BUF634T Availability
Hello folks,
I am frustrated at every turn in my attempts to find BUF634T. Digikey, Mouser, Newark in One ... all with lead times of 4 months before availability.
I can get them here in Australia but they are $22 each (approx $18 US)!!
1. Any ideas?
2. Is there a discrete component buffer which I could build instead??
(Getting desperate here ... will probably build a Nelson Pass originated design to keep me going for the time being, which would be a good thing though, I believe, but even then, affordable IRF mosfets will still need to come from the USA 🙁 )
Regards,
George.
Hello folks,
I am frustrated at every turn in my attempts to find BUF634T. Digikey, Mouser, Newark in One ... all with lead times of 4 months before availability.
I can get them here in Australia but they are $22 each (approx $18 US)!!
1. Any ideas?
2. Is there a discrete component buffer which I could build instead??
(Getting desperate here ... will probably build a Nelson Pass originated design to keep me going for the time being, which would be a good thing though, I believe, but even then, affordable IRF mosfets will still need to come from the USA 🙁 )
Regards,
George.
Re: BUF634T Availability
"Diamond" style buffers, like those suggested by Makura seem to be a good alternative to chip buffers.
Why don't you have a look at Nuuk's discrete preamp which he found better sounding that chip and other buffers?
http://myweb.tiscali.co.uk/nuukspot/decdun/gainclone2.html#discrete
They are a simple and very good sounding way to go.
Carlos
GeorgeBoles said:
"Diamond" style buffers, like those suggested by Makura seem to be a good alternative to chip buffers.
Why don't you have a look at Nuuk's discrete preamp which he found better sounding that chip and other buffers?
http://myweb.tiscali.co.uk/nuukspot/decdun/gainclone2.html#discrete
They are a simple and very good sounding way to go.
Carlos
Re: Re: BUF634T Availability
Note there is given certain limitation concerning output load, as the maximum output current is equal to the quiescent current of the current source and the negative output voltage is limited to the product of said current and the load impedance. As the positive one is virtually unlimited, then an unsymmetrical clipping and DC shift can occur at too low load impedance and/or too high input=output voltage. The symmetrical configurations, e.g. push-pull or diamond, are better in this regard, particularly if some "impedance-matched" wiring (50 ohm e.g.) is used.
carlmart said:
Note there is given certain limitation concerning output load, as the maximum output current is equal to the quiescent current of the current source and the negative output voltage is limited to the product of said current and the load impedance. As the positive one is virtually unlimited, then an unsymmetrical clipping and DC shift can occur at too low load impedance and/or too high input=output voltage. The symmetrical configurations, e.g. push-pull or diamond, are better in this regard, particularly if some "impedance-matched" wiring (50 ohm e.g.) is used.
Buffers:
Thanks Carlmart and Bobilox.
I am feeling way out of my depth a bit here and so have a few questions.
1) Considering Nuuk's discrete buffer circuits (the one with normal transistor and the second with Jfets, a little further down the page - http://myweb.tiscali.co.uk/nuukspot/decdun/gainclone2.html#discrete ):
CarlosFM has said that the design with the IC buffer (BUF634T) makes his pre-amp relatively independent of distance from the power amplifier ... and that this has something to do with the 0.25mA current available. Carlmart, you implied, if I understand correctly, that the two designs which are on Nuuk's page are somewhat limited in their current capacity.
a. Will that limit their performance over connections of about 2.5 to 3 metres?
2) Regarding Pavel Makura's "diamond buffer" design http://web.telecom.cz/macura/dispre_en.html:
The buffer is integrated in a "unity gain, zero feedback pre-amplifier". I believe that an LM3886 chip amp with a gain of about 20, or a Nelson Pass Aleph or Aleph-X amplifier with a similar gain, will need more than "unity gain".
a. Please correct me if I am wrong on this matter.
I have insufficient knowledge to tease out the "diamond buffer" so that I can use it with a higher gain pre-amplifier.
b. Are there any other "best links" on learning about these matters, or can you dissect out the "diamond buffer" for me so that I can incorporate it in a higher gain pre-amp design. (It doesn't even look like a diamond to me!)
3. What is "impedance matched wiring"? I have tried to get to the bottom of this in the past, but got way-laid. Does it only relate to the 50 ohm resistor in series before the cable and 50 ohm in parallel after the cable as illustrated elsewhere on his site http://www.pha.inecnet.cz/macura/buffer_en.html ? Does it require the purchase of pre-made cables/cabling? Does it relate the cable you get everywhere called "75ohm coax"? Is it doable as DIY cabling, you know, silver wire in teflon or cotton?
Sorry about this complex question, but I have got to start somewhere on this.
Best regards,
George.
Thanks Carlmart and Bobilox.
I am feeling way out of my depth a bit here and so have a few questions.
1) Considering Nuuk's discrete buffer circuits (the one with normal transistor and the second with Jfets, a little further down the page - http://myweb.tiscali.co.uk/nuukspot/decdun/gainclone2.html#discrete ):
CarlosFM has said that the design with the IC buffer (BUF634T) makes his pre-amp relatively independent of distance from the power amplifier ... and that this has something to do with the 0.25mA current available. Carlmart, you implied, if I understand correctly, that the two designs which are on Nuuk's page are somewhat limited in their current capacity.
a. Will that limit their performance over connections of about 2.5 to 3 metres?
2) Regarding Pavel Makura's "diamond buffer" design http://web.telecom.cz/macura/dispre_en.html:
The buffer is integrated in a "unity gain, zero feedback pre-amplifier". I believe that an LM3886 chip amp with a gain of about 20, or a Nelson Pass Aleph or Aleph-X amplifier with a similar gain, will need more than "unity gain".
a. Please correct me if I am wrong on this matter.
