New Quickie nice but too loud

[cpaul]

Just got my green quickie (hey, mine came with kisses!) and built it last night and the night before.  Checked voltages and plugged 'er in and it's playing beautifully as I type.  This kit was so dang easy to build and it's sound quality is impressive indeed.  That's in large part due to the thorough instructions.  Way to go!  I haven't even built or installed the PJCCS yet, and I could happily live with this sound.  Even the bass is nice, tight, and not at all shy.

But one thing bugs me.  I'm currently listening at about 7/8 attenuation - 1/8 turned up (pot is at, oh, 8 o'clock where noon is mid-way up the control).  In other words, I've barely got the thing turned from it's lowest point.  And...if I twist it further down, it rapidly shuts down.  It's evening and the volume is nearly too high (young children asleep and such).  Wondering why and what I should do about it.

Here's my particulars:
Room:  approx 14x16
Source:  CDP Rotel RCC-955 (max output 2V)
Amp:  Marsh A200 (input sensitivity 1Vrms, input impedance 56k unbalanced)
Speakers:  Vandersteen 1C (6 ohm, 90dB or so)

I have the same problem using the CD input of my older Yaoin MS-12B tube phono/linestage.  It too is quite loud on the .7V output (it has .25V and .7V outputs) while the phono portion is much more realistic.  That unit has input sensitivity (I think - it's hard to decipher) of "<= .25V" for the CDP input.  It uses 12AU7 for linestage and 12AX7 for the phono stage.

So what is the input sensitivity of the Quickie?  Can I up the grid resistor value?  I think the pot is 100k, so should I go to a higher value pot?  For that matter, how about a LDR-based pot, which seem to go to very high resistances when fully attenuated?

Finally, the quickie is indeed microphonic when I touch anywhere near the unit, yet its much less annoying than the microphonics I get from the Yaoin.  That unit will whistle away at random moments even though I've tried rolling tubes with tubes that are supposed to be resistant to microphonics and tube dampers.  Time will tell, as the Yaoin developed it's microphonics problem over time.

Anyway, I'm quite pleased.  Excellent job Doc, Paul and company.  It's my first experience with directly heated cathodes, and so far, if that's largely responsible for the sound quality, I'm hooked. 

[Paul Joppa]

It's the fairly common problem of too much gain in the system. You can read my white paper on the subject on the Bottlehead Community page if you want to get into the details. There are several approaches mentioned in that article. Not included there but quite reasonable is an output attenuator, especially when combined with a current source plate load.

There's a recent post on converting the Quickie to cathode follower format, which will give you an idea - by reducing the gain you will reduce the microphonic noise, and increase the volume control setting at the same time. That post uses a choke as the cathode load. Perhaps we should look into a version of the PJCCS as a cathode load, for those who need this change.

I'll try to find some time in the next week or so to look into better gain control options for the Quickie, when the system gain is too much.

[cpaul]

Thanks, Paul.  I will read the article.  I did notice the cathode follower post by Dr. Toobz.  I'm interested in some of the options you mention, but my current setup isn't necessarily my final one.  I have an 8W push-pull DIY amp (based on 12AQ5s) and a SE based on 6BM8 tubes, as well as some other options (13EM7 SET design, a 5W single ended mosfet amp and more).  I'll be trying various combinations over the next 6 months or so, so not sure if I want to radically shift the design of the Quickie unless I decide to buy another one as my experimental version.

Anyway, I am certainly interested in the CCS loaded cathode follower idea.  I'll keep my ears open.

[corndog71]

My Quickie was a bit sensitive too so I just added some resistors to pad the input down around -10dB.

Here's my reference for figuring it out.

http://www.goldpt.com/mods.html