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valleyman 24th February 2008 04:49 AM

Active ZD5s

I am considering building a pair speakers based around Zaph's ZD5 design. I was hoping to put together a gainclone amp to drive them, but am now wondering if making them actively driven might be a neater solution.
These speakers are not the most sensitive in the world (I believe around 83dB) so I was thinking I could go with one audiosector LM4780 kit per speaker run in paralell.
Remote controlled volume is an absolute necessity for me so I thought I could buy a nice preamp to go with them (possibly a tube pre)which has a remote control.

I would then put one 4780 amp and psu board into the base of each speaker along with a transformer such as this:
which supplies 2x25V with a power rating of 225VA.

Does anyone have any comments as to the suitability of this setup. I would like some feedback from a more experienced DIYer before I buy anything and I also have a couple of other questions.
Do you think I might be better off with a 2x18V transformer?
Also I'm not sure how effective these chips are run in paralell. I never really listen to music very loud, always low to moderate volumes, so might I be better going with an LM3886 kit (maybe from chipamp) instead of the paralelled LM4780.
Can anyone recommend a suitable preamp? I'd be happy to pick one up second hand and willing to pay around 100-150 ($200-300).

Many thanks


zdr 24th February 2008 05:18 AM

I was about to try the same thing. I already have ZD5s built, but I wanted to see how they would perform with active linkwitz-riley crossover. I would definitely take a look at Linkwitz's Plutos as a reference design for active xover/equilizer/amp. They are still using 22v at secondary, 50VA, single 3886 for tweeter, two bridged 3886 for woofer. Actually, I am finishing a pair just now.

valleyman 24th February 2008 09:23 AM

Thanks zdr, thats certainly something to look at.

The pluto xo/eq/amp is designed specifically for those speakers, however, and unfortunately I do not have the ability to modify it for the ZD5.

If you would like to share your modifications with me I might well be interested, but also I would like to keep the project simpler than that.

One other thing I note is that the pluto uses bridged chips for the woofer. I think I would rather use a paralell config as stated before as it might be easier on the chips. Feel free to correct me if I'm wrong here

I should probably also have been clearer in my first post about the transformer. I see the recommended voltage is 22v at secondary, but I can't find any 22v for sale, only 18v or 25v. I suppose I could always try to unwind a 25v down to 22v but if I would be fine just using 18 or 25 that would be easier. If I'm not mistaken, using an LM4780 in paralell gives around 100W which would be more than enough for me even driving such insensitive speakers. I think then using an 18v transformer might be sufficient albeit with slightly reduced power output, but on the plus side the chips would run cooler and I would feel slightly better about that.

Finally, as I said before, any suggestions on the pre?

valleyman 24th February 2008 11:47 AM

With regards to the pre, I have come across something.

The only source I use is an HTPC via an M-Audio Delta 2496 card which has line level RCA outputs.

I came across this site:

I believe a Remote1 kit + alps motorpot would give me the required remote volume control for relatively little money.

A very nice consequence of using this is that everything would be built into the speakers. 2 rca cables run from the HTPC into 1 speaker, through the remote control pot, then one channel to the chip amp onto the xo and drivers in that speaker, the other channel to an RCA out on the back run via an RCA cable to the other speaker, through it's chip amp and then to it's xo and drivers.

Can anyone suggest a reason why this is not a viable solution? It looks good to me.

Many thanks in advance

zdr 24th February 2008 12:50 PM

I haven't done any modifications for Pluto design, I was trying to say that maybe we should learn primarily from power amp section. For xover, I plan to use Elliott's (ESP) linkwitz-riley PCBs, equalization is 3rd part of the story. Bare in mind that you need a lot less power in toroids if the xover is active and before the amp, as there will be no losses in passive xo. Pluto's are using only 50VA toroids per channel, and reports say they can play loud. Detailed article here:

I am having second thoughts about parallel 4780 config if I need to run primarily 8 ohm drivers.

valleyman 24th February 2008 02:00 PM

I'm very wary of abandoning Zaph's xo. He clearly put a lot of time and effort aswell as his not inconsiderable experience into getting it right. While I suppose a well executed active xo could do a very good job here, I certainly do not have the knowledge or experience to implement it. On the other hand, I suppose theres no harm in giving it a go (aside from maybe a few pieces of silver) and I'll never learn anything unless I'm willing to spend on potential failures.

Elliott's XO does look decent though so maybe I would give it a try, but I think I'd want to have the passive xo Zaph designed too so I could compare the two

valleyman 24th February 2008 02:49 PM

Also I take your point about using them paralelled with an 8Ohm load. I can't find any data on how these chips would fare with an effective 16Ohm impedance, but I could easily go with an LM3886 chip instead which the datasheet shows would provide around 60W into 8Ohms using a 25V transformer - easily enough for my requirements.
Not really sure why I thought of going with 4870 in the first place, 3886 will probably just work out easier and cheaper.

danielwritesbac 24th February 2008 06:16 PM


Originally posted by valleyman
. . . Not really sure why I thought of going with 4870 in the first place, 3886 will probably just work out easier and cheaper.
Because the 16 ohm load pulls half the amount of amplifier power? Maybe that's why you were looking at the 4870?

Say, these chips don't mind running headphones from 380 ohm resistors, so there's no problem with 16 ohm speakers. ;)

Have fun! ;)

valleyman 25th February 2008 06:08 PM

I suppose, but I see no real advantage of using the 4780 in parallel over the 3886. If anything it only brings with it the complications of parallel amps. Given that the 3886 kit is only $100 all in I decided to just buy it and go from there.
I am fairly certain that for my modest listening levels 60W should be enough power so I'm definitely going to be using 25V transformers rather than 18 though just to be safe.

My plan is to put together the sealed boxes Zaph recommends with extra compartments at the bottom for the extra kit.

I am slightly worried that if I put the amps into these compartments they may not have sufficient airflow about the heatsinks. A possible solution to this would be to leave the backs of the bottom compartments open and put the heatsinks there, but even then, as they are likely to be placed against walls this might be restrictive. Could I get away with this by using excessively large heatsinks?

Many thanks

danielwritesbac 25th February 2008 09:11 PM

Its possible to put the heatsinks onto the exterior of the cabinet as part of the cabinet. Siliconized waterproof construction adhesive (Liquid Nail) can thermally connect the heatsink to the cabinet. You might even think of a way to use heatsink channel as a decoration. Its very shiny. ;)

To have your amplifier boards make the same sound as your reference, look at the voicing option of capacitance at the rails. Only the kit uses 100uF there, while others use 1000uF and 1500uF. So this voicing option is worthy of exploration.

25v secondaries (a 50vct rated transformer) are hot with 8 ohm loads. However 22v secondaries, while much cooler, may lack sufficient power for great enthusiasm with 16 ohm loads. The optimal voltage is relative to the load on the amp, so I couldn't answer that question. ;)

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