Why is lead dress important?

[Lowerleftcoast]

I've been reading up on it, and it seems as though, barring any deficiencies, it's just the nature of the beast.

According to the Fender layout, the 57 Deluxe uses the chassis (and a conductive plate) for the ground return path. It wouldn't surprise me if this, and the lack of keeping ground nodes together were the cause of some hum.

Hum can come from other places. Yes, even lead dress.

 

[loopfinding]

I have found this post to be very interesting. In as much as all of the replies have been read, this one caught my attention as you specifically mention the Fender tweed amps. I have both the Fender Custom 64 Princeton Reverb Hand Wired and the 57 Custom Deluxe (also hand wired). The PR is so damn quiet when the volume is on 5 on the amp and 5 or 6 on the guitar that you wouldn't know the amp was on save for the pilot light.

The 57 on the other hand, as soon as those tubes warm up, you can definitely hear a hum. Now, that may have something to do with the settings, but still. Using the same guitar, either a Strat with single coils or my LP, with guitar volume on 5, plugged into Instrument input 1 (not jumpered), tone control on 8 or 9, and volume on 5 or 6 (roughly 12 o'clock) there is noticeable hum when the amp is idle. I've noticed that when the tone control gets dialled down to 5 (roughly 3 o'clock), there is a definite drop in the hum. I know the amp is working properly as I had it serviced by a top notch tech sometime ago and he reported nothing unusual about it. Is the hum purely related to the tone control being set to 9?

classic fender amps from tweed to BF all have suboptimal grounding. aside from that, some not trivial things that poke out to me with the deluxe vs the PR are much less filtering, and no negative feedback on it. those two things are going to result in noticeably less hum rejection.

if you up the filter caps to PR values, that will reduce hum with no major effects on the amp's sound - just makes it a little stiffer instead of loose, but it's still loose as hell as far as amps go. see if you can get them upped by a tech to 22uF instead of the 16uF in there. i personally wouldn't think twice about doing this to my own amp.

if you add negative feedback, the hum is drastically reduced...but then it sounds different, not as good IMO. without adding negative feedback you could get a tech to put the cathode cap on the second stage on a switch. when the cap is disconnected, you get a bit less gain (still plenty at max), which makes the hum way less noticeable and the volume knob range more useable.

 

[Nogoodnamesleft]

I know that all wires have resistance and capacitance inherent in them, but it shouldn't be enough to significantly impact the tonality of the amp.

Don't forget inductance. Which is what we're primarily dealing with here.

 

[printer2]

Don't forget inductance. Which is what we're primarily dealing with here.

Inductance in which wires?

 

[rdjones]

Parasitics

Parasitic oscillation - Wikipedia

en.m.wikipedia.org

Usually a result of stray capacitance combined with poor lead dress.
It's more of an issue with radio receivers and transmitters.
It gets more critical the higher in frequency you go (VHF, UHF), but will affect audio circuits in more blatant cases.

 

[Nogoodnamesleft]

Inductance in which wires?

I guess it would depend on the circuit and the layout. It's been a while since I was into the physics of it, but any wire in an electro magnetic field could be vulnerable. Twisting a pair together is often used as a defense.

 

[JPKmusicman]

I've heard this so many times, and I understand keeping high voltage and high current wires away from where the signal is going, but in general, why is lead dress important? I can't really see much more of an improvement in sound by cutting the wires short, and to get rid of noise, all you need is proper placement. I know that all wires have resistance and capacitance inherent in them, but it shouldn't be enough to significantly impact the tonality of the amp. Well, if you're Ken Fischer, I guess it really matters, but otherwise I just don't see the point other than making it look pretty.

And if lead dress is such an important factor, why are PCB amps looked down on? You have perfect (if the designer knows what they're doing) lead dress and placement for pennies on the dollar of what it would cost you to have a competent builder do the same thing.

Not bashing people who take the time to do it, I'm just trying to understand why people do it.

Easiest way is to build your own amp. Just throw the wires and all the components in there willy nilly and you will soon understand why wire dressing is so important. It's more about the unwanted noise than anything. Also you want to build it so it stays together for years. You want to wire dress it so it's easy to service and not a rats nest. Making it look pretty makes it easy to see where all the wires are going. Wires should cross at 90 degree angles so they don't couple. Electric and magnetic fields was the hardest class in electrical engineering school for most people. Invisible s*h*i*t is hard to understand. Build an amp. You will learn like you've never learned. It's a lot. No single forum thread will explain it thoroughly. Just Google it and you'll see.

