An absolute noob's modding question

[Nubtam94]

I know this might sound stupid but I just had the idea that if my amp could only be as good as my components, what could I do to rid of the bottlenecks in the system? I'm not an electrical engineer whatsoever just a curious DIYer but... here are just some of the mods that I was thinking of and wondering what sort of improvements should I expect because I have no idea, and there hasn't really been a thread where someone just lists out the sort of mods they were planning on.

-Is it possible but why spend $100 on Rhodium plated RCA jacks instead of wiring the signal from the pot straight to a pair of RCA plugs?
-Solid silver chassis wiring for the signal path, higher the conductivity means improvement to some extent? (Knowing the loss or recession of bass frequencies)
-Stepped attenuator (Do I even need this over a Alps Blue velvet pot?)
-Kiwame or AN resistors on speedball board and PSU resistors (I don't know. It's an aftermarket resistor and it's green and looks fun to throw in...)
-Film/oil capacitors and coupling capacitors (big big caps the better? bypass caps, what?)


I don't mean to sound stupid to you electrical engineers out there... just wondering how to get the most out of my Crack after the tube rolling fun is over

 

[Paul Birkeland]

This is certainly a question that develops in many people's minds, no need to be apologetic. 

I don't know why somebody would spend $100 on rodium jacks and not touch anything else.  Granted, the nicer jacks will make a difference, but that would be a strange choice on its own. 

I'd shy away from the silver if possible, instead opting for OCC if you can afford it.  Yes, it is worth the price.

The stepped attenuator vs. Alps Blue debate at Bottlehead HQ results in the Apls Blue winning out most of the time.  I came up with a new attenuator design that sounds a little better, but it requires at least 2 switches and some serious chassis space.

The Kiwame resistors are the same as a certain KOA Speer resistor available from Mouser for less $.  On the Speedball PC boards, you would want to replace the R1 resistors (237 and 31.6 ohms).  These values are very specific, the 237 ohm can vary by a couple of ohms, the 31.6 could vary by an ohm or two, with 33 ohms running slightly less current than stock, but still functioning just fine. 

For power supply caps, yes, film caps will sound better.  For a headphone amp, however, the size and ESR of these capacitors was chosen specifically to knock down the ripple in the power supply to an extent where you can't hear it in your headphones.  If you were interested in going to something like 100uF @ 250V film power supply caps, you would want to drop in a power supply choke to assist these caps in accomplishing the goal.  The Triad C-7X at Allied Electronics will do the job nicely without destroying your parts budget. 

For coupling caps, we do indeed like the film output caps in place of the electrolytics, but boy are they large, heavy, and expensive.  If you have the space, go for it! 

-PB

 

[Grainger49]

For sonics, no consideration of price, this is a list of things to change starting at the biggest sonic difference to the least sonic differences.  Looking at the schematic...

This is my personal opinion:

C4S, in this case the Speedball upgrade
NOS tubes
Film output caps
Improved power supply, upgrade the final cap and a choke replacing the second resistor, maybe even both resistors
Upgraded volume control "device"
Improved, thick film, R1 resistors for the Speedball
Fred, ultra soft recovery, diodes replacing the UF4007 diodes
Improved signal path wire
Improved RCA Jacks
Improved headphone Jack

I think that is all.  

 

[Nubtam94]

This is certainly a question that develops in many people's minds, no need to be apologetic. 

I don't know why somebody would spend $100 on rodium jacks and not touch anything else.  Granted, the nicer jacks will make a difference, but that would be a strange choice on its own. 

I'd shy away from the silver if possible, instead opting for OCC if you can afford it.  Yes, it is worth the price.

What I meant was to wire the signal straight from the volume pot to a pair of RCA plugs into my source actually. What struck me is that my RCA interconnects aren't high-grade stuff, so why not just wire straight out from the chassis wire? I know I still have to ground the plugs but is this even possible or feasible?

