Blackface Fender layout

[Mike McLane]

This is something @vigilante398 and I have discussed offline. It is a layout for a Fender blackface preamp. I would appreciate any feedback. It will be built off of Sushi's HV-PSU. I think I have the basic circuit routing, etc., but I'm particularly concerned about having the unit grounded properly. Can I ground both the HV and the 9V aux feed to the Signal board as shown without problems (the 9V is for powering the LED's)? I can separate the 9V similar to the 6.3V, but I would then need a 4PDT footswitch for the bypass because the signal path and the LED would have to be alternately grounded to separate ground points. Also, I would like to insure that the unit discharges the caps when powered off. The Signal board will adhere to the back of the pots via an insulating harness that ties the pots together so that they can lift in and out as a unit. The PSU will be set on the side of the enclosure with stand offs. The foot switches will be at the bottom of the enclosure, but for purposes of having a cleaner pictorial layout I showed them up top. Also, for those of you unfamiliar the "R" stands for RAW. As turned up the tone stack is progressively eliminated and the amp gets louder and dirtier. By running it to GRD thru a footswitch you can turn the effect on/off. Will appreciate any thoughts.

 

[Brett]

You may be better served with a dedicated star ground fastened to the chassis of the enclosure provided that:
a. the enclosure is conductive
b. the contact point where GND mates to enclosure surface is clean allowing for a solid electrical connection

Depending on how you plan to mount the tube, you may be able to add your star ground at that location (if using standoffs in the style of Kingsley).

 

[RetiredUnit1]

Interesting. How does one ground 250v when there is no earth ground? Very carefully I would think. Even tho it's going to a ground location, it's still positive. I would avoid grounding to the chassis, if someone were to pick up the pedal while standing in a bucket of water it could be *nasty*....

I've experienced the bucket of water turned over while playing electric guitar. Stupid bucket, what the hell was a bucket of water doing on a bench on stage??? I had a two inch bruise going from my spinal cord to my belly button from *my muscles contracting*. This was in 1976, if it happened today I'm sure it would be my last solo......

 

[Mike McLane]

I can mount the tube on a standoff and stick a "master ground" there or underneath one of the jacks. But no GRD run transits thru another component to get to ground. They may share a common wire, but all converge on pin 3 of V pot which I can run to the "master ground". But this is exactly why I made the post. The 250v comes via a SushiBox PSU was designed for this kinda thing, similar to the PS design into the Space Heater. This all goes in a 1590CE aluminum box.

BTW, my bad experience was NOT with a bucket of water. . . . . . it was beer!!!

 

[RetiredUnit1]

I can mount the tube on a standoff and stick a "master ground" there or underneath one of the jacks. But no GRD run transits thru another component to get to ground. They may share a common wire, but all converge on pin 3 of V pot which I can run to the "master ground". But this is exactly why I made the post. The 250v comes via a SushiBox PSU was designed for this kinda thing, similar to the PS design into the Space Heater. This all goes in a 1590CE aluminum box.

BTW, my bad experience was NOT with a bucket of water. . . . . . it was beer!!!

So is that a switching buck up, or? I couldn't find much info on the details, found the site. Nice looking pedals. Two Ground wires is what I use in my amps. One for the power caps, one for the inputs, etc.

I've recently made a 16 x 18650 4.2v battery pedal power supply. Four 4S parallel sleds wired in series to put out 20 AH at 16vdc, then I use a 1.5 mhz buck down converter to get that to 9v. I can power my pedals for WEEKS without recharging!!!

This is a layout I made in Visio of the Bassman I'm doing, showing the two star grounds layout I stole from the Hiwatt DR504's I used to make in the 00's...... It has two independent bias pots, and a three way switch on the NFB for 'bassman', 'plexi' or Raw....

 

[vigilante398]

I would recommend just keeping a common ground throughout, no reason to worry about separating them. If you probe the ground points on the HV PSA PCB you'll find that the 9V, 6.3V, and HV rails all share a common ground. This isn't because it's the absolute "best practice", it's because the amount of current you're dealing with in a single-tube preamp is significantly less than what you're dealing with in a full tube amplifier. You're far more likely to add noise to the circuit through improper lead dress than from ground loops.

 

[Mike McLane]

This look OK? Also, how 'bout draining those pesky caps on shut down??



BTW, looking fwd to the DIY AB763 coming our way!!!!!!!!!!

 

[vigilante398]

This look OK? Also, how 'bout draining those pesky caps on shut down??

View attachment 35126

BTW, looking fwd to the DIY AB763 coming our way!!!!!!!!!!

Looks fine to me, though you don't need a separate ground connection from the 9V supply and HV supply as they already have a shared ground through the HV PCB, so that's one less ground wire you need there.

The HV power supply drains the caps when input power is removed so the board becomes safe to handle within seconds. I've been zapped too many times to let HV hang around, I always provide means for the caps to discharge in anything I do.

 

[Mike McLane]

Woo Hoo!!!! Thx!!!!

 

[Mike McLane]

Do you have any preference for running time based FX before or after your preamps? I am planning on using an HX Stomp for time based FX and am planning to put it after because a) I often read that's generally preferrable and b) so that it could also function as an cab IR host and provide the opportunity to split the signal into stereo. Also, the HX can adjust its input impedance based on the output impedance of the source. . . do you have a read on the output impedance of the Space Heater or Underground Accelerator?

 

[Dan0h]

Whoa just saw this thread. We must be on the same wave length man. I just breadboarded a blackface preamp too. Sounds awesome. I like what you did with the power for the tube. How do you like the sound?

 

[Mike McLane]

Sounds pretty good. Actually, I sent it to a friend who is a professional player who is running it through its paces running through a PowerStage 170. If it passes initial muster he's going to try a couple of gigs with it. . . says that's the only way to see if it REALLY works. Anxious to hear his evaluation.