Restoring and modifing a Parasound HCA-2200II power amp.

Hello and welcome to the What is HiFi blog! This time I am hosting a post from Panos, he finally got the time, energy and courage to restore and modify one of his power amps, the Parasound HCA-2200II. The cost of the mod is low, 20 Euro for a lot of small capacitors, some bridge rectifiers and resistances, plus 100 Euro for the four big main capacitors - but this 100 Euro mod was optional, done for piece of mind mostly. (UPDATE: As it turned out, there was no reason changing the big main capacitors; with the help of our tech guru we measured the old ones (he meausred capacitance and equivalent series resistance), they were at top condition).

So, from now on it is Panos' words!

Chris

PARASOUND HCA 2200 MKII restoration & mods (or how to make a Parasound HCA-2200II sound like a Parasound Halo A21).

The Parasound HCA-2200II in front of the Halo A21.

A small background story.

Back in 2011 I wanted to upgrade my HiFi system. Some of the components I wanted to upgrade were my two NAD 216 THX power amps. After searching and reading several reviews, I feelt that Parasound power amps are a good value for money.

Since I wanted to replace two NAD 216 THX (used for bi-amping my main speakers) I had to get something more powerful, so I set my sights for a Parasound HCA 2200 MKII. 

Luckily after a couple of months I spotted on eBay a 2200 MKII and the seller was from Greece, also the price was very low.

After the biding had ended I called the seller and an appointment was arranged. So me and my good friend Christos went to pick up the amp. I still remember how exhausting it was just to carry this 27kg beast from the seller's apartment to my car… 

When we got back home, first thing we did was to open the top cover of the amp and have a look inside; man it was in ugly shape, dirty and with spider webs. So we pulled out the vacuum and a paint brush and we cleaned it as good as we could.

Next thing was to power it on, we were so curious and excited listening to it! But the power switch was dead and ejected like a faulty doorbell in a Benny Hill's episode. Any way this was an easy fix - we replaced it with a new one.

So finally we were ready to integrate it at my system and listen to it. Man there was a big improvement over the two NADs!

Time passed and after a couple of years I decided again to make an upgrade. Since I liked the sound of Parasound, I set my sights for a HALO A21 - OK my dream is two Halo JC-1 but the price is out of my reach. So I happily managed to get myself a brand new A21 at a very good price and since then the HCA-2200 MKII was left in storage.

However, ever since I bought the 2200 I wanted to upgrade it / mod it but either I didn’t have the time or I was too afraid to do it myself in case I do something wrong, even though I have a good knowledge of electronics and I am very skilled with the soldering iron.

The final push for moding the 2200 were some posts from Mr. John Curl that were suggesting removing / replacing some capacitors that were not at his original design. 

Let's do some work!

So, first thing was to disconnect all cables from the driver boards. I took pictures of every cable and I labeled them using masking tape indicating the number of the connectors on the board.

Every cable is connected at a certain position on a board, in the case above that is E204.

Each cable was marked with the position number it belongs.

Next thing was to remove the two center boards which have a double task. They are used for powering the driver board and to accommodate some film capacitors (white blocks) which are in parallel with the big electrolytic caps of the main power supply.

I removed all the electrolytic and all except two film capacitors, two resistors which looked suspicious and the bridge rectifier. Let's have a look at some "before" pictures:

Ohhh these white capacitors, there are lot of them!

The electrolytic capacitors were removed in order to be replaced with new ones; some of them had leaked. The idea for replacing the film caps came from a quote by Mr. John Carl:

“Finally, if you see a lot of 'extra' film caps across the main power caps, you can cut the majority of them out.”

http://www.diyaudio.com/forums/solid-state/31169-how-mod-parasound-hca-2200-mk2.html

 

“I can't tell you precisely why, but many caps can be removed from the power supply and the unit will most probably work better. Compare the schematics of the JC-1 and the HCA-3500 and note the caps in the power supply. It is possible that the extra caps, while looking 'impressive' actually add resonances as much as reduce noise.”

http://www.diyaudio.com/forums/solid-state/262902-hca-3500-questions-2.html

So I decided to remove all but two of the film caps (22 units in total per channel!!!) and replace them with just 6 units of almost equal total capacitance sum (~1μF).