I know OCC is well worth the price, but I also know that I'm looking at more refinement at the higher frequencies over bass refinement if musical warmth isn't my priority, just wondering if what people say about an expansive soundstage is true.

 

[Nubtam94]

For sonics, no consideration of price this is a list of things to change starting at the biggest differences to the least sonic differences.  Looking at the schematic...

This is my personal opinion:

C4S, in this case the Speedball upgrade
NOS tubes
Yup I already have speedball, rolled in a TS5998 and a 1960 Dimple-D Getter Black Plate RCA 12BH7 so that concludes the tube rolling upgrades
Film output caps I was looking at a pair of Mundorf MKPs and coupling them with a Mundorf Supreme or SO 1uF?, I'm not sure what to get because I'm somewhat limited by budget and choices if I were to buy locally. Film caps and oil caps? I don't know what I should be getting actually
Improved power supply, upgrade the final cap and a choke replacing the second resistor, maybe even both resistors  I suppose I can couple the caps with a 2.2uF as well? Choke goes for the 270Ohm resistor connected to the caps right? I don't think I'll have the room to upgrade the final cap though
Upgraded volume control "device" I think I'll settle with an ALPS Blue Velvet
Improved, thick film, R1 resistors for the Speedball Which thick film resistors? I'm not sure, also curious but could I use Tantalum resistors?
Fred, ultra soft recovery, diodes replacing the UF4007 diodes Not sure about this one
Improved signal path wire Thinking OCC if I dont get solid silver instead. I also know that silver plated crap doesn't do s***
Improved RCA Jacks Might skip this?
Improved headphone Jack I don't have the tools to drill a larger hole for clearance though

I think that is all.  

I've already dived into quite abit of research, but need more time to consider the parts that I can get.

 

[Laudanum]

"The Kiwame resistors are the same as a certain KOA Speer resistor available from Mouser for less $"

I knew about this but wasnt going to dare write it anywhere, especially on any forum, ever  ;D

 

[earwaxxer]

What I meant was to wire the signal straight from the volume pot to a pair of RCA plugs into my source actually. What struck me is that my RCA interconnects aren't high-grade stuff, so why not just wire straight out from the chassis wire? I know I still have to ground the plugs but is this even possible or feasible?

I know OCC is well worth the price, but I also know that I'm looking at more refinement at the higher frequencies over bass refinement if musical warmth isn't my priority, just wondering if what people say about an expansive soundstage is true.

IMO the problem you are describing is related to wire. I dont have the crack, but from my experience with Bottlehead parts is that the stuff that comes with the kit is already pretty good. I dont think your 'main' focus should be there. With interconnects, I think you should focus on the wire itself (not the connections). Connections will make a small improvement IMO. Smearing of sound is due to poorly designed wire. Clear highs and mids with good 'soundstage' comes from well designed wire. I know this sounds like fingernails across the chalkboard to many. I'm afraid, IMO and experience, as well as many other reviewers and crazy people like myself, that its true. If you add new components you have to take a look at the wires that you are connecting to it. Many times the weaknesses of wires you have been happy with for years are now showing through. Solve those problems first, then tweak the component itself. Caps of course are an easy target. They can get expensive but if you keep it sane, you can enjoy some improvements there. I agree with Grangers list of priorities as far as parts are concerned. Lots of variables, lots of opinions. Thats what makes this hobby fun! ;-)

 

[Grainger49]

I'm with Eric, the stock parts are precisely selected.  None of them are even average.

Yet, there are places to improve.  But that improvement comes at a price which would not be best for Bottlehead Corp to supply in the kit.

 

[Noskipallwd]

In my case, after the Speedball itself, the second most effective upgrade was installing good film caps in the output coupling position..

Cheers,
Shawn

 

[Nubtam94]

Film caps could technically be used in anywhere in the circuit right? Just not to significant effect on the power circuit except for the last cap?

I'm thinking of switching out the final power cap with some Mundorf MKPs, do I still need a higher quality bypass cap to go with it?

