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I’ve been told that increasing filter cap values in the MC30 can enhance things like bass response..

angelaudio

angelaudio

Super Member
But how exactly does this work?

What is going on electromically that allows for this perceived increase in bass, mid or high frequency response?

Are there any detrimental effects on other components because of increased filter cap values? Say...200uf instead of 100uf 40uf etc..
 
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I'm sure that McIntosh missed that detail in their design, ... the thougt of a larger capacitor improving SQ was not part of power supply design 101 until we just thought of it this week (blatant sarcasm, I was designing circuits 40 years ago).

You can measure voltage drop vs power output with a scope if you want, or look for clipping, it would be part of the spec as distortion however and there isn't much distortion in the MC30 to improve.

Usually the capacitor is limited by the capacity of the transformer and rectifier to charge it without overload and during the available input phase/timing, sometimes simply by the physical space available. A larger capacitor can also change the charging timing of the capacitor which can have detrimental effects on the audio, but only the original designer really knows why the original value was chosen and unfortunately he is no longer available.

Where I typically doubt that there's a perceivable difference between a new correct capacitor and a new oversized capacitor, I do not doubt that there is a difference between a new oversized capacitor and an old worn-out original and this is where I believe most of this myth originates.

YMMV and I haven't actually tested an MC30's power supply vs maximum output. If you exceed the rated capacity of the rectifier tube you will create a new bottleneck and possibly other problems, and certainly not pass enough current to feed the capacitor.

Another way to look at the filter capacitors is as a water tank. If you don't increase the flow into the tank you can't keep it filled if the output exceeds the input, ... no matter how large the tank. Spikes in demand and output can possibly be larger (if the capacitor was undersized or worn-out) but will never exceed the capacity of the rest of the system (including the power tubes) without increased distortion.
 
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SaturationPt said:
I'm sure that McIntosh missed that detail in their design, ... the thougt of a larger capacitor improving SQ was not part of power supply design 101 until we just thought of it this week (blatant sarcasm, I was designing circuits 40 years ago).

You can measure voltage drop vs power output with a scope if you want, or look for clipping, it would be part of the spec as distortion however and there isn't much distortion in the MC30 to improve.

Usually the capacitor is limited by the capacity of the transformer and rectifier to charge it without overload and during the available input phase/timing, sometimes simply by the physical space available. A larger capacitor can also change the charging timing of the capacitor which can have detrimental effects on the audio, but only the original designer really knows why the original value was chosen and unfortunately he is no longer available.

Where I typically doubt that there's a perceivable difference between a new correct capacitor and a new oversized capacitor, I do not doubt that there is a difference between a new oversized capacitor and an old worn-out original and this is where I believe most of this myth originates.

YMMV and I haven't actually tested an MC30's power supply vs maximum output. If you exceed the rated capacity of the rectifier tube you will create a new bottleneck and possibly other problems, and certainly not pass enough current to feed the capacitor.

Another way to look at the filter capacitors is as a water tank. If you don't increase the flow into the tank you can't keep it filled if the output exceeds the input, ... no matter how large the tank. Spikes in demand and output can possibly be larger (if the capacitor was undersized or worn-out) but will never exceed the capacity of the rest of the system (including the power tubes) without increased distortion.
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Thank you for your input. Very interesting points you bring up. I see others recommend capacitor value increases so often that I have begun to wonder just how much is too much of an increase. In some cases they recommend 20uf increases for things like filter caps and I’ve even seen in some cases people recommend 100uf and up increases. It’s confusing since there is usually no data to back up the claims. I’ll need to do some further research into the matter but you’ve given me some good starting points to guide me in the right direction. Thank you!
 
I think that someone brought up the recommended capacitor size for your rectifiers (5U4?) as 40uf in another thread some time back, but looking at the rectifier tube specs might be a good place to start.
 
C12A in an MC30 should not be higher than 40uF, but there is benefit to increasing C12B to 100-110uF for reserve power available. This is where the perceived benefit in bass comes in. It doesn't increase bass, but provides more steam (power reserve) to drive the bass.

@SaturationPt 's analogy is correct, the output cannot be greater than the input, but that is exactly why we have well tanks to compensate for the temporary increase in demand. Once demand drops, it refills. That's what the larger C12B will do. It is not infinite reserve, but it does make a noticeable difference.

