Cornerstone - Royal Antique
I kinda wish I'd tried something easier for my first trace. Does anything look very wrong here?
This looks like a TS (with some mods) with a switch that adds in extra gain on the op amp plus a JFET boost on the back. There's also a separate JFET boost stage on an external footswitch - I've added that as a separate trace below, but it's a duplicate of the output boost on the main pedal. I believe it's also the same circuit in the Flame Boost by Cornerstone.
This looks like a TS (with some mods) with a switch that adds in extra gain on the op amp plus a JFET boost on the back. There's also a separate JFET boost stage on an external footswitch - I've added that as a separate trace below, but it's a duplicate of the output boost on the main pedal. I believe it's also the same circuit in the Flame Boost by Cornerstone.
- mauman
- Resistor Ronker
The biasing arrangement for U2.2 looks a little odd (blue oval in the center), there's DC continuity from U2.1 which will serve to bias U2.2. Could there be a series DC blocking capacitor missing after U2.1, maybe before or after the 1K?insidecircles wrote: ↑07 Jun 2023, 19:11 I kinda wish I'd tried something easier for my first trace. Does anything look very wrong here?
The diode/EL cap arrangement in the power section (blue oval, upper right)will protect the cap from reverse polarity, but won't help with DC noise reduction. Putting the cap after the series 8.2R resistor would do more.
<edit> my apologies, I forgot to upload the marked schematic with the mysterious blue ovals! It's attached.
Last edited by mauman on 08 Jun 2023, 19:03, edited 1 time in total.
Good spot, I've taken another look, but pin 1 connects directly to the 1k and the other end connects directly to pin 5. So, no DC blocking between those stages.
I have re-counted the caps and realise I've missed a couple. The Wima looks like it's in parallel with the 82n off the tone pot (I can't get the value without removing the part). Fine-tuning that tone response, I guess - maybe 82n is just a bit too small and 100n is just a bit too big. And there's also a 100n from the power rail to ground. I've updated the schematic with those below.
Yes, I thought the power section looked weird. As I say, I've added a missing 100n, but I'd really expect that 100u in that spot. I've deliberately left off circuitry around the relay, and there's a few power components for that in this area. There's a 78L05 connected to the node between the diode and the 100u for that. Maybe I've simplified weirdly - maybe I should leave out the diode/100u from this schematic entirely. But I'm still left wondering why there's no (large) filter cap on 9V.
- bajaman
- Old Solderhand
Information
- Posts: 4549
- Joined: 26 Jun 2007, 21:18
- Location: New Brighton, Christchurch, NZ
- Has thanked: 595 times
- Been thanked: 2058 times
The 8r2 resistor needs to be connected to the junction of the 1N4001 and the 100uf capacitor surely ?
be kind to all animals - especially human beings
You'd think. Image below shows trace/node at 9V/8R2/diode.
I did however mess up the position of the other diode, which is after the series resistor. Updated schematic below.
ETA: Argh, it's 82R, not 8R2. Yesterday, I was convinced I'd ironed out all my errors in this.
- Manfred
- Tube Twister
Information
- Posts: 1937
- Joined: 04 Apr 2009, 23:42
- Has thanked: 1672 times
- Been thanked: 1344 times
The series connection of the 100uF electrolytic capacitor and the 1N4001 diode makes no sense.
When the voltage is applied to the circuit, the capacitor is charged up to this voltage and then it has no more purpose,
because no current can be taken from it by the diode in reverse direction and the stabilization does not work any more.
I think the circuit is rather in this way:
When the voltage is applied to the circuit, the capacitor is charged up to this voltage and then it has no more purpose,
because no current can be taken from it by the diode in reverse direction and the stabilization does not work any more.
I think the circuit is rather in this way:
Last edited by Manfred on 09 Jun 2023, 00:16, edited 1 time in total.
- bmxguitarsbmx
- Cap Cooler
MPSA18 bias resistor (510k) should go to some positive voltage. Likely connected to Vr.
Good call - you're right. Updated below.bmxguitarsbmx wrote: ↑08 Jun 2023, 23:51 MPSA18 bias resistor (510k) should go to some positive voltage. Likely connected to Vr.
I completely agree. It's just... that's not what is on the board.Manfred wrote: ↑08 Jun 2023, 19:10 The series connection of the 100uF electrolytic capacitor and the 1N4001 diode makes no sense.
When the voltage is applied to the circuit, the capacitor is charged up to this voltage and then it has no more purpose,
because no current can be taken from it by the diode in reverse direction and the stabilization does not work any more.
I think the circuit is rather in this way:
If I were to build this myself, I'd definitely just use a 'normal' power section, like this.