Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Joel on August 19, 2018, 11:25:07 pm

Title: Some questions about the Carolina ODS circuit
Post by: Joel on August 19, 2018, 11:25:07 pm

Morning all!

I have some questions about the Carolina ODS circuit and I'm hoping the collective wisdom can help me out.

Referring to the attached schematic;

1.  FX Loop question 1: the red circle around the parallel combo of 470k and 0.001u cap.  What does this do?  I've seen this pair in some FX loop schematics.  This FX loop is very similar to the D* style loop, but they don't have this pair.  And this arrangement isn't in Merlins book either that I can see.

2.  FX Loop question 2:  in purple - the FX Level pot.  Isn't this really a Master Volume in this instance?  Without a PPIMV this would be the MV right?  What effect would a 250k vs 1M have in this spot?

3.  OD output question:  What's the function of this 100k resistor in series with the signal path? 

Thanks in advance.

Title: Re: Some questions about the Carolina ODS circuit
Post by: tubenit on August 20, 2018, 08:22:04 am

1) allows some dry signal to bypass FX pedal


2) could be viewed as a master volume if you want


3) reduces signal


With respect, Tubenit

Title: Re: Some questions about the Carolina ODS circuit
Post by: Joel on August 20, 2018, 10:12:22 pm

Thanks mate.  I appreciate the response.

1.  A poor mans parallel fx loop?  In your opinion how does this improve over the standard series loop?

2.  I figure, why have a "Master" pot in front of the fx loop which isn't necessary (due to having the loop permanently in circuit)?  And why have a "FX Level" pot after the loop which actually functions as a Master Volume?  Confusing for the guitar player if you ask me.  I've read somewhere that people who use a D*style amp with D-lators tend to use the FX Level as the Master Volume.  So I figure, if I'm making one I'll just simplify.  Just wanted to make sure I'm not missing something fundamental.

3.  I did wonder how simply removing the "Master" would effect the circuit.  You discovered the signal needs to be tamed a little did you?

Title: Re: Some questions about the Carolina ODS circuit
Post by: tubenit on August 21, 2018, 06:29:11 am

1)  I tried series & parallel & simply preferred parallel. Not "better or improved" just different with my delay & reverb
     Easy enough to try with insulated alligator clipped wires or put on spst switch.


2)  I almost never adjust send or return pots in FX. The FX level is essential in shaping the tone,IMO.  For example,     
     with FX level at 3 and PPIMV at 7 (1-10), it sounds very different then both at 5.


     IF I lacked space & needed to use fix resistors,  it would be on send and return with FX level pot. Maybe 22k send
     & 39k return but that's something you'd have to experiment with?


     The FX level shapes the OD tone/feel when used with PPIMV. Sort dialing in clear sustain vs. on edge of distortion.


With respect, Tubenit