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Old 8th September 2004, 07:21 PM   #1
ainami is offline ainami  United States
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Default Sunfire Power Supply Capacitor

Hi,

I'm looking at ways to improve my Sunfire Cinema Grand. I see that the rectifiers are supplying a couple of odd size power supply capacitors. They are sized at 9300 uF and 150VDC (with a surge rating of 175 VDC).

Does anyone know if power supply really needs the 150 VDC? I know the power supply tracks the voltage for the amp rails, but 150 VDC seems really high. Will a 100 VDC cap work? Or is there a big risk of a spike over 100 VDC?

I can put 4 caps in there and series/parallel them, but it's getting really crowded.

Thoughts, anyone?
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Old 9th September 2004, 04:58 AM   #2
anatech is offline anatech  Canada
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Hi ainami,
Why not measure the voltage? One thing I know is that Carver designs may run close to the cap rating. In this case, the power is drawn from the caps via high frequency switching transistors. The amp is supplied with a voltage that is varied by the duty cycle from the switchers. These are called "down converters".
I don't think that performance will be improved in a normal sense. This is not a classic power supply. If you want to improve the performance, look at things after the supply. Pay attention to op amps, signal caps and bypass caps. Do not go nuts and oversize any capasitors.

Remember too, if you break it, send it to a Sunfire Warranty shop. Most other techs will break it more.
I was warranty for the Carver Lightstar product. The best sounding Carver amp I know of. Never listened to the Silver 7's.
-Chris
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Old 9th September 2004, 05:07 AM   #3
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Default Don't touch the power supply ...unless...

IMHO don't touch the power supply unless you know how it works.
Even the designers take a long time refining the supply. So if you have just figured out how it works , it is unlikely that you could better it easily.
Normal supplies can be improved because they are usually designed to a cost target . You can easily upgrade that.
Like Chris sugested. Try to look at other areas for improvement.
Your warranty will go out the window of course.
Cheers.
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Old 9th September 2004, 06:54 AM   #4
ainami is offline ainami  United States
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It looks like you were right about Sunfire's designs running close to the power rating of the cap. The idle voltage across each cap is about 87 volts. The voltage from the caps will drop to somewhere in the 70's under load. However, there are a pair of bridge rectifiers which are summed to supply the current to the caps and that voltage is 174!! Right at the surge limit of the cap!! Yow!!

My original thought was to replace these with a couple of Black Gate 10000uF/100VDC. I can see now that this is out of the question.

The drop in voltage across the caps under load would suggest that you are right in saying that the power is drawn from the caps via high frequency switching transistors. I could put a couple of 39,000uF/100VDC caps in series to simulate a single 19,500uF/200VDC cap. This would be well over the spec of 9300uF/175VDC.

Normally I wouldn't increase the size of any capacitor, but power supply caps are usually okay. Would you consider this idea safe for this power supply?

Since this is not a normal design for a power supply, do you think changing the rectifiers would improve anything? Or does the power supply design override any improvements to the DC supply?

I'm already changing out the signal capacitors. I'll look into the opamps, too.

-Aaron
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Old 9th September 2004, 11:14 AM   #5
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Default Time constants.........

The charge , discharge, times of the switched supply may be critical for proper operation of this circuit. Altering supply cap values might throw this out of gear.
Like I said , better to understand thoroughly how it works before making changes. It is not a regular power supply.
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Old 10th September 2004, 04:54 AM   #6
anatech is offline anatech  Canada
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Hi Aaron,
Do not play in any way with the supply or down converters. Besides, if you did change the main caps, you would never hear a difference. The supply is PW modulated and refiltered. DO NOT PLAY HERE.
Yelling over, sorry. Stay in the audio section. Watch very carefully for oscillation. We had to change some op amps to slower ones in the Lightstar series 1. Keep in mind that the circuit works and Bob Carver loves op amps. He really does.
-Chris
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Old 10th September 2004, 06:11 AM   #7
ainami is offline ainami  United States
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Hi Chris,

Alright, point taken. Stay off of the power supply. Actually, the PS main caps would have been the only thing I would have changed in the design. If you're saying that changing those wouldn't affect the sound at all, would I be correct in saying that changing the rectifiers wouldn't have an impact as well? I only ask because I've already ordered some, but I will definitely shelf them if I need to.

I do already have a set of Black Gate capacitors to replace everything in the Power Supply as well as the Audio boards (a lot!). My intention is not to change the design of the amp, but to replace the existing caps with Black Gates of the exact same value. If the power supply is that touchy, is this even recommended?

You're right about Bob loving his opamps. The audio boards are littered with them. Lots of TI TL072 and some TL081's. I'm not sure about replacing these as I'm not familiar with the opamps enough to know what to replace them with.

Actually, hearing your comments and reading other postings on the Sunfire amps, I'm not even sure this amp is worth spending time on. I've already modded an old Adcom Series II and it sounds better than this Sunfire now. The Sunfire, in comparison, doesn't sound as smooth and true as the Adcom now. Also, the sunfire doesn't have the impact. I'm wondering if this is a by-product of the power supply not being able to produce an increase in voltage fast enough for the signal. The Adcom really made my speakers sing (and I thought they weren't great speakers at all).

If I didn't mod this amp, I would probably sell it and buy a late B&K Reference 200.7, and then improve from that. I'm wondering if that's just a better platform. The speakers I'm planning will be extremely clean and will reveal flaws in the electronics.

Thoughts?
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Old 10th September 2004, 10:38 AM   #8
djk is offline djk
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Changing out opamps will make a good improvement for the money invested.

TLo72, 82 are duals, 71, 81 are singles.

I really like the sound of the OPA2604 (dual) and OPA604 (single).

Many people like the OPA2134 (dual) too, its about $1 cheaper.

Carver is stingy with supply bypass caps, plan on adding some with the OPA2134, it seems to be more sensitive to this (10F + 0.1F on both rails to ground).
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Old 10th September 2004, 09:37 PM   #9
ainami is offline ainami  United States
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So let me see if I'm understanding you right. I should connect each of the V+ and V- pins of the opamp to ground with two caps (10uf & .1uf in paralell)? That's four bypass caps per opamp, right?

The (+) lead of the caps should be connected to the V+ pin? The (+) lead of the second pair of caps should also be connected to the V- pin?
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Old 10th September 2004, 10:33 PM   #10
anatech is offline anatech  Canada
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Hi Aaron,
You are quite right. You will not hear any changes from the rectifiers, or power cords. You are also right about the op amp bypass caps. 4 caps per OPA2134. Approach this with caution. The op amp changes will change the sound a fair bit.
Having said that, there is a "sound" to Carver. And they are really tough to kill.
I'd like to make a comment here. I've found that a two channel sound system and a surround sound system are two different things. Mine are separate. As soon as the signal goes through a solid state switch or volume control, it's all over. Never mind the surround sound processor. Your Sunfire will do very well for surround.
-Chris
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