UcD180AD dual mono amplifier
I have become very pleased with the clean and neutral sound of UcD amplifiers. I have built my own UcD amplifier based on the UcD180AD from Hypex. The module is not available anymore, it has been replaced by the new audiophile version UcD180HG.
The power supply is the Hypex UcD supply HG. I found this product somewhat expensive and because I don't require much current for the bass when driving my monitors, I removed two of the four slitfoil elco's and used these to built a second power supply myself.
This power supply starts with a rectifier bridge based on 4 ultra fast soft recovery diodes BYV79E200 which are provided with snubbers (lossy 22nF or 47nF multilayer ceramic capacitors). The rectifier is connected to the slitfoil elco's which are provided with bleeder resistors of 6800 ohm 2W parallel across their pins. Powered by a trafo of 2x31V/160W a supply voltage of +/-45V is obtained to feed the UcD180AD modules.
The power supply is equipped with a DC-protection by means of the circuit shown below. +/-45Vin shall be connected to the power supply and the +/-45Vuit shall be connected to the UcD180AD amplifier module. LS must be connected to the +output of the amplifier.
Furthermore the power supply board is equipped with a circuit to turn the UcD module on and off automatically, so that no strange noises or plops exist when the mains power is switched on or off. AC1 and AC2 shall be connected to the 2x31V AC voltage of the trafo, NOT the null wire. /ON must be connected to the proper pin on the UcD module (pin4 next to the in and output pins).
The power supply board is also equipped with a +/-12V supply, to feed a pre-amplifier and/or separately feed the onboard opamps AD8620 of the UcD module (after modification for this purpose). This power supply consists of a B250C1500 rectifier with 4 22nF snubbers across its pins, 2 elco's 470uF/63V fed via two resistors (fusible) of 22 ohm, this gives a current limitation of 100mA, then a combination of 7812 and 7912 voltage regulators each equipped with an elco 22uF/50V at the output. If use is made of the Hypex trafo, specially designed by Hypex for the UcD180, no separate 2x12V trafo will be needed. This trafo comes with 2x31V and 2x12V AC voltages each provided with a null wire.
The dual mono amplifier is equipped with an audiophile step attenuator of 10k ohms. This is a DIY-kit obtained from DIYfidelity
To improve the sound of the UcD180AD I applied a number of audiophile tweaks.
1. Coupling elco's removed and replaced by wire.
2. Bootstrap elco replaced by elna cerafine 220µF/16V.
3. Buffer elco's replaced by BC Components 136, value 470µF/63V.
4. PSRR of the onboard +/-12VDC power supply vastly improved by placing elna cerafine 100µF/63V at the 1000 Ohm resistors between +/-45V and the transistors of the +/-12VDC power supply.
5. SMD resistors 1000 Ohm and 560 Ohm at the AD8620 replaced by 3300 Ohm and 1800 Ohm.
6. (Not shown on the pictures) The opamp AD8620 replaced by the LM4562MA, so now it is not anymore a UcD180AD. I call it a UcD180LM. This last tweak is a significant improvement, the UcD is very close now to the sound of a class A amplifier. There are two CRD's (Current Regulator Diodes) connected between the negative power supply rail and opamp outputs, these have to be removed for this upgrade.
In fact nobody should carry out these tweaks anymore. Currently Hypex sells the UcD180HG. This module is equipped already with audiophile components and Hypex sells a fully discrete +/-12V supply to be able to power the onboard opamps separately. In addition, the UcD180HG comes with the excellent LM4562 opamps that I also use for my active filters.
The enclosure is a simple housing of silver painted MDF. The aluminium panels on the back side for the connectors are separated to consequently maintain the dual mono building principle. So this amplifier could be viewed as 2 mono blocks in one enclosure. All extra gold colored connectors are in and outputs of the active filters that I have put into the enclosure at a later stage (not on the picture).