I was thinking of getting Mundorf Supreme 2.2uFs to use for bypass on the power side and Mundorf SO 1uFs for bypass on the output. I know I might sound dumb because those are $$$ but for me they are the best I can get around here, a step down would be the Obbligato Golds. Not many choices where I am...

 

[Grainger49]

The output caps are in series with the signal.  In other words, everything you hear passes through them.  The power supply is what is "modulated" by the tube, it is kind of a part of the music.  That is the second most important capacitor in the amp.  

You are on the right path with a final PS cap upgrade.  This is the one that has the 270k ohm, 1W resistor around it.  It is on terminals T12U and T13U.  (Page 28 of the manual, bottom picture and instruction of the page).

Somewhere Paul Joppa has given some guidelines on replacing a power supply electrolytic cap with a film cap of a lower value.  Since the film releases energy much faster than electrolytics the cap need not be the same value in uF.  It needs to be the same voltage rating or higher, but a lower value works better than an electrolytic.  I just can't find that post at the moment.

You can replace the output (I think you called it input above) cap with a film cap.  There are 100uF  and 70 uF films available.  Matter of fact Obbligato makes a 100uF@400V power supply cap that is film that would be an improvement on the stock electrolytic.  The same thing goes for using the Mundorf MPK as an output cap.  It would surely be an improvement on the stock.

I think that does it.  There is one audio path cap per channel and one power supply cap that will benefit from upgrading.  

 

[Nubtam94]

Ah yes I meant to say output, but the fact that the Obbligato that was designed for power supply doesnt really mean it can't be used as an output cap provided it falls within the desired voltages?

What I was really worried about is using non AC rated film caps or DC caps that don't have a high enough DC rating to use on the power side, although what I was also asking if there was a need for a bypass if I've replaced the final power output cap with a film cap?

Also I haven't read much but are Mundorf Tube Caps designed for use as a sort of drop in replacement for power caps like the power caps in the Crack?

Thanks~

 

[earwaxxer]

From what I have read, and experienced, with cap bypassing, there are complex interactions that are difficult to predict when you parallel caps of different values (uF) together. I would probably not do it unless I had some very low value mega bux caps (ex. v-cap) that I wanted to experiment with. I had some Mundorf S/O's that I bypassed into my speaker crossover with very good effect on some caps, not good effect with others. You mentioned Mundorf S/O's. I use them in the 2.2uF output cap spot (Quickie) and they sound very good. Granger mentioned replacing the electrolytics with film. That I also did, and found them to sound better as well, not as much so. I think the MKP's are a good choice there. I have Obbligato's as well. IMO, not as good as the Mundorfs, of course the Mundorfs are much more expensive. Enjoy!

 

[Nubtam94]

Actually I'm looking at a difference of $10 between the Obbligato Black Film and the Mundorf MKP of choice. Well I'm just going to go for 2 Mundorfs 1uF SO, if they really dont work i could just keep them and get lower cost obbligato golds. What I'm also wondering what sort of capacitance should I use for a bypass on the final power capacitor? I've seen people using 2.2uFs but some people suggest that a higher capacitance around 5.6-10uF is more likely to impact sound.

Opinions? Thanks~

 

[Grainger49]

Ok, let's see...  Edited, There is no AC in the power supply after the rectifiers, just ripple.  I don't know what I was thinking.

Yes, I believe the Mundorf Tube Caps were intended for power supplies, I could be wrong.  At least I have seen them used often in power supplies.

The last cap in the power supply sees no AC (there is no AC after the rectifiers at all), but eliminates a tiny ripple.  The first two caps filter well.

You can always use an AC rated cap on DC. In the power supply or at the output cap use the same DC voltage rating as Bottlehead.  

I have film/oil caps in my Paramour amps for the power supply.  I have Obbligato black Film/Oil you mention above as my output (Parafeed) caps in the same Paramour amps.  I have Mundorf Silver/Oil as the output caps in my Eros and FP 2.  I think you and I seem to have the same taste in caps.  

