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Capacitor change in preamp


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7 replies to this topic

#1 of 8 OFFLINE   Yogi

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Posted May 02 2003 - 04:18 AM

I am going to replace the output capacitors in my ASL 2004DT preamp with auricaps. I have never done something like this. So are there any special skills I need to acquire before I embark on this endevour? Any special tools apart from a saudering iron some silver solder? I am thinking its a plain pull out the old cap and put the new one in and solder away. I did some soldering about 15 yrs back but it was simple soldering of wires. So please advice me if there is anything else that I should know about. Also what kind of improvement should I hope to see with this change? Any advice to this novice would be greatly appreciated.
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#2 of 8 OFFLINE   GaryBo

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Posted May 02 2003 - 05:06 AM

Hi Yogi,

Cap rolling is just as fun as tube rolling IMO. Auricaps and Hovlands sound accurate and "hifi-ish", foil/paper/oil sounds a little smoother on the top end, and teflon (there are some cheap Russian teflon caps on the market now that look interesting though I havn't tried them) is also popular. Results will be dependant on the architecture of your preamp though, although to make a generalization the less you have in the signal path (and some would also say the B+), the more difference individual discreets will make.

The best advice I can give is to use a new (freshly tinned) bit on your iron if you havn't used it for a while, keep the cap leads as short as possible, clip a heat sink on the lead between the solder point and the cap body (to minimize the chance of frying an expensive part), and watch the polarity on the cap when you install them.

I have tried many caps in my Bottlehead preamp (my current favorite - great bang for the buck), and I am pretty happy with Hovlands. I know others who have used Auricaps and they are happy with those also.
Best,

Gary.

#3 of 8 OFFLINE   GaryBo

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Posted May 02 2003 - 05:24 AM

Oh yeah - safety stuff.

Some caps can hold a charge (something like a battery), so discharge the ones you are removing by shorting the cap leads with a 1 meg resistor held with something non-conductive. This is a good practice to get into, some power caps can hold a hefty jolt if not discharged in this way.

When you have soldered the new caps in place, pull continuity on the joints with a voltmeter (on the setting that beeps when you touch the probe leads together). This is important, because just because the joint looks good doesn't mean that it is good.

Perhaps you should practice soldering a few connections before you tackle the caps.

Best,

Gary.

#4 of 8 OFFLINE   Michael R Price

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Posted May 02 2003 - 10:30 AM

Yogi,

It can't hurt to put in better caps. Also, if your amplifier has DC blocking caps on the input you can remove them.

#5 of 8 OFFLINE   Yogi

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Posted May 03 2003 - 04:29 AM

Thanks guys for all your suggestions. Last night I changed the two output caps from Multicaps to Auricaps. I also changed two DC blocking Benning caps with Auricaps of same rating and two other Benning caps in the signal path with Auricaps. Took me two hours to do it mainly because of the inaccesability of the PCB (had to dissassmble almost everything). In any case changed everything and soldered them with silver solder. Hooked it to my system and fired the preamp. Initial findings are that the mid-range now seems a little more juicier with a little more body. The top end also seems slightly smoother. The bass is the same with either caps. Cant really comment on the soundstage or the image specificity. I am already loving the new sound. Currently breaking it in for the next 24 hours. Do caps require a break in? or is that unnecessary?

Thanks again guys for your suggestions. Love this DIY businessPosted Image
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#6 of 8 OFFLINE   Allen Ross

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Posted May 03 2003 - 06:24 AM

i never knew that caps could affect the sound of a preamp that much, i can see where you would notice in XOs but i guess you will notice it.

Also have you measured the drop in voltage in the caps when you are putting it through its paces? because if you notice a big drop then you could think of adding some joules to that puppy, my friend is doing this to his fideck. he us using an external capicitor ban. it should be pretty sweet once he gets around to it
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#7 of 8 OFFLINE   Michael R Price

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Posted May 03 2003 - 07:52 AM

Allen, Yogi's changed the capacitors in the signal path, not the power supply. Adding more power supply capacitance could help, but in a preamp it's a better idea to modify/upgrade the regulators.

Yogi, nice work. You could try removing the output caps entirely, if there is not much DC there or your amplifier has an input cap. Or, remove the amplifier input cap. Then you can move on to things like changing opamps. Posted Image

#8 of 8 OFFLINE   Neil Joseph

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Posted May 03 2003 - 04:47 PM

If these are the laregr caps, make sure not to install backwards either and just don't let the iron sit on a lead for too long causing the cap to heat up.
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