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Diamond Buffers

Discussion in 'Sound Science' started by jonesy512, Sep 8, 2012.
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  1. Jonesy512
    Hi guys I've been on the forums for a while now but never have actually posted anything.
    I have a question about diamond buffer amps, I am building the RJM Sapphire headphone Amp for an electronics project (Amp found here: http://phonoclone.com/diy-sapp.html
    What I want to know is what is a "Diamond Buffer" and how does it work.
    Any information would be helpful.
    Thanks In Advance Guys!
  2. Chris J
    It's basically a variation on the emitter follower.
    Like a a basic emitter follower, Voltage gain will always be slightly less than 1.0, bandwidth will be extremely high, i.e. far more than you need for audio.
    Output impedance will be low without using global feedback, but will be even lower if you place the buffer within the feedback loop.
    Depending on how much bias current passes thru the output transistors, (Q5 and Q6) and how much current your load draws, the amp will operate in Class A or Class A/B.
    I wouldn't try to adjust the bias to increase quiescent current, hopefully the designer has designed in the optimal bais current for minimum distortion.
    Douglas Self has written an excellent book about audio amp design:
    "Audio Power Amplifier Design Handbook".
    "Self On Audio"
    "Small Signal Audio Design"
    Currawong likes this.
  3. dvw
    This brings back memory. 30 years ago, I was the product engineer for the LH0002. LH0002 is a buffer from the fast buffer family in National. If you look up National (now TI's) library, you'll find a lot of information on it.
  4. Chris J
    Who made up the name "Damn Fast Buffer"?
    I always thought it was funny!
  5. dvw
    It was the design engineer. At the time, National was wild and crazy. We were also known as the animals of silicon valley. I don't think we'll be able to do the same things we did today. Nowaday, all documentation needs to go through legal review. I don't think they'll allow the word 'damn'.
  6. Steve Eddy
    It's just BARELY allowed here. [​IMG]
  7. Chris J
    I always enjoyed reading Bob Pease'e articles!
  8. dvw
    Bob is the face of National. I don't know Bob well because we worked in different group. If you look, National has LMxxx and LHxxxx as part number. M stands for monolithic and H stands for Hybrid. I worked in the Hybrid group. A lot of the veterans in National moved to Linear Technology. That is why you see a lot of similarity in the product line. Any way, it was a lot of fun trying to make something instead of chasing the all mighty dollar.
  9. Steve Eddy
    Sadly Bob is no longer with us.
  10. dvw
    There were quite a few colorful guys. Some had passed on and some are still with us. Bob was infamous because of his column. But there were quite a few game changers came out of that group of people. Simple things we took for granted like op amps and band gap reference. They truely made a difference.
  11. Chris J
    I think Widlar worked for NS?
  12. dvw
    yes, so did Dawkin. Widlar used to commute to work by flying from Mexico. He flew a small plane. Together they invented the 7xx series in Fairchild. They worked for NS and then Linear Tech. We didn't have offices or cubicle then. Their desks are just down the hall from mine.
  13. Chris J
    What do you make of all this Audiophile stuff?
    i.e. this amp sounds different, that Op Amp sounds different?
    I know Bob Pease was extremely sceptical.
  14. dvw
    IMO, historically audiophile tried to get the playback as accurate as possible. The original design all had imperfection because of bandwidth of the devices. There were a lot of smart people came up with lots of good design. The competition was to get the lowest distortion and the flattest response. As technology advanced, the differentiation becomes less and less. Amplifiers become almost interchangable. However, there is a difference in sound between the newer technologies vs old. My friend told me people are just not used to distortion free sound.
    This of course has an impact on media circulation. If all amplifiers sounded the same, why do I need review? The media (Stereophile) started promote subjectivity as a measure. Around the same time, Monster cable debuted their cable. Stereophile at the time even made lamp cord on the recommended list. Monster cable at the time was reasonablly priced.
    Then came the digital revolution. CD player replaced turntable. There is no longer any adjustment or tuning. The audiophile magazine will be out of business unless there is a new twist. So they are touting cable and subjective listening. Now come the IC power cable, cable stand even a machine (limited edition, why?) that will demagnetize LP, CD and cable. Are you serious?
    But consumers are not educated by anyone. Cable being the highest margin item, the sales guys will relentlessly praised them. Magazines are promoting them. There is no consumer advocate to help them. The cable myth exploded. People don't know better.
    My opinion is that the quality at the lower end of the market is getting better and better. The price of high end is getting higher and higher. Why would Sennheiser discontinue the  HD580 with no comparable product at the same price point HD600, IMO sounded the same as HD580 is twice as expensive. There is a thread on headphones that are giant beater on this board. Someone actually suggested HD580 is a giant beater. Today's "audiophile' have a herd mentality and a fixation on price. If the price is low then it can't be any good. Ah yes, we don't like EQ because it will color the sound, but we loved this $1000 cable because it has a warm tone. You, the noob, after you get the cable don't forget the cable lift and the power cable. For all these purchases, we will give you a discount on these audiophile grade fuses. 
    El_Doug and ultrabike like this.
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