2nd Gen Build Started (that didn’t take long…)

[martin manning]

With power off
Set the output of the Bluetooth receiver at 200 mV on the bench.
Make the check of the input resistance to ground to make sure it's 1Meg, i.e. there is no short to ground there.
When you plug the signal in you should have 200mV on the input tip and V1a grid.

[Raoul Duke]

Ian,
I have signal on pin 2, but get a wicked buzz when I probe pin 1.
Oddly, I have signal on pin 6.

I get that same buzz at the 100k resistor where it meets the treble cap, but signal returns at the other end of the cap. When I sweep the treble, mid, and bass pots, they seem to work in reverse.

I have signal off the board to NO2, NC1, and COM 1 also.

[Raoul Duke]

With power off
Set the output of the Bluetooth receiver at 200 mV on the bench.
Make the check of the input resistance to ground to make sure it's 1Meg, i.e. there is no short to ground there.
When you plug the signal in you should have 200mV on the input tip and V1a grid.

I have 204mA at the tip and 180 at V1 pin 7.

Just to be sure I’m checking input resistance to ground correctly - does this sound right?

[martin manning]

Yes, so far so good, but don't you mean pin 2? Unless you have your sockets rotated 180 degrees re the layout... This is to make sure that the signal is in fact getting to the V1a grid.

[Raoul Duke]

I have the tube sockets as drawn in the layout - with pin 1 at 1 o’clock. With 196mA AC at the BT receiver tip in the normal jack, I get
162 at pin 2 and 230 at pin 7.

[martin manning]

That’s reasonable. Note I show 1V at the top of the volume pot. Can you hear the tone clearly?

[Raoul Duke]

Yes. It’s stronger on pin 3, but does increase as it should from the wiper.

With the controls at 50% I get .59vac at pin 3 and .08. at the wiper (Jazz).
With switch on Rock - 1.4 and .2 respectively.

[martin manning]

Ok so does it get through the tone stack?

[Raoul Duke]

It seems to get through and sweep each control until I get to OD - nothing on either pot lug. Level and Accent seem to work though.
Does this narrow it down to the OD co-ax or are we still moving toward the problem?

Nice strong signal at NC1 and COM 1.

Faint signal at V1 pin 3 (trying to work my way back - I think).

[Raoul Duke]

The 100k from the bottom of the bass cap jumped to the bottom of the 100k at the bottom of the treble cap gives me the same “buzz” as pin 1 on V1. The jumper next to it from the bottom of the mid cap to the bottom of the bass cap has good signal.

[Raoul Duke]

Also, I was trying to work through the schematic with the voltages in it and here’s as far as I got (all readings in mV AC):

200mV at tip in Normal jack to the bottom of the 1M to the co-ax at terminal strip to pin 7.

Treble pot reads 12.1 at lug 1, 5.1 at lug 2, 15.1 at lug 3

At the eyelet where .01uf cap meets NC1-NO2 I got 7.9

Preamp out tip - 7.9

Volume pot lug 2 reads 4.9, lug 3 is 4.2

[martin manning]

Seems like there is something wrong in the tone stack. V1 Pin 7 should be higher, 150mV or so. Treble wiper/top of the volume pot should be ~1V.

[Raoul Duke]

Would that isolate the problem to the switches and cluster of resistors/caps in that area, or should I be looking toward the board?

I’ve verified all the connections from the layout to make sure those are done according to the drawing and to make sure nothing is inadvertently grounded. This is where my inexperience really jams me up I think.

Treble wiper to Volume CW is 7.3 mV on either end. Got to be on one of the connections in between, no?

[martin manning]

Upstream of that, yes.

[Raoul Duke]

Upstream of that, yes.

Upstream meaning between there and the input, right?