Fender Hot Rod Deluxe to Single Channel AB763

[emerson909]

Ok.

This has to be changed.

I’m not disagreeing but it was working fine before the layout change. Happy to try any recommendations tho!

[Willabe]

I’m not disagreeing but it was working fine before the layout change. Happy to try any recommendations tho!

I don't understand.

Working fine before what layout change?

Did this amp ever work right?

[Willabe]

There's 2 black wires hooked up to the 1st B+ filter cap ground lead. 1 of those wires go over to the solder lug strip with the -bias ground wire. Which I think now you moved that over to the preamp ground buss?

And the other black wire goes from that 1st B+ filter cap's ground lead over to the FWB's ground?

[emerson909]

Yes it was sounding pretty good at one point, there’s a link to a demo of the reverb and trem in reply 15 but I tried to optimise the layout and rebuilt it and it’s gone to shit 

[Willabe]

It looks like both ends of your buss wire are connected to the chassis?

It can only be connected to chassis ground on 1 end, or you get a ground loop.

[emerson909]

There's 2 black wires hooked up to the 1st B+ filter cap ground lead. 1 of those wires go over to the solder lug strip with the -bias ground wire. Which I think now you moved that over to the preamp ground buss?

And the other black wire goes from that 1st B+ filter cap's ground lead over to the FWB's ground?

.

Yes, that’s correct

[Willabe]

Yes it was sounding pretty good at one point, there’s a link to a demo of the reverb and trem in reply 15 but I tried to optimise the layout and rebuilt it and it’s gone to ... 

Ok, so it worked, then you changed some things and now problems.

So, what things did you change? How many things?

List all the changes 1 at a time please.

[emerson909]

It looks like both ends of your buss wire are connected to the chassis?

It can only be connected to chassis ground on 1 end, or you get a ground loop.

No the PT end is insulated and it’s grounded at the input jack end

[emerson909]

So, what things did you change? How many things?

List all the changes 1 at a time please.

I appreciate how ridiculous this sounds, I had some issues as explained at the start of the thread and with the help of some of the guys here I got it working pretty well however the engineer in me couldn’t resist trying to optimise the layout. I made some what I thought were relatively minor  changes and wasn’t expecting such drastic consequences! I couldn’t list everything but the revised layouts are posted in previous reply’s, the schematic hasn’t really changed. I guess the question I’m asking is, it is making a horrible static noise now, what is that a symptom of? From reading online I am lead to believe it could be resistor noise hence focusing trouble shooting on the resistors although think I’m going down the wrong path and it’s more likely the new ‘optimised’ layout and grounding

[emerson909]

Also wanted to post results just in case somebody thought about copying it!

[Willabe]

Well, if it worked before, put it back the way it was.

A bad solder joint can cause all kinds of noise problems.

I thought you said it was oscillating? 

[emerson909]

Yes that might be the solution although I was hoping it might be a case of, amp sounds like a gieger counter, change component x. Seems not! Hadn’t appreciated what a fine art the layout was, ah well lesson learnt.

[emerson909]

Yes it is also oscillating but was hoping to solve one problem at a time although starting to appreciate all these things are usually linked.

[Willabe]

As far as the grounding.

The 1st B+ filter cap is the nosiest ground in the amp because of the charging pulses. This cap has the most current drawn from it and has the highest ripple in the B+ power supply chain.

So, you want to isolate these charging pulses from the rest of the power supply chain.

You have done part of it, you have the FWB ground going directly to this 1st filter caps ground lead. But, when you took the B+ power amp chassis ground from this point, everything that goes through that junction gets dirtied up by those pulses. You should pull the B+ power amp chassis ground connection from the screen cap's ground lead.

You want to try and get rid of as many chassis ground connections as you can.

Merlin shows using 1 chassis circuit ground. But, many guys use 2, 1 for the power amp, the other for the preamp. The PI gets grounded with the power amp IF it has a -FB loop. If it doesn't have a -FB loop, it gets grounded with the preamp.

And from looking at the pictures, you really don't have the circuits grounds tied to the B+ filter caps ground lead. You gather them together to form a ground star. So you make the caps star ground, send a single wire from the star to the buss, then form the next star and buss it over to the next star. This way the circuit's current draw can go round and round, without disturbing/modulating any other circuit.

