Hypex UCD400Hg 400Wpc Monoblocks

Last year I was very happy and a bit shocked when I finished my OBL-15 speakers. Sound coming from that open monsters were like a dream. My only fear was the lack of bass performance but it was ok although a single 50 watt class a amplifier handling all drivers alone. After a short time I tried bi-amp configurations taking some mid level class AB amplifiers to woofers..Wouvv bass became stellar. OBL-15 is certainly deserving a powerful amp. I had another good reason even more important to me. 15" woofers definitely put some extra stress (may be mechanical noise), on the feedback circuity of my class A resulting in degradation of sound. When woofers run on their private amps I get the best of my class a which is dedicated to mid and high.

What I'm doing.

400 wpc Hypex class d based amplifiers with toroidal transformer and CRC (capacitor, resistor, capacitor) based power supply. 

This is the schematic of bioplar power supply which I designed for each monoblock. I'm using 400W toroidal transformer, 10.000uf  as a first capacitor, resistor array with cumilative value 0.5ohms and then 22.000uf  "final" capacitor bypassed with 0.22uf MKP.. Total value of capacitance is 64.000uf 

Here is my part list for each monoblock :

Hypex Ucd400HG module. I decided to go with shunt type HXR regulators installed. Well this is not the new nCore but I think still good value with HXRs. HG (high grade) series comes with LM4562 buffer OpAmp on it's input. Using low noise, quality power supply for input opamps is the key point for performance enhancement. Although this baby will drive woofer only, benefits of HXRs located on opamp supply should not be ignored.
Audio grade toroidal transformer from Toroidy. 400W total output power with dual 42V secondaries. I always use quality transformers for all my gadgets. Torodiy may not be a top performer in audiophile industry but certainly it is one of the best if you focus on price / performance ratio.
2X  Vishay BC power smooting capacitors 10.000UF / 63V. They will be used as a first capacitor (just after rectifier) on CRC smooting filter.
2X  Kemet Peh 169 power smooting capacitros 22.000UF / 63V for smoothing reservoirs (final caps on CRC smooting filter) These are really big I mean bigger than a coke can. I have been keeping some of them as a spare for future projects. Now it's time to go..
Soft starter module. Luckly I found this unit on Aliexpress. a well made, reliable starter and doing it's job perfectly. I have been using one of them on my class A amplifier for year. It can power two transformers having total power of 1000 watt
Chasis type rectifier, IXYS made, comes from my diy class A amplifier. (A short time ago, I transferred from IXYS to Silicon Carbide "SIC" Diodes on my class A amplifier)  It is FRED type with soft recovery behavior.  My previous experiences showed  me that rectifiers built with Fast Recovery Epitaxial Diodes (FRED) is a good choice for solid state amplifiers and soft recovery behavior is another bonus.

Internal wires, used on power supply, comes from Neotech as always. I used Jantzen audio wires for binding post connections. Meanwhile binding posts have pure copper body as well as IEC power entry. Audiophonics.fr sells very good IEC sockets using pure copper conductors with reasonable price. Just 3 Euros. It's a stellar.

Chassis was built using 8mm thick alloy plates plus my enormous effort. It was not easy! If I go back I would definitely choose a pre built case.

I used some copper plates to cover "shield" the transformer.. Later I will cover the back side with copper also..

Here I'm testing new babies on my setup. They were connected to speakers binding post with 30 cm. length jumpers diy made with Neotech Nes 3002 speaker wire. For signal connection I used 2 meters balanced cable which is also diy made with Mogami W2534 Neglex Quad Microphone Cable.. Later I will add diy Belden power cords to the chain.

Now It's time to equalize the gain level of Ucd400 exactly to my Pass F5 Turbo amplifier's level. At fitst I thought that it would not be easy. Later I noticed that replacement of just one resistor located on input circuit of UCD400 is enough to fix the gain to desired level. I think this is the better way "in audiophile manner" with respect to adding some extra equipment (pre amplifier or a simple attenuator) between devices..

After some measurement and also a simple calculation using that formula above, I found that the resistor with 7.2 Kohm value is my thicket. Luckly I could find very good (1% tolerance) smd type 7.2Kohms on local shop. Please note that they are so small. You need some soldering skill.

Tip : to measure the voltage gain of your device use (or play) 50-60 hz test tone. This is the most ideal frequency range for simple measurement equipments..