BF862 Preamp

200mW per one BF862 is OK, and here you won't have more than 130mW (especially when you don't have to worry about thermal drift).
I prefer to keep small signal circuits as compact as possible and this way Gates are too exposed for my taste. OTOH those are line level signals and there shouldn't be much of a problem. Let's see how it works - you have a nice box and shielded transformer, I guess it'll be all right.
 
Working!

Hi Guys,

Well, at least two out of the four buffers are working - one didn't work when I tested it, but it's probably something simple since two are OK. (I didn't check the fourth yet... I wanted to listen for a while first...)

In the end I managed to get the boards out and switch the 1k for 10R without nasty band-aid type solutions, although it was pretty hard work.... Maybe that'll teach me to check things more thoroughly... ;)

All off-board wiring inside is strictly temporary, just good enough to test whether things work, since it'll all have to be redone after the crossover section is done. Nonetheless, I've been listening to the music I use to check new projects (Artur Pizarro playing Beethoven Piano Sonatas, Elisabeth Schwarzkopf singing Strauss, among other things), and it sounds very good indeed! Right now I'm testing it with the mini-Aleph-J juma helped me with (which is also BF862!); I'll have to wait to try it with the F5 in the living room, which is where it's really intended for.

I've included two photos of the box closed up - I'm using 10-turn wirewounds for left and right volume, hence the complicated knobs. One switch for on/off, the other for choosing between two inputs. The hole in the middle is for a LED to show power, when I get around to it... I've decided there is no reason that hifi equipment has to be black or silver, so I decided to use what in the UK we call "British Racing Green" (probably people from other places don't call it that :)) but in the end it looks a little like a piece of army surplus equipment... Oh well... (Next time I'll use fire-engine red...)

As always, any comments on the build are most welcome. I'd be particularly grateful for any suggestions on how to economise space, since I am beginning to think I'll have space problems for the crossover section. (Posts about that stage will be in the corresponding thread on the B1 crossover.)

Cheers

Nigel
 

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Hi Guys,

... I've decided there is no reason that hifi equipment has to be black or silver, so I decided to use what in the UK we call "British Racing Green" (probably people from other places don't call it that :)) but in the end it looks a little like a piece of army surplus equipment... Oh well... (Next time I'll use fire-engine red...)
...

Actually we do. Well, okay, I do--I can't speak for the other 299,999,999 people in the US. :cool:

Anyway, it looks very nice, indeed.
 
...
I've decided there is no reason that hifi equipment has to be black or silver, so I decided to use what in the UK we call "British Racing Green" (probably people from other places don't call it that :)) but in the end it looks a little like a piece of army surplus equipment... Oh well... (Next time I'll use fire-engine red...)
....

Absolutely famous all over the world and that will be the colour of my next Aston Martin! :D

But pls leave red to Italians and our Ferrari! Even if few people know that the "official colour" of Maranello team is yellow. Red was the racing colour for all the Italian cars, as well as white (and later silver) for the German ones, blue for French, etc.
 
Was your repair what one might refer top as a "Pitt Stop"? :D

(My old Maseratis were each finished in Italian Racing Red with natural light tan interiors....BRG did not suit them and Irish Emerald Green was even worse. THey always used to say that only the Gods should wear green or flaunt emeralds!;))
 
can i ask a stupid question? whats the VAC rating of the transformer used. ~.~

It's not a stupid question, although maybe someone else has a better answer for you.

I am using one transformer for four output buffers and up to 14 symmetrical buffers - you can see the planned circuit on the thread about the B1 active crossover if you're interested. For this I have a 3A trafo, at 24 -0 -24, which comes out to 144 VA. I should point out, however, that a 2A trafo would likely have been enough, and that here in Brazil trafos are sold by current rating, not power rating, so these values may be a bit misleading. (Also, I tend to overengineer...) If you are planning a stereo preamp like juma's original design something much smaller should suffice.

Cheers

Nigel
 
Whoooaaaa.... I know it's OT, but tell us more!!:cool::cool:

Well - it's your thread so I hold you responsible!

Two, the old early 1960s 3500GT model, were non-starters - so I totally rebuilt the engines. The third was a rather rare 4 litre Mistrale which had been badly treated and allowed to go downhill; the requirement was a head-off revalve, timing chain etc. Sold them all not long after their repairs were completed. This was back in the early 70s when - poor examples - were easy to find at well under £800.00. Even nice examples running properly made less than £1500.00 without a full Maserati service record. But their great grace was that they were perfectly balanced quite fast tourers which were more pleasure to drive than almost any other car I have had. I would have kept one except for a divorce at that time made it impossible.
 
200mW per one BF862 is OK, and here you won't have more than 130mW (especially when you don't have to worry about thermal drift).
I prefer to keep small signal circuits as compact as possible and this way Gates are too exposed for my taste. OTOH those are line level signals and there shouldn't be much of a problem. Let's see how it works - you have a nice box and shielded transformer, I guess it'll be all right.

Hi juma,

I'm considering redoing the boards for the output buffers - the ones you remarked on in this post. Reasons are: 1. I'm going to have a problem with space on the board for the rest of the project, so making these smaller would help 2. The little test setup I posted in the crossover thread proves that you were right and the big surfaces are unnecessary 3. I've been thinking about the part of your post I put in boldface, and while there doesn't appear to be any major problem the way I've done it is somehow inelegant, so you are right.

So, a couple of questions.

1. How hot do your original adaptor boards from post #2 get? They appear to be about 1/4 sq. cm., and have about 8 sq.mm. or so of copper on the gate. Is that about right? This would help in estimating a minimum size for boards.

2. You mention above "no problem with thermal drift". If my boards were smaller, and therefore hotter, might this become a problem?

3. It may be a bit optimistic to put three jfets on a DIP-8 board without heatsinking it, but a DIP-16 board should certainly be possible. This might allow for bypass caps C12, C13, C19, C20 to be on the board, helping with the space problem, and except for the output caps (which people like me tinker with anyhow) would put the whole preamp on a plugin board, like EUVL did with his "turbo B1". Does this sound to you like a good way to do it?

As always, much obliged for any help

Cheers

Nigel