This project is a custom modification of the original Ampeg Heritage B15. You can download the schematic HB15.pdf.
- Use 6L6GC valves that support 500V at the screen
- Always checks that all capacitors are discharged
- Even if the 470k 2W resistor shoud discharged the capacitor
Valves used in this project:
- TAD - 6L6GCM-STR REDBASE
- Philips USA as JAN 12AT7WC (6201) [NOS military grade]
- JAN 6SL7WGT Philips [NOS military grade]
- Shuguang 6N9P J level [NOS military grade]
- The 100K 2W resistor in parallel with the standby switch reduce all the inrush current which is better for the capacitors
- Boost switches increase the gain of the triode by adding a bypass capactor
- Enable or disable the bright capacitor (boost in 8kHz)
- Effects Loop (buffered) is built to be transparent and you can do severals things around:
- Enable or disable the effects loop
- Can be used as a buffered preamp out
- Can be used as an input for a "preamp in a box"
- Can be used as distortion stage on the cathode follower by increasing the send volume
- Eventually a clean boost of the preamp
- Post Phase Inverter Master Volume (PPIMV) allowing to push the preamp while keeping the amplifier not too loud
- Negative Feedback loop for rumble fix and different voicing (see schematic)
- Midranges boost is a custom version inpired from Pignose B100V amp
- Adding a 4.7nF capacitor in series with C1 and C3 to cut sub frequencies
- It may be a side effect by replacing all 22nF by 47nF in order to support a 5 strings bass
- It also due to the frequency response of my PF-210HE cabinet which have a greater low frequencies response
- 3.3nF may be better depending your cabinet (and taste)
- Use a rubber seal inside the chassis to easily mount a APEM 644 for example
- Use teflon tape and rubber seal to insulate metalic jack plug (e.g. Switchcraft 11) from the chassis to avoid ground loops
- Avoid soldering ground on the potentiometer's cover (gound loops enabler)