Bottlehead Forum
Bottlehead Kits => Legacy Kit Products => Quickie => Topic started by: Dr. Toobz on October 19, 2009, 03:16:58 PM
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I've installed Hammond 150H 3.7k ohm chokes in place of the stock 4k ohm plate resistors, and the mod definitely seems worth the $30 or so it cost. Gain has increased noticeably, and the amp is even clearer and more punchy than ever! High-frequency response is very noticeably crisper over the plate resistors. This is a much different sound than the C4S S.E.X. - the Quickie is intimate, putting you right in the middle of the instruments, whereas the S.E.X. puts you a few rows back. In other words, soundstaging is still different, even with the chokes. But, that's ok. I actually sort of like the Quickie better for rock already.....maybe it has to do with the DHTs? It should make a great partner for my iMac, as it even sounds good straight from the headphone jack. If I want delicacy, I can always listen to the S.E.X. in the other room!
In any case, this was a worthwhile mod! Does anybody know where to get good transformer standoffs for the chokes, though? I haven't yet decided if I will mount these inside the wooden base I built, or hanging from standoffs.
I've been working on the wooden base lately, and even chiseled out some room on the inside of the front for a headphone jack to fit (I got down to about 1/4" and then drilled a hole for the neck of the jack). The old non-shorting jack from my S.E.X. amp worked perfectly, and looks good on the front of the wooden base (right under a brass Bottlehead badge). I'll post some photos in a few days, once I've put the clear finish over the mahogany stain.
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I think I bought some "nylon" standoffs at Mouser.
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... Does anybody know where to get good transformer standoffs for the chokes, though? I haven't yet decided if I will mount these inside the wooden base I built, or hanging from standoffs.
http://www.audioasylum.com/forums/bottlehead/messages/13/138809.html
I decided not to use a headphone jack. I have a headphone jack to RCA adapter that I use. I also picked up a pair of Cardas clips for the Senns, and am planning of making a direct cable to RCA's (one day!)
I think Doc mentioned that the DHT's would be the killer attraction of the Quickies.
Thanks for the post on the chokes. Sounds like it's worth it. Maybe we could put in a mass buy through Doc and let him make the mark up on them?
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Does anybody know where to get good transformer standoffs for the chokes
I would go to McMaster Carr. Those chokes will probably mount well with 6-32 hardware. Do be sure to use a large flat washer between the bottom of the chassis plate and the standoff, as you want to spread the pressure that the standoff places on the chassis plate.
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Does anybody know where to get good transformer standoffs for the chokes
I would go to McMaster Carr. Those chokes will probably mount well with 6-32 hardware. Do be sure to use a large flat washer between the bottom of the chassis plate and the standoff, as you want to spread the pressure that the standoff places on the chassis plate.
You're right. I was thinking of those itty bitty chokes I'm using for my low pass filters. These chokes must be bigger.
I still plan to use the 4-40's if I mount the Hammonds, but with those really wide (pan?) washers (also available at McMaster). The Quickie is loaded with 1/8" holes and I don't want to change that in case I mod them again. I think the top plate would distort before the 4-40's give out, and I can probably use fiber shoulder washers when mounting the chokes to the standoffs to take up the slack in the mounting holes.
What do you think of using the Hammonds in a Quickie headphone amp to drive Senns, which IIRC are 300 ohms rated. Wouldn't the chokes raise the output impedance of the Quickies to 500 ohms, more than what should be used to drive 300 ohms input?
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What do you think of using the Hammonds in a Quickie headphone amp to drive Senns, which IIRC are 300 ohms rated. Wouldn't the chokes raise the output impedance of the Quickies to 500 ohms, more than what should be used to drive 300 ohms input?
The choke won't really cause any problems like that. The current source that PJ drew up might raise the output impedance a little, but into the autoformer it suddenly isn't as important.
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I am REALLY happy with the improvements the chokes made, such as better imaging and clarity.
However, now there is a fairly strong hum that was not audible (or just barely) before the chokes were put in.
