Adding a Slope Control

[roberto]

Greg,
now it works, great sound! what mods have you done?

El_Martin,
please stop repeating "all work and no play make Martin a dull boy"

jerrydyer,
as the input impedance raises, high-mid rolls of, and the whole eq works totally different. A post CF eq stack has a 1k input impedance, a trainwreck has 38k to 47k. A 10k slope in a trainwreck amp can reduce dynamics because the load is too low (with mids scooped, the first stage has a load of 7k). For my opinion, is better not to go down more than 33k for the slope (but better with more than 56k).

[gcenker]

Greg,
now it works, great sound! what mods have you done?

I started with Kelly '90 and did the following mods:

1. Removed the 25W resistor on the power supply board & replaced it with a 10H choke.

2. Removed the stranded, shielded wire going from the input to V1 and replaced it with solid core shielded wire.

3. Installed same type of wire going from the volume pot to V1 (seriously tames unruly microphonics).

4. Installed a 33k grid stopper resistor going to V1 from the input. Keeps from turning the express into a radio.

5. Removed bias pot on the power supply board & installed a 50k pot with a locking dial (and test points) on the chassis. Dialing in bias is a snap now.

That's it. I kept it simple.

-Greg

[roberto]

Thanks Greg!
I like inductances too, in supply, for everithing above 40w. More punch, more airy, less low-mid colour. I think supply is one of the main thing on an amp with master above 4.
I've got an OT idea reading your post. Have you ever used tv shielded cables? They are solid-core, low capacitance (works on UHF), and low cost.