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Old 31st December 2005, 06:38 PM   #1
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Question Hafler pwr supply caps

I've got a few questions regarding the power supply caps that my amps use and how I can/should mod these.

1st let me tell you what I've got and how I use them.

2 hafler pro500's (lot like the dh500 but with ball inputs and vol control)
2 P225's
1 DH200
1 Pro2400 (whole diff animal)

I run these amps in a 4 way amped home system with active crossovers. The 500's are running the lows/mids and the smaller haflers are for the horns/tweets.

My questions:

1) I picked up some Sangamo 42kuf/90VDC caps awile back (from soundvalves) to use in my 500's, but at the time I didn't reilaize the orignal caps are 100VDC. Can I use these even though they have a 10v less ratting? Or is it unsafe to do so?
I've attached a picture of the caps.

2) Since my smaller Haflers are not used for low freq is it unnessessary to beef up the pwr supply caps in these? My understanding is that this mod improves bass responce only.

PS: I've read all the threads on modding these amps will be implementing what I can understand. Awsome info in this place!
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File Type: jpg sangamo caps.jpg (95.7 KB, 535 views)
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Old 31st December 2005, 09:05 PM   #2
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Hi maxwedge,

You need to measure the operating voltage rails on your 500's. I am not familiar with these but I doubt the rails would be even as high as 90V.

A manufacturer usually uses capacitors of rating at least 10% higher than operating voltage with the nominal mains supply.
This is to allow for the vagaries of mains supply. So an 82V supply will be safe with 90V OR GREATER capacitors. This may be the case with Hafler 500 but the availablity was 100V rated parts.

For mid-top amps I would favour multiple paralleled smaller C's or the existing ones heavily bypassed with , say, 100uF, 1uF, 100nF, a progression of smaller types - all of equal or greater V rating.

You should not increase the rated C of the amp substantially unless you know the bridges and fuses can cope with the increased switch on surge.

Having said all that, there may be ways within the amp topology to improve the PSRR of the amp proper, and desensitize the sound to power supply artefacts. This is a more elegant approach with potential for a much bigger result but requiring design talent.

Hope that helps.

Cheers,
Greg
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Old 31st December 2005, 10:33 PM   #3
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We are crazy, Greg... Instead keepinng bottle of wine and holding of our wife's back side ( ), we are talking about some funny devices... Happy New Year to all, my friends...
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Old 1st January 2006, 02:32 AM   #4
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Thanks for the info Greg.

I'll get my dvom out see what the real voltages are at the rails and if it's under 90v then I guess these larger caps will be ok.

Yeah I'm 100% aware of the need for bypass caps, and all off these amps have none., so I'll add those at the same time.
The smaller amps have 10000uf/75v pwr caps.

I'm not an electrial tech so I pretty much need to look at some sort of guide or detailed information and I'll probably invest in some musical concept kits down the road.

Thanks again and happy new year all,
Scott

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Old 2nd January 2006, 12:20 PM   #5
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A Hafler DH500 has 93V rails, 100V is barely adequate.

The DH200 has a 10F electrolytic input cap, and an electrolytic feedback cap. Bypass with 0.1F film types and add 47F 100F power supply bypass caps.

Early 500s were the same as above, later they had 2.2F film input caps and 0.1F film bypass on the 470F feedback cap. They need supply bypass caps, I recommend 47F at 160V.

The amps will sound better in the bass with the power supply bypass caps, but nowhere as 'tight' as a BJT amplifier. If you go much above 30,000F on the main filters the rectifier will blow.

I used to have many of the DH200/220/500 series with extensive mods. I ended up with BJT amps for low end. A friend still uses my 25 year old modified DH500s for mids and highs in his tri-amp PA.
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Old 3rd January 2006, 07:21 AM   #6
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Quote:
Originally posted by djk
A Hafler DH500 has 93V rails, 100V is barely adequate.

The DH200 has a 10F electrolytic input cap, and an electrolytic feedback cap. Bypass with 0.1F film types and add 47F 100F power supply bypass caps.

Early 500s were the same as above, later they had 2.2F film input caps and 0.1F film bypass on the 470F feedback cap. They need supply bypass caps, I recommend 47F at 160V.

