Bottlehead Forum
Bottlehead Kits => Crack => Topic started by: Tubejack on May 17, 2010, 06:40:06 AM
-
I was curious if anyone say an advantage to replacing either one or both of the 270R PS resistors in the CRCR with a choke, e.g., Hammond 155H - 270R @50MA. I am also planning to install the Speedball. C4S.
-
This is interesting, Bottleheads often replaced one of the power supply resistors with a choke in the FP 2. The Paramour upgrade used a power supply choke. The Paramount uses a choke in the heater supply.
It seems that with fully shunt regulated circuits there is no advantage (Paramount and Eros). But it would be interesting to see if someone tries it in Crack.
-
In a highly modified Crack that I have here, I did indeed use a choke in the power supply (Triad C7X). The Hammond 155H won't work so well, as the Crack draws more than 50ma.
I would suspect that a single Hammond 157L or 158L would do in place of the two 270 ohm resistors. Just double up the power supply caps after the choke. (I haven't tried this, so don't be too shocked if it might be nosier than it should be)
-
Paul,
Are you suggesting a CLC (doubled) filter or an LC (doubled) filter? I think I remember that the stock filter is CRCRC.
-
CLC. Just LC would have tremendous voltage drop.
-
Was just reading this post, because I'm thinking of replace the first 270R resistor with a Triad choke and before doing so I wanted to review previous posts and see if there was anything on the subject. I already have 1 choke installed in a CRCLC configuration. Since I have a second choke I thought what the help why not use it. From what I gather from the previous posts If I install the second choke in a CLCLC configuration I should at least double the capacitance of the last cap.
-
I was hoping to get some feedback on my last post. Anyone?
-
There has been discussion back and fourth. I would think that the second resistor replaced with a choke makes it closer to the audio circuit. I think PJ suggests replacing the first resistor. So the Triad for the first one would be a good step.
-
Since I have a second choke I will put it in and look at doubling all the caps in the power supply to something like 470uF.
-
The biggest improvement in caps is the final cap. Making it a low ESR cap makes an audible difference.
-
Right now I'm using the supplied electrolytic caps and have a 2.0uF Clarity bypassing the last cap. I want to double all the electrolytic caps when I install the second Triad choke.
-
Doubling all the caps in your power supply is not necessarily a good idea.
There is a very nice and simple power supply design application available for free on the net called PSUD2. It lives on a site called duncanamps. You should definitely install it and play with the simulations, if you want to get your power supplies to work properly.
-
Thanks for the information. I will give it a try and see how it works and if changing the caps makes sense.
-
+1 for PSUD2!!
Cheers,
Geary
-
I downloaded the PSUD2 software and played with it a little, but not sure what I'm looking at. Is there a site with information on interpreting the data?
-
I don't know the answer to that one. PSUD2 is a popular program for being so specialized. I suspect that you can find some info at duncanamps and much more by doing google searches.
Other than that you might just start your own journey: [1] why do I want to change the power supply? possible answers to reduce noise, to reduce distortion [2] how is the ps built up right now? all components with necessary values and schematic [3] how does this ps perform in the psud2 simulation? voltages, voltage variation, voltage at startup in various components, currents dto [4] where does the choke fit in and what happens? with all of those steps it helps to check frequently, if the psud2 simulation matches measured performance just to make sure you are using the correct values for components and the correct circuit layout.
It's worthwhile, if you care. If you don't, you might want to ask for advice how to change your power supply rather than swap parts on a whim. The Bottlehead power supplies are pretty good to begin with and you don't want to spend money and effort making them worse.
I downloaded the PSUD2 software and played with it a little, but not sure what I'm looking at. Is there a site with information on interpreting the data?
-
Well I installed the second Triad choke in the power supply. Damn this amp is getting heavy.
I like the results. There seems, to my ears, to be improved clarity and more definition to the music. Everything seems to have very good impact with and seperation. I was going to replace the electrolytics with film, but think I will save my money for now.
This is such a fun amp that only cost $300 with speedball and I only spent about $60 in parts upgrades, not including tubes. I can't imagine finding a better deal.
I still have a Bottlehead power cord on the way.
