Hayden Speakeasy ground hum

[Mick Bailey]

I have a Hayden Speakeasy combo in right now that's got a really bad ground hum coming from the preamp (I've eliminated heater hum). It's a difficult amp to work on due to having layered boards linked by bare jumper wires and the design is unconventional. Does anyone know where the circuit grounds to the chassis? I've been through this amp time after time to find out where it grounds and can't locate anywhere it makes contact or any wiring point. The chassis is grounded, because the reverb sockets are mounted directly on the chassis and only conncted by the hot signal wires. The reverb though is very weak and very noisy so I'm thinking there's some resistance in the grounding somewhere. It has grounding wires run all over the place between boards, controls and sockets and the PCBs are marked with grounding symbols on pads where you'd expect there to be connections but there aren't any. The speaker output is grounded to the 1st preamp capacitor node, after the C/L/C main filtering but I can't even see where the first filter cap is grounded - there's a connection symbol but no wire.

Its unusual in design - V1 heaters are powered off a 5v regulated DC supply. The PI has one plate connected directly to B+ and appears to run a CF one side and attenuated gain stage the other, with the outputs connected to another gain stage. The bias supply is via a bridge rectifier. Slightly less unusual is the reverb being capacitor coupled from a 6V6. It runs a pair of 6L6 and pair of EL34 which can be run in combination (though the OT impedance is fixed) B+ is only 390v, though the PT has multiple HT output voltage taps.

I contacted Hayden but no joy with any information or schematic.

[g1]

I guess you've checked for any board mounting screws lugs making contact with board.
How about those funny plastic jacks that have the tiny little hooks in their face?

[Mick Bailey]

Yes, I removed every screw and slid plastic underneath every standoff to make sure there's no contact and still get about 4 ohms to chassis. The jacks are a regular type on this amp - also removed and pulled away from the chassis. I've had three of these amps (all from the same early production batch) and all have had problems with connections - mainly the solder doesn't properly wet the component leads and gives rise to all kinds of obscure faults. It could be this is the problem and I wanted to start by making sure the grounds are good. This particular amp had been left unused for a few years and It had a high resistance between mains earth and chassis where the terminal had oxidised. There is another connecting lead from the transformer to the mains earth but its an internal screen and no other connection.

I'll post some pictures later on when I get it back on the bench.

[Mick Bailey]

I spoke to Hayden (Dave Green) and he pointed to the ground being off channel 1 volume pot shell. I then saw it relies on the crimp between the shell and the rest of the pot being good - in this case it was a few ohms. It's reduced the hum slightly, but not enough. I've gone right through the amp resoldering and checking all of the board interconnecting jumpers and grounding points. Still not good enough. There are no schematics becaus every amp is built differently. On the drive channel before the tone stack there's 45mv of noise - a 50hz fundamental with a rasping 100hz on top. On the clean channel it's 5mv. Interestingly paralleling a cap across any of the supply nodes increases hum. Maybe bad rectifier? First node ripple is just 1.6v.

More work required.

[Jon Snell]

You will get no help from Hayden.
The issues with these and the Blonde combos is earth loops and noisy valves.
I have re wired a Blonde and mostly all of the mains hum has now gone. Maybe the 100HZ hum is a poor smoothing capacitor or just wired to the wrong ground point.
Good luck.

[Mick Bailey]

I temporarily tried star grounding and this got the hum down to Fender Deville levels. When I put it back to stock the hum was back. I checked every connection with my low resistance meter and everything is good. This morning I was looking at the grounding again and lifted the ground connection to the channel 2 gain pot and the hum disappeared on both channels, so there is a ground loop. I tried everywhere on the amp to get a better ground, but wherever I connect it the hum is back.

Now, something is going on here because I'm the only person ever to look at this amp and on close inspection there's a blob of solder on the back of the channel 2 gain pot and signs that a lead was attached here. Instead, a flying lead is attached to a ground point at the channel 2 1st gain stage cathode resistor. Also, there's a bus wire that has solder on it where it appears to have been once soldered onto the gain pot ground for channel 1. The easiest thing to do is to isolate the reverb sockets and star ground it.