The leads to the chokes have been trimmed as short as possible, and the frames are grounded.
I tried reversing the in and output wires to the chokes, with no success in quieting them.
Any suggestions? Did anyone else pick up more noise when doing this modification, or is it just my luck?
I sure like (most) of what the chokes do, but want to get my Quickie as quiet as it was before if at all possible.
Thanks in advance for any ideas or helpful pointers.
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I am REALLY happy with the improvements the chokes made, such as better imaging and clarity.
However, now there is a fairly strong hum that was not audible (or just barely) before the chokes were put in.
The leads to the chokes have been trimmed as short as possible, and the frames are grounded.
I tried reversing the in and output wires to the chokes, with no success in quieting them.
Any suggestions? Did anyone else pick up more noise when doing this modification, or is it just my luck?
I sure like (most) of what the chokes do, but want to get my Quickie as quiet as it was before if at all possible.
Thanks in advance for any ideas or helpful pointers.
Did you try ungrounding the chokes? Obviously it's not AC filament hum or unfiltered HT, so I would guess a ground loop. Is it on both channels? Are the grounds short and to their respective channels? Just guessing until the heavy hitters get here.
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I am REALLY happy with the improvements the chokes made, such as better imaging and clarity. . . .
I don't know if this is the right place to ask but would plate chokes be good in the FP 2 or Seduction (already has C4S)? This because I am an admitted imaging freak!
I can start a thread about this in the Legacy Products area.
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I am REALLY happy with the improvements the chokes made, such as better imaging and clarity. . . .
I don't know if this is the right place to ask but would plate chokes be good in the FP 2 or Seduction (already has C4S)? This because I am an admitted imaging freak!
I can start a thread about this in the Legacy Products area.
I think Gary Pimm went into this in one of his iterations. IIRC, his opinion was that for a small frequency range the choke helped get rid of a little graininess of his CCS, but otherwise did not do much. The question became where to put the choke, and I think his answer was after the CCS.
When I was looking into it, I couldn't get many replies about it. But the fact that the choke would allow storage of current whereas the CCS keeps it constant seems, to me, to show that the two effects would be fighting one another.
I'm interested (academically) in what other people have found, too.
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Len, I started a thread here to keep this one from skidding sideways:
http://www.bottlehead.com/smf/index.php/topic,79.msg279.html#msg279
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I've installed Hammond 150H 3.7k ohm chokes in ...
Dr. T,
Would mind giving out where you ordered the chokes from and what part number they were?
Thanks,
Alan
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Alan, looks like a 156C from his numbers. I'll bet Parts ConneXion stocks them.
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However, now there is a fairly strong hum that was not audible (or just barely) before the chokes were put in.
This is almost certainly the choke picking up a magnetic field, probably from a nearby power transformer. Move the Quickie away from any such device and see if that does not make it quieter.
Shileding is the old-fashioned commercial answer. The best shields are mumetal and completely surround the choke; these are hard to come by but can give some 30dB attenuation of hum fields.
Remember, mumetal loses its performance if physically bent. The cans are tempered after forming. The Seduction power transformer uses a high-permeability tape that can be bent if you are careful; it's called "molyperm" and has a high molybdenum content. That's all I know about it - I don't know a source for it. My measurements were that this reduces hum by 6 to 20 dB depending on the relative position and orientation of the hum source. The variation is because the tape does not fully surround the iron.
Some people have used iron pipe (like 2" diameter drain pipe) for homemade magnetic shields. Because the permeabilty of iron is hundreds of times less than mumetal, it will I believe provide only 5-6dB attenuation, and for that the pipe needs a thick wall, like 3/16 inch or more. Very heavy.
Best solution is still to move the Quickie away from power transformers in other devices.
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You can actually do magnetic shielding with aluminum! Thick aluminum (say 1/4" to 1/2" thick) has a high enough conductivity that external fields induce eddy currents which generate their own fields which counteract the original field. You can get 5-6db or so at 120Hz with 1/4" thick aluminum. It actually gets more effective as the frequency goes up.