 

[BoomTexan]

Easiest way is to build your own amp. Just throw the wires and all the components in there willy nilly and you will soon understand why wire dressing is so important. It's more about the unwanted noise than anything. Also you want to build it so it stays together for years. You want to wire dress it so it's easy to service and not a rats nest. Making it look pretty makes it easy to see where all the wires are going. Wires should cross at 90 degree angles so they don't couple. Electric and magnetic fields was the hardest class in electrical engineering school for most people. Invisible s*h*i*t is hard to understand. Build an amp. You will learn like you've never learned. It's a lot. No single forum thread will explain it thoroughly. Just Google it and you'll see.

I've built my own amps before. So far a 6G7a Bandmaster and a 5F1 Champ. I have used lead dress properly, but I wasn't sure why I should. I've also serviced a lot of old British big iron, and dealt with some vintage solid state stuff and measure my wires and etc. I understand the practical advantages in not having a rats nest amp, I was more wondering why it is done for the sake of tone.

 

[fender4life]

Build an amp. You will learn like you've never learned.

Not exactly what you were eluding to, but related. Aside from learning the technical side of tube circuits, after building a number of amps and tweaking them endlessly i learned more about tone and began to hear and understand tone probably 10 times as much in the few years i did that than in the previous 40 years of playing. It's a blessing and a curse but i can hear things i never did before and the blessing part is that now i often know what i have to try and do when i'm not happy with a tone. I hear exactly what it is that's missing or overbearing or just not right. The curse part is it now takes tone that's far closer to perfection to make me happy, so i waste a lot of time F'ing with things. I then got into modeling in part to try and stop the tweaking but then began going down the rabbit hole of deep editing LOL!

But anyways, point is that building and tweaking amps will develop your ears like crazy. Kinda wish i never got into it. I feel i didn't get a fraction of benefit compared to the endless hours i put into it. But then it can be kinda fun too....sorta like a treasure hunt.

 

[Dan_Pomykalski]

I have found this post to be very interesting. In as much as all of the replies have been read, this one caught my attention as you specifically mention the Fender tweed amps. I have both the Fender Custom 64 Princeton Reverb Hand Wired and the 57 Custom Deluxe (also hand wired). The PR is so damn quiet when the volume is on 5 on the amp and 5 or 6 on the guitar that you wouldn't know the amp was on save for the pilot light.

The 57 on the other hand, as soon as those tubes warm up, you can definitely hear a hum. Now, that may have something to do with the settings, but still. Using the same guitar, either a Strat with single coils or my LP, with guitar volume on 5, plugged into Instrument input 1 (not jumpered), tone control on 8 or 9, and volume on 5 or 6 (roughly 12 o'clock) there is noticeable hum when the amp is idle. I've noticed that when the tone control gets dialled down to 5 (roughly 3 o'clock), there is a definite drop in the hum. I know the amp is working properly as I had it serviced by a top notch tech sometime ago and he reported nothing unusual about it. Is the hum purely related to the tone control being set to 9?

I would guess you’re hearing more noise from the Deluxe because of the different circuits. The Princeton having NFB alone would be enough to cut down on the noise significantly. Then you have the tone stack and the reverb circuit in the Princeton cutting down on gain.

 

[Jared Purdy]

I would guess you’re hearing more noise from the Deluxe because of the different circuits. The Princeton having NFB alone would be enough to cut down on the noise significantly. Then you have the tone stack and the reverb circuit in the Princeton cutting down on gain.

What is "NFB"?

 

[Dan_Pomykalski]

What is "NFB"?

Negative feedback. It’ll cutdown on noise and tighten things up. The Deluxe doesn’t have any NFB, unless Fender changed it for the Custom Deluxe or whatever it was that you have.

Edit: it’ll also drop the output some. Breakup will happen a bit later. I like the idea of no NFB, but I can’t stand the hiss.

 

[Dan_Pomykalski]

classic fender amps from tweed to BF all have suboptimal grounding. aside from that, some not trivial things that poke out to me with the deluxe vs the PR are much less filtering, and no negative feedback on it. those two things are going to result in noticeably less hum rejection.

if you up the filter caps to PR values, that will reduce hum with no major effects on the amp's sound - just makes it a little stiffer instead of loose, but it's still loose as hell as far as amps go. see if you can get them upped by a tech to 22uF instead of the 16uF in there. i personally wouldn't think twice about doing this to my own amp.

if you add negative feedback, the hum is drastically reduced...but then it sounds different, not as good IMO. without adding negative feedback you could get a tech to put the cathode cap on the second stage on a switch. when the cap is disconnected, you get a bit less gain (still plenty at max), which makes the hum way less noticeable and the volume knob range more useable.