The same can be said for increasing the value of C13 in the bias supply. Terry D recommends a 22uF to "stiffen up" the bias supply. (His words.)

Why weren't larger caps used originally? Space perhaps? Cost? Can't say.
 
x3workshop said:
C12A in an MC30 should not be higher than 40uF, but there is benefit to increasing C12B to 100-110uF for reserve power available. This is where the perceived benefit in bass comes in. It doesn't increase bass, but provides more steam (power reserve) to drive the bass.

@SaturationPt 's analogy is correct, the output cannot be greater than the input, but that is exactly why we have well tanks to compensate for the temporary increase in demand. Once demand drops, it refills. That's what the larger C12B will do. It is not infinite reserve, but it does make a noticeable difference.

The same can be said for increasing the value of C13 in the bias supply. Terry D recommends a 22uF to "stiffen up" the bias supply. (His words.)

Why weren't larger caps used originally? Space perhaps? Cost? Can't say.
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I see I see. What exactly is C12A responsible for feeding power to?
 
x3workshop said:
C12A in an MC30 should not be higher than 40uF, but there is benefit to increasing C12B to 100-110uF for reserve power available. This is where the perceived benefit in bass comes in. It doesn't increase bass, but provides more steam (power reserve) to drive the bass.

@SaturationPt 's analogy is correct, the output cannot be greater than the input, but that is exactly why we have well tanks to compensate for the temporary increase in demand. Once demand drops, it refills. That's what the larger C12B will do. It is not infinite reserve, but it does make a noticeable difference.

The same can be said for increasing the value of C13 in the bias supply. Terry D recommends a 22uF to "stiffen up" the bias supply. (His words.)

Why weren't larger caps used originally? Space perhaps? Cost? Can't say.
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And in regards to the C13 increase, he recommended around a 9.1k resistor or so in series after it, iirc?
 
angelaudio said:
I see I see. What exactly is C12A responsible for feeding power to?
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I don't have the schematic in front of me but typically the power supply of a tube power amp has several sections with inductors and or resistors between each of the capacitor sections. All of this serves to smooth out the AC ripple that is present in all AC to DC linear power supplies. Typically, the first filter cap in the supply feeds only the following stages as it usually has too much ripple to be used effectively.

Shelly_D
 
shelly_d said:
It is likely that input to C12A is the cathode of the 5U4. The cap would not feed the tube, the tube would feed the cap.
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Dang now I’m confused, I thought power flowed from the cathode to the anode. What am I missing here? A lot I know, but can someone remove my blindfold? :(
 
The full wave rectifier converts AC to (rippled) DC feeding the first cap which filters (smooths) the fluctuating current (ripple).
 
angelaudio said:
Dang now I’m confused, I thought power flowed from the cathode to the anode. What am I missing here? A lot I know, but can someone remove my blindfold? :(
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In a simple "grounded cathode" triode, tetrode or pentode amp stage that is true and the anode is the output. So you are right in that. For tube rectifiers, I will leave the explanation of their working to someone that understands them more fully then I. By the way, it is not power that flows, it is electrons. Power is produced by the device when there is a voltage drop across the device accompanied by current flowing through the device. Keeping the terminology correct helps people, especially folks new to the concepts, communicate the basics when all we have is words on paper or a screen.

Shelly_D
 
KentTeffeteller said:
I recommend keeping the MC 30 sounding like a MC 30, want a different sound, buy a different amplifier. A McIntosh tube amplifier is something I would not modify, and McIntosh amps aren't really very hot rod friendly. Want to mod something, get a Dynakit and do that.
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Fair enough, but increasing that cap value doesn't really qualify as a mod in my book. A change in circuit certainly does. Some folks (@Bill Ferris ) have gone the ss rectification route. Not sure I would call that a mod in a true sense either as it still hews to the schematic.

BTW, there were at least 3 versions of the MC30 made that I know of using slightly different circuits or component values. I own two pairs, each pair a different iteration of the circuit.
 
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KentTeffeteller said:
I recommend keeping the MC 30 sounding like a MC 30, want a different sound, buy a different amplifier. A McIntosh tube amplifier is something I would not modify, and McIntosh amps aren't really very hot rod friendly. Want to mod something, get a Dynakit and do that.
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I agree. One thing's for sure, I would not buy one of these amps (or probably any body else's) if it has been modified. If it was refurbished with new ORIGINAL spec'd parts, then maybe.
 
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