Another quick project that did not go quick at all in the end: for my revised HT system I needed more amplifier channels. Nothing in recent classifieds would have worked from a size, performance or cost perspective so DIY was attractive again.
I recalled Achim had an old blown class-D amplifier from about 17years ago where the modules were no longer available and he kindly donated the wreck. So I thought, great, plonk in a suitable modern class-D module, change a few connectors and a few drilled holes and Bob's your uncle. The very slim casing made it great for stacking amps.
Sadly, Bob proved no family member:
- The ICEPower 400A2 module I have identified was 2mm too high and would have short-circuited to the chassis lid.
- The existing power supply had no gate driver power supply i.e. an extra power supply rail was needed.
- The existing DC-block circuit had a novel approach but sadly it blew as a short-circuit sometime.
- Front power LEDs were blown
- Filtered IEC inlet module had its fuse cover lost. Not available separately so the whole module had to be replaced.
- Only RCA inputs. I don't do RCA, XLR only.
- A RJ45 plug on the back is labelled "remote" which I was hoping was meant as a 12VDC trigger input. It was not, whatever it did just presented a static 5V output which will also blow any Ethernet port if accidentally connected.
Then on top I was not happy with:
- Preamplifier module was very basic and not balanced-capable
- Preamplifier power supply was very underrated: 220uF and a 7815/7915 only
- Ratty DC/signal wiring of poor quality and so badly oxidized even a fresh cut struggled to be solderable
- Thin piece of cabtyre AC wire
So, I ended up removing altogether not just the broken amplifier module but also the AC soft-start/DC-blocker, preamp power supply, preamp, AC switch, front panel LEDs and all wiring. So I just retained the chassis, transformers, power supply and speaker terminals.
To address the mechanical issues, I copied the original rear panel and had Chingy lasercut a new one that got sprayed black. This now has holes for the XLR and trigger module. For the amplifier height issue, a large 3mm alu plate was bolted at the bottom instead of the top of the original, which gave the few mm clearance needed and also moved the heatsink to the outside for improved cooling.
AC inlet was upgraded from 6A to 10A, not because 10A is needed but because oversized AC filters cause the least harm.
Soft-start was made with a massively oversized DC-block and industrial high-reliability relays. A 15V 2W SMPS module is used as standby PSU as well as serving as the missing gate driver power source.
Trigger was a standard affair of an opto-isolated 12V input and override toggle switch.
Main power supply was retained because the amp has not had a long operational life and likely still intact. However, an additional bulk PSU bank plus MKP capacitors were added from an old project: it's only an extra 30% capacitance but the capacitors are extremely high ripple rated, which will prolong the life of the main caps.
Preamp power supply is made out of a snubber, big pi filter and LM317 regulators, all as a pre-regulator stage.
Preamp was mostly recycled from past projects with a fully differential input and driver stage, together with appropriate control circuitry to the ICE module. All power rails (analog and gate driver input) are locally down-regulated with ultra-low noise regulators. Some sensitive cabling got wrapped in copper tape and added a ferrite clamp for HF protection.
Before and after pics shown here. Bottom left is the DC blocker & standby PSU, top right is the preamp and top middle the amp.
Measurements are excellent and can push 400W/ch into 8Ohm. Since this amp will be for center channel duty, I'll likely just bridge it.
I recalled Achim had an old blown class-D amplifier from about 17years ago where the modules were no longer available and he kindly donated the wreck. So I thought, great, plonk in a suitable modern class-D module, change a few connectors and a few drilled holes and Bob's your uncle. The very slim casing made it great for stacking amps.
Sadly, Bob proved no family member:
- The ICEPower 400A2 module I have identified was 2mm too high and would have short-circuited to the chassis lid.
- The existing power supply had no gate driver power supply i.e. an extra power supply rail was needed.
- The existing DC-block circuit had a novel approach but sadly it blew as a short-circuit sometime.
- Front power LEDs were blown
- Filtered IEC inlet module had its fuse cover lost. Not available separately so the whole module had to be replaced.
- Only RCA inputs. I don't do RCA, XLR only.
- A RJ45 plug on the back is labelled "remote" which I was hoping was meant as a 12VDC trigger input. It was not, whatever it did just presented a static 5V output which will also blow any Ethernet port if accidentally connected.
Then on top I was not happy with:
- Preamplifier module was very basic and not balanced-capable
- Preamplifier power supply was very underrated: 220uF and a 7815/7915 only
- Ratty DC/signal wiring of poor quality and so badly oxidized even a fresh cut struggled to be solderable
- Thin piece of cabtyre AC wire
So, I ended up removing altogether not just the broken amplifier module but also the AC soft-start/DC-blocker, preamp power supply, preamp, AC switch, front panel LEDs and all wiring. So I just retained the chassis, transformers, power supply and speaker terminals.
To address the mechanical issues, I copied the original rear panel and had Chingy lasercut a new one that got sprayed black. This now has holes for the XLR and trigger module. For the amplifier height issue, a large 3mm alu plate was bolted at the bottom instead of the top of the original, which gave the few mm clearance needed and also moved the heatsink to the outside for improved cooling.
AC inlet was upgraded from 6A to 10A, not because 10A is needed but because oversized AC filters cause the least harm.
Soft-start was made with a massively oversized DC-block and industrial high-reliability relays. A 15V 2W SMPS module is used as standby PSU as well as serving as the missing gate driver power source.
Trigger was a standard affair of an opto-isolated 12V input and override toggle switch.
Main power supply was retained because the amp has not had a long operational life and likely still intact. However, an additional bulk PSU bank plus MKP capacitors were added from an old project: it's only an extra 30% capacitance but the capacitors are extremely high ripple rated, which will prolong the life of the main caps.
Preamp power supply is made out of a snubber, big pi filter and LM317 regulators, all as a pre-regulator stage.
Preamp was mostly recycled from past projects with a fully differential input and driver stage, together with appropriate control circuitry to the ICE module. All power rails (analog and gate driver input) are locally down-regulated with ultra-low noise regulators. Some sensitive cabling got wrapped in copper tape and added a ferrite clamp for HF protection.
Before and after pics shown here. Bottom left is the DC blocker & standby PSU, top right is the preamp and top middle the amp.
Measurements are excellent and can push 400W/ch into 8Ohm. Since this amp will be for center channel duty, I'll likely just bridge it.