-
Am I correct in that at least electrically, the benefit of a choke in the PS is twofold: a) greater isolation of supply-related noise from the output signal, and b) the ability of the inductor to hold electrons in its magnetic field, which would indicate the potential for reserve capacity when the amp "asks" for more juice during a loud transient? The Triad choke is cheap, so I might try one out as well. I have to say, though, the Crack is already near perfection as-is, between the Speedball, good tubes (including the E80cc in the driver's seat) and film capacitors in the output position (previously, large-value electrolytics bypassed with small films - but I've recently given up on using AKG's with this amp and will just stick to Senns).
-
Well, Brad, your ears are the only two that have to be happy.
Bottlehead is not adverse to chokes in the power supply. It was a frequent, and suggested upgrade for the FP 1 and 2. The Eros PS PCB has spare solder pads for a choke. In that case you have to remove the resistor, of course.
Some of the finest scratch built amps I have ever heard had enough iron to sink a small ship.
The function is several fold. The choke not only drops a little voltage and slows the charging of the next cap creating smoother DC like the resistor. A choke resists rapid current changes through it.
This feature of chokes slows the inrush current at startup. And it feeds back some current when you turn it off. That last bit doesn't harm anything. It just slows the drain of the B+ a little bit.
Chokes pose a high impedance to high frequencies and low impedance to low frequencies. You can see why they are used in crossovers. But in a power supply this characteristic blocks noises that are high frequencies while passing anything DC to low frequency (120 Hz rectified, and lumpy DC). This high frequency noise will pass right through a diode and resistor.
And some day I will sit and do some serious work with PSUD. BTW, it is standard fare for all electrical engineers today, not when I was in school. I was a recruiter at Georgia Tech and UT for Kimberly-Clark. Every applicant had PSUD on their list of skills.
-
Chokes are great in power supplies. I never argued against the choke in Brad's amp by the way, but you don't want to increase the size of the capacitors in front of the choke. On the contrary, compared to an RC arrangement you really want smaller capacitors in front of the LC. It has multiple benefits. You can still increase the capactor value towards the end of your filter chain.
-
Am I correct in that at least electrically, the benefit of a choke in the PS is twofold: a) greater isolation of supply-related noise from the output signal, and b) the ability of the inductor to hold electrons in its magnetic field, which would indicate the potential for reserve capacity when the amp "asks" for more juice during a loud transient? The Triad choke is cheap, so I might try one out as well. I have to say, though, the Crack is already near perfection as-is, between the Speedball, good tubes (including the E80cc in the driver's seat) and film capacitors in the output position (previously, large-value electrolytics bypassed with small films - but I've recently given up on using AKG's with this amp and will just stick to Senns).
Hi Dr. Toobz - I know its a bit off topic, but you mentioned switching out the electrolytics for films - curious as to what size films you used and what effect it had. Thanks much.
-
Shortly after building the Crack I replaced the last 270ohm resistor in the PS with the Triad choke. There was an improvement, not earth shaking though. It brightened up the top end most notably, and considering I listen with HD 650s was a welcome change. Replaced the last 220uf cap in the PS with a Mundorf mkp, not sure that was worth the expense, replacing the 100uf output lytics with Mundorf film caps was a definite improvement. The Triad choke is less than 20 bucks, so imo it's a no brainer.
Cheers,
Shawn
-
I have to order some things from Mouser and Angela Instruments for my Stereomour kit before I move to the wiring stage, so I'm still debating whether I should pick up the Triad choke while I'm at it and replace the first PS resistor in the Crack. Problem is, I don't see how this is going to be worth it - the amp is now absolutely dead silent with the 6CG7, shielded heater wiring, grounded center shield (pin 9), upgraded, non-metallic pot (Alps), and this is even with the pot wide open. It's so quiet that I have to look over at it to know if it is on. Plus, I have the Speedball boards, which no doubt contribute to the quiet, effortless sound. So, what would the choke really accomplish at this point?
-
You're right. I'm not even going to do a speedball upgrade on mine (for now).
BTW, what upgrades/parts are you trying to put in your Stereomour? I'm expecting a Stereomour next month. I already have a Mundorf silver oil parafeed and coupling caps.
Good luck on your build. I think a choke is more useful on the Stereomour but the problem is where to install them.
-
You're right. I'm not even going to do a speedball upgrade on mine (for now).
BTW, what upgrades/parts are you trying to put in your Stereomour? I'm expecting a Stereomour next month. I already have a Mundorf silver oil parafeed and coupling caps.
Good luck on your build. I think a choke is more useful on the Stereomour but the problem is where to install them.
