are you hard at hearing
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gavinbirss

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Hello,

It there anyone that would agree that most op amp headamp combo's have the inability to achieve more that 30V p-p and thus do not have the voltage swing to drive >= 600 ohms ?

Most op amps swing more that 2V from the supply and this limits the gain you can choose accordingly.

I was thinking that the following design with tackle this problem.



Sorry about this but this link needs to be opened in a window since remote linking if not allowed where I stored the picture.

Note : That the resistor and cap values are arbitrary and can be substituted with any other value of choice.

I have made a prototype but found that with my poor power supply and 0.5 ohms resistors instead of 4.7 ohms resistors is causing the OPA604 to heat up. (more that what I would like).

Combining a op amp and buffer as with the BUF634 there is no thermal affect on the op amp. The OPA547 is not a buffer and is used as a op amp and I may need some help here but I think in this circuit the op amp is affected thermally.

My idea with this circuit was to provide for 40 V p-p and 500-750 ma of current. I was thinking that this unit would provide enough guts to drive say the K 1000.

What do you guys think ? Please be gentle.


Gavin
 
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post-199235
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ppl

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What you are trying to do is what is called a Composit Opamp that is most often used to get the Best of different Types of opamps. However this is not what you need. What you need is the Attached cascoded opamp. This allowes any Opamp that is free from Phase rev. to Operate at any Supply voltage you want. like any of the Newer opamps and a select few of the Older types like The OPA-627 & OPA134 series. The data sheet will boost about the Opamp Being free of phase Inversion if the Max input is reached. The Output will swing to within a few volts of the supply rail. The Zener is selected to give the desired opamp voltage - the 0.6 Volt of the transistors Vbe. thus a Opamp that is designed to operate on +/- 15 Volt rails can be operated at any voltage consistent with the Voltage of the Transistors. The resistors are to set the Zener current and should be about 10 Ma. replacing the resistors with Constant curent sources will allow Improved Power supply rejection ratio. This should get you started. Oh BTW please see the Headwize artical on protecting your Hearing.
 
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gavinbirss

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Hello, ppl

I sent you a email message through head-fi and assume that it got lost in cyberspace.

From one of your previous posts I noticed that you listen and like jean michel jarre's music. Do you have "Concerts in China" on LP or CD.

Do you like Mike Oldfields : "The Songs of Distant Earth" and "The Millenium Bell".

With my circuit I was hoping to obtain a amplifier as with the OPA548 but with lower current ratings. If this circuit was not used for driving >600 ohm headphones or AKG K 1000. Otherwise it can double up as a loudspeaker amplifier.

I am asuming the attached cascoded amp that the opamp is responsable for the precision and the transistors are responsable for current gain. My father will probably have one look at the circuit and yell that "zener diodes cause niose in audio circuits".

Thanks for you input.

Gavin
 
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ppl

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I have The concerts in china on CD only. my Other jarre I have on both CD and Lp. Mike Oldfield' Tubular bells I have on Lp Only will check out your Recomendation. Noise from Zeners. Well use what ever Voltage reference you want LED string or somthing like BB Ref 01. if that is a concern to you. this circuit also works with Buffers. I have used +/- 100 Volt rails on an OPA-627 to get about 90 Volts RMS out. if your looking to drive Loudspeakers Then Current and lot's of it are needed. Check out NS LM-3886 one of the best sounding Power opamps i have heard I use a 4 ch version on my PC with 4 RS LS-5's.
 
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gavinbirss

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Hello, ppl

"I have used +/- 100 Volt rails on an OPA-627 to get about 90 Volts RMS out."

Could post a schematic on how one would go about doing this. What did your use as voltage refs.


What vinyl setup do you have. (table, arm, cartridge and phonostage).

Thanks
Gavin
 
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ppl

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The Cascoded Opamp only Boost Voltage not current so the Transistors should be selected to have an SOA of 40 Ma at VCE 100 Volts thus High Voltage transistors rated at 150 volts or greator should be used . I used 300 Volt 1 Amp transistors I think the types are 2n3440 & 2N5416 TO-39 can types and 15 volt Zener. 10K Resistors.

My Present Phono setup is Technics SL-1200 MK II with both a Sure V15 type IV and Audio technica LC-155 LC. using the Phono section of My Mac C-33 Solid State Preamp. Ya I know all Old stuff.
 
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gavinbirss

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Hello, ppl

Old means it is better made.


My father is still using a Pioneer PL wich he bought in 1976 with a technics tonearm and hybrid empire cartridge with shure stylus.

He used to use a grace tonearm and AT-OC9 MC but one channel on the OC-9 died.

He has brough a Technics SP-10 MK II, with a Audio Technica Tonearm and he has ordered two Denon cartridges : DL 103 and DL 160.

Gavin
 
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Dreamslacker

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Quote:

Originally posted by ppl
What you are trying to do is what is called a Composit Opamp that is most often used to get the Best of different Types of opamps. However this is not what you need. What you need is the Attached cascoded opamp. This allowes any Opamp that is free from Phase rev. to Operate at any Supply voltage you want. like any of the Newer opamps and a select few of the Older types like The OPA-627 & OPA134 series. The data sheet will boost about the Opamp Being free of phase Inversion if the Max input is reached. The Output will swing to within a few volts of the supply rail. The Zener is selected to give the desired opamp voltage - the 0.6 Volt of the transistors Vbe. thus a Opamp that is designed to operate on +/- 15 Volt rails can be operated at any voltage consistent with the Voltage of the Transistors. The resistors are to set the Zener current and should be about 10 Ma. replacing the resistors with Constant curent sources will allow Improved Power supply rejection ratio. This should get you started. Oh BTW please see the Headwize artical on protecting your Hearing.


Question: Is there a way to implement that into the Tangent - Meta circuit? I'm using their schematic in the Meta article (some minor changes on the input side but multiloop unchanged with Cascode JFET) and built on Proto-type boards so I can modify the voltage inputs easily.
 
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ppl

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Yes> Just treat the Meta board as an opamp. However higher current Transistors will be needed. I also do not feal comfortable recomending High Voltage circuits as the Real possibilitty of Electric Shock, and i would feal Real Bad if this happend to someone. so I gess I should say

WARNING High Voltage Can Kill Use of circuits operating at voltages over 50 Volts should only be done by Pro's. Kid's Don't try this at Home

META42 Edit> Remove all Power supply caps since thay will not be needed a Film cap from rail to rail is Good. Power supply caps now go on the High Voltage rails. caps rated for the Voltage you are using.
 
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