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Old 10th February 2013, 11:04 PM   #181
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Default output caps

Thanks so much for the info on output caps for protection of speakers. Could you explain to me why it's OK to use polarized caps? I know that it is OK, as the Dyna ST120 that I'm using as a donor chassis has 3300u polarized output caps, but I want to understand why they don't need to be non-polarized. (though I'm certainly glad they don't need to be. Much cheaper this way.) And do they need to have smaller non-polarized caps in parallel with them for high frequencies?

Many thanks,
Keith
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Old 11th February 2013, 04:45 AM   #182
JMFahey is online now JMFahey  Argentina
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Unless I'm mistaken your Dyna 120 is single supply, so Polarized caps are fine.
Too sleepy to search for that schematic now.
Now, if you build a split supply amp, they are not needed.
And if for any reason you happen to put them in series with the speaker, they'll have to be NP or Bipolar .
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Old 11th February 2013, 05:05 PM   #183
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Quote:
Originally Posted by Keith Cary View Post
Thanks so much for the info on output caps for protection of speakers. Could you explain to me why it's OK to use polarized caps? I know that it is OK, as the Dyna ST120 that I'm using as a donor chassis has 3300u polarized output caps, but I want to understand why they don't need to be non-polarized. (though I'm certainly glad they don't need to be. Much cheaper this way.) And do they need to have smaller non-polarized caps in parallel with them for high frequencies? Many thanks, Keith
A reasonably decent quality parallel pair of 3300u or parallel trio of 2200u does not need an additional treble bypass cap because you already have parallel caps. However, it is okay to add an additional treble bypass cap. Nichicon ES 10u, 4.7u is an example of an excellent performer for this use.

It is extremely popular for maximizing subwoofer amplifiers, due to the easily tunable bass that can thunder instead of boom. No amount of brute force with an equalizer is as effective as harmonic tuning. Works fine with full range amplifiers too. So, there is fun aspect to it.

Blocking subharmonic that the speaker wouldn't reproduce is helpful to both headroom and durability. If the polar cap successfully protects the amp then it also protects itself.

Necessarily, if the model of cap used can survive a bridge rectifier, it should be able to survive speaker output too (especially considering little 25 watt amplifier chips). Likewise, if a cap can't survive being used as an output cap then that model cap is totally unsuitable for use at a power board. Check capacitor datasheet for more complete information. When the amplifier is healthy, there's no DC offset anyway.

However, if the amplifier were to eventually wear out and break, it may be able to damage polar caps, but they do still cost less than speakers. I'll say bipolar caps are preferred.

Optionally, at slightly more cost, you can create a bipolar cap array using multiple polar caps in parallel-series. That prospect is what we'd do for enhancing the durability of output caps if used for a larger size split rail amplifier.

To do the high durability approach with polar caps costs about $8 per speaker, which is quite favorable for costing less than speakers. The 35v caps are quite compact and inexpensive.
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Last edited by danielwritesbac; 11th February 2013 at 05:08 PM.
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Old 21st February 2013, 05:41 AM   #184
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Default High end sound and sturdy too, for about $3 more.

I wonder if the discussion of speaker protectors might make the more durable Parallel LM1875 look a lot more attractive?

The Parallel LM1875 amplifiers are more laid back due to sending crossover noise into ballast, not speakers. This "makes room" or tolerance for so easily using a NFB-shunt cap (prevents amplification of DC, gives more durability and is more dynamic) while also maintaining a level harmonic response. It won't sound like a typical chip amp. These parallel amplifiers imitate the tone of a rather expensive discrete amp, but also maintain the high resolution of the LM1875 chip. Of course, the Parallel handles more current, without breaking down; so, the parallel is lower risk than the solo.

As with the solo LM1875, again Monoblocs are preferred, not only for wider sound but also to be able to Choose the chip's access to current. Parallel LM1875 simplifies the protection issues when you provide chip current handling tolerance higher than transformer current capacity.
Suggestion: LM1875 monoblocs, not more than 1a worth of transformer per chip or LM1875 stereo, not more than 0.5a worth of transformer per chip. SO, Parallel LM1875 monobloc can use a 2a transformer per each monobloc, and that will sound good. Sort of like this 72va*0.6=43W, which is a bit less than the 50W tolerance of a Parallel LM1875. And, we need that "bit less" for protection. You'll still get your 50 watts on bass peaks from the power supply reservoir/tank section. SO, it will have protection, not shyness.

