Tweaking a CeeJay 11 style build

[pullshocks]

My breadboard amp has morphed from cathode biased Princeton reverb ( capacitor driven)to the CeeJay 11 style circuit that has been discussed a few times on the forum.  It was really just a matter of swapping some cathode resistors and bypass caps, and wiring up the boost switch.  I also disconnected the reverb, as another builder reported a tradeoff between good reverb and the sound  Once I get things dialed in, I may try to add an effects loop.


FWIW, I have added a mid pot, and I only have a single input jack wired in.  B+ on the power amp plates is 330 volts, maybe a little low for this amp?

I mostly play guitars with vintage or medium output humbuckers, my current favorite being the Dimarzio Blues Bucker.


With harder picking, I heard a zappy, crackly  non-musical distortion along with the notes and chords.  Yuck. 


Reducing the V1A cathode cap to4.7 uF and then 1uF didn't really help.  Neither did grid resistors on V1B or V2A.  A 470 K grid resistor on the cathodyne PI finally seems to take care of it (thanks Merlin).  I may try a couple higher and lower values, but I'm on the right track.


I'll probably bring the V1A cathode cap back to  10 uF, and spend some time playing it.  We'll see  if the cold biasing on the preamp tubes stands the test of time.

[tubenit]

I would suspect a bad tube,  bad tube socket not making good contact on pins or poor solder joint.  I am presuming the amp doesn't have NFB like a PR, but if it does then I would disconnect it.

With respect, Tubenit

[ac427v]

For me the crackling sound has always meant bad contact somewhere. In addition to tubenit's list, I have had bad solder joints--invisible on tube sockets, bad switches, and debris in pots. The common factor was that they made sufficient contact at low volume to sound fine but vibrated bad at higher volume. Chop-sticking was the only way to identify the culprit.
--Craig

[pullshocks]

Tubenit and AC427v, thanks for the suggestions.  This being a breadboard, with mostly screw clamp connections, it is certainly possible that there is an imperfect connection. 


But since the unmusical sound was eliminated or significantly reduced by adding the cathodyne grid stopper, I have to conclude the issue was the cathodyne being overdriven, as described on Merlin's web page http://www.valvewizard.co.uk/cathodyne.html


One of my other amps has developed a crackle problem that is probably due to bad connections or bad plate resistors, or bad tube.  The crackling is constant, regardless of signal.

[pullshocks]

Egg-on-face time.  I  went to work  this amp some more, and heard the bad distortion worse than ever.  How could this be?  Because it wasn't coming from the amp.  It was my hearing aid overloading.
The hearing aid is set up with several programs, for different situations, with different types of signal processing, to (supposedly) improve speech intelligibility in different types of background noise.  One program is for music listening, it is simply eq'd to compensate for my high frequency hearing loss.  In general, music sounds pretty dull to me without it.
I had never noticed it overloading like this.  I guess in the excitement of trying out a new amp I must have had it turned up louder than my usual playing volume, enough so to overdrive the hearing aid. 


Master volume is a must for me.


Anyway, I'll probably leave the 470K grid stopper on the cathodyne (Merlin recommends it) and put everything back to the values in the schematic and start over.

[jojokeo]

I guess in the excitement of trying out a new amp I must have had it turned up louder than my usual playing volume, enough so to overdrive the hearing aid.
Anyway, I'll probably leave the 470K grid stopper on the cathodyne (Merlin recommends it) and put everything back to the values in the schematic and start over.

Classic - something nobody would know to even ask or to figure out? Overdriving the grid (due to your hard pick attack reported) can cause a tube to go into conduction and also forgetting to have a grid return resistor can cause weird issues also both creating bias issues.

[pullshocks]

OK, I have the component values back to those in the schematic values except for the 470k grid stopper on the cathodyne.


For a speaker, I am using an Eminence Lil Buddy.  It seems to have a cleaner sound than any other speakers I have on hand, making it easier to tell what the amp is doing distortion-wise.  It also has a pretty firm low end, so I have kept the bass control turned down.


With Duncan '59 neck and Pearly Gates bridge it stays pretty clean up til 4 or 5 on the gain knob, and builds from there.  It sounds great wide open, and even more so with the boost switched in.  I would say it is a pretty versatile circuit.


I was kind of curious about the v1b and v2a grid stoppers so I left them on the bread board but hooked up some switches to bypass them.  To my damaged ears, the grid stoppers on the gain stages do not make any audible difference.  No reason to leave them.


I experimented a little with a 3rd switch for hot/cold biasing on the 3rd preamp stage, with 820 ohm unbiased, vs 4.7k ohm +4.7uF.  I could tell a difference in volume, but the tone did not seem that different.  Those with better hearing might notice more of a difference.