Crate VC50 mods

[rockon1]

Lead channel
R11 - change from 221k to 100k
C1 - remove
R12 - change from 2.74k to 1.5k
R59 - change from 470k to 242k
C11 - change from 470pf to .0068uf
Add 47pf ceramic cap between pins 1 and 2 of V2 (this improves high frequency stability, and a smaller value may work just as well)

Clean Channel
C40 - remove


http://schematicheaven.com/newamps/c...112_preamp.pdf

(The VC3112 has the same pre as the VC50)

Tinkering again. Some one posted these mods on another board. I guess I rubbed him the wrong way since when I asked specifically what they would do he told me to "examine the schematic and see for yourself". OK so Im an ass arent we all sometimes? Honestly besides a modest diagreement Im not aware of anything more...At any rate I looked at the schematic and Im guessing.....


Lead channel
R11 - change from 221k to 100k-reduce gain

C1 - remove-- reduce treble

R12 - change from 2.74k to 1.5k reduce gain in conjuction with R11 (typical values 100K with a 1.5k here)

R59 - change from 470k to 242k- not sure

C11 - change from 470pf to .0068uf-not sure

Add 47pf ceramic cap between pins 1 and 2 of V2 (this improves high frequency stability, and a smaller value may work just as well)

Clean Channel
C40 - remove- bright cap

Any how if some one might give the schematic a look i'd surely appreciate it. Thanks Bob

[Enzo]

From the input jack, the signal goes through a common gain stage for all. Out of that the signal branches into two channel circuits. The upper strip is the clean, while the lower more complex circuit is the dirty channel.

On the way to the dirty channel, the C41 branch goes through a voltage divider - R67, R59. The ration between them determines the amount of signal division. Stock is 1meg over 470k, roughly 2 to 1, so that means that whatever the signal voltage was coming through C41, about 1/3 of its level goes to the grid at V2-2. Think of R67,R59 and a 1.47M volume control set 1/3 up.

Now change the bottom resistor to 242k makes the formula 1meg over 242k. ABout 4 to 1. That means grid V2-2 sees about 1/5 of the C41 signal. HE turned down the volume, essentially. This is exactly how guys adjust bias in amps - change the voltage divider resistors.

[Enzo]

C11? Look in the clean channel at the tone stack C3,4,5. pretty standard. Now look down at C11, C12. DO you recognize them as another tone stack? It just isn't adjustable. C11 WAS the treble cap at 470pf. .0068uf is 6800pf, so he has widened the bandwidth of that "treble" circuit to include a more full range. Try playing with that circuit and part vales in DUncan's tone stack calculator.

REmove the clean channel bright cap? I suppose you could. is the clean overly bright? MAybe replace the 220pf with a 100pf? I like them bright on clean myself. I almost always have the bright switch on on a Fender.

[rockon1]

Thanks Enzo! I wish I knew more about this stuff since I love tinkering with it! Ive always been a "fixer" I guess thats how Ive managed to roll with the changes in the automotive industry for 32 years.

I liked the lower input into the V2 with the swap of R59 to 242K but didnt care so much for the reduction of gain caused by the change to 100K and 1.5K respectively on R11 and R12 so I changed R11 and R12 back but kept R59 at 242K.
I removed the C40 and kept C11 stock.

I also decided to change the R20 to 56K from 33K. From my limited understanding it is the slope resistor and judging from the change I think I got it right. Its more mid "meaty" now. Again thanks very much for taking the time to answer my questions!

dang-one more question- Should I put the C1 back in since I went with the higher value 220K R11? I found out its a "snubbing resistor? Without it I may get oscillation? Bob

[Enzo]

Well, DO you get oscillation?

[rockon1]

Originally Posted by Enzo

Well, DO you get oscillation?

I dont hear anything bad. EDIT: Didnt hear anything because I never took it out! Duh! Misread the board and took out the C4-realised I did someting stupid when my clean channel bass control didnt work!


BTW- I actually took C11 completely out. The tone seems fully ,thicker but still has enough treble range.

So this is how it stands for now

Lead channel
R11 - change from 221k to 100k-- 200K

C1 - remove--Yes

R12 - change from 2.74k to 1.5k- No

R59 - change from 470k to 242k-yes

C11 - change from 470pf to .0068uf-no -removed it

Add 47pf ceramic cap between pins 1 and 2 of V2 (this improves high frequency stability, and a smaller value may work just as well) -No

Clean Channel
C40 - remove-yesEDIT- Put it back in. The treble control barely worked at lower volumes.

The thing sounds much meatier,marshally. Thanks again! bob