I have insufficient knowledge to tease out the "diamond buffer" so that I can use it with a higher gain pre-amplifier.
b. Are there any other "best links" on learning about these matters, or can you dissect out the "diamond buffer" for me so that I can incorporate it in a higher gain pre-amp design. (It doesn't even look like a diamond to me!)
3. What is "impedance matched wiring"? I have tried to get to the bottom of this in the past, but got way-laid. Does it only relate to the 50 ohm resistor in series before the cable and 50 ohm in parallel after the cable as illustrated elsewhere on his site http://www.pha.inecnet.cz/macura/buffer_en.html ? Does it require the purchase of pre-made cables/cabling? Does it relate the cable you get everywhere called "75ohm coax"? Is it doable as DIY cabling, you know, silver wire in teflon or cotton?
Sorry about this complex question, but I have got to start somewhere on this.
Best regards,
George.
George, I will let somebody more expert answer your question about driving longer interconnects, except to say that I used a version of the Les Sage circuit in my active crossovers and it drove 2.4 metre interconnects to the power amps with no trouble at all. 
Re: Buffers:
Let me see if I can answer this at once. 😎
Well, it's not only a question of current output.
Both buffer stages on Nuuk's page will be fine for relatively long interconnects (and ok for those distances), because they both have low output impedance.
The difference here is that the op-amp+BUF634 will drive better a low impedance input stage. Also with lower distortion.
If that means it really sounds better, that's another story.
Those discrete stages should not be used with lower than 10k input impedance on the amp, distortion will rise.
You are correct.
Go to Erno Borbely's site, on the Articles page:
http://www.borbelyaudio.com/special_articles.asp
Download these two pdfs:
The New Frontiers, Part 1
The New Frontiers, Part 2
READ them. 😉
Basically that means you have the same output impedance on the sender device as on the receiving device (as used in video and also S/PDIF transmissions).
But on a line preamp, 50R to ground on the end of the cable will attenuate the signal, so the preamp must have more gain.
Although Pavel reported good results doing that, I have never tried it.
Not that I think it wouldn't work well, but it's against my principles to attenuate, amplify, attenuate amplify the signal again.
Also, I have later built a preamp that trances this one on this thread by a not small margin (AD815), and I dropped this.
PS: TV antenna cable is 75 ohm coax.
Have fun. 😎
Let me see if I can answer this at once. 😎
GeorgeBoles said:
Well, it's not only a question of current output.
Both buffer stages on Nuuk's page will be fine for relatively long interconnects (and ok for those distances), because they both have low output impedance.
The difference here is that the op-amp+BUF634 will drive better a low impedance input stage. Also with lower distortion.
If that means it really sounds better, that's another story.
Those discrete stages should not be used with lower than 10k input impedance on the amp, distortion will rise.
GeorgeBoles said:
You are correct.
GeorgeBoles said:
Go to Erno Borbely's site, on the Articles page:
http://www.borbelyaudio.com/special_articles.asp
Download these two pdfs:
The New Frontiers, Part 1
The New Frontiers, Part 2
READ them. 😉
GeorgeBoles said:
Basically that means you have the same output impedance on the sender device as on the receiving device (as used in video and also S/PDIF transmissions).
But on a line preamp, 50R to ground on the end of the cable will attenuate the signal, so the preamp must have more gain.
Although Pavel reported good results doing that, I have never tried it.
Not that I think it wouldn't work well, but it's against my principles to attenuate, amplify, attenuate amplify the signal again.
Also, I have later built a preamp that trances this one on this thread by a not small margin (AD815), and I dropped this.
PS: TV antenna cable is 75 ohm coax.
Have fun. 😎
Carlos - my TV antenna fell in love with my neighbour's antenna and they got married last week. The wedding was much but the reception was fantastic! 🙄
Thank-you for excellent response
Dear Carlos,
Yet again, many thanks for your excellent response to my questions, which are always of many parts.
The solid recommondation about power amplifier impedance is useful.
I shall download those pdfs (and read them 🙂 !)
If I need to, I will get back on that impedance matched wiring.
Any chance of letting us see your AD 815 pre-amp idea??
Regards and thanks again,
George.
Dear Carlos,
Yet again, many thanks for your excellent response to my questions, which are always of many parts.
The solid recommondation about power amplifier impedance is useful.
I shall download those pdfs (and read them 🙂 !)
If I need to, I will get back on that impedance matched wiring.
Any chance of letting us see your AD 815 pre-amp idea??
Regards and thanks again,
George.
Nuuk and Le Sage
Dear Nuuk,
Are these from your site called Le Sage circuits, or is that another reference I have to chase up? 😉
(Your site seems to be unavailable from work ... in case you have already answered that question there.)
Regards,
George.
Dear Nuuk,
Are these from your site called Le Sage circuits, or is that another reference I have to chase up? 😉
(Your site seems to be unavailable from work ... in case you have already answered that question there.)
Regards,
George.
Re: Thank-you for excellent response
George, it's all here, you just have to hit the 'search' button.
Here it is:
http://www.diyaudio.com/forums/showthread.php?postid=765880#post765880
GeorgeBoles said:
George, it's all here, you just have to hit the 'search' button.
Here it is:
http://www.diyaudio.com/forums/showthread.php?postid=765880#post765880
Yes George, the Les Sage circuit is what the three transistor discrete buffer is based on.
I have an arrangement with your employer to block your access to DD during working hours! 😀
In the UK, Cricklewood Electronics do them.
But they have put the price up a lot from around one to three pounds each! If that's due to people making this buffer, then where's my cut? 😀
GeorgeBoles said:
It's easy to see why someone might think this was an esoteric French name, not, as is actually the case, by Mr Lesley Sage, UK. I had this problem with Les Paul when I was younger 😀
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