 

Also, the bridge rectifier was replaced by one with better specs (more volts and amperes) to stay cooler. Let's have a look at some "after" pictures:

Yes, I also did some board cleaning...

First new capacitors on their position.

All capacitors at their position. I left two white old ones, no reason to replace these...

On the left a board before modification, on the right a board after modification. Pop quiz, can you spot the difference?

Next (optional) step was to replace the big main electrolytic capacitors; even though I do not now the state of the original ones, since I am overhauling the amp I thought that it is a good idea to install new ones.
 

Their dimensions are: height (length) 105mm max, diameter 51mm, lead spacing 22mm, 80V min. I used Trobo 25.000 μF computer grade capacitors, they fitted perfectly.

Regarding the two main power supply bridge rectifiers, they were already changed with faster ones (36MB80A) in the past. It is an easy and low cost mod worth doing.

Next step was replacing the three electrolytic capacitors on the side amplifier boards - the middle capacitor is bipolar or nonpolar. I also thought about replacing the white thermal conductive paste that is between the power transistors and the heat sinks but that was not necessary; there was some paste around the transistors and I could easily see that it was at a good, creamy state.

There are two trim pots on the main amplifier boards for adjusting the bias voltage. According to Mr. Tony from Parasound the flat one (on the left at the picture below) is 200 Ohm for fine tuning and the other one (on the right, over the cables) is 1K is for coarse adjustment. After marking their original position, spray some contact spray at these pots and twist them in order to allow the spray to go everywhere. Be careful to return the pots at the original position after the procedure, you don't want to set the bias at maximum level by mistake!

You will find more details regarding bias adjustment at the end of the post.

The bias adjustment trim pots. The one on the left is for fine adjustment.

So, we have done most part of the job but there is still some more.

 Next in the list was the driver and protection board.

Parasound HCA-2200II protection and driver board.

The idea is to replace all the electrolytic capacitors for obvious reasons and to remove some film capacitors, here is a quote from Mr. John Carl:

“First locate any bypass caps that seem 'tacked on' or paralleled with other similar caps. Just remove them, except for one 0.1 uf or so cap in each board location. Any bypasses across power electrolytics should be removed. Second, make sure that your feedback resistors (47K) are 1/2W Resista or Holco (old), nothing else will do. This should get you started.”

http://www.diyaudio.com/forums/solid-state/31169-how-mod-parasound-hca-2200-mk2.html

Let’s take for example the six capacitors in parallel on the lower right side of the board, their markings are C125, C118, C123. If we check the schematic, originally there should be only two film caps in parallel (C118 and C123) so the other three on top must go.

Note: the brown "burned" area on the board near the XLR plugs is a common problem on all the 2200 MKI & MKII.

Let's see a quote from bigskyaudio (http://www.bigskyaudiomt.com  Stereo Power Amplifier Restoration & Repair Service, Audio Upgrade Modifications):

 “I can see heat damage to the driver board in your picture right by the XLR jacks resulting from heat dissipation from the 2W dropping resistors. Examine the pc board underneath for any cold or cracked solder joints in the area and make sure that none of the pc board traces have burned or cracked by the eyelets from the heat. The resistors are used in the protection circuit and for driving the LED lamps. I see heat damage in virtually every HCA-2200 including the series II. If you are replacing capacitors, change the electrolytics (NP and standard) in the protection circuit with new. “

http://www.diyaudio.com/forums/solid-state/203603-parasound-hca-2200-problem-need-some-help.html 

These resistors were replaced during a previous service with grater wattage (so they will not become very hot) and also they were mounted a bit lifted up of the board for better heat dissipation.

Let's see some "before" pictures:





And some "after" pictures:



For the most observant reader something is missing from the picture below! Try to find the difference, if you can’t just look at the picture that follows.

The four yellow capacitors have been replaced with new ones; maybe this was not necessary but there are two reasons: the first is pure aesthetic for a cleaner look on the top of the board. The other reason is that the originals were too close to the transistor’s heat sinks and although they do not get very hot, overtime the capacitors might be affected (I do not know if the above effect produced a “warmer sound” :-).

