Throwing metal film resistors in Fender amps

[J M Fahey]

FWIW using those 22uF caps is "vintage compatible", whatever that means , since typical electrolytic capacitor tolerance in the old days was -30/+50% , so anything between *real* 11uF and 24uF is solidly within Leo´s specs.

By FAR the most important "vintage" parameter is using well worn 50 y.o. speakers and I´m constantly amazed by people obsessed with irrelevant parameters such as capacitor colour and ignoring the most important parameter of them all.

[Wil]

FWIW using those 22uF caps is "vintage compatible", whatever that means , since typical electrolytic capacitor tolerance in the old days was -30/+50% , so anything between *real* 11uF and 24uF is solidly within Leo´s specs.

By FAR the most important "vintage" parameter is using well worn 50 y.o. speakers and I´m constantly amazed by people obsessed with irrelevant parameters such as capacitor colour and ignoring the most important parameter of them all.

That's what I told myself. 16/22uf, they're might not be a big difference because of the tolerance.

I don't have the budget to buy an older speaker, but I found the one my ears do appreciate, it's the WGS G12C... Cheap and absolutely killer.
You have to play it for a minimum of 5/6 hours to hear the way it will sound/feel once broken in.
Highly recommended.

About the caps/resistors "quality", I can't disagree. But well, it's a first build and in my mind I want things to be done perfectly. It might not be a big change in sound, but I want to be sure I pick the best things and see if the extra $$$ are really justified. But it's quite obivous some people are "making their butter" (as we say here) in an less honest way out of the amp parts business
For the moment, the objective is not to build the perfect amp (if it is once finished, that's obviously better ...) but to experiment with component quality. I expect to come to the same conclusion as you do.

Have a nice day, everyone.

[Wil]

Well, I received the parts and start building.
The dude at Banzai forgot to send the wires so I'm stuck with the loaded board and can't continue.
This is probably the ugliest board I've ever seen, see the pics to understand why, haha.















Poor quality pics, shot with my iphone.

RN65D are amazing resistors! less than 1% tolerance !
Note that, not all component are soldered, or partially soldered. It's to keep them in place be have enough space in the eyelet to fit the wires.

Have a nice day everyone.

[J M Fahey]

Cool !!!!!! Congratulations!!!!

[tubeswell]

Metal vs Carbon film. Some topics are timeless aren't they?

[Wil]

Is this grounding schematic any good ?
If not, what do you recommend ?

[tubeswell]

Can't see where the filter caps are in that layout pic. But from what I can see, it could well be fairly hummy. You need to think about the ground returns in terms of whereabouts in the circuit that the various component parts draw their power supply from.

Have a read of this article http://www.valvewizard.co.uk/Grounding.pdf

[Wil]

Very very interesting article but I'm afraid it goes beyond my knowledge... and my english skills, haha.
I'll take an hour to read it after work.
Does a "fender amp style grounding schematic" exist ? I might want to copy that in the first place to try to understand a little before going into the highly accurate piece of knowledge you've just shared, haha!

[tubeswell]

The nub of it is that if you mix up the ground returns, then you're more likely to get hum. But if you lay the ground returns out so that each ground connection goes (in the 1st instance) back to the ground return point of the filter cap from which that gain stage (part of the circuit) takes its power supply, then you will reduce the possibility of micro-ground-potential-rise (in the form of 'micro-wobble') getting into a more-sensitive part of the circuit.

Electrolytic caps used for filtering power supplies are not perfect shunters of AC to ground - they have some ESR (effective series resistance). What's more, 'ground potential' is not the same potential everywhere in the ground (and this is the case, even for the earth).

Therefore when filter caps experience variation in current - wobbling at the 'charged' side of the cap, this can be mirrored with a 'micro-wobble' on the 'ground' side of the cap, especially where the ground return path itself is comprised of pieces of wire connected to other pieces of wire etc (like a lattice). Resulting localised bits of micro-wobble in the ground return 'lattice' can cause other parts of the ground return to also 'ride on' the micro-wobble where these parts of the ground return have more 'micro-wobble' than other parts (because each bit of wire has its own resistance and when micro-current goes through micro-resistance it results in micro-voltage, in this case 'AC' current and 'AC' voltage). This 'micro-wobble' can then be then 'reverse shunted' back through other filter caps and thence into the power rail and thence into other gain stages and into the signal path as hummy noise.

Therefore if you keep each respective bit of circuit ground return going, in the 1st instance, back to the ground return point of the filter cap from whence that part of the circuit draws its power supply, you minimise the possibility of 'micro-wobble' 'cross-infecting' other parts of the circuit.

(That's my theory anyway - happy to take it on the chin).

[Wil]

The nub of it is that if you mix up the ground returns, then you're more likely to get hum. But if you lay the ground returns out so that each ground connection goes (in the 1st instance) back to the ground return point of the filter cap from which that gain stage (part of the circuit) takes its power supply, then you will reduce the possibility of micro-ground-potential-rise (in the form of 'micro-wobble') getting into a more-sensitive part of the circuit.

Electrolytic caps used for filtering power supplies are not perfect shunters of AC to ground - they have some ESR (effective series resistance). What's more, 'ground potential' is not the same potential everywhere in the ground (and this is the case, even for the earth).

Therefore when filter caps experience variation in current - wobbling at the 'charged' side of the cap, this can be mirrored with a 'micro-wobble' on the 'ground' side of the cap, especially where the ground return path itself is comprised of pieces of wire connected to other pieces of wire etc (like a lattice). Resulting localised bits of micro-wobble in the ground return 'lattice' can cause other parts of the ground return to also 'ride on' the micro-wobble where these parts of the ground return have more 'micro-wobble' than other parts (because each bit of wire has its own resistance and when micro-current goes through micro-resistance it results in micro-voltage, in this case 'AC' current and 'AC' voltage). This 'micro-wobble' can then be then 'reverse shunted' back through other filter caps and thence into the power rail and thence into other gain stages and into the signal path as hummy noise.

Therefore if you keep each respective bit of circuit ground return going, in the 1st instance, back to the ground return point of the filter cap from whence that part of the circuit draws its power supply, you minimise the possibility of 'micro-wobble' 'cross-infecting' other parts of the circuit.

(That's my theory anyway - happy to take it on the chin).

Thank you for the time you took to answer. I have to admit it's difficult to understand everything. Do you have a layout pic or schematic to illustrate your interesting theory ?

[Wil]

I might follow this layout suggested by Hoffman since I'm using Hoffman's board style

[tubeswell]

Hoffman layout should be fine.

[Wil]

Hoffman layout should be fine.

Okay !
But what about the grounding of the preamp tubes ?

[tubeswell]

If you use whichever of Doug Hoffman's specific layouts for the amp that you are contemplating, all of the grounding points for the pre-amp gain stages' grounds will be grounded with the appropriate filter cap ground. His board layouts are designed that way.

(Sorry I should've looked closer at the pic you posted - its a bit too generic - Try one of his specific board layouts, e.g.;

for a blackface fender type amp http://www.el34world.com/Hoffman/ima...TwoChannel.gif,

or a 5F6A circuit http://www.el34world.com/Hoffman/images/5f6aOld.gif

or a plexi circuit http://www.el34world.com/Hoffman/images/Plexi50Old.gif

etc)

[Wil]

Thanks for all the infos tubeswell.
Here is the most recent picture of the project.
I just realised I have ordered 3 standard mono input jacks... So I will use the plastic one that came with the DRRI.