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In Reply to: RE: HK Citation 2 rebuild questions posted by Ping on April 16, 2015 at 18:47:48
Ping
You have to understand that the variables have changed since these amps were built.For one thing,the music material we listen to today is much more dynamic than in the 1960s.Where 40db dynamic range was the norm,most material today whether it be LPs or CDs runs between 90db and 105db dynamics.
This puts an incredible drain on the power supply under peak dynamic conditions. You also have to understand that rebuilt Macs and Citations are not powering old speakers anymore.Many of the McShaned Macs and Citations are powering modern Electrostatic speakers such as Martin Logan,Quad,and even the planar magnetics such as Magnepans and these speakers require more energy when played above moderate levels.
Even on the efficient speakers of the day,you can no longer depend on stock values because of the garbage on the power lines today from all the digital noise.You will hear that noise come thru with an anemic power supply on quiet passages and it's very irritating.
You have to also understand that these amps are capable of much more than when they were originally made.You aren't changing the circuitry by building a stout and quiet power supply with greater energy and a lower impedance.You are just purifying the wonderful sonic attributes of what is already there.You could keep the original filter cap values if you were using all film caps because they are much faster and much more efficient than an electrolytic of the same value but let face it,there just isn't the room to do that in most cases. Always remember that an amplifier is nothing more than a DC power supply that we modulate with an AC signal.The more we purify the power supply and give it more joules of energy,the happier our amplifiers and speakers will be.The stock value Mac or Citation cannot drive modern speakers in the 87db to 91db range with 95db dynamic material with stock values because on the first heavy transient,you hit the DC rail in a hurry and then you have an inferior sounding amp on your hands.Read this thread and see what I mean.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Edits: 04/18/15 04/18/15Follow Ups:
Hi Mike,
First off, I'm glad to hear you are feeling better!
Just one thing - while the lower ESR, DF, and other desirable factors of film caps are nice to have, the added energy storage from the larger value caps in my kits makes it possible for the amp to deliver more peak power and deliver it for a longer period of time. While the larger caps have but a minor impact on RMS power they have a significant and measurable impact (for the good!) on short term peak power. This is VERY important with wide dynamic range material!!
Think about it - the Cit II was rated by H-K at 60 watts/channel RMS power and 130 watts/channel peak power into 8 Ohms. With the Cit II OPTs that requires a swing of just under 22 volts into the 8 Ohm load, and pushing 22 volts across 8 Ohms requires about 2.75 amps of current in the secondary. This is available from the power supply continuously.
To produce 130 watt peak power requires just over a 32 volt swing in the secondary and requires a primary swing of 635 volts (yes, the primary CAN swing above the rail for short periods). 32 volts into an 8 Ohm load requires 4 amps of secondary current. IF the power supply can deliver the current, the peak power can increase and be maintained for longer periods. This means the power supply should be capable of delivering well over the current requirements to meet its RMS spec - it should be capable of supporting peaks well above the RMS rating. In the Deuce that means more energy storage - bigger (and much higher quality, if not quite to the level of a good film cap) power supply caps. This results in improved peak power performance.
Do note that yes, I left out trafo losses and frequency related issues in the explanation to simplify things a bit.
Just one thing - while the lower ESR, DF, and other desirable factors of film caps are nice to have, the added energy storage from the larger value caps in my kits makes it possible for the amp to deliver more peak power and deliver it for a longer period of time. While the larger caps have but a minor impact on RMS power they have a significant and measurable impact (for the good!) on short term peak power. This is VERY important with wide dynamic range material!I agree Jim.I was just making the point that the only possible way you may get away with using stock values would be to use film caps and even then you will run into issues.The caps that you have in your kits perform like film caps only they have the energy storage snd delivery as well. The Panasonic ED series are the best electrolytics in existence right now AFAIC and as you say peak power delivery is what it's about..If you would have told someone 30 years ago that you can power a set of ESLs or Magnepans to dynamic levels with an Mc240 or Citation 5,they would have thought we were on something,that is until your wonderful kits came along.You also use one or two film caps in your kits on the smaller values.
BTW,your kits have the lower ESR,DF,and all the desirable factors of the film caps..Just because they are electrolytics,doesn't mean they don't produce much better specs than the old 55 degree cans.I only use film caps in a few places such as off a GZ34 rectifier tube or as added decoupling at times like in the Mc240.It doesn't mean you have to use film caps and in most applications it just isn't feasible because of size restraints.In a couple places it can be a blessing.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
Edits: 04/18/15
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