Also helpful, a center tap style bridge rectifier (conveniently elegant with a pair of Fairchild Stealth Dual) and a CRC power supply, which is a system that flexes a bit (protection) and also runs cleaner (decreased power noise = decreased amplifier workload). We should also consider KeanToken's variable RC from "~" to "~" of the bridge rectifier, snubbing the transformer for much cleaner power. You just turn the dial for whatever is most appreciable for higher resolution audio. That works well with our theme of high end audio done easily. When and if non-audio workload is decreased, then we have proportionately increased capacity for audio power. And, you'll like that.

An interesting prospect for a Parallel LM1875 is to have the pair of low loss 220u power caps in-between the chips so that they both share it. Likewise, it is interesting to use only 1 input cap, only 1 nfb-shunt cap, because there's no need to create differences. Then all of the resistors are arranged as standard 2-resistor mixers. So, they share all of the caps, not the resistors.

Similar to Ashok's stereo board, it is probable that the parallel amp could use 100u||100u (creates a high end, low loss 200u) per each rail at the power circuit for an easier job with capacitor selection.

I would love to see what Ashok would do with a "share all of the caps (evenly) and none of the resistors" Parallel LM1875 monobloc. Possibly, input load resistor can be shared because there's only one input anyway. To maintain the 2 resistor mixer structure, we probably need to add ~470R (input stopper) series to the IN+ pin of both chips.
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Last edited by danielwritesbac; 21st February 2013 at 05:50 AM.
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Old 21st February 2013, 06:29 AM   #185
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Default Speaker protection

Many thanks for both of these last posts. I ordered my caps today. And I think the next amp I build, after I build these two, will be parallel 1875.
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Old 21st February 2013, 12:31 PM   #186
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My board cannot take parallel chips. First of all it isn't a very well designed board. It was done in a hurry and there is plenty of scope to improve on it.
I tried some experiments with it and shall post on that later.

Pity I cannot find the board layout. It might be on my 'dead' computer. One hard drive died and the other is still on it. Will have to pull it out to see if it is still there on the good drive. No time for all that now. Too busy.

I'll take some pics of both sides of the board and post that.
Cheers.
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Old 21st February 2013, 12:46 PM   #187
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Default Applied, in comparison to 1969 JLH amplifier. . .

Speaker protection? Well, that's actually just a good excuse for really rockin your house. Audio Engineers like to say "define the audio band" and that works wonderfully if we do it thoroughly. To me, "define the audio band" means, remove all non-audio workload. For small scale amplifiers, I think that driving a speaker efficiently is worthy of consideration, such as. . .

Compare the New 15W JLH amplifier from 1996 versus the really rockin 10W Classic JLH amplifier from 1969. The new edition did better with a scope but the classic edition did better with a speaker. The Classic has an audio-only workload and progressive current drive bass extension. This difference in output is the output cap, and the Classic has had 44 years of successfully driving speakers. Just 3db more of desired signal is similar to doubling the amplifier power, which is approximately how 15 watts of New booming failed to compete with the Classic's 10 watts of deep, clear, high resolution bass.

Likewise, when adding the output caps to LM1875, I noticed when I cranked up the bass boost on my computer. . . instead of a lot of booming, I got a lot of thunder and what seems to be a lot more audio power, but it really was a lot less non-audio workload in combination with a lovely bit of bass extension.

See also Bob Cordell's website on the topic of bass extension. His method looks elegant indeed, but I think that my methods are more efficient for power and easier to build. Or you can use both for nightclub force. Anyway, it is probably necessary to read about Bob Cordell's speaker port tuning. CordellAudio.com - The Athena Active Loudspeaker
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Old 21st February 2013, 03:00 PM   #188
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Quote:
Originally Posted by ashok View Post
Pity I cannot find the board layout. It might be on my 'dead' computer. . . . I'll take some pics of both sides of the board and post that.
It would be great to see the pictures. Thanks!
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Old 21st February 2013, 04:24 PM   #189
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@danielwritesbac, my request is to make complete system. How do advice to use this amp with active system or passive system.
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Old 22nd February 2013, 08:58 AM   #190
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Both is good. You can make the amp to suit the speakers. However, passive crossovers are valid.
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