This is why I said the -bias ground should be changed, -bias should be grounded with the power amps ground, which is where the chassis ground is for the screen filter caps ground lead. That is the power amp ground.

You need to read this, if you have read it, read it again.

https://www.valvewizard.co.uk/Grounding.html

   

[Willabe]

Yes that might be the solution although I was hoping it might be a case of, amp sounds like a gieger counter, change component x. Seems not!

Sometimes happens that way. It could be a bad solder joint. They can make the noise you seem to be describing. It can also be parasitic, wires in wrong place, grid wire to close to high output wire.   

Hadn’t appreciated what a fine art the layout was, ah well lesson learnt.

Yep.

There are layout things you learn. You need a good grounding scheme, some space can help, wire lead dress, keep grid wires short and plate wires long if need be - after the coupling cap the plate wire is now a grid wire, shorten up excess wire runs, twist certain wires together tightly and evenly, keep output away from input, etc.

[Willabe]

Yes it is also oscillating but was hoping to solve one problem at a time although starting to appreciate all these things are usually linked.

Wasn't doing these things before you changed some things, so they could be linked. 

[pdf64]

How was the oscillation stopped?

Is the rev2 layout in post 25 the one used? https://el34world.com/Forum/index.php?topic=32112.msg354945#msg354945

Chassis photo https://el34world.com/Forum/index.php?action=dlattach;topic=32112.0;attach=116474;image

Does the rustling noise stop if the valve in V3 is removed?

A full voltage survey may be beneficial.

[emerson909]

I've not managed to stop the oscillation since the rebuild, with the channel volume at max, increasing treble or middle above 7/8 will induce squeal in the speaker. Unfortunately all of the anode bypass caps I installed to fix the first version are installed on this version so there is something else wrong. the 47pf cap across the PI plates isn't shown on the drawings or photos but I added it this morning and made no difference.

I tried playing a guitar through it earlier and maxing the reverb causes the volume to drop significantly so seems to be an issue there!
Also the tremolo seems to affecting the noise if it is enabled or not which is leading me to think it is an issue with the grounding.

The layout is pretty much as per the previous version I posted although I corrected a couple of errors, I've attached an as built and schematic. Photo is correct.

The rustling/static is significantly reduced when removing V3, lifting V3B plate or grounding V3B grid but not eliminated.

Yes I agree voltages are needed for further troubleshooting but it seems so fundamentally wrong atm that I think I'm going to change the grounding back to the previous version that I know was good (enough) and go from there, hoping to not have to do a full rebuild as I need to pay the family some attention :)

Plan is to restore the previous grounding and see if still bad.
If still bad replace all components/reflow all solder joints working back from the Phase Inverter.
If still bad revert to previous layout

I've got a couple of days off work next week so hopefully get some time to give it a good dose of looking at, will post results.

[emerson909]

Strongly suspect this underboard wire to V3B grid is part of the problem, not sure how best to route it, might try a shielded cable

[pdf64]

What's the yellow cap by the input sockets? I can't see it on the layout.
A screening plate around the input sockets may well cure the oscillation.

[Willabe]

.... Unfortunately all of the anode bypass caps I installed to fix the first version are installed on this version so there is something else wrong.

Then the layout or something was wrong with this amp at the start, you put band aids on it.

[Willabe]

Strongly suspect this underboard wire to V3B grid is part of the problem, not sure how best to route it, might try a shielded cable.

Why do suspect this under board wire?

Is it a grid wire?

[emerson909]

.... Unfortunately all of the anode bypass caps I installed to fix the first version are installed on this version so there is something else wrong.

Then the layout or something was wrong with this amp at the start, you put band aids on it.

Yes that is why I rebuilt it! I was hoping the revised layout wouldn't need them but it's even worse! 

[emerson909]

Strongly suspect this underboard wire to V3B grid is part of the problem, not sure how best to route it, might try a shielded cable.

Why do suspect this under board wire?

Is it a grid wire?

Yes it goes to V3B grid.

[emerson909]

What's the yellow cap by the input sockets? I can't see it on the layout.
A screening plate around the input sockets may well cure the oscillation.

.022 Tried it for RFI based on Merlin/Aiken but it made no difference, it's not connected now

[Willabe]

I'm going over your latest schematic and lay out.

