Acoustic Guitar tube PreAmp & FX

[tubenit]

Built for my son-in-law to play thru a church PA system.

CHECK for ERRORS!  Compare schematic with layout.  If discrepancy, go with schematic.

Changed a few values in the Low Pass filter  which I call the Frequency Control.  And I added a notch filter switch.  See added schematic.  Layout would be modified accordingly

With respect, Tubenit

EDIT:  This system had some hum with my son in law's church PA system.  See below for the resolution to this.

[tubenit]

Cab head        Sapele, flamed maple trim , black walnut front panel

[tubenit]

Chassis

[DummyLoad]

Cab head        Sapele, flamed maple trim , black walnut front panel

nice! beautiful wood and construction.


--pete

[tubenit]

Update!

OK, the Edcor trannie did NOT work with my son-in-law's PA system!  There was some hum.

I got him to bypass the Edcor trannie  and run a 1/4" shielded cable from the FX send to a direct box to the PA.

He said it sound absolutely fantastic and was totally DEAD quiet !!!   He said it was the best acoustic tone that he has ever gotten, that he got numerous compliments about it.  He stated it was the best acoustic PreAmp that he has tried or even heard. 

So the current plan now is simply to remove the Edcor trannie and install a speaker jack which will go to a direct box to the PA system.  The direct box will be permanently velcroed to the inside top of the PreAmp cab.

With respect, Tubenit

[Glennjeff]

Wow Jeff, Fantastic Workmanship, or does one call it Artisanship.

A thing of rare beauty.

Strange that the transformer caused a hum, most probably ground loop problem with the PA.

Running a centre tapped (balanced ) transformer secondary might have been a solution.
Centre tap to pin 1 with ground switch.
Nice to have things fully balanced if possible.

[tubenit]

Running a centre tapped (balanced ) transformer secondary might have been a solution.
Centre tap to pin 1 with ground switch.
Nice to have things fully balanced if possible.

Nice to hear from you!  Been missing your posts on the forum.

That Edcor trannie has pin 2 as center tap on the input side and pin 6 as center tap on the output side.

Are you saying to ground one of those?  And if so,  which one?   Could this be tested with an insulated alligator clipped wire?

Tubenit

[Glennjeff]

Hi and thanks / kind regards.

TRY

Centre tap of the Edcor output, pin 6, to pin 1 of the output XLR.
Ground lift/apply switch from chassis ground or star ground point to pin 1 of output XLR.

If you wanted to cover every possible option you could have a switch on the connection between output transformer centre tap (pin 6) and pin 1 of the XLR [ labelled as TRANSFORMER LIFT ] as well as a second switch between chassis ground and pin 1 of XLR [ labelled as GROUND LIFT ]

Yes you could test both these ideas in situ with insulated alligator test leads.


All the best.

[tubenit]

Thanks for the information.  I contacted my son -in-law about trying that and he opted for using a direct box instead and removing the Edcor trannie.   Wished I could've found out whether grounding the trannie would've resolved it?

Here is a picture of what he did.  He says it sounds fantastic and that he is very pleased with it.

All the same controls on the front panel still work using this method.

Tubenit