Can I give the Quickie a passive option?

[pnx]

I love to spend time doing "serious" listening, but I also often have my system on for hours at a time while I'm doing other things. I hate the idea of my batteries running down during background listening. I'm wondering if it wouldn't be too hard to rewire so that there is one input and two outputs - one active and one passive. The source selector switch would become the output selector switch.

What I'm thinking of doing is having the output from the volume pot go to the switch. One position would send the signal to the active section and the other position would send it to the other output. Would that work? Does the passive preamp need anything more than the volume pot to work?

*EDIT* I should add that I'm working with a first generation Quickie.

**EDIT** I found some info about conventionally wired potentiometers in passive preamps vs shunt or Haller types. It's a lot to digest, but either way I decide to go I still think I can make it work unless there is something I'm not considering.

 

[Paul Joppa]

Most "passive preamps" use a much lower-impedance volume control; the quickie is 100K and 10K is most common. You can push it to 155K or even 25K if you keep the output interconnects short and low capacitance. Also, for casual listening a little loss of treble may not be a big deal.

I would substitute the 100K pot with a lower value, depending on the needs of whatever the source is. CD players can drive 10K easily; tube phono preamps usually want at least 20K and prefer 50K or more. Depending on the impedance chosen, keep the interconnects short enough and low-capacitance enogh and you should be in good shape.

As a passive, you'll run the pot at a higher setting - so the poor balance at low settings of inexpensive but good sounding carbon pots won't be a problem. Something like the PEC pots would be a good choice.

 

[WK3K]

Following up on this thread as I'm interested in a similar setup. I often like having some music going while I'm cooking or doing chores, so I'd like to find a way to make the quickie passive during these times, and active while I'm in the listening room really taking in the music.

I have the 1.1 quickie with PJCCS. I added a third input (DAC, iPod/phone, and will be adding a Reduction Phono), so I've already installed a basic on off switch in the chassis (between battery and source selector). I'm hoping for an easy rewire so that instead of on/off I would have active(on)/passive(off).

My main questions are: Do I need to install another set of outputs or can I just wire volume pot>DPDT>existing single output? Is the DPDT I currently have in there the correct kind of switch for this application? I know I'm going to explain it poorly, so I attached a drawing below with what I'm thinking will work. I've also attached a picture of my present arrangement.

While I'm messing around, I'm also thinking about swapping a Goldpoint 50K stepped attenuator for the stock pot. Will this be a good fit in this application? Goldpoint recommends 25K for both tube and passive preamps, but PJ - it sounds like you'd vote for 50K?

All of this will eventually run out to either a SEX or Paramount (TBD).

Surely appreciate any and all help here!

EDIT: I should qualify that I plan to remove the current switch and restore the direct connection from the source selector to the volume pot. Also, I noticed in my drawing that it looks like I wrote "no charge" it is, in fact, "no CHANGE".

 

[WK3K]

Just wanted to bump this thread as I'm going to attempt it tomorrow and was hoping to get some feedback before I try something magic smoke inducing. I snagged a 50k Valab stepped attenuator off eBay and I'm going to but that in the quickie along with a (hopefully) active/passive switch just after the attenuator.

Again, the main question is just whether I need to add a separate set of outputs, or if I can just have the passive circuit go straight to the outputs that are already installed - essentially can I use the same outputs for both active and passive?

Any feedback totally appreciated. I will, of course, post results once I've given it a shot.

Thanks!

Witold

 

[Grainger49]

A simple switch that swaps the input to the tube grids with an output to the output RCA jacks might work.  But I am concerned with the open grids of the tubes.  I would ground the inputs to the grids at the same time as switching to the output RCA jacks. 

It might work either way, but if the tubes oscillate because of the open inputs then you get that on top of the passive output.

 

[WK3K]

Grainger, thanks so much for the feedback. Reporting back here. Finally got around to taking this on this morning. There's good news and bad news.

Good news first, Valeb attenuator went in super easy after about 5 minutes spent with a pocket knife widening the mounting hole. With my switch in the active position everything sounds great and I think the attenuator was a nice upgrade in and of itself.  8)

Bad news now.  :-\

A simple switch that swaps the input to the tube grids with an output to the output RCA jacks might work.  But I am concerned with the open grids of the tubes.

This does indeed appear to be a problem. I ran the output from the attenuator to the switch and then straight to the solder cup of the output jacks. When the amp is in this "passive" setting, it creates TONS of hum (way louder than the music), so it seems grounding is an issue.

I would ground the inputs to the grids at the same time as switching to the output RCA jacks.

How would I go about doing this? Do I need a different switch? Just a rewire?

Thanks again for all the help!

Witold

 

[Grainger49]

Hmmm, that might be the open grid feeding noise through the circuit and that appearing as well.

I was writing about grounding the grids but I realized that that would also ground the passive output.  I'm going to have to think on it. 

One way to eliminate this is to lift the output from the output capacitors when you go passive.  Do you follow me?

 

[WK3K]

Grainger,

Yup, I follow, just trying to think of a practical way to do that. My goal here was to not have to rewire, pull interconnects, etc... when I wanted to switch between active and passive. I suppose I could throw in a second switch that toggles the connection of the output caps to the solder cups on the output. I'm just wondering if there isn't, perhaps, a more elegant solution.

Thanks again,

Witold

 

[Grainger49]

I agree, that is why I'm still pondering it.

 

[WK3K]

But if I did just add that other switch, then I would probably have to upgrade the output caps while I'm at it.... 

 

[Paul Birkeland]

This does indeed appear to be a problem. I ran the output from the attenuator to the switch and then straight to the solder cup of the output jacks. When the amp is in this "passive" setting, it creates TONS of hum (way louder than the music), so it seems grounding is an issue.
How would I go about doing this? Do I need a different switch? Just a rewire?

That wiring configuration won't work.  You would be allowing the grid of the 3S4 to float and wander off, which may damage the preamp. 

A 100K Valab is going to make a terrible control to use as a passive preamp.  You'd want a 15K control, which will be much harder for your source components to drive.

 

[WK3K]

Thanks for the reality check PB.

So I put in the second switch to "lift" the caps from the outputs when I switch into passive mode - sweet success. I know it compromises some of the simple elegance of the circuit, but it fits my needs a lot better.

The passive mode obviously doesn't sound as good as the full active quickie, but that's to be expected and works for me - the main point is to have jams at a party or while I'm doing chores or whatever.

Thanks for everyone's help, I really learned a lot during the project.

Here's a pick of the quickie with it's new facelift.

Thanks again y'all,
Witold.