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Old 9th June 2009, 12:36 PM   #1
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Default Need help with SLA battery capacitor bank

Hi guys,

I am relatively new to electronics and was hoping for some of your advice please.

I'm running a couple of tripath amps from 12V SLA batteries and I've read that installing a bank of capacitors between the battery & amp is often worthwhile to help increase bass output.
I have 4x 10,000uF Nichicon electrolytics on-hand that I'd like to use for this purpose but I don't know how they should be soldered in properly.

In other words, I'm not sure if I should place them in series or parallel with the positive & negative power cables and I also need to make sure the orientation is correct given they're electrolytics.

If anyone can help me out I'd be much obliged, thanks guys.
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Old 9th June 2009, 12:51 PM   #2
gareth is offline gareth  Wales
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By the sounds of things you have a standard 12v battery with a positive and a negative terminal ? Is that right?

What the capacitors will do is, after a period of time they will charge themselves from the battery and act as a 'current pool' if you like for the current. The bigger the caps, the more current held but these caps, as they are DC will take a specific time to reach their maximum capacity.

Ideally you would need to know the maximum sort of current (or charge - Amps) that would be drawn.

Do these amplifiers need an earth?

If you could give some more detail please....

Gareth

P.S. Parallel is the way forward, maybe add a 0.1uF metal film capacitor in parallel with the Nichicon's too so the smaller caps help charge the big Nichi's quicker! So they are more responsive in their ability to put out the current. I have found that in some amps different brands of these small metal film types have slightly different sound charcteristics, at least to my ears anyway. I tend to use Wima or Vishay when I by-pass.
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Old 9th June 2009, 03:22 PM   #3
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Thanks for your help gareth, yes it's a standard 12V SLA battery with both positive & negative terminals.

The particular amp I was to set up the capacitor bank for is a 41hz AMP6 basic:
http://www.41hz.com/shop/item.asp?itemid=43&catid=


Does that help at all?
Thanks again for your assistance.
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Old 9th June 2009, 03:53 PM   #4
AndrewT is offline AndrewT  Scotland
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Batteries need some help to deliver transient current peaks.
The electrolytics will help with the slower delivery peaks.
Yes, they go in parallel across the battery terminals. Do research whether connecting them direct to the battery is safe for both battery and capacitors.

Small caps across the amplifier terminals will help deliver the faster current peaks. These are usually film type, but some use ceramic here to help with high speed decoupling.
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Old 12th June 2009, 04:50 AM   #5
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Quote:
Originally posted by AndrewT
Batteries need some help to deliver transient current peaks.
The electrolytics will help with the slower delivery peaks.
Yes, they go in parallel across the battery terminals. Do research whether connecting them direct to the battery is safe for both battery and capacitors.

Small caps across the amplifier terminals will help deliver the faster current peaks. These are usually film type, but some use ceramic here to help with high speed decoupling.

Cheers for your help AndrewT.

Just one further question please- when placing electrolytics in parallel with the battery's terminals should the caps be oriented with the terminals, eg. postive of the cap with positive of the battery?

Regarding placing small caps across the amp's terminals I now recall that the original sonic impact t-amp I once owned used this method with a pair of 0.1uF poly caps. I couldn't figure out at the time what the purpose of these caps was so thanks for solving that mystery for me!
I have a number of Russian 0.1uF teflon caps lying around so I'll try those across the AMP6's outputs and study the results.

Thanks again.
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Old 12th June 2009, 09:05 AM   #6
gareth is offline gareth  Wales
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Yes, the positive side of the cap goes to the positive of the battery, and negative to negative, negative having a stripe down it's side on the cap.

I sommetimes when running from batteries place a small film type cap (0.22uf) before the main, in this case Nichicon, cap and directly connect the by-pass cap on the underside, direct to the terminals of your main Nichicon.

That's my way, others may choose different. I find it works fine though.

Gareth

P.S. Nice looking piece of kit you have bought, I am working on something similar myself. I hope you enjoy.
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Old 12th June 2009, 02:06 PM   #7
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Quote:
Originally posted by gareth
Yes, the positive side of the cap goes to the positive of the battery, and negative to negative, negative having a stripe down it's side on the cap.

I sommetimes when running from batteries place a small film type cap (0.22uf) before the main, in this case Nichicon, cap and directly connect the by-pass cap on the underside, direct to the terminals of your main Nichicon.

That's my way, others may choose different. I find it works fine though.

Gareth

P.S. Nice looking piece of kit you have bought, I am working on something similar myself. I hope you enjoy.

Many thanks Gareth, I will try placing one of the Nichicons across the battery's terminals later tonight and see if I notice any improvement.

The 41hz AMP6 I'm modding is already a spectacular little amp, especially for the money. I've owned a couple of Tripath amps and this is hands down the best one I've heard yet.

I only started teaching myself electronics last year, so when my knowledge has improved enough I'll consider building a 41hz Truepath, which looks to be the "mother-of-all" Tripath amps and supposedly sounds excellent.
Of course for that kind of money one could probably build a very nice tube amp, but it would be very interesting to hear just how 'high-end' a good Tripath amp can sound I reckon.
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Old 19th June 2009, 09:16 AM   #8
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I've finished building the capacitor bank using 4x 10,000uF Nichicons, each one bypassed with a 0.1uF Russian teflon cap. (not sure if these actually help but I had them sitting around so I figured they can't hurt)

The improvement was immediately noticable, much more "flow" to the music, tighter bass and a slightly improved soundstage. Overall things sound less forced and more effortless - I've been very impressed!

I have one more question though, is there a limit to how much capacitance I should use?
I could easily add another 6x 10,000uF caps for example if I thought it would help but I'm guessing there is a point where diminishing returns start to kick in.
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Old 19th June 2009, 10:06 AM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
the big caps will tend to help the bass response and bass power.
But, there is a limit.
This limit is very dependent on the time constants incorporated into the amplifier and it's input filter.
Generally, I use +-20mF for 8ohm speakers, +-45mF (= six * 15000uF) for 4ohm speakers and +-75mF for ClassA, with ~90ms RC time constant for the input filter.

Describe precisely where and how you have fitted the Teflon bypass caps.
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Old 20th June 2009, 08:35 AM   #10
Gopher is offline Gopher  United Kingdom
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I'd be interested in views on how a battery and caps compares to standard transformer, diode bridge and caps.

In my opinion, the main reason for using a battery as the feed for the cap bank rather than a transformer and bridge is that you don't have RF switching noise from the bridge which extends to several MHz which any subsequent regs are unable to stop. This will then feed through to sensitive audio circuitry which has equally poor PSRR at RF frequencies, causing intermodulation distortion.
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