One of the best places to get small amounts of magnetic shielding material is lessemf:
http://www.lessemf.com (http://www.lessemf.com)
They have several flexible foil type products. I've used the metglass ribbon to shield preamp tubes and it worked very well.
John S.
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Thanks Paul! Now why didn't I think of that... an easy fix is sometime the least obvious to me.
It did just what you thought it would, now I just need to shuffle some gear around!
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To answer some earlier questions, the chokes are Hammond 156C. I bought them from Angela Instruments for $14 each.
Also, I'm not getting even a trace of hum. Right now, the chokes are just "hanging out" underneath the Quickie in the temporary cardboard box I've been using as a base while I finish the wooden one. I don't have them near (or aligned with) the OPT's to avoid coupling any noise into the signal. I also don't have the Quickie near any power transformers or the like.
I've been playing some Eric Dolphy and Sonny Rollins this evening and it sounds great! I should have a photo or two to post in the next few days.
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Be bold, post the cardboard box first!
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To answer some earlier questions, the chokes are Hammond 156C. I bought them from Angela Instruments for $14 each.
Dr T,
Thanks, I ordered mine today from RadioDaze. Can not wait to try them out.
Cheers,
Alan
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Hi all,
My Hammond 156C chokes arrived on Tuesday, installed them about 5 minutes ago. I took my time with the modification. I wanted the chokes to look like they belonged where I placed them. As stated earlier in the post they fit perfectly on the mounting screws for the D cells.
This made a number of changes to my system. Usually my first test materiel is Dire Straits LP "Brothers in Arms" however today I picked The Derek Trucks Band CD "Songlines" The first thing I noticed was a dramatic increase in the base response in Crow Jane. I was not prepared for the biggest change! When the first Derek Trucks guitar solo on Crow Jane I was blown away at the increased depth of his guitar. All I can say is, WOW. This modification is the best $26 I have spent in a while. Do it you will not be disappointed!
Three cheers to Dr. Toobz for this brilliant modification.
Cheers,
Alan
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Hi all,
My Hammond 156C chokes ... fit perfectly on the mounting screws for the D cells.
This made a ... dramatic increase in the base response ...
Alan
Thanks for the info! Since my first Quickie is being used for a low pass filter, bass is important! I'll be ordering a pair today.
Thanks also for the mounting tip.
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Three cheers to Dr. Toobz for this brilliant modification.
Cheers,
Alan
I can't take any credit for this mod - at least one other member thought of it first on the old forum (I can't remember who, though). I actually was looking to build CCS's for the Quickie and stumbled upon a mention of the Hammond chokes and the possibility of using them to load the plates. In any case, they definitely are worth the money and bring the Quickie to another level!
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Dr. Toobz,
Thanks for the update, I'll try and find the original post and give proper credit.
Alan
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I can't take any credit for this mod - at least one other member thought of it first on the old forum (I can't remember who, though). I actually was looking to build CCS's for the Quickie and stumbled upon a mention of the Hammond chokes and the possibility of using them to load the plates. In any case, they definitely are worth the money and bring the Quickie to another level!
I'm pretty sure it was DynaSaur (hey, that rhymes).
I'm glad you guys like the mod. I ordered them today. Then I got the Quickie running tonight as a low pass. It is stunning. I was starting to regret ordering the chokes, because I figured the low end couldn't get any better. I hope to post results of the choke upgrade next weekend.
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I can't take any credit for this mod - at least one other member thought of it first on the old forum (I can't remember who, though). I actually was looking to build CCS's for the Quickie and stumbled upon a mention of the Hammond chokes and the possibility of using them to load the plates. In any case, they definitely are worth the money and bring the Quickie to another level!
Since I found different post author suggesting the Hammond Chokes, I will simply say this. Who every suggested the idea, it is a great upgrade. I thank you!
Sincerely,
Alan
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I'm another happy user of this mod. It is incredibly easy to do (you don't even have to drill any holes!), and it increases gain, bass authority, and increases the amps overall resolution (at least to my ears).
