Try ODNF error correction, I can supply you info and case study of a similar design using it. It has several advantages over hawksford error correction.
BTW where did you get the idea of the mirror you are using. Dont turn it into a commercial product, a large opamp corporation will sue you for patent infringement
.Hawksford is ok. I used to like idea but there is complexity, difficulty driving low impedance loads beyond a limit and appears to have difficulty with reactive loads. one caveat, All these views are based on simulation and not real life.
The ODNF info manso talks about is a good read.
Try ODNF error correction, I can supply you info and case study of a similar design using it. It has several advantages over hawksford error correction.
BTW where did you get the idea of the mirror you are using. Dont turn it into a commercial product, a large opamp corporation will sue you for patent infringement
Yes please supply the info and case study, I am very interested, heard about ODNF EC but that's all.
I am not interested in comercial product, this is just a hobby. I started with first generation of current conveyor and with the help of some friends here came to present solution. Could you be more precise, what patent you are talking about?
Your initial schematic seems very simple to build....
Would you care to help me debug it if I try it p2p ?
I like the idea of a gain variable amp with constant SN ratio ... you stated first Mirror is very sensitive to load.... does the pot not contribute to variable load ?
PS: I allready have the shunt psu
Would you care to help me debug it if I try it p2p ?
I like the idea of a gain variable amp with constant SN ratio ... you stated first Mirror is very sensitive to load.... does the pot not contribute to variable load ?
PS: I allready have the shunt psu
Hi dadod
Drop me your email in a pm and Ill send you the paper.
The part of the circuit Im referring to is only the current mirrors. Basically it consists of the EF mirror and the baxandall cascode. This is protected by US and EU patents, held by texas instruments. I cant recall the number but you can google it. I think its named ultra high output impedance mirrors. Part of the reason for the ultra low THD of tpa6120.
Fortuneatly for diy its no problem.
Yes I will help you and it should be very simple as there is no global feedback. To achieve lowest distortion select current mirrors degeneration resistors to be equal value. It is not imortant to have 0.1% type(better if you can get) but equal resistance. I select with ohmmetter between 1% type.
The mirror is sensitive to capacitive load and off course the gain buffer input inpedance should be high enough not to influence the gain ratio(P1/R9).
BR Damir
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Joined 2009
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The most interesting option is no feedback around the output stage - for the purists at least. Otherwise it just looks like a pre-amp and a global feedback buffer - it all depends on how you want to look at it I guess. And error correction is often just negative feedback with another name (the gain can be in the feedback path instead of the forward path). I'm not sure I've ever seen a class AB buffer without negative feedback wrapped around it.
You could try tackling some of the limitations of the EF (whether diamond buffer or not) - there are some other threads around here somewhere where it is talked about augmenting a diamond buffer to boost the current to the stage as the signal climbs in order to compensate for the Vbe drop of the output devices. Or use an output transformer like Susan Parker did (and many others back in the good ol days)
The most interesting option realy is no feedback around output, but distortion of that buffer is quite high(0.1%?) and low distortion of the gain block is lost then, so I am not sure yet. Transformer output is not for me, to expesive, I would rather make a valve amp with transformer.
Thanks Bigun for your comments.
I remembered now that I have that OP and I used it some years ago. Data sheet says that it is current feedback amp and there is no internal circuit diagram. I was thinking that I use Baxandall super pair, why do you call it cascode?
BR Damir
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Joined 2009
Paid Member
I read that valve amplifiers with much higher distortion than that are popular for their good sound. I have a SET which sounds good and I'm sure it's distortion is higher than 0.1%. If you can make the distortion profile 'acceptable' it may sound good despite the lack of feedback. It may not sound as clean and accurate but there are many customers for warm and lively.
First picture is wilson mirror and Q7 is a cascode, right?
Then next picture is a mirror I used (here with no super Baxandall) but there is Q4 connected on other side from a cascode transistor so it's not exactly wilson type. Use of Baxandall super pair should not be protected with patent if used in a current diferent current mirror, I expect. A current mirror I am using, I suppose, is not the same Texas Instruments patented?
By the way Q4 lowered distortion(don't remember how much) in my preamp.
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Yes I know that but it's bother me to have very low distortion gain block and then output buffer destroys all the fun.
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