[Willabe]

The 10K/.5w grid stoppers have to be soldered on the tube socket grid pin for them to work. With as little lead as possible with in reason.

on grid stoppers, how to use them;

https://www.valvewizard.co.uk/gridstopper.html

https://www.aikenamps.com/index.php/grid-resistors-why-are-they-used

[Willabe]

You should read this also on grounding from Aiken Amps;

https://www.aikenamps.com/index.php/grounding

[Willabe]

Your missing grounds in your trem on the layout.

There's a couple/few places that should be grounded back to the B node screen grid B+ filter cap ground lead.

[emerson909]

Not sure which ones are missing 

I updated the trem grounding earlier, looks like this now. Not made any difference, will look at reverb next.

[Willabe]

Not sure which ones are missing 

That's a problem.

This is where   you   go back and fix your layout drawing.

You need to fix your layout and then match your layout to your actual amp.

[emerson909]

Ok there is a link missing across the bias grounds on the layout. It is installed on the board although I just chopped it half to make the changes. The trem grounds where all on the layout, I’ve just moved them tho

[Willabe]

You have to up date both your schematic and layout when you make changes so you can find your way and so we can see if we see any things wrong.

[emerson909]

Will update it when I get chance, wife and kids getting in the way of my amp building 

[Willabe]

Will update it when I get chance, wife and kids getting in the way of my amp building 

Amps come and go, love on the family. 

[Willabe]

Did you ever try disconnecting the -FB loop?

Disconnect it either at the output speaker jack or disconnect the -FB R, 820 ohm, R51.

Any better?

Reversed OT primary leads with a -FB loop doesn't always cause a high pitched sequel, it can cause all kinds of weird things.   

[emerson909]

Yes I should have written this down but was one of the first things I tried as suspected the wire routing, disconnected but no discernible difference so it’s back in the circuit.

[emerson909]

I'm measuring around 0.7 - 1 VDC downstream of V1B coupling cap C13. I understand there should be no DC present here, is that correct?
I've changed C13 for a new cap but the DC is still there. It peaks at about 9VDC when I first flip the standby switch then decays to around 1V. Not sure where this DC is coming from??

[pdf64]

I'm measuring around 0.7 - 1 VDC downstream of V1B coupling cap C13. I understand there should be no DC present here, is that correct?
I've changed C13 for a new cap but the DC is still there. It peaks at about 9VDC when I first flip the standby switch then decays to around 1V. Not sure where this DC is coming from??

Correct there should be 0 V DC.
With amp off and deenergised, what's the resistance to the chassis at that point?

[emerson909]

3.47M

[emerson909]

Suspected there was some leakage on the board earlier, it was looking pretty dirty after all the mods so I gave it a good cleaning with isopropyl and some contact cleaner, it’s down to 150mv dc there now. Still scratchy static noise but reduced

[emerson909]

Think it's back to the drawing board with this one, I'm going to move some things around and rebuild it. Thanks for everyone's help so far, got some good info to work with. Will report back when complete although it might take me a while.

Cheers

[Gregwor]

Did you try replacing C17?

Greg

[pdf64]

3.47M

That's too high.
Edit - oops it's fine.

[emerson909]

Did you try replacing C17?

Greg

Hi Greg, yes I had already replaced C17. Just feel I’m chasing my tail with this now, may stumble across the static/rushing water noise issue by replacing a component or reflowing a joint eventually but the feedback issues are still going to be there. I suspect the tone stack is too close to the reverb drive circuit. I think I can rearrange that section by adding half a dozen terminals but obviously need to remove the board.

[emerson909]

something like this

[pdf64]

Did you try replacing C17?

Greg

Hi Greg, yes I had already replaced C17. ...

If a leg of C17 is lifted and the amp powered up, is there still voltage on that turret / node?

[Willabe]

I suspect the tone stack is too close to the reverb drive circuit. I think I can rearrange that section by adding half a dozen terminals but obviously need to remove the board.

I was going to suggest this for your rebuild. It greatly shortens up the grid wire feeding the TS. And it makes room on the turret board. Now you can and should move the B+ D node filter cap over to where the TS components were. Grounding is now much better too.   

No, you can hang most of the TS caps and R on the TS pots. You would only need a couple turret's to pick up the other side of those components. 

[Willabe]

And don't put any grid wires under the board on the new layout.

[emerson909]

Board updated