Sound impressions since I finished my quickie.

[bundee1]

Hi guys I just finished my stock quickie 2 days ago and Ive been listening for a few hours since. Here is my system so you have a point of reference for my impressions:

Sound before:
Wide soundstage with deep bass. Details were hard to pinpoint but you could hear them in the mix. All music sounded good.

Squeezebox SB3>>stock Quickie (with herbies tubedampers)>>>Red Dragon Minis (100wpc icepower digital monoblocks)>>>Synergistic Research Alpha Speaker Cables>>JM Labs Chorus 706 speakers.

Sound after:
Narrower but way deeper soundstage with lightweight bass. Cymbals and some drums dont sound good. It sounds like the drummers brush is hitting paper or cardboard. You can now pinpoint sounds in the image both vertically and horizontally. This preamp is VERY microphonic without Herbies Tube Dampers.
I also painted my Hammond case with black truck bed liner. This has flecks of black rubber in it. This deadened the case ringing alot. I also placed bluetack on the seams of the case. The microphonics have been greatly reduced.

I have a PJCCS kit that I havent installed yet. I hope this helps the bass a lot, as Rush's Tom Sawyer is sounding a little weak. 

Is anyone else getting any interference through the quickie? It seems like my interconnects were picking up a high pitched hum coming through my left tweeter. I moved the interconnect a little and it went away.

[Doc B.]

Red Dragon Minis

I was googling for info to see what the input impedance spec of this amp was, but alas, the Red Dragon Mini seems to be an "electronic cigarette". Can you point me to some specifications, in particular the input impedance? It may be that it is fairly low. The Quickie has a fairly high output impedance and is happiest running into loads up in the 50K ohm and higher range.

By high pitched hum do you mean a 120Hz "buzzy" sound? That would most likely be from a poor ground connection, perhaps between the interconnect and the RCA jack.

[bundee1]

The input impedance of the Red Dragon Amp-1 (my mistake they have a different name) is 10k. Would this account for the light bass? Are there any modifications I could do to help? Would the PJCCS help with this? BTW my interconnects are 1m long and have fairly low capacitance specs.

[Paul Joppa]

Give it some time for the output capacitors to break in. Your description of thin bass and nasty highs are classic for an new capacitor. And of course you won't find $150 boutique capacitors in a $99 kit!

Is the amp gain fairly high, or are the speakers sensitive? This combination will result in using a fairly low gain setting on the preamp, and increase the system sensitivity to preamp microphonics and probably buzzy noises as well. See my white paper on signals and noise for solutions.

A 10K load ought to work OK, without loss of bass due to the output cap. Seduction has 1/4 the capacitance and drives 15K pretty well.

If high sensitivity and/microphonics is a problem the PJCCS will make it worse.

[bundee1]

The speakers have a sensitivity of 89.5db. I like a lot of aspects of the sound but was surprised at some of the weaknesses. Would bigger caps help with the bass? Ill run it in a little more and see if it makes a difference.
Thanks for all of your help. I had a ton of fun building it.

[Grainger49]

Using a larger value capacitor will not change the low frequency response.  Like PJ says, capacitors need to break in.  As a matter of fact tubes need to break in too.  PJ is also saying that you can buy a "better sounding" capacitor (the same value is still appropriate).  If you do, the break in starts over.  Or you can break them in before you put them in.

The result of having a lower than recommended amplifier impedance is going to slightly roll off the very high frequencies.  It is not a big deal.  But it doesn't affect the bass.

89.5dBW sensitivity speakers probably fit well with your power amps.  What PJ is asking about is the amplifier sensitivity.  That is the voltage your amplifier takes to reach full rated output.  Some amplifiers take 0.5V to reach full power some take 2.0V to reach full output.  The lower the voltage it takes to reach full output the more noise will creep through.  It means the preamp will be operating down close to the noise floor.  

[bundee1]

You guys are awesome! Thanks for all of the advice and guidance.

Here are the specs for my amp:

[Paul Joppa]

Unfortunately the specs do not include sensitivity. I did a quick search and found a post somewhere identifying another amp (a Bel Canto I think?) as being "identical" and it has a gain of 27dB. Sorry I have to run, I'll try to get back to this with calculations but I do think you can use 12dB of attenuation at the input of the power amp to reduce audible microphonics.

Give the caps at least 50 hours of music. To be quite sure, run music until you need to replace the batteries (about 200 hours).

[bundee1]

so should I skip the PJCCS? The sound has gotten a little better but Im thinking it may just be the tubes. They are Amperex tubes. Ill give them until the end of the day to break in the caps and then switch to some RCA's I ordered last month. Ill post the results soon.

[Paul Joppa]

so should I skip the PJCCS? ...

It's easily reversed, and you already have it, so you might as well give it a try.

I'm an analytical guy, so if it were me I'd first determine whether I needed an input attenuator at the power amp input, and put one in if needed. Then I'd try the current source.

But an experimental approach is good too. On the plus side, the results are authoritative. On the minus side they are hard to extrapolate - if the CCS sounds worse, that might be because you don't like the CCS, or it might be that the gain is raised so high that the gain budget problem swamps out the CCS sound. You would then need to do more experiments. Back on the plus side again, more experiments means more careful, attentive listening, which is fun in itself, makes you a better listener, and helps you learn what kind of sound you really respond to.

[Grainger49]

I would suggest you attack the input attenuator first if you need one.  This way you don't have to reverse anything.  Then once the gain problem is solved you can best assess the sound of the PJCCS.

My two cents worth.  Just because I hate having to do things over again.

[bundee1]

any easy way to attenuate the signal? can I add some resistors somewhere? Hey Paul have you had a chance to crunch numbers? Sorry to be a pain but I hear great potential in this pre.

[bundee1]

I burned in the Quickie for 100 hours with Amperex tubes. The sound became more refined but the bass didnt improve as much as I expected. I switched in some RCA's and the soundstage widened but its a lot harder to differentiate instruments. The bass is better but still not up to standard. I feel like the preamp is being overdriven when I hit 11 o'clock on the volume dial as the soundstage compresses. 

[corndog71]

An easy upgrade would be to get some better output caps for the quickie.  My first choice is to use Sonicaps.  They are just very clean, neutral caps that don't hinder dynamics.  Some time this week I'm going to pull the pair I have in my Foreplay 2 and try them on the Quickie.

[Paul Joppa]

OK, 105 watts into 8 ohms is 29 volts RMS. Speakers are 89.5dB/w/m so a nominal peak power of 102dB would require 11.9 volts. Amp gain might be 27dB assuming the Bel Canto is in fact identical; that's a factor of 22.4 so the peak input you need to the amp is 0.53 volts.

Stock Quickie gain into a high impedance is 2.2; into 10K I would expect about 1.8 gain. Assuming your source has a peak output of 2vRMS, it would be possible to generate 3.6 volts RMS output peaks. This is about the absolute maximum output from Quickie with fresh batteries, so turning up the gain on Quickie can result in clipping if the batteries are worn.

With depleted batteries a stock Quickie can put out about 2.2vRMS, which is 12dB greater than the needed 0.53 volts. Hence an input attenuator of up to 12dB at the power amp input would allow the Quickie to appear less microphonic, at the expense of pushing its output capability (increasing distortion).

Personally, I would opt for tube rolling and vibration control to get the microphonics down - 12dB is not that great. I might try a 6dB input attenuator as an experiment. You might also experiment with passive preamps as well, since you do not need gain in a preamp - again, assuming your source has 2vRMS peak output.