Upgrading the power supply capacitors in the Crack

[deltaunit]

Has anyone experimented with upgrading the PS caps, either with higher quality electrolytics or larger sizes?

I understand that lowering the size with have a negative audible affect due to the ripple getting through but are there any disadvantages to fitting larger caps, will they have an increased smoothing capability?

I'm interested in hot-rodding my amp up so am interested to hear if there are any benefits of upgrading these caps.

 

[Maxwell_E]

Capacitor values in the power supply are specifically chosen to filter out certain frequencies of noise. When replacing caps, I stay as close to spec as possible. I am a firm believer that Doc and Paul are much smarter than I am, and they chose those values for a reason.

 

[STURMJ]

You mean like this? I cant say exactly how much of an improvement is was, since I built it initially with the cap in place.  I was said earlier that upgrading the final cap in the power supply would improve the performance significantly, so I did.

 

[deltaunit]

That's the type of thing! Well, I hadn't thought of going that large but yes!

I'm getting access to an oscilloscope in a couple of weeks and was just wondering if the larger the caps the better the smoothing or if there were any drawbacks of going large...?

I'd also be interested to know why the main improvement is to be made on the last cap in particular, rather across the board (expense?) or on the first taking the largest ripple...

 

[Paul Joppa]

The output audio current flows through the power supply, mostly the last capacitor, as well as through the output coupling cap and the output triode. So the final power supply cap should, in theory, be as important as the output coupling cap with regard to the sound of the amp. This is a characteristic of cathode follower circuits, such a the Crack and the Foreplay.

 

[Doc B]

An alternative to bigger 'lytic caps might be to try a film bypass cap across the last filter cap.

 

[deltaunit]

Thanks Paul, I think I understand you, it's the quality of output on the last cap that matters most in the PS caps, improvements further up the chain could be lost otherwise.

Are there any drawbacks or benefits to increasing a smoothing reservoir sizes, in general?

I am planning on upgrading the coupling caps to some big polyprop caps at some point, the reason I'm asking about the PS caps now though is that I might be able to sneak some free components from RS!

I have my eye on a military spec 6080 too. Lot's of fun this Bottlehead project

---

Ah, thanks doc that confirms my suspicions! I was thinking that a big reservoir further up the chain and a very high quality last cap might be ideal, but not knowing anything about electronics (yet!) the hq bypass sounds like a good idea. I might do both!

One of the great things about your kits is the amount of new stuff you learn - thanks again.

 

[Grainger49]

In a two capacitor power supply the first cap sees horribly lumpy DC.  It does filtering/smoothing for that.  There is no need to buy a better sounding cap for this position.  The second does a little smoothing and is the source of energy for the tubes if it is a two stage filter.

In two or three cap power supplies the last capacitor is the energy source for your tubes.  The energy release (lower ESR caps and higher uF) is important here.

I'm also a big fan of the bypass cap that Dan mentions.

After last weekend I also think that you could use a choke to replace the resistor between the first and second cap in the power supply.  The DC resistance of the choke should be similar to the resistor.  The inductance will block high frequency noises that a resistor will pass on like a piece of wire.

 

[STURMJ]

I have two cracks, one "stock",one speedballed.  Both have these Jensen caps in the #3 cap position , in the "stock"crack I put a even larger cap in the first position.  This cap is however a 350uF cap (I understand this is a deviation from the original design). I put it in as a experiment, because it was cheap from a surplus shop. And I like the results.  I ALMOST like it better for simple music (instrumental, solo vocal). It really surprised me at first, but I soon realized that the speedballed version did more complex passages better.  Could this cap have changes things for the better?or am I imagining?

 

[Paul Joppa]

I post this with some frequency: "I never met a power supply improvement that was not also a sonic improvement."

 

[Billyk]

An alternative to bigger 'lytic caps might be to try a film bypass cap across the last filter cap.

I like the idea of the bypass, any recommendations for this? I was thinking of one of those Russin PIO or teflons to bypass the Erse cooupling caps...

 

[Grainger49]

I would try both, even at the same time.  First the PIO then add the Teflon.  You can try this with jumpers to see if you like the sound first then solder them in if they appeal to you.

 

[Billyk]

Thanks.
I am planning on using 1.0uf for bypassing the Erse output caps. What would be a good range for bypassing the PS cap? Prolly 400V for both.

 

[Grainger49]

Anything at the 250V range or higher will be safe.  I bought groups of KK PIO and Teflon caps.  I have used a 2.2uF and a 0.1uF both bypassing power supply caps.

Again, try it with jumpers first to see if it sounds right.

 

[Billyk]

OK Thanks, sounds like a plan!

 

[intojazz]

Check out this sitehttp://humblehomemadehifi.com/Cap.html
Look at the comments for the Vishay MKP 1837. I ordered some and plan to test them in a crossover network.
John

 

[hopeful]

Check out this sitehttp://humblehomemadehifi.com/Cap.html
Look at the comments for the Vishay MKP 1837. I ordered some and plan to test them in a crossover network.
John

The reviewer certainly seems to like them, but it looks like they are only rated to 160V (at least in so far at what's available on mouser and partsconnexion).  Per Grainger's post, bypass caps in the crack power supply should be in the range of 250V or higher.

 

[Grainger49]

I said that 250V or higher "would be safe."  I don't know what the power supply "floats" to before the tubes start conducting.  The highest voltage in the manual for checkout is 205V.  But it will probably be higher when starting.

 

[hopeful]

Thanks for the clarification Grainger!  If you have a chance, could you elaborate a bit on your 4/18 post from page one?

I'm trying to better understand exactly what is accomplished by adding a small bypass cap in parallel with the third cap in the power supply.  Are you basically just further reducing ripple voltage, as discussed on: http://www.seattlerobotics.org/encoder/jun97/basics.html

 

[Grainger49]

Thanks for the clarification Grainger!  If you have a chance, could you elaborate a bit on your 4/18 post from page one?

I'm trying to better understand exactly what is accomplished by adding a small bypass cap in parallel with the third cap in the power supply.  Are you basically just further reducing ripple voltage, as discussed on: http://www.seattlerobotics.org/encoder/jun97/basics.html

Dang!  And I thought I had written too much already. 

There can be reactions between the larger power supply caps and a bypass cap because of the combination of capacitance, resistance and inductance in capacitors.  (BTW, resistors and inductors also have capacitance, resistance and inductance.)  For my pragmatic way of doing things I first put the bypass caps in with jumpers.  If I like the results I then solder them in.  I have bypassed my Foreplay power supply caps (220uF@250V) with Russian military surplus 2.2uF paper in oil (PIO) and 0.1uF Teflon caps.