After connecting all the cables back on the boards, it is time to power the beast up and adjust the bias. Put your DMM to the DC mV scale and connect it across any of the emitter resistors - I found out that it doesn't matter in which one. Please connect and disconnect the DMM to the resistors while the amp is off! Put the pot intended for fine tuning at the middle position and try by using the other one to get the desired bias as close as you can; then use the fine tuning pot for micro adjustment.

Please note that you have to leave the amp on for at least 30 minutes before adjusting the bias, the setting should be 20mV = +/- 2mV. At this amp I did not find it necessary to make an overbias adjustment, the factory value makes the amp hot enough.

Everything connected!!!

Finished and powered ON, no sparks & no magic smoke escaped. I hooked it up to my test rig and had a listen, everything sounded OK. I will leave it playing for several hours for the capacitors to burn in and to make sure that no faults are developed during the operation.

The critical sound testing will follow, we will compare the sound of the modified 2200II to the performance of  a Parasound A21. Unfortunately a long time has passed since I listened to the 2200 so I can’t know for sure what effect all these mods have on the sound. However, me and Christos know that an unmodified Parasound HCA-3500 sounds inferior to the A21. Let’s see how the 2200II will do. Stay tuned!

Panos

Christos writing: After a week of letting the modified amp playing, everything looked fine so it was time for the listening test. Problem is that a lot of time has passed since we listen to this amp, so we could not remember well how it was performing before the modification. Still, there was a way for driving some safe conclusions. Let me give you some facts:

- The unmodified 2200II was playing better than the two NAD's.

- The unmodified 2200II was replaced by an unmodified A21. A21 was playing better than the 2200II.

- A used Parasound HCA-3500 was then added to the collection, but it turned out that the A21 is a much better performer. The 3500 had a "lazy" or "slow" low end and the mid / high end & sound stage were inferior compared to the A21.

The best track that highlighted the weakness of 3500 compared to A21 was Dire Straight Sultans of Swing from an 180g audiophile edition vinyl album. We decided to use the very same track in order to compare the performance of the modified HCA-2200II with the A21. So we let both amps warm up a bit and we proceeded with the listening test, trying to change the power amps as fast as we can. As always we took good care of listening to the same level. What we found was that the sound of the modified 2200II was equally pleasing with the sound of A21. We couldn't be certain if we could spot any difference. We were certain that nothing was missing or was disturbing in the sound of our modified 2200II. We are also certain that the modified 2200II is much much better than the unmodified 3500...

Now, even though the speakers we use are not an "easy load" - they are a 3 way, 5 SEAS speakers design - none of the amps found it hard to drive them. I am sure that one of the amp can do better in destroying the house and blowing the neighborhood, however for loud listening levels of civilized people none of the amps seemed to lack current. So, our judgement is somehow limited to sound quality and not sound quantity - but I repeat, none of the three amps lacks quantity and I am sure all of them are suitable of making you deaf.

Also, unfortunately we can't know how critical each step of the mod was. However, the 4 big capacitors cost 100 Euro and all the rest was under 20 Euro, so I see no reason why not to do at least all the rest - if we manage to measure the state of the big original capacitors we replaced I will make an update at this post. (UPDATE: As it turned out, there was no reason changing the big main capacitors; with the help of our tech guru we measured the old ones (he measured capacitance and equivalent series resistance), they were at top condition. So now we know, with just 20 Euro you can do miracles to the sound of this amp!)

Last but not least, even though you can get the same sound quality of the A21 with a moded 2200II, you can not get the construction quality that the A21 has, a quality that helps it stay in top shape even after years and years of use. I won't say much - only the fact that all the boards inside the A21 are at horizontal positioning so they won't "feel" the heat of the transistors is very helpful. Just have a look inside the A21:

Everything is in place inside the Parasound Halo A21. Nice and tidy!



So, that's all for now. Hopefully soon we will have a new post "Restoring and modifing a Parasound HCA-3500". Until then, happy listening!

Christos

P.S. If you liked this post, you will probably like most of this blog. Why not having a look at all the things we have wrote about here.