Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on November 12, 2012, 10:42:51 am

Title: Modded 5F1 with active FX Loop - Help about grounding & other - Update
Post by: kagliostro on November 12, 2012, 10:42:51 am

I'm trying to help an italian guy who has build a 5F1 clone and now want to build one other amp based on the 5F1

The characteristics he wants are:

1) Active FX Loop
2) VVR
3) Feedback contol
4) ToneStack
5) Anti Hum Triks
6) Headphone exit
7) Recorder exit

Putting together the received councils he tried to draw a layout (starting from a Ceriatone 5F1 Layout) but the result was very confused, so I tried to help him drawing a schematic (and a new layout)

As I like it I chose for him a James Tone Control (with Merlin's Shift control)

I need councils about the ground scheme, I've labeled with a red number all the ground connections of the schematic and hope someone can help me to connect it in groups in the better way as to avoid Hum

I used the Active FX Loop posted few time ago by Tubenit (Thanks Jeff)

For the headphone output I cloned a circuit that is present in Koch Twintone II

For the recorder exit I don't know what to use, the Koch schematic I used has also this feature, but it uses a 100mH inductor and I'm unsure about its use

Many Thanks in advance for any council and indication

K

Title: Re: Modded 5F1 with active FX Loop - Help about grounding & other - Schematic Here
Post by: PRR on November 12, 2012, 04:31:58 pm

The effects loop is inside the power amp's NFB loop. The amp will try to minimize anything the effect does. This also affects the reason we use NFB around the power stage: to control the speaker's bass resonance.

FX loop goes between tone controls and V1B.

Your VVR acts only upon the 6V6 screen grid, not plate+screen. The usual connection controls both.

Hum: PT CT goes *directly* to first filter cap (22 to 18). 17 16 and 14 connect together. IMHO none of this should connect directly to chassis. Earth ground from wall (not shown) goes to chassis. Input jack goes to chassis. Ground follows signal from input jack to the 17 16 14 power-stage ground, then to the 22 18 power supply common.

Title: Re: Modded 5F1 with active FX Loop - Help about grounding & other - Schematic Here
Post by: kagliostro on November 13, 2012, 01:50:00 am

Mannaggia !, I didn't remember the action of the NFB   :BangHead:

Thanks PRR for pointing to that  :worthy1:

I've redraw the schematic, is this what you mean ?

about VVR I posted something about this solution few time ago

http://www.tube-town.net/diy/tt-needfull/03-ttvoco.html (http://www.tube-town.net/diy/tt-needfull/03-ttvoco.html)

anyway I can go with plate VVR if the effect is better

Thanks

K

Title: Re: Modded 5F1 with active FX Loop - Help about grounding & other - Schematic Here
Post by: kagliostro on December 13, 2012, 09:05:26 am

Here is the revised Schematic and a Layout

I tried to have the filter capacitors near the plate they supply (I hope I've do that in the correct way)

so there is a completely new arrangement of the ground connections to be considered

If you see errors, please, report it

Help about the new ground connections arrangement is highly appreciated

Thanks

K