Quicksand That Sinking Feeling

[aleman]

My Quicksand finally arrived  decided to build mine modified from the outset and change some the components to my favourites. as you will see from the pictures,as bottlehead design good circuits from the outset dent straight for the modifications. Sound quality is very good treble light and airy with good definition  bass solid tuneful informative midrange detailed balanced and even handed the sound of this little amplifier is extremely good.,i do use fostex 206e in a solo206 horn cabinets and have done so for at least ten yearswith these speakers there is a little too much midrange emphasis the quicksand seems to have tamed this somewhat resulting in a lovely listen .Imuzt temper these observations as the components will have to break in especially the Russian Teflon bypass caps and the wima poly props capacitors I have used also the battery pack has not been used as prefer to use  car or sla battery as well as trichord  never connected power supply .Anyway that's all for now going to listen to some more music.again thanks to the bottlehead crew for bringing fantastic gear to the impoverished among us .

[Paul Birkeland]

There are some reasons for the capacitor choices on the Quicksand PCB, especially C5/C6.  Did you listen to the Wimas vs. the Tantalum caps? 

[aleman]

Iam not an engineer I go with what I have used before if it does not breach  any trade secrets could please enlighten me as to why they were preferred  so that I may learn for future reference . the amp still sounds very good to my ears I must confess I did not listen prior to installing the caps.

[Paul Birkeland]

The datasheet for the chip itself calls for a tantalum or ceramic cap for C5, and that would be the one place where I wouldn't mess around too much.  Other selections may or may not lead to a noisier amplifier with additional distortion that wouldn't otherwise be there.

The other recommendations in the application sheet tend to make some assumptions (in my opinion at least) that the power supply available is marginal, so experiments with the power supply caps dotting the PCB should be harmless and fun to experiment with.  The cap at C5 functions in a more isolated fashion with respect to the power supply, so I deferred to TI's recommendations in its selection. 

Another thing you could try is making C2/C8 much, much larger, or considerably smaller.

-PB

[aleman]

Thanks for the reply I suppose I should google the chip and specs and have a good read ,changing the caps value of c2 /c8 what would the effects be I had considered some sanyo oscons low esr types however the voltages seem to be limited any advice on the lowest voltages for c2/c8 I could get away with as well as upper and lower values as guidance .look forward to your reply.

[Natural Sound]

I know that to some of you this is beating a dead horse but... It is recommended to build these kits with the supplied parts first. Listen for a while to get a baseline and then experiment away. The only other thing to add would be to only make one change at a time. If you change a bunch of parts at once and something goes wrong you won't know where to start troubleshooting. I know from years of experience that some "upgrades" make things worse. Always start with a stock build first.

[mcandmar]

For reasons i don't fully understand ceramic/tantalum caps are far better at decoupling high frequencys then poly caps so personally i would leave those ones alone.  The electrolytics i would change for Wimas, assuming those are MKP series and not MKS.

[Paul Birkeland]

any advice on the lowest voltages for c2/c8 I could get away with as well as upper and lower values as guidance

I wouldn't go below 20V.  For C2/C8, try 100uF caps, then maybe 10,000uF.

-PB

[aleman]

This is a truly fascinating hobby and one will always learn something new will take on board what has been discussed withn regard to the cap choices despite all that the amplifier sounds very good thanks for the advice.

[aleman]

C5 replaced with original ceramic capacitor sat with wife to listen amplifier sounded in my wifes word oh very nice fronted of course by the unmodified quickie  preamp looks like TI were right  have changed nothing else further listening required, also to allow the components to run in.Have acquired some lowther dx3 drive units refurbished with receipt's for work done would like to use with this amplifier but due to switch on thump unlikely to use unless anyone has any suggestions for getting around this problem.Advice appreciated.thanks

[Paul Birkeland]

Is the thump actually louder than the music played through the amp?

[aleman]

The switch on thump is loud thus  I would fear using lowthers with this amp which is a shame .

[Paul Birkeland]

But is it louder than something like a large drum playing through your system? 

If it's a ton louder, then you can just pop off the speaker connections while you switch the amp on.  If the thump is consistent with loud transients in the source material you listen to, there's nothing to worry about. 

If you had super high efficiency horns and wanted to run the Quicksand directly to the horn with no blocking cap, that would be the kind of situation where the turn on thump could cause a problem.

[aleman]

I aim wondering if putting a switch in the positive  line of the cables going to the speakers then switching them on after preamp and. quicksand would work .any advice  appreciated.thanks

[Paul Birkeland]

It's probably easiest to have a switch that shorts the + outputs of the Quicksand to ground.  (No harm done)

That way, once the Quicksand is on, you can open the switch and let it play, and the switch will be out of the signal path.

-PB