Steel String Singer #005 build

[captaincoconut]

Check out this sticky on setting up the FET: https://ampgarage.com/forum/viewtopic.p ... 91#p211891

I've seen and studied this file before, yes. My question is in regards to the ratio of R1 to the 150k/1W resistor. Without knowing the value of B+5 how can I be sure that R1 = 18k will get me in the ballpark? Or should I just replace R1 with a resistor decade box and see what I can get?

[martin manning]

You won't know exactly what B+5 is until you have everything dialed in, but it will likely be 325-350V. I would choose the resistor based on the Vd you want, either the ~18V or ~9V, and then bias the FET to taste. The FET bias strongly affects the voltage divider output due to the high impedance (150k). Based on the posting by C Wilson linked in the FET bias post, HAD seemed to prefer the lower Vd. I and others have tried and liked the higher voltage. It comes down to whether you want to create distortion in the FET or drive V1a harder and create it there.

[captaincoconut]

Thanks!

[captaincoconut]

Am I correct in understanding the Mid Boost circuit as follows: when the switch is engaged, it bypasses the 390pF capacitor, effectively increasing the total capacitance to 2.2nF and thereby shifting the range of the treble control? And when the switch is disengaged, the capacitance drops to around 331pF?

I’m planning to omit the Mid Boost switch and replace it with a Deep switch, since the original #005 didn’t include a Mid Boost function. I assume the 4.7MΩ resistor is just there to prevent switch popping, correct? If so, leaving out both the switch and the resistor and wiring the two capacitors in series should work as intended — or alternatively, I could just use a single 330pF cap.

[martin manning]

Am I correct in understanding the Mid Boost circuit as follows: when the switch is engaged, it bypasses the 390pF capacitor, effectively increasing the total capacitance to 2.2nF and thereby shifting the range of the treble control? And when the switch is disengaged, the capacitance drops to around 331pF?'

Exactly.

I’m planning to omit the Mid Boost switch and replace it with a Deep switch, since the original #005 didn’t include a Mid Boost function. I assume the 4.7MΩ resistor is just there to prevent switch popping, correct? If so, leaving out both the switch and the resistor and wiring the two capacitors in series should work as intended — or alternatively, I could just use a single 330pF cap.

Again correct. IMO, the PAB was an evolution of the Dumble tone stack EQ, and considered to be an improvement, i.e. more useful than the older Deep function.

[captaincoconut]

Thanks!

[captaincoconut]

In the meantime I finished wiring the reverb section, the relay for the reverb and the footswitch jack. Just missing the cathode bypass cap for the reverb driver... I also started wiring the two filter rotary switches!

[timrobertson100]

The quality of your workmanship is just awesome. Everything about the build is fabulous.

[captaincoconut]

Thank you, Tim!

[captaincoconut]

Filter section finished. Value-wise I followed Martin's revised filter section. It's also really cool to have that little daughterboard. Makes wiring the whole section a lot easier and cleaner!

[martin manning]

Very tidy! I'll be interested in how you find the functioning of the filters.

[beasleybodyshop]

Can confirm the Manning Filter setup is an improvement, in the sense that the steps are more predictable and useful.

ive often thought it would be cool to build this as an effect with buffered in/out so you could add it to any amp with an effects loop. Post preamp EQ in general is really powerful.

[captaincoconut]

Thanks to both of you for your work!

[captaincoconut]

@beasley looking at your schematic, shouldn't the 100k leg of the Jazz/Rock switch connect to the middle lug of the Treble pot?

[martin manning]

Correct.