I don't know if a bypass on a film last stage power supply cap would help, but try it.  It might!

BTW the existing cap on the output of Crack is a power supply cap type cap (electrolytic).  

Yes, bypassing rules are odd and the only thing I can suggest is Experiment.  

 

[Nubtam94]

You can always use an AC rated cap on DC but need to know the AC rating for DC caps used in the first stage of a power supply.  The second stage is already filtered to DC.  In the power supply or at the output cap use the same DC voltage rating as Bottlehead. 
 

I'm not quite sure what you meant there, do you mean the output cap DC ratings have to be matched to the last capacitor used in the power supply?

 

[Grainger49]

You are right, the output cap needs the same or higher voltage rating; those two points are connected.  Only go higher if you can't find the value you want with a matching voltage rating.  Otherwise you are wasting money and the cap will be bigger. 

When the amplifier turns on the power supply passes the output of the rectifiers right to the plate of the tubes.  This is because the tubes are not conducting.  It is a higher voltage than when the tube is conducting and the power supply is filtering. 

But... in what you quoted I was meaning to say that you can use AC rated caps in power supplies.  Many of us here use motor start/run caps for power supply caps.  They are better sounding than electrolytics but very large.  I mean really large for their uF value.

Also, I meant that Bottlehead will use a capacitor that will not explode on surges.  Paul Joppa likes a conservative design.  There is also a consideration of temperature with all capacitors "under the hood."  PJ likes 80 degree C rated caps.  That is what you will find in Bottlehead kits.

Electrolytic caps are DC rated with the possibility of an AC rating.  After the rectifiers you have very lumpy DC, no AC at all. There is no AC at the first cap of the power supply, just awfully lumpy DC.

Electrolytics can be used as a cathode bypass cap because there is much more DC there than AC.  Electrolytics are intended for DC rather than AC.

 

[Paul Joppa]

To clarify, the last cap in the power supply carries exactly the same AC signal current as the output capacitor - in a cathode follower circuit. Neither cap has any significant ac between its terminals, but both have plenty of AC current.

I normal amplifier stages, the same thing is true - the AC signal current (not voltage) goes through the power supply. However, in parallel feed circuits the plate choke resists that current and the current loop is closed through the parafeed capacitor instead of the power supply.

 

[Noskipallwd]

I contacted Mundorf support a couple of years ago wih question about their different product lines, and general use. The tech that replied stated their general rule for bypass cap values are 1% of the larger caps value. 220uf bypassed by a 2.2uf, and so on. The size of the output caps limits the choice of caps you can install, no teflons, no Mundorf S/Os, and so forth.There is a good choice of affordable Metallized Poly. caps. though, from Dayton Audio, Solen, Mundorf, Axon true caps at 91uf, which folks that have used them state that 91uf was large enough. I replaced the last cap in the PS with a 220uf Mundorf Mkp, but that was darned expensive. Almost as much as the kit itself, not worth the expense I think. You can have a lot of fun rolling caps in the Crack! Hope this helps.

Cheers,
Shawn

 

[Nubtam94]

This M-Cap?

http://www.royalkabel.com/mcap-250-mkp250-vdc-220-uf-p-330.html

I was somewhat confused before when you guys were saying that the output caps are actually power caps, probably because the ones that came with my kit are those "audio grade" FW caps from nichicon so I was never sure.

I'm planning on replacing those with either the M-Cap MKPs or Obbligato Black Film 100uFs because those are the only 2 caps that are readily available in local stores. There's also Solen as well but I'm not going to bother with those. The power range for those are 250VDC and 400VDC so they should be fine.

As for the power cap, I read somewhere that it is generally unsafe to use a non AC rated capacitor in an AC circuit, which I assumed the power circuit was completely AC, but apparently the circuit at the last power cap is already filtered to DC. You guys were also saying that the power cap should not have a higher VDC rating than the output caps? So I guess I could cross off the TubeCap unless I upgrade all of the output caps to the same voltage?