Parasound HCA 2205AT - Modications / Upgrades

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snapo6

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Joined 2018
#1
Hi All,

I'm very happy with my just acquired vintage Parasound 2205AT, these thing is a beast 🙂

The amp is now being serviced.
Just received a call from the service company and I was very disappointed to hear from them that, although everything looks fine from outside, the inside is not the case, it's very dirty and full with nicotine as the amp has been exposed to a smoking envirionment for years and years. Cann't imagine how people can be so careless!!! 😡😡😡

The amp will be serviced and cleaned completely and it will show as new so I will be a happy man. But now that the amp is open and all parts are removed, we would like to apply all possible modifications for the sound quality.

Can anyone or (former) owners advise which modifications/upgrades are needed to make the amp sound its best?

Regards,
Anoep
 
#2
I would search, there are numerous threads here and on a couple other forums where some key advice is given from some very good sources.

Basics are to remove the tiny yellow capacitors that are everywhere in groups, and replace the groups with a single .1uf polystyrene, either a Reliable Capacitor brand, or the k71-5, Russian surplus.
The main filter capacitors are probably in need of replacement, the smaller electrolytic capacitors can be replaced with some Nichicon Muse kz.
Check the bias, the recommended settings sound pretty good, the heat sinks are small, so that works out.

Those are a great sounding amp for the money, especially with some updates.
 
#4
I’m sorry, has been a couple years since I went through a parasound amp here, but they are all pretty similar as far as capacitors go. The circuits have their differences, but you’ll find many similarities once you start to look inside the various models.
Most of the documented modifications are based on the hca3500 model, try and search for that, there’s a also a thread or two on here regarding the 2200 as well.
 
#8
Actually I believe the existing small, yellow capacitors are not any less performing than the mkp1837, from my experience fiddling around here. The risks associated with performing modifications are not worth it for just average parts, unless the component is inexpensive to begin with, in my opinion anyways. I found that the smaller packaged parts like that are best served for low-level filter circuits more than power, tend to resonate easily.
I would go and find these through a distributor;
Capacitor Sourcebook - AudioCap RT

These will really wake things up and help make that amp one you’ll want to use for a very long time! They do take a while to settle in though, but well worth it.

There used to be more of the Russian surplus parts available, but it seems the supply is drying up. Those can work well if you’re on a budget, and if you can find them that is. I’m using a pair of the K71-4 1uf in the servo circuits on our HCA1000A, as well as on a dac.

The HCA1000A, was the one with average-sized heat sinks, the rest of that series are larger, so excuse my oversight there...
 
#12
Another upgrade that I always try and fit in, is to put a snubber onto the rectifier diodes. This helps to lower the switching noise.
A .01uf film across the dc side, and another .1uf+18R in the same manner as well help to clear up the highs and tighten the bass a bit.
 
#14
Marc Johnston’s Quasimodo snubber is more efective, cheaper, and smaller.

It’s a .01 uf cap across the AC secondaries in parralell with a series RC network.
The second C is 0.15uf and the R is determined with an inexpensive test jig and a scope.
See his thread on the subject.
 
#15
Well maybe I didn’t quite phrase that clearly.
Same thing you just said, minus the investigation and test jig for the last 10% of performance for the average tinkerer...
Things also work much better if they are as close as possible to the diodes, forget about the transformer.
 
#16
phase said:
Things also work much better if they are as close as possible to the diodes, forget about the transformer.
Click to expand...
Not correct; the diodes provide the stimulus but it is the transformer's leakage inductance which actually rings. So for maximum possible benefit, you want the damping mechanism ("snubber") as close as possible to the transformer. In practice that means: at the ends of the transformer's lead-wires, where they are soldered to the PSU board. Next to the diodes. 🙂
 
#17
Hi all .. while playing at a low volume level my HCA2205A jumped into standby and remains there. No issues with speaker wires or inputs. No damage appears to be visible to any of the components. Amp didn't run hot at all. No prior indications something would go wrong.

What could it be? I've read about a possible dc voltage on one of the inputs? Any other ideas?
 
#19
Thanks Phase 🙂

I'll start by looking at DC voltage at the output of each amp, before the relay(s) or other switching, etc. If that's not within 100 mV of zero when there is no signal or load applied then that amplifier has probably an issue. Else I'll be looking at the protection circuit itself.
 
#20
Sometimes it’s interesting to notice how the offset goes from a cold start, usually isn’t good the first couple seconds, but can become acceptable pretty quickly.

Perhaps there’s an overlap between that and the protection circuit?

All just a guess at this point however...

Probably a good idea to plan on replacing the electrolytic capacitors if you do keep it, amps about 20 years old by now I’m guessing.
 
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