thinking about building a quickie

[aragorn723]

Hi, so I have have been thinking about building a quickie to drive a solid state amp, and have been wondering if anyone has considered building a regular power supply for it instead of batteries?  I like the idea of quiet battery power on the one hand, but over the long term wonder how expensive that would get?  At the moment I can listen to the stereo maybe an hour a day if i'm lucky (got a 3 month old son) so maybe headphones are an option too.  Is there a way the Quickie could be used for both a headphone amp and preamp?  Any thoughts

[corndog71]

When I was using regular duracell batteries for my original quickie (w/PJCCS upgrade) I would get about 3 months or so before needing to change the batteries.  The D cells tend to go faster as they draw more current.  One of the mods I did for my ultimate quickie was to swap the 9V batteries for 3 Power Sonic 12V rechargeable batteries.  In the last 6 months or so I've only had to charge them up once!  No easy replacement for the D cells unless someone else has any ideas.

Then again I tend to listen for several hours at a time so perhaps you could get a bit longer playing time.  If you haven't done much soldering then the Quickie is a great way to get some practice in.  Mine mated well with my solid state Class D Audio SDS-258.

[Paul Birkeland]

Batteries for the Quickie are far less expensive than a wall supply.  I have built (and still have around) one Quickie with a wall supply.  It took two power transformers and several PC boards to create.

I would guess that the parts cost if we sold it as a kit would be about $300. You can buy a lot of D-cells and 9V batteries for $300.

There is a thread on the Quickie forum that's a sticky about converting your Quickie for headphone use, though it's more of a novelty IMO.

[aragorn723]

Thanks for the replies.  At this point, i'm not the most saavy on building power supplies, so the kit build will be stock (but of course it's nice to know what options are out there!).  Will this preamp be ok to drive my amp and a 10" b&w powered sub?  I don't listen to music super loud, but like to turn it up to hear specific instruments or a singer's voice from time to time.  Also, are the 3S4 tubes easy to find?

[Paul Birkeland]

3S4's are very easy to find and generally not all that expensive (~$5)

How long are the cables to the amp and subwoofer? (and what kind of cables are they)

Also, what is the input impedance of the amplifier and the subwoofer?

[earwaxxer]

You can use AA rechargables for the D cells - get a couple of AA battery adapters at radio crap.

[aragorn723]

here is my cable and input impedance info:

sub cable- 6ft rca from target (nothing special) and the sub input impedance is 22K
main amp cable- 3 ft cardas crosslink, and the amp input impedance is 10K

 

[Grainger49]

The cable capacitance is a concern when it will roll off the high frequencies.  The cable connecting a sub need not be high $ stuff.  The 22k input impedance helps keep that from being a problem. 

The lower impedance and almost assuredly lower capacitance of the Cardas cable passes everything on tho the main amp.

I'm saying you are in high cotton. 

[Paul Joppa]

You can use AA rechargables for the D cells - get a couple of AA battery adapters at radio crap.

Most of the cheap rechargeable D-cells are actually AA cells in an otherwise empty can - built-in adapters?!

Real ones, with around half the capacity of an alkaline, are available but hard to find without going to the web.

[Paul Joppa]

here is my cable and input impedance info:

sub cable- 6ft rca from target (nothing special) and the sub input impedance is 22K
main amp cable- 3 ft cardas crosslink, and the amp input impedance is 10K

That's marginal - in parallel, the impedance is 7K ohms; normally I have said 10K is the minimum. But it should work reasonably well. You might eventually want to try a larger output capacitor - I'm not certain the difference is audible, but it could be. It won't be dramatic.

[Grainger49]

Oh, crap!  I didn't look at the main amp's input impedance.  Most likely a series 10k ohm resistance with the amp's input will put you back where you want to be.  That will cut the input to the main amp in half.  You will need to make adjustments to the sub volume control to bring it down in volume.  The Quickie has a lot of gain.  So overall it will only take a pair of good sounding resistors (~$6 each) and a rebalancing of the sub will do it.

[aragorn723]

what is the difference between output voltage and gain?  They sound like similar terms to me, the sound and vision magazine article measured the output voltage at 1 volt, which doesn't sound that high compared to the specs of some other preamps i've seen like NAD, etc.  Please educate me, i'm asking out of ignorance here   

[Paul Joppa]

Gain is the ratio of input voltage to output voltage. In the stock Quickie with a high load impedance, gain is about 2 - so for a 0.25 volt input, the output voltage is 0.50 volts. For an input of 1 volts, you get 2 volts output. Near the end of the battery life, the maximum output is around 2.3 volts RMS.

With a low impedance load, the gain and maximum output will be reduced. For a 10K load, the gain is about 1.7 and the maximum output at the end of battery life about 1.9v.

A "standard" CD player will generate a maximum voltage o2.0 volts RMS; that's sometimes called "full-scale" output, so 2.0vFS is a common abbreviation.

The gain control works by reducing the input voltage (e.g.2.0vFS from a CD player) to something smaller (e.g. 0.25v) which is then stepped up by the gain (i.e. 0.5v).

You can look in the specs to see what voltage a power amp needs to generate full output; it's usually around a volt but can vary a lot.

=========

Changing the subject a little - decibels are calculated from a voltage ratio, so gain can be expressed in decibels but voltage cannot. Voltage gain is 20 times the base-10 logarithm of the voltage ratio, so a gain of 2 is 6dB. To confuse the issue, the Powers That Be have invented the dBv, defined as the ratio of a voltage to 1.0 volts and expressed in decibels.. So 2.0 volts is 2.0dBv, while 0.5 volts is -6dBv.

[aragorn723]

so the output voltage depends on what you put into it.. never thought of that.  I see from the delivery status page that orders thru 12-21 have shipped, how long does it usually take to gather the parts and send out a kit?  Also, after placing an order, do they give you an idea of anticipated delivery, and how far along it is, or waiting for parts.. or whatever the status is.. (sorry i do planning for a living lol  Just trying to decide if i'd be able to handle the waiting

[corndog71]

While I only have a few Bottlehead kits, they were all worth the wait.