I think the max filter cap for a 5Y3 is 10uF though (although obviously Fender used 16uF).

 

[Dan_Pomykalski]

I've heard this so many times, and I understand keeping high voltage and high current wires away from where the signal is going, but in general, why is lead dress important? I can't really see much more of an improvement in sound by cutting the wires short, and to get rid of noise, all you need is proper placement. I know that all wires have resistance and capacitance inherent in them, but it shouldn't be enough to significantly impact the tonality of the amp. Well, if you're Ken Fischer, I guess it really matters, but otherwise I just don't see the point other than making it look pretty.

And if lead dress is such an important factor, why are PCB amps looked down on? You have perfect (if the designer knows what they're doing) lead dress and placement for pennies on the dollar of what it would cost you to have a competent builder do the same thing.

Not bashing people who take the time to do it, I'm just trying to understand why people do it.

On top of what everyone else said, it’s also financially responsible. Shorter wires means less wire used, which means wire needs to be bought less frequently. Disregard if you don’t care though.

 

[Powdog]

I think the max filter cap for a 5Y3 is 10uF though (although obviously Fender used 16uF).

Fender used a three section 20uF on the AA764 Champ with a 5Y3 recto.

 

[Jared Purdy]

Negative feedback. It’ll cutdown on noise and tighten things up. The Deluxe doesn’t have any NFB, unless Fender changed it for the Custom Deluxe or whatever it was that you have.

Edit: it’ll also drop the output some. Breakup will happen a bit later. I like the idea of no NFB, but I can’t stand the hiss.

I have the stock 57' Custom Deluxe. Fabulous in every way. I suspect the tone control at 9 or 10 is the culprit because if I dial it down to 4 or 5, the hiss/hum disappears. However, the tone changes.

 

[Dacious]

Hey, I would if not for my college's wildly powerful radio station just a quarter mile from my dorm. That thing causes everything to exhibit ridiculous levels of microphony that just don't happen anywhere else.

Hence consider your amp to be like a small environment with radiating components. All your transformers and coils put out EMF radiation.

Even resistors put out a sizzle

And if lead dress is such an important factor, why are PCB amps looked down on? You have perfect (if the designer knows what they're doing) lead dress and placement for pennies on the dollar of what it would cost you to have a competent builder do the same thing.

Because PCB carrying heater current and sockets mounted on boards conducts and radiates a lot of heat which can damage the boards leading to problems longterm. Plus some of the traces end up running long runs around others which a) increases resistance in the runs b) increases potential for capacitance introduced by close parallel runs and C) I don't know amyone who prefers soldering on traces compared to solid wires in eyelets. It's possible but easier to damage too. Crosstalk is a problem endemic to both if not carefully designed. Which is why Fischer and Dumble made the bucks. Probably not as much as deserved or you'd think.

Not to say well designed and constructed PCB amps can't work well and provide excellent service, repairability and easy maintenance. They can.

Or that handwired can't be a nightmare. It can. But the shortest runs with the best component and wiring placement are possible in handwiring. It's harder to correct poor design on a PCB than with handwired. Layout is everything.

 

[tele_savales]

My first build picked up broadcast radio quite well, and the band practicing in the next rooms guitarist AND vocalist as well. The rehearsal space I use is built like a bomb shelter.
I stripped and rebuilt it, and it doesn't do either of those things anymore. It actually sounds killer.

 

[King Fan]

I just don't see the point other than making it look pretty.

LOL, @BoomTexan , I wanted to check I hadn't been misreading you as skeptical about lead dress, but, no, I see that in post 1. So is the info above getting you any less skeptical?

 

[Snfoilhat]

I wonder if I'm reading the original question differently from other folks answering they question as they see it

I read the question as "Above and beyond an amp that doesn't hum and doesn't produce self-noise or catch and amplify environmental noise, does lead dress change the tone of an amp through subtle, purposeful tone shaping of wire lengths, between-wires capacitance, and other ephemera that a builder might claim makes their amp sound better than the same schematic and same components laid out differently (like by a less savvy competitor/cloner?"

And I think the answer is no. Or maybe?


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