I mounted them as follows:
1. Replace the four #4-3/8" screws holding the D cell battery holders with #4-3/4" screws. Use the existing nut and tighten according the manual.
2. Place 1 small rubber grommet on each screw (poor man's standoff).
3. Place the chokes on the screws on top of the grommets.
4. Place #4 washers on top of the choke tabs and snug down with 4 #4 nuts.
5. Remove the existing 4K plate load resistors.
6. Solder the choke leads exactly the same way the resistors were soldered.
It took about 20 minutes total including the soldering.
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Sort of an update here - since moving my Quickie to use as a linestage in my main system (between the DAC/Seduction and S.E.X. amp), the Hammonds are picking up some hum when the pots are turned all the way up. Now granted, I never turn the pots up very high, as there's plenty of gain, but I don't like the idea of any added noise to my signal, however small. (When used as a headphone amp with my iMac, the Quickie was dead quiet - but this was likely due to it being the only electronic device on the desk). Since I want my chain to have the same inky-black background as the S.E.X. amp when used alone, I ordered the PJCSS and will be swapping that in once it arrives. That should take out all of the "iron" between my components and the S.E.X. amp, as I already did surgery to remove the Specos and accompanying headphone circuitry some time ago.
If anybody is interested in buying my chokes, I'd sell them for a decent price (perhaps $20, including shipping, for the pair?).
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Those are nice chokes for other projects. You can throw them in a preamp instead of plate resistors to check out the sound.
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I had thought of that, actually. I already have a box of tube-related parts (in addition to my ongoing junk boxes of assorted resistors, caps, etc). from my various Bottlehead projects and upgrades, so maybe a homemade amp is the next place to go. I may eventually try out designing something simple on my own, though I'm a psychologist, not an electrical engineer.....
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I'm probably not the only one who thought of this mod, but here is my posting "lifted" from the old forum:
The Hammond C156C chokes are readily available from AES, Angela, etc. Same size as the Dynaco C354 and Hammond 156R. I measured one of my 156Cs and it has a DCR of 3460 ohms.(They're still not yet in my "modder" Quickie)
Posted by Dyna Saur (A ) on September 25, 2009 at 18:48:32
In Reply to: RE: Transformers posted by Paul Joppa on September 25, 2009 at 13:45:03:
Hammond has a couple of high inductance, low current chokes which may be usable as suitable plate loads for the Quickie's 3S4s.
155C, 60H, 8 mA, DCR = 2750 ohms, about $14 each.
156C, 150H, 8 mA, DCR = 3700 ohms, about $15 each.
Since these are both below the nominal 4.02K plate resistor value, one could insert an LED in series between the B+ line and the choke's "hot" side, for a pilot light, or tube activity indicator. Depending on the LED color, it will introduce between 1.6 and 3.6VDC voltage drop, which is pretty much minimal. Don't connect the LED on the plate side, it could introduce some unwanted noise into the equation.
Now, these inductors aren't going to be of Magnequest quality, but at the cheap prices, they may be a good deal for this application, along with the SPECO matching trannies. I'd SWAG that 2.2 to 3.3 uF would be a good coupling cap value , into the reflected 4K ohms. Voltage rating could be as low as 100V, but I'd probably go with 250V (basically because I have lots of such caps in my stockpile).
This topic alone has intrigues me to the point that I put in an order for not just one, but two, Quickies ;-)
Being one who can never leave "well enough" alone, these Quickies are a very interesting and readily modifiable project, which I just can't resist.. A little research indicates that 1S4s can be used with a simple re-conenction of the filament leads (use pins 1 and 7, leave 5 open). Just becuzz....
All of this talk of "quickies" reminds me of a very old, rude joke involving a pastor and a nun, but since this is a polite family-oriented site, I won't post it here ;-)
/ed B in NC
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If I installed these chokes, would I not need the CCS?
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I had the chokes in my Quickie and they were an improvement, but the PJCCS is much better.
One or the other but not both at the same time.
