Parasound HCA-1206 Amplifier: Recap & High-bias Setup

I bought this amplifier by the end of last year and I can say this Parasound HCA-1206 is the best sounding solid-state amplifier I've ever heard.

Previously, I've owned and heard many amplifiers in my own audio system. Not on others system to be clear. So, I know the difference in the sound quality. This amplifier is a keep. Although it is very heavy, about 40 kilos, but the weight is equal with its built-quality. The designer of this amplifier is one of the most famous amplifier designs: John Curl. Probably you may know that this guy also designs the amplifier for Mark Levinson.

In this post, I will do some improvement with this amplifier. Let's check it out.

Previously, I already did some modification with this amplifier. This Parasound HCA-1206 is 6 channel amplifier. I disable the 4 channel and only using 2 channel instead.

What is the concept of this?

Imagine that you have 6 channel power amplifiers that all of them drawn the constant current to the power transformer. Those un-used channels take the load from the power transformer and the others components around it also creating some noises. By disable the un-used channels, I can hear the improvement on more silent back-ground music and also mechanical noise from the main transformer is reduced.

The next steps are replacing the old capacitors.

I am quite disappointed with the original capacitor use here. Those capacitors are Taiwan made and this is pure for cutting the production cost. I checked their capacitors capacity and they are still good, but many of them start to show some coloration cause from the electrolytic leak at the bottom of the capacitor.

I tried to source the capacitors and I will be replacing them with Nichicon capacitor. A famous Japanese capacitor brand.

The only capacitor that hard to find due to its capacitance value and the physical size is the main capacitors for power source. So, I will leave them as is.

I gathered all the capacitors and start to replacing them one-by-one. The main power supply board have 9 capacitors and each amplifier channel has 11 capacitors, with all of them have different capacitors value.

I start with the power supply board first, since this one is simpler to do.

This is the result when finished.

Next step is the amplifier board.

The capacitors are smaller and many of them require careful attention when remove it. This to avoid any broken PCB trances.

All capacitor has been replaced with the new one. This amplifier recap is now done.

I turn on the power switch and all seems okay. At least there is no smokes or pops.

Now is the next important step, is adjusting the amplifier bias.

Amplifier bias is very important. The higher the bias, the more linear amplifier to work because the cross-over distortion between push and pull signal is minimized. The sound quality result is easy to distinguishable: airy, more liquid, more impact on every music note, higher amplifier bias sound more natural and engaging.

The downside is the heat, which should be careful when increasing the bias outside the amplifier circuit to handle. It can be damaging the amplifier with overheat. The good news is Parasound specify the bias level on each amplifier they've made. Especially for this Parasound HCA-1206, the bias level is at 8 mV (tolerate 2 mV).

To check this bias level is easy. First, turn on the amplifier without connecting all of the input and output. Leave it about 30 minutes until it reaches normal operating temperature and by using the volt meter, set to milli-volt value, put the probes on any output resistor. Then adjust the potentiometer on each channel to set as the specify value.

This amplifier has initial bias at 7 mV, bellow the standard value, although still on the tolerance. I readjust it higher to 10 mV. The heat is a little bit higher than before but pretty safe to run this amplifier all the time.

I put back this amplifier to the system and the sound is now so much better.

I wondering if I increase the bias to 12 mV, is it safe enough for this amplifier? Will the sound improve? Maybe next time, this amplifier is too heavy for me to work on:)

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