Express lead dress

[jestaudio]

Can some of you guys give me some advice on the correct lead dress and earthing to stop my wreck build being a oscillating mess, it looks deceptively simple to build but i gather that its sensitive to lead dress and want to avoid unnecessary stress
Cheers in advance

[eazilyled]

The safest strategy would be to try to replicate the wiring of Francesca as closely as possible. There are detailed gutshots in the Files section. Also follow Ron Worley's step by step build guide. I did this and my amp turned out fine.

[jestaudio]

The safest strategy would be to try to replicate the wiring of Francesca as closely as possible. There are detailed gutshots in the Files section. Also follow Ron Worley's step by step build guide. I did this and my amp turned out fine.

Do you have a link to the guide
Cheers

[eazilyled]

Build guide and schematic etc can be found here:

http://ampgarage.com/forum/viewtopic.php?t=5691

Also gutshots are here if you haven't already found them:

http://ampgarage.com/forum/viewtopic.php?t=19

[Jackie Treehorn]

I've found it helpful to think of the lead dress in terms of what is negative feedback and what is positive feedback. The plate is out of phase with the cathode and grid so if you run those parallel, you're stabilizing the amp. Avoid positive feedback by crossing at 90 degree angles, etc.

You also need to have a methodology for determining which part of the amp is unstable. Scope helps!

I don't agree that just copying an existing amp is the best. Copy the process!

[eazilyled]

Thanks for the insight, Jackie. I've never considered the feedback of a circuit in this way before. That certainly makes sense.

[Ukko75]

Hi!

I've found it helpful to think of the lead dress in terms of what is negative feedback and what is positive feedback. The plate is out of phase with the cathode and grid so if you run those parallel, you're stabilizing the amp. Avoid positive feedback by crossing at 90 degree angles, etc.

I am a beginner, and my english is not so good so do I understood this right:
Positive feedback is bad thing?
Negative feedback is good thing?
When cathode and grid wire runs together it generates negative feedback wich is good thing?
Cathode or grid wire should always stay as far as bossible or 90 degree angle to plate wire?

[Jackie Treehorn]

Hi!

I've found it helpful to think of the lead dress in terms of what is negative feedback and what is positive feedback. The plate is out of phase with the cathode and grid so if you run those parallel, you're stabilizing the amp. Avoid positive feedback by crossing at 90 degree angles, etc.

I am a beginner, and my english is not so good so do I understood this right:
Positive feedback is bad thing?
Negative feedback is good thing?
When cathode and grid wire runs together it generates negative feedback wich is good thing?
Cathode or grid wire should always stay as far as bossible or 90 degree angle to plate wire?

Sorry, that was an iPhone post. If you want to stabilize the amp, then negative feedback will help, and positive feedback will make things worse. The McIntosh MC75 utilizes positive feedback to increase drive to the power tubes, so I guess it's not always bad!

Running the plate and cathode wires parallel from v2 (negative feedback, plate and cathode being out of phase) and experimenting with the distance (amount of capacitive coupling) goes a long way towards getting things sounding good. Keeping the plate wire against the chassis helps, too.

I'm unclear on the effect of parallel cathode and grid wires, I tend to think of them as somewhat neautral as they are both inputs to the tube; you're not really taking an output and coupling it to an input. Maybe someone else can chime in on that.

I just think it's helpful to have a methodology rather than just move stuff around.

The tonestack wiring is crucial, too. I have no idea why, but the mid and bass wires to the pots, keep them parallel and down against the chassis and experiment with the distance between them. Treble wire can be short and floating.

Hope that helps!

[Ukko75]

Thank you!
This was wery helpful, now i will try these with my own amp.

[C Moore]

Are you running a NFB wire from the Impedance Selector to the Presence pot.?
If so, THAT wire can really cause problems. Try moving it around, especially if it comes near the grid or plate wires of the power tubes..
good luck

[keithshapiro]

You also need to have a methodology for determining which part of the amp is unstable. Scope helps!

This sounds like an excellent idea. How does one learn about using a scope to find the noise. I have a scope but I must admit that I don't really know how to use it, much less how best to use it.

Any info on this would be greatly appreciated.