tubing for one of the leads that will cross over, or just bend the leads into a fancy orientation so they fit right in...... no big deal.
I went ahead and installed the MPSA devices becuae I have alot of them and because it gives me a chance to do measurements and listening tests with both sets of devices... I do believe however that the SA/SC devices will win out easily.
Ohhhhhh K Jacco... Yea, that Stinkin Bage is far more important than whats inside......
Mark
I will certainly be interested in the measured results, as my test equipment isn't exactly cutting edge. As I said earlier, they sounded pretty alike to me. YMMV, of course, I wouldn't dare to give a definitive parts selection. 😉
Mark A. Gulbrandsen said:Ohhhhhh K Jacco... Yea, that Stinkin Bage is far more important than whats inside......
Call me sentimental.
I am thinking of making this one completely in slotted and polished stainless, a brass plate on it would look nice.
And i even desire an original Krell style central switch.
Glad we agree on the Stinkin Tosh, M.A.G. !
center mount switch
Jacco,
What type of switch are you thinking about?
Bulgin makes an illuminated switch available as ring illuminated. In colors! It is low voltage so it requires a relay. This could work well with soft start.
http://www.bulgin.co.uk/HTMLDocs/news/IllumVandalSwitches.html
Jacco,
What type of switch are you thinking about?
Bulgin makes an illuminated switch available as ring illuminated. In colors! It is low voltage so it requires a relay. This could work well with soft start.
http://www.bulgin.co.uk/HTMLDocs/news/IllumVandalSwitches.html
Jacco,
Look again..... that plate and its screws are actually gold plated... donno how many carrots but Bugs Bunney certainly does. That plate was a purchase option for any Krell owner of that era. The color of the plate that came with it depends on what color hard coat the front panel is. My KSA-80B had a black anodized Krell Logo insert...... I coulda bought the Gold plated one but it was pretty expensive though..... musta been alot of carrots
Mark
Look again..... that plate and its screws are actually gold plated... donno how many carrots but Bugs Bunney certainly does. That plate was a purchase option for any Krell owner of that era. The color of the plate that came with it depends on what color hard coat the front panel is. My KSA-80B had a black anodized Krell Logo insert...... I coulda bought the Gold plated one but it was pretty expensive though..... musta been alot of carrots
Mark
Hi Apassgear,
on reading your quote out of context I think Nelson is referring to the RC filters formed by the input and output capacitors.
Although the output capacitor does not strictly apply here (smoothing *load =RC) there is some consensus that the time constants from input thro' NFB to output should become longer as you progress through the amp. On that basis Nelson is confirming this idea.
However I was referring to the inherent speed of the active stages forming LTP, VAS, predriver, driver, output.
As amps get upgraded over the years (decades) and new models are dissected it has become fairly clear that faster transistors are being used in the middle stages and in the output. Many of the LTP transistors have had Ft over 200MHz for longer than I have been following this avenue. So it seems to me that a progression has become the aim, but an equalising in speed could be read from the same source information. That might justify adoption of MPSA in the LTP & VAS. However when slower outputs (MJL21193/4) were suggested, immediate condemnation appeared because it would increase distortion, surely this argument would apply to earlier stages as well? Comments?
on reading your quote out of context I think Nelson is referring to the RC filters formed by the input and output capacitors.
Although the output capacitor does not strictly apply here (smoothing *load =RC) there is some consensus that the time constants from input thro' NFB to output should become longer as you progress through the amp. On that basis Nelson is confirming this idea.
However I was referring to the inherent speed of the active stages forming LTP, VAS, predriver, driver, output.
As amps get upgraded over the years (decades) and new models are dissected it has become fairly clear that faster transistors are being used in the middle stages and in the output. Many of the LTP transistors have had Ft over 200MHz for longer than I have been following this avenue. So it seems to me that a progression has become the aim, but an equalising in speed could be read from the same source information. That might justify adoption of MPSA in the LTP & VAS. However when slower outputs (MJL21193/4) were suggested, immediate condemnation appeared because it would increase distortion, surely this argument would apply to earlier stages as well? Comments?
Mark A. Gulbrandsen said:
You American blokes are so lucky.
Overhere Krell offered a giant range of versions, as long as they were anthracite grey.
Always with the goldplated bagel and screws, it became synonymous for Krell's.
Here's a copy from the KSA80B data, in 80s catalogues only one version was listed.
I have never seen Krell's with other front plate colors or badges.
The data also shows the very high S/N number of 80s series Krell's.
I sure am not going to spend cold hard cash on stinkin goldplated badges !!
Attachments
Here is an idea of what i am thinking of for the Krell mono's.
This is a pre i made, allround chromed 1/4" steel plating, on a welded and tapped rectangular chassis frame.
All the knobs are hollow, machined out of solid brass, 2 pieces welded together and chromed.
Beware of chroming, yesterday i was cleaning and polishing for the zillionth time.
I spent 3 days and $50 of diamond paste on getting the front plate right for the chroming job, which took 3 runs to get it right.
Going stainless steel for the Krell's, i have a pro polishing device in my garage.
(no, i dont like chromed screws)
This is a pre i made, allround chromed 1/4" steel plating, on a welded and tapped rectangular chassis frame.
All the knobs are hollow, machined out of solid brass, 2 pieces welded together and chromed.
Beware of chroming, yesterday i was cleaning and polishing for the zillionth time.
I spent 3 days and $50 of diamond paste on getting the front plate right for the chroming job, which took 3 runs to get it right.
Going stainless steel for the Krell's, i have a pro polishing device in my garage.
(no, i dont like chromed screws)
Attachments
Chrome can be a pain but if done right can look good. There are alot of good chrome plating houses in the U.S. because of all the Harley motorcycles here. Polished SS might be more practical but every finger print will still have to be kept off the face plate or wear white gloves when operating. I don't mind that Anthraite font panel at all, no finger printing problems and its alot easier and less expensive to do. It can be re-done is some scratches or dings show up down the road.
My favorite front panels ar the Rowlands...... cheap to do and very beautiful.
Mark
My favorite front panels ar the Rowlands...... cheap to do and very beautiful.
Mark
ksa-1hp
Hi Folks,
I just crawled out of bed, barely caffeinated at all, but wanted to let you know status for work on the big amp...
Yesterday we broke the 1hp barrier, I can get 800w RMS into 4 ohms, for as long as my 440w test load can stand it...about 5 minutes on then 25minutes off...
I rebuilt the power supply using a bigger transformer, the rails hold up better, yielding about 160v peak to peak, starting from approx. ~99v, with 1A idle current.
I changed some more stuff around in the front end to make it less sensitive to rail voltage, the random noise floor dropped 5db and the hum is now at about the same level as the noise...and best of all, the front end now works with rails from 15v-120v with no adjustments, very handy...any guesses?
Stuart
Hi Folks,
I just crawled out of bed, barely caffeinated at all, but wanted to let you know status for work on the big amp...
Yesterday we broke the 1hp barrier, I can get 800w RMS into 4 ohms, for as long as my 440w test load can stand it...about 5 minutes on then 25minutes off...
I rebuilt the power supply using a bigger transformer, the rails hold up better, yielding about 160v peak to peak, starting from approx. ~99v, with 1A idle current.
I changed some more stuff around in the front end to make it less sensitive to rail voltage, the random noise floor dropped 5db and the hum is now at about the same level as the noise...and best of all, the front end now works with rails from 15v-120v with no adjustments, very handy...any guesses?
Stuart