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Old 5th January 2010, 11:36 PM   #101
njepitt is offline njepitt  United Kingdom
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Originally Posted by dviswa View Post
Hi Guys,

I would like to report some success. I had been toying with this idea of using a B1 for active crossover using Sallen-key filters for over an year, but some how never got around to building it. Finally I built one channel P to P on a proto board. Th improvement in sound quality over my passively crossed over speakers are huge. However, building it P-P is just too much work and a big challenge. Not recommended for noobs.

The sound is so much more fuller and rich. The notes well defined, you can sense the separation between instruments so well. My son can't wait for me to get the other channel finished.

Dave (Planet-10),
You really should give this a try, it might change your mind about Sallen-key filters.

Regards,
Dinesh
Dinesh,

I can't wait for you to get the other channel finished, either... Any chance of more info/photos/listening impressions???

AndrewT,

I only just noticed that our last posts crossed.... I'm going to do a slight variant of what you suggested - will post and tell if it works...

Cheers

Nigel
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Old 6th January 2010, 01:50 PM   #102
juma is offline juma  Serbia
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Nigel, allthough simple by its self, the preamp you chose (after x-over) is very demanding when it comes to PS (almost no PSRR for +U and worse than that for -U). If you want optimal results, use suggested shunt reg, at least for -4.6V
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Old 6th January 2010, 02:08 PM   #103
njepitt is offline njepitt  United Kingdom
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Nigel, allthough simple by its self, the preamp you chose (after x-over) is very demanding when it comes to PS (almost no PSRR for +U and worse than that for -U). If you want optimal results, use suggested shunt reg, at least for -4.6V
Thanks juma, acutally I am planning on using essentially the same circuit from post #23 on your BF862 preamp thread (if this isn't the one you mean please let me know...).

The only differences are the following: I am using one transformer to power everything including filters and output buffers. Trafo is centretapped 24 - CT - 24, one regulator, will give me about +/- 33 Vdc unregulated and unsmoothed. Pair of 2200uF electrolytics (with 0.47uF snubbers do preliminary smoothing. This will then run the +ve regulator of your circuit, giving the +24.65 V needed, and a pair of preliminary regulators 7815/7915 (probably with a 7824/7924 pair before them, to share the heat issue). This pair gives +/- 15V which will then be regulated further by two regulator circuits: one is the -ve part of your circuit which gives -4.6V, and the other is the symmetrical regulator from the "symmetrical B1 buffer" thread, which will give me +/- 8 to 9 V to run the filters. This gives a slight lack of symmetry, since the current draw from the 7915 will be a little higher than from the 7815, but I don't think it's enough to matter. (??)

If anything looks odd or a bad idea please let me know - I'm off to buy more parts after lunch!

Cheers
Nigel
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Old 6th January 2010, 02:20 PM   #104
AndrewT is offline AndrewT  Scotland
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why are you running the filters from +-9Vdc?
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Old 6th January 2010, 02:57 PM   #105
njepitt is offline njepitt  United Kingdom
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why are you running the filters from +-9Vdc?
I will be using BF862 in place of 2SK170. Reducing voltages to +/- 9V (more or less) was suggested by Jacques above (post #43), since BF862 has a lower absolute max voltage. Seemed prudent, so I'm planning on doing it.

Cheers

Nigel

Last edited by njepitt; 6th January 2010 at 02:58 PM. Reason: typo...
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Old 6th January 2010, 03:22 PM   #106
AndrewT is offline AndrewT  Scotland
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that's a good reason.
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Old 6th January 2010, 03:27 PM   #107
juma is offline juma  Serbia
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Nigel, +/-9V for x-over is a good idea - not just because of Vds max, the dominant criteria is Pd max. They'll be working on Idss (about 13mA) x 9V = about 120mW which is OK for such a tiny part. More than that and worries about temp. drift will start - remember your last project with BF862
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Old 6th January 2010, 05:49 PM   #108
njepitt is offline njepitt  United Kingdom
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Nigel, +/-9V for x-over is a good idea - not just because of Vds max, the dominant criteria is Pd max. They'll be working on Idss (about 13mA) x 9V = about 120mW which is OK for such a tiny part. More than that and worries about temp. drift will start - remember your last project with BF862
Oh, don't worry I remember well.... In fact, the amp is doing daily duty, and performing very well indeed - I'm very pleased with it. Let's hope the experience building it helps here.....


Cheers

Nigel
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Old 7th January 2010, 07:01 PM   #109
dviswa is offline dviswa  United States
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Dinesh,

I can't wait for you to get the other channel finished, either... Any chance of more info/photos/listening impressions???

Nigel
Nigel,
Here goes. I have 4 stages of "B1" configured as Buffer->Stepped Attenuator->Buffer->LP & HP Filters

PSU is nothing special, just vanilla LM317/337 regulators supplying +/- 9V.

As far as impressions are concerned, give me a few days and my second amp will probably be done, then I can run one speaker active and another passive. As already mentioned, this is definitely the way to go, compared to passive crossovers. The sound is much more fuller, and clean, not to mention much more dynamic and punchy.
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Old 8th January 2010, 11:15 PM   #110
njepitt is offline njepitt  United Kingdom
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Hi Dinesh,

I'm most interested to hear your impressions. Can I ask a couple of stupid questions?

Quote:
Originally Posted by dviswa View Post
Nigel,
Here goes. I have 4 stages of "B1" configured as Buffer->Stepped Attenuator->Buffer->LP & HP Filters
In the photo I can see three jfets pairs on the board; are these the parts after the attenuator? I guess you have the earlier Buffer in your list as
part of some different board. (Maybe in a preamp?) In any event, you are doing the 12db/octave original version, right?

Quote:
Originally Posted by dviswa View Post
As far as impressions are concerned, give me a few days and my second amp will probably be done, then I can run one speaker active and another passive. As already mentioned, this is definitely the way to go, compared to passive crossovers. The sound is much more fuller, and clean, not to mention much more dynamic and punchy.
I'll be very interested to hear how it sounds. How are you planning to fit this into your system? I'm being nosy - what crossover point, amps, speakers et cetera.... Do you plan on doing a more sophisticated PSU later?

My build is proceeding OK. I have a habit of always building the PSU first, and in this case I plan on getting the output buffers working next, to give a functional BF862 preamp, then do the filter section last. So it'll be a while before I can hear how it sounds....

Cheers,

Nigel
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