I rebuilt the board for this amp using Hoffman's board material but with a paralleled turrets. The amp is super quiet at idle but can crank to be a pretty loud amp using a Cannabis Rex speaker cab.
I rebuilt the board because the tagboard was flimsy and after numerous tweaks it looked awfully messy. I bought a Hoffman blank board and narrowed it by cutting it with a hack saw. The hack saw made short work of the board.
Why two cathode followers??? Because I figured out it smoothed the 5879 OD and that it seemed to help sweetened the tone of the digital delay. This allowed a CF on the clean and the OD channels prior to the effects loop with the digital delay.
I tried bypassing the mosfet CF to see what the difference was. The mosfet CF seemed to give a little bit more gain but with NO loss in transparency that I could hear. I think the digital delay sounded better with the mosfet CF in the circuit also.
I used Orange Drop SP series caps everywhere except two locations. I used a Malloray 150 .001 across the 5879 plate resistor. I also used a Orange Drop 715p .001 in parallel with a Orange Drop SP .0042. I actually tried a .001 Mallory, .0012 OD SP & then an .001 OD 715P. The .001 OD 715p made a signficant difference in giving some brightness to a smooth tone. I feel like the paralleled SP (smooth) and 715P (bright) allowed a nice balance ending up with a smooth reasonably bright tone. It did allow more harmonics also than using two paralleled SP caps in that place.
I found that ceramic disc caps would sound better in some place than Silver Mica. In other cases, they sounded equally good with no signficant difference for some reason. I want to emphasize that IF one sounded better than the other, it was always the ceramic disc ........ otherwise they sounded pretty much the same. I have NO idea why in some cases it made a difference and in other locations, no difference.
I've learned that using a cathode cap on the triode before the cathode follower dramatically shapes the tone of the entire amp. For example, removing a 2.2uf cap on V1-8 (prior to the mosfet CF) gave the amp a MUCH smoother tone and eliminated some grit that I didn't want. AND reducing the 2.2uf to a 1uf on the 5879 cathode made a dramatic difference also. Completely eliminating the cathode cap on the 5879 removed alot of harmonics. 2.2uf gave it some grit but the blooming was excellent. Using the 1uf made no difference in the blooming that I could tell, but gae it a much smoother tone.
Again, I want to emphasize that cap, or no cap or cap value/size really made a HUGE difference in my amps on the triode cathode prior to the CF. It made an amazing difference that I would have never suspected.
I used RV65D Vishay 1/2watt metal film resistors on the plates and most other locations except the cathodes. The except was the cathode of the Mosfet CF and the cathode of the V2-8 which was the cathode follower after the 5879.
I reworked the tone stack. There is a 121k trim pot on the board for the bass. It actually measured around 95k. I used a 500k min-pot in a hole that previously held a DPDT switch. The hole had to be slightly enlarged for the mini-pot. This tone stack really does work and you can hear a very clear difference turning either the treble, mid or bass pot.
I noted on the voltage chart what my favorite pot settings and noted the voltage divider values that the pot gave in that particular setting. I usually have the OD trim pot at "3" but occasionally will move it as high as "5".
I believe at this juncture, that this is the best sounding amp I've made. The clean sounds rich and full and the notes are smooth and each note stands out clearly in chording. Kicking in the OD is really cool because the OD tone remains a clear tone but sounds very overdriven and the blooming and sustain is remarkable, IMO.
I hope someone will build this and report on their own results.
EDIT: I removed the master volume on the clean channel and added what I call a "chime" pot. This tone stack is switched in when the PAB is engaged. Note the tone stack prior to V1b is partially removed when the PAB is engaged. This mod adds a tone stack that has more chime and more of a vowel/wah type tone. I think the chime pot would help cut thru a band mix more easily.
EDIT: I added the "TEC" enhance cap across the LTPI plate resistor. This allowed me to lower the value of smoothing caps in the preamp and OD section. Lowering the cap values removed some mid frequency grit/grind. I feel like it allows for clearer sounding chording. It seemed to brighten the tone somewhat and improved harmonics some. I also changed the .033 mid cap to a .033 + .0052 making a .038 cap. This seemed to define the mid tones more clearly. All of these mods are in the 12-11-11 schematic.
With respect, Tubenit
Topic: TOS & CF (Read 16374 times)