Hum Question

[Bombacaototal]

Many thanks for your time Richard. Answering your questions:
1) grid stopper is 22K
2) I have not tested a different 1M resistor, I could potentially replace it to try
3) I am using a 60’s Custom Shop stratocaster and the pickups are between 5.6k and 6.1k
4) I will measure all DC mentioned but when I reported back to Xtian seems I had 1.9VDC at start up which slowly decreased to zero (measuring the other side of the jack which was into the input), which may explain the pops and crackle
5) input schematic attached. The toggle is as per my old wiring, this has been updated to yours now
6) yes there is a local feedback on the first triode of V1, 10M / .05uF which probably explains the issue?

[Richard1001]

Yes, i am sure the feedback loop is causing your problem.

When the amp is off, there is no voltage on either side of the cap. Turning the amp on (or from standby to on) the voltage on one side of the cap goes up to +/- 200V.
This change in voltage passes through the cap. Now the other side has to be pulled down to 0 volt (ground) through the 10M resistor. (Loading the cap) This causes a small DC current to flow through the 10M resistor and (if your guitar is connected) the pickups of your guitar. This current results in a small DC voltage over de pickup resistance. The crackling in the pot is the current flowing through the pot (changing the resistance to ground canges the voltage over de pot's resistance). When using the 5 pos switch, selecting 1, 2, 1, 2, 1 pickup (s) this also changes the resistance to ground and causes sudden voltage changes what sounds like popping.

When the other side is pulled fully to ground the cap is loaded and current is no longer flowing. Your problem is than gone. Untill you switch to standby and back on, because the process of loading the cap start all over again.

Fix:
The load time of a cap depends on the size of the cap (capacity) an resistance (limiting the maximum current and therefor speed in wich the cap can load up.)
This is called RC time.

In order to load the cap fast enough you need to lower the capacity or lower the resistance. Both will change the effect of the loop and therefor the sound.

What you could try is offer the loadcurrent an alternative path to ground. You can do this by connecting an extra resistor after the cap (between the 10M resistor and cap) to ground. A 1M resistor would do. This will also change the loop some though.

You could also use a input capacitor before the 1M grid resistor.

The alterative is to take out this loop. This is what i would do.

I personaly don't think a loop like this in this place is a good idea. If you want a feedback loop on the first triode, i would find inspiration in a loop like the one on the SSS. It feeds back signal from the anode of v1b to the cathode of v1a.

[Bombacaototal]

Thank you very much Richard for taking the time to go through the science behind the issue, very educational. Also thanks for the fix suggestion

Below you can see on the left the original HAD SSS, which has the 10M / 0.05uF network on the first triode of V1, like mine. The guys from 2rock when cloned this amp, switched this network to 4.7M / 0.05uF / 4.7 M (although not very visble on the picture I posted). The guys from Ceriatone, when cloning the 2rock amp switched this network to 4.7M / 0.05uF / 4.7 M with a third 4.7M and a ground reference and the advent of a LNFB switch (schematic on the pic), which as per your suggestion would mitigate the issue.

What gets me confused is how did HAD manage to make this work, and subsequently 2rock, although a safe solution would go Ceriatone way (but without the switch) I would really like to remain close to the original design

HAD is full of surprises and still puzzles me how his Borderline and 001 tremolos worked in the configuration laid out, as neither worked when I tried them, unless he is hidding things under the board...Sometimes I think the physics on his bench are not same as ours...

[Richard1001]

I don't know if his physics are diffrent, or he just doesn't care for a few seconds of crackling.
With a 10M resistor and .05 uF cap and somewhere around 200 volt on the plate, the RC time constant is 0,5 seconds. After this time the cap is half loaded. The loadcurve is not linear because as the cap is loading, the voltage diffrence gets smaller and therefor the loadcurrent gets smaller.
It takes about 6 X RC to load the cap to 99,8%. This means 3 seconds to load the cap 99,8%. Your problem should fade away by this time.
You could just leave it and live with it now you know it is normal behavior.

[Bombacaototal]

I don't know if his physics are diffrent, or he just doesn't care for a few seconds of crackling.
With a 10M resistor and .05 uF cap and somewhere around 200 volt on the plate, the RC time constant is 0,5 seconds. After this time the cap is half loaded. The loadcurve is not linear because as the cap is loading, the voltage diffrence gets smaller and therefor the loadcurrent gets smaller.
It takes about 6 X RC to load the cap to 99,8%. This means 3 seconds to load the cap 99,8%. Your problem should fade away by this time.
You could just leave it and live with it now you know it is normal behavior.

You are absolutely right, I have had a bit of time today and ran some tests. If I change the guitar volume right after start up the crackles are super loud, but of I let the amp sit for a few seconds (less than 10), then it is barely audible. Gold to have the confirmation that this is per design, I can therefore just live with it. Many thanks again

[martin manning]

What gets me confused is how did HAD manage to make this work, and subsequently 2rock, although a safe solution would go Ceriatone way (but without the switch) I would really like to remain close to the original design.

Note that in the D circuits where there is a FB loop (102, 124), it's on the second stage. Which circuits have it on the first stage?

[Richard1001]

I think it is the SSS 004.

[martin manning]

Is that something that C-tone added? There are no FB loop switches on the back panel of the D amp photos I have.

[Bombacaototal]

Yup, 004 indeed. The switches for the LNFBs are a Ceriatone mod

[martin manning]

Yup, 004 indeed. The switches for the LNFBs are a Ceriatone mod

Is there a SSS 004 schematic posted somewhere that shows NFB on the input stage? I see M Hartman's layout from 2008 shows it, including the switch, but he says it was not actually copied from any particular D amp. The 002 seems to be pretty well understood now thanks the the recent effort of RColgan; the 004 not so much.

[Bombacaototal]

Hi Martin, Not that I am aware, the closest available information is the C-tone, but fairly easy to spot the LNFB on the original via the pic I posted

Hartman amp started out (before he modded values and lastly the PI) as a clone of the Sterling which is a copy of the HAD amp in question, and I think having the LNFB in switches he either copied from C-tone or the other way around, cannot recall exactly, but I think the latter

[martin manning]

I see the R and C there on top of the board, but which triode is it connected to?

[Bombacaototal]

This specific one is the first triode, there is another on the second triode which is also visible on the pic posted