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looks like the cost is the same
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With Dr. Toobz enthusiasm for the choke mod on the Quickie how could I resist. Well, they delivered today and I decided to set up an experiment. After all, who can resist a good experiment.
Basically I wanted to measure the spl in the room at given frequencies before and after the chokes were installed. I had just picked up a RadioShack Sound Level Meter on clearance at the local Rat Shack ($14) and was looking for a way to put it through some paces anyway.
So here is how I set up the experiment. I used a tripod to mount the meter in the room right at my normal listening position. I used TrueRTA on my laptop to generate the tones and I ran them through my Tascam 32 tape player so that I could use the VU meters to insure that each set of tones was at the exact same level. I set the meter to "C" weighting and Slow Response. The volume on the Quickie was set to 12 o'clock as well as the volumes on both of the monoblocks. I didn't want to be blown out of the room with test tones. I then ran through several test tones at different frequencies adjusting the VU meters to zero as needed. This seemed to compensate for some non-linearity in my laptops output. I recorded the results, then installed the chokes and repeated without moving anything in the room.
Here are the results:
Frequency 4K Resistor Choke (150H)
25 55 58
30 60 63
35 61 64
40 64 68
45 68 71
50 72 77
100 82 86
500 81 83
1K 66 69
2K 64 67
4K 78 80
8K 65 75
12K 62 67
16K 58 63
18K 56 58
20K 56 57
Definitely an overall increase in gain. Especially around the 8K mark. Interesting.
After all of that, I just sat and listened. It still sounds just as wonderful as ever. Maybe better, but I'm not really good at those qualitative sort of assessments.
Final note: I run my quickie from an HP 6205C Dual Power Supply. Since installing the chokes, I am picking up some hum that is probable from the transformers in the power supply. With the resistors installed I could set the quickie right on top of the power supply with no problem. Looks like I will need to move the PS further away. I'm quite confident that will reduce the hum but will post later after making the change.
Final Final note: If anyone has some suggestions about how the experiment could have been improved please let me know. I tried to control for everything I could but good science needs peer review and if I'm not open to that then I'm not doing good science.
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I applaud your efforts! This kind of thing is usually best done by measuring signal with a scope or DMM right at the output of the preamp. The room is going to affect the measurements too much to give more than a rough idea, which in this case says that the average overall gain increase is roughly 3dB (which sounds about right). It's just too likely that moving the mic even a small amount could have created the peak you saw at 8kHz, particularly when you use two speakers to generate the tones. Also, the RS meters are not very linear above about 4kHz.
You might adjust the experiment by running the laptop into the Quickie and monitoring the output of the Quickie by running it into the line inputs of your Tascam and monitoring the signal on the VU meters.
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Thanks, that would definitely narrow things down. I think I made the mistake of trying to include the whole system when I should have just focused on the item that I changed. If I hooked the DMM (or my scope) to the preamp outputs would it be best to disconnect the power amp or do I need that load on the outputs?
Also, I moved the power supply well away from the Quickie with no real effect on the hum issue. I tried with and without the DAC turned on and even switched the inputs to the unused RCA jacks. No change. It's not a bad amount of hum. In fact, it is barely audible from ten feet but it is definitely more than with the resistors installed. The air-conditioner gives me way more signal to noise problems than the hum and if you're in Southern Missouri, like I am, it just runs constantly right now.
I think Dr. Toobz is on to something here. It is certainly worth experimenting with.
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If you like the chokes, I would definitely recommend checking out the PJCCS. I find the CCS to be quieter and more linear than the chokes, though I still prefer the little bit of distortion the chokes add to warm up a sterile sounding digital source. The PJCCS is preferable, IMO, if you seek more gain and better frequency extremes without adding anything to the mids. The downside to the chokes, as I've discussed elsewhere, is that they start to collapse the soundstage and sound too "mushy" as the gain increases. At lower levels, there's not as pronounced of a difference between the chokes and CCS. This is probably attributable to non-linearities in the choke's behavior, but I'll let somebody with an "official" electrical background get into that mess!