Hammond Chokes w/ Quickie - Cheap and Worthwhile!

[sbelyo]

If I installed these chokes, would I not need the CCS?

[Wanderer]

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. 

[sbelyo]

looks like the cost is the same

[porcupunctis]

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.

[Doc B.]

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.

[porcupunctis]

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. 

[Dr. Toobz]

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!