Nothing fancy - just a better potentiometer, different output capacitors, and two stereo 1/4" jacks, to allow me to squeeze a sub or headphone amp output in there without losing the third input or drilling extra holes in the plate. I also ordered a red nut for one of the jacks, to differentiate the output jack from input.
Since the parts I ordered weighed all of four or five ounces and made the shipping cost kind of ridiculous for such a small parcel, I went ahead and grabbed a Triad choke while I was at it. I will report back any improvements to the Crack once it's installed.
-
Thank you. Please do report back with your impressions.
-
Shortly after building the Crack I replaced the last 270ohm resistor in the PS with the Triad choke.
HI, Does it matter which wire goes to which terminal? I'm thinking no but...
-
John,
I think I have this right, if it has a dot, the dot goes to the higher voltage.
-
Sorry, I just noticed your post, Grainger is right about the dot. Unfortunately I can't remember if it had one, I will take a look in the morning when I get home.
Cheers,
Shawn
-
Crap! Somewhere someone posted a way to determine which lead should be dotted and I didn't bookmark it.
-
You test the capacitance between each wire and the core. Usually, you want the higher capacitance farther away from the plate of your tube. I think that's right.
Michael
-
Michael,
Thanks, so lowest capacitance (should be the dot) toward the plate/high voltage.
I will dot my Triad for the Eros today!
Edit: the higher capacitance was on the left hand lead so the dot and wire on the right go to the second capacitor in the power supply, closer to the plate.
-
Thanks for the info, Triad's docs don't mention that at all. I got the crack right by chance, need to check the Eros. I'm a little burnt-out, just got home. We had to evacuate all of our patients at the hospital due to the Waldo canyon wildfire. I got out just before they closed the highway. They believe the fire was arson, just don't understand people like that.
Cheers,
Shawn
-
OK, here's a question for those of you who have already installed the Triad choke: where did you find standoffs with a sufficient diameter to connect to the bolts holding down the power transformer? Nothing I have on hand seems to be the correct gauge.
-
OK, here's a question for those of you who have already installed the Triad choke: where did you find standoffs with a sufficient diameter to connect to the bolts holding down the power transformer? Nothing I have on hand seems to be the correct gauge.
Mouser.com
6-32 screw http://www.mouser.com/Search/ProductDetail.aspx?R=8420virtualkey53400000virtualkey534-8420
8-32 screw http://www.mouser.com/ProductDetail/Keystone-Electronics/8433/?qs=1eFRaVyeUDVBTujGLm7s9OVyuZjjX5tpZdrvxESCFCw%3d
-
Thanks! The Crack manual states that the screws holding down the power transformer are #8-32, so I'll go with the #8 standoffs listed at Mouser. Too bad these aren't available at Home Depot or something - it stinks to pay so much shipping for such little parcels.
-
Find the manufacturer's part number and order it from Digi-Key. They offer a first class mail option for just a few dollars.
-
Great idea - I completely forgot about DigiKey! I've ordered things from them in the past via USPS.
Here's the link for the same part at DigiKey: http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=keystone+8433
-
Despite not yet having the standoffs to mount the choke, I did install it in place of the first 270 ohm resistor, and simply set it behind the amp until the hardware arrives. Now, I'll admit to not really knowing how this is possible, but the choke definitely does improve the amp. Is it a gigantic improvement? Not really, but it is definitely noticeable.
The first thing I noticed is that bass notes are a bit deeper and more solid, yet not as forward in the soundstage. I can actually hear a bass note and its harmonics (or the strings vibrating, etc) rather than just a low tone or rumble, which is perhaps the biggest change. The bass actually is detailed and tuneful. Secondly, the soundstage has opened up a bit. Perhaps as a result, I noticed that things are a bit better balanced, in that the amp paradoxically seems less bright while revealing more tiny details in some songs (background noises, fingernails on strings, etc). Loud transients are now less startling and very smooth, almost effortless. The sound is even more natural than before. Finally, the leading edge of transients seems to be ever so slightly better defined, again without making the amp sound sharp or treble-heavy.
In short, a good upgrade, and likely my last! When an amp is so good that you forget you are wearing headphones, I don't know how much better things could get. This is definitely a "last 1%" type of upgrade, and to be honest, I didn't expect any difference with active plate loads following the power supply. I can only surmise that the choke is making their jobs easier....
-
I've been using a choke at the second 270 ohm resistor for over a year now. Still sounding great.
Actually, it sounds even better since I finished my Buffalo 3 Dac a few weeks ago. I love the way my Crack sounds. :)