First official Bottlehead Quickie upgrade - the PJCCS

[Doc B.]

I guess the best you can do at this point is compare my description of what I hear against what you hear, as I have not tried the chokes. I heard much better definition of notes and the image became much more clear and realistic in terms of proportion and sense of depth. A hunch is that it is probably doing more good stuff since the impedance of the choke is lower than the current source, and it appears that what we are hearing is primarily due to a lowering of distortion at any given level vs. the stock setup - a result of the high impedance load.

I have been forming a theory over the past 15 years that a lot of folks prefer a particular change to a tube circuit because it may help the bottom end or the image or whatever and doesn't change the treble, and part of the reason they went to tubes was to smooth out an edgy digital setup. IME a CCS will make the treble more quick and concise than a plate choke. Since a lot of listeners do use digital front ends, that change in the treble definition that I consider an improvement may not be to their taste because it may tend not to help downplay any digital mid-treble edge coming from upstream.

That is perhaps a circuitous route to say that I think a CCS often does more good for the sound than a choke, and that any problems that are upstream should be addressed upstream rather than trying to iron them out them after the fact. BUT I'm also saying YMMV.

[Paul Joppa]

...
I can almost hear the response of "try it and let us know" ...

I see I may have been too consistent in my responses lately ...  :^)  It's not an experiment I have done. But here's one I did do:

Some years ago I built an experimental parafeed preamp with a 6BL7. I had some tapped chokes on hand, whose basic inductance at the tap was about what I think is right for those impedances. end to end, I could get 20% more inductance. So I added a second choke per channel and wired it all up to a switch - I could select 100%, 120%, 220%, and 240% of the "right" inductance. Sure enough, every increase of inductance was an improvement in the sound. Doc B wanted to swap in a C4S, but that would have changed the operating point (plate voltage specifically), making it hard to interpret the result reliably, and I never got around to resolving that issue.

I conclude more impedance is better. Now the PJCCS is not a cascode (it would rob too much of the limited available compliance voltage) so it is not as high an impedance as a C4S. I don't know the Early voltage of the MJE350, but assuming it's around 50v (typical for transistors) the dynamic impedance would be 25K ohms. A 150 henry choke is 19K at 20Hz, 190K at 200Hz, and 1.9Meg at 2kHz unless its capacitance is dominant at the frequency. So it's possible the choke would sound better than the current source.

[Doc B.]

OK folks, the manual is getting written today and the order button is ready to push!

http://www.bottlehead.com/store.php?crn=220&rn=441&action=show_detail

[booangler]

Hot Damn!!!

[Doc B.]

Got behind a little, but I finished the PJCCS manual yesterday and tomorrow we will be getting out all the PJCCSs that have been ordered so far. Thanks for those orders!

[Wardsweb]

Perfect timing...I placed an order about an hour ago.

[BNAL]

I assume you can use the PJCCS with the headphone design?

[Len]

I assume you can use the PJCCS with the headphone design?

I think I posted on the old forum but can't find it right now. Anyhow, the problem is the battery voltage will drop as they age. Using the fixed bias of an LED in the cathode will cause an exaggerated change in tube current as the battery ages; the cathode resistor provides negative feedback at DC to maintain the appropriate operating point.

A quick look at the curves shows the plate current dropping from 2.5mA to 1.0mA as the battery drops from 36v to 24v.

A reasonable solution would be to use a current source to replace the plate load - that way the tube maintains a constant operating point, and operation will cease suddenly when the battery no longer provides sufficient compliance for the current source. I'd suggest 1.5mA as a good value to use. Note this will not work well for headphone operation where a substantial output voltage is going to be needed, unless you also add more battery voltage. Now this is starting to get complicated!

Would the above long post apply with the PJCCS, too?

It's probably a moot issue, since many of us will be adding more battery power anyway (a milliwatt power binge!)

[Paul Joppa]

I assume you can use the PJCCS with the headphone design?

Yes, it is designed to adjust the current as the battery ages.

[Paul Joppa]

...

...

Would the above long post apply with the PJCCS, too?...

No, that post is old - it's actually what started me thinking about a self-adjusting current source. The PJCCS should work well and give fairly good battery life whether implemented as a preamp or as a headpone amp with output transformer.

[Len]

...

...

Would the above long post apply with the PJCCS, too?...

No, that post is old - it's actually what started me thinking about a self-adjusting current source. The PJCCS should work well and give fairly good battery life whether implemented as a preamp or as a headpone amp with output transformer.

Cool!

Can it work with higher voltage?

[Wanderer]

Does the PJCCS offer the same gain increase as the Hammond choke modification?

I have a choke mod Quickie and can't give up a db of gain.

[Paul Joppa]

Does the PJCCS offer the same gain increase as the Hammond choke modification?

I have a choke mod Quickie and can't give up a db of gain.

Yes.  :^)

[cpaul]

I'm having trouble with wiring up the PJCCS I just received.  The PCB is a bit different from the one pictured in the manual and some solder points are missing/not the same.  The partially stuffed board is here:  

http://picasaweb.google.com/103078014592468973736/Bottlehead#5537786106126040610

In short, p.13 talks about soldering a wire from points bA to bB with an "S" shaped wire.  My board has no such points, though it has all other solder points in different orientations from the manual.  I can't make sense of the solder points that DO exist to match them to the board as represented in the manual.  Can anyone help me figure out what points are the bA and bB on my board?

Thanks.

Edit:  Hnmm.  I can't seem to get the pics to post, so I've tried just posting the link.

[Wanderer]

I am currently working on a PJCCS myself. Follows the manual just fine.

The board you have looks nothing like mine. I am thinking you may have gotten the wrong board with your kit. 

Call the Queen - bet she needs to ship you a new/correct board.