The amps will sound better in the bass with the power supply bypass caps, but nowhere as 'tight' as a BJT amplifier. If you go much above 30,000F on the main filters the rectifier will blow.

I used to have many of the DH200/220/500 series with extensive mods. I ended up with BJT amps for low end. A friend still uses my 25 year old modified DH500s for mids and highs in his tri-amp PA.
Thanks djk, I've read a lot of your posts with great interest.
I guess I won't be using those Sangamo's on the 500's.

I've looked in the amps and all the input caps are 2mfd 50v film (as are the spec sheets I have say). The original owner of the DH200 added these in place of the electrolytic ones. Looks like these should stay. They have no by pass caps though.....Is this where the .1uf film cap should go? In parallel?

I'm not sure which one is the feedback cap but looking at the schematic for the 220, C8 is the only one with a 470mfd cap. Is that the one? And bypass that with the .1uf film again?

Thanks again.
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Old 4th January 2006, 08:33 AM   #7
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Here is a generic amp schematic.

http://sound.westhost.com/p72-f1.gif

C1 is the input cap, C3 is the feedback cap, C7, C8 are power supply bypass caps.

C1 and C3 are the ones needing 0.1F film bypass caps added (ones with the 2.2F film for C1 don't need a bypass). C7 and C8 don't exist on a Hafler, they need to be added.

If you want to add C5 and C6, be very careful, it is easy to get oscillations here. I usually don't add these. If I do I use something around 0.33F~1F and add a 0.5 ohm resistor in series. If you don't use the resistor it will probably oscillate.
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Old 5th January 2006, 03:39 AM   #8
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Hi djk.

I've atached a picture of the schematic for my P500 driver driver board. It's a 19c like the 220's and others use. To me it looks like the feedback cap, in this schematic, is C2. Can you confirm? This cap is a 330 pF film, fyi.

I was looking over instructions for Musical Concepts PA3C board, and for the pwr supply caps they say to bypass them with a 2.0mfd film cap and a 6800 2 watt resistor. What do you think of that resistor being there?

Quote:
Originally posted by djk
If you want to add C5 and C6, be very careful, it is easy to get oscillations here. I usually don't add these. If I do I use something around 0.33F~1F and add a 0.5 ohm resistor in series. If you don't use the resistor it will probably oscillate.
I don't need to get into that. I'll do the easy stuff 1st.

Thanks again,
Scott
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Old 5th January 2006, 10:26 AM   #9
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C2 is the RFI filter.

The PC19 input cap (C1) is already a film type, and the feedback cap (C8) already has a bypass (C7).

Just add some 47F across the main filters (C404, 405) and that will help. I replace the single strand of 16ga wire that serves as a ground buss between C404, 405 with a 3/8" wide copper strap.
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Old 5th January 2006, 07:43 PM   #10
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Maxwedge,

There is some confusion between posts on this thread. You have a DH-220 or DH-500, they both use the same PCB and schematic.

The early DH-200 was a threadbare design and the addition of better and a few additional passive parts helped its sound a lot. Basically, all electrolytics on the DH-200 should have bypass film caps added and many replaced C1 with a 5mF polpropylene film cap. The Dh-220 came out and incorporated into its manufactured design most of the mods published for its earlier sister, the DH-200. There is very little you can do to the DH-220 or DH-500 as they already are about as good as they can get. DJK mentioned using a larger guage wire between the two P/S which is also the system's "star" ground. After that, some improvements in the large P/S caps might help, either larger uF caps or caps that use newer technology.

Musical concepts adds the film cap to help bypass high frequency "junk" which is a common practice for many amps. MC also uses a 6800 ohom resistor to bypass each P/S electrolytic. This is a safety feature to ensure that these large caps do eventually get completely discharged before somebody's hands get in there and get a lethal shock! Also, a large cap is like a battery and it will peform better over time if completely discharged when the amp is shut down and not left to linger with a small amount of charge. Electron distribution is enhanced if the cap is completely discharged when turned off. Again, this is fairly common practice followed on some of the better amps. The bypass resistor is a safety feature and helps with the health of the capacitor and has no immediate sonic effect. MC is correct in its features.

There is little you can do to your Hafler amps except perhaps get some newer P/S caps. Relax and enjoy them.
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