Hafler P500

H

Huck1969

Member
Hello all. Quick question. I recently picked up a nice condition
P500 which I understand is the pro version of the DH500. I have it
driving Epicure 400+ which are of average efficiency (89 db) and an
easy 8 ohm load. I've been using it at a fairly low level for the
month I've had it. Today though, the wife and children were out so I
decided to crank it a bit. I drove it fairly hard, but not as hard as
I've driven my Adcom's and SAE amps. It sounded fine but I was
surprised to notice the red 'clipping' light blinking during heavy bass
sections. I assummed that the amp should sound distorted as it clips,
but it sounded fine. I'm not sure where to get a manual to confirm
the true indication of that light blinking so I thought I'd ask. Is it
really clipping or is it normal to see this light blinking
occasionally? I of course reduced the output immediately and it
contined to sound and work fine. I am a little dissapointed that if
it is really clipping it was far sooner then I expected.
 
Do the others have clip indicators?

The others may not be as tightly regulated as the P500. Perhaps the P500 lights at .1% while the others are 1 or 3%?

My ABI never indicated clipping until I put it on EQ'd subwoofer duty.

Do you have an SPL meter?
 
No I don't have a SPL meter. Right after that I drove tha Adcoms and SAE much harder then the Hafler. The Adcoms (GFA 555) have a 'instantaneous distortion alert' light which I've never seen lit. So if the amp sounds fine with not distortion should I worry about it?
 
The only other thing I can think of is that the P500 was dialed down so that the input was being overdriven. Not sure.

Perhaps it needs a checkup? Do you have the SM / a meter with which to check bias / offset thingies? I had a Hafler for a short time and it sounded 'strange'. The manual contained a bit of tech info and I checked some values, they were off the recommended mark, and dialing a few pots per the instructions improved things AFA measurements were concerned.

I was never really happy with the sound. That was a 9180.
 
I've got a P500 and like after I upgraded the filter caps and the driver boards with Musical Concepts retrofit kits. BTW, that's me, Doodlebug, posting in the Lansing Heritage link from Clmrt. I've had experience with Hafler gear since the 80s but found that the driver boards are a weak link compared to what John Hillig at MC has done with them.

To your problem:

The clip indicators are part of the input board which is also the balanced-to-unbalanced converter. There were a couple of versions of this board. Each of them have comparitor circuits to determine when the clip indicators kick in. These are, in turn, set by an adjustment on the board.

If one is kicking in before the other, then this _might_ be the problem. If both are kicking in at the same time, then I'd doubt there is a problem with level adjustments but it _could_ be an indication of the voltage regulation on the input board.

Otherwise, you'll need some load resistors, and a setup to determine actual max power output vs input levels to confirm that the clip indicators are, indeed, correct or not.

One other question, there are various ways to wire these amps up; what are you using? Reason I ask is that there are a couple of connectors on the same board that bypass the balanced input converters and have the amp run in unbalanced mode only. Also, the stereo/mono switch below the fan output on the back - it gets dirty and needs to be cleaned and reseated to the stereo position.

I have the P500 service manual that the Hafler folks kindly provided before they were closed down - it was never posted on the web site. They are quite large scans so I can't post. Contact offline if you'd like them.

Cheers,

David
 
Both channels light at the same time...
I'm using some Rat Shack 1/4 to RCA converters for the input side.

I'll send you a PM regarding the manual.

Thanks!
 
I just brought home a P500 today and had the same sort of problem, the right channel wasn't getting a good signal and was clipping where the left channel wasn't. I could have the gain all the way to the right and the left gain pointed at somewhere between 6 & 9 before they both clipped at the same time.

After checking connections and cables then pondering the lack of right signal, I played around wiggling the preamp balance control. At first I realized no difference but once I had the knob cranked all the way right, the right channel essentially burst to life and all seemed well and the entire system gained volume.

Not sure just what this means although after reading this thread I am getting a better idea which direction to head. At first I thought it was poor speaker connection because the banana jacks fit quite loosely but after playing around with the balance this proved to not be the problem
 
goodolpg said:
You might try cleaning the balance control with Deoxit....
Click to expand...
Is that just your basic electrical connection cleaner? And how do I clean it, just open the top and spray the outside of the control or so I need to get inside the control? Never did this before, thanks
 
JB1962 said:
Is that just your basic electrical connection cleaner? And how do I clean it, just open the top and spray the outside of the control or so I need to get inside the control? Never did this before, thanks
Click to expand...
If you read just the first page of this thread it will give you the kind of info needed. There are other electrical cleaners. Deoxit is known to work well and is preferred by many AK'ers.
https://audiokarma.org/forums/index.php?threads/the-idiots-guide-to-using-deoxit-revisited.207005/
You may need to follow the cleaning with a lubricant. There are many types of Deoxit. It is important to use the right one.

You need to get the cleaner inside the control. Simply spraying the outside rarely does any good. Fluid has to reach the parts that are corroded/crusty/etc
Look for any openings. For example, with this control you can see an opening in back of the brown wafer with the 3 contact points.
images






Sometimes there is a small slit where the contacts come out of the control that you can spray using a small tube tube usually included with the can. Deoxit also comes in small bottles with a needle type dispenser
upload_2021-10-24_20-43-30.jpeg
 
dshoaf said:
I've got a P500 and like after I upgraded the filter caps and the driver boards with Musical Concepts retrofit kits. BTW, that's me, Doodlebug, posting in the Lansing Heritage link from Clmrt. I've had experience with Hafler gear since the 80s but found that the driver boards are a weak link compared to what John Hillig at MC has done with them.

To your problem:

The clip indicators are part of the input board which is also the balanced-to-unbalanced converter. There were a couple of versions of this board. Each of them have comparitor circuits to determine when the clip indicators kick in. These are, in turn, set by an adjustment on the board.

If one is kicking in before the other, then this _might_ be the problem. If both are kicking in at the same time, then I'd doubt there is a problem with level adjustments but it _could_ be an indication of the voltage regulation on the input board.

Otherwise, you'll need some load resistors, and a setup to determine actual max power output vs input levels to confirm that the clip indicators are, indeed, correct or not.

One other question, there are various ways to wire these amps up; what are you using? Reason I ask is that there are a couple of connectors on the same board that bypass the balanced input converters and have the amp run in unbalanced mode only. Also, the stereo/mono switch below the fan output on the back - it gets dirty and needs to be cleaned and reseated to the stereo position.

I have the P500 service manual that the Hafler folks kindly provided before they were closed down - it was never posted on the web site. They are quite large scans so I can't post. Contact offline if you'd like them.

Cheers,

David
Click to expand...
The preamp is a 110, I currently have a Marantz PDM-370 CD changer, a Fisher Studio Standard FM-2121 tuner, and a Realistic LAB-440 TT (of which all I get is hum, it is grounded to the preamp ground on the chassis next to the phono input) hooked up to the preamp. So far have used a set of home built speakers consisting of Eminence and Dayton drivers and what is now wired up, a set of Performance Series Paradigm Titans
 
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