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Old 4th November 2012, 09:57 PM   #1981
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Quote:
Originally Posted by hitsware View Post
Thanks for this hitsware. So Ro = 1/hoe

Quote:
A quick experiment measuring 1, 2, and 3 matched diodes in parallel gives about 35 Ohms series R so they behave "ideally" only up to 10's of uA.
So my crude estimate of 20R for 1n4148 is in the ballpark and so is the 'cure' .. tweaking the simple current mirror resistors.
_______________________________

I propose to yus gurus SPICEing that we also do a more stringent load test

3.162Vp 20kHz into 15R. OPA configured as Voltage follower

This is from NwAvGuy: O2 Headphone Amp

I'm having difficulty getting the various contenders to show THD above -140dB on a 600R load which implies no sensible real life results with a 24b soundcard. It will also show up important 'CMR' effects.

It's already showing up some of the BJT models at high currents.
_______________________________

BTW, IMHO, even with seriously PITA matching, I think we will need tweak pots for offset and maybe for Iq. The first guys who build a breadboard get to pontificate on this.

Last edited by kgrlee; 4th November 2012 at 10:15 PM.
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Old 5th November 2012, 02:53 PM   #1982
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Quote:
Originally Posted by kgrlee View Post
I'm having difficulty getting the various contenders to show THD above -140dB on a 600R load which implies no sensible real life results with a 24b soundcard. It will also show up important 'CMR' effects.

It's already showing up some of the BJT models at high currents.
_______________________________

BTW, IMHO, even with seriously PITA matching, I think we will need tweak pots for offset and maybe for Iq. The first guys who build a breadboard get to pontificate on this.
Of course you will need to trim or select resistors if you want really low offset. We also went over the output current thing before, if you want a 32 Ohm headphone amp it will be different.
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Old 5th November 2012, 03:08 PM   #1983
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Scott, I'm really interested what you think about my little baby?
Attached Files
File Type: pdf Sansui-Rush Opamp.pdf (19.4 KB, 260 views)
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Old 5th November 2012, 03:19 PM   #1984
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Regarding the follower stage of the open OPA, There are some Sanyo BJT's available in SOT89 (Sanyo PCP) package that are supposedly compliments (although not very well matched) 2SA2125 2SC5964. Data sheet doesn't specify use for linear applications but the transfer function looks pretty good in the range it will be used (<300mA) and they have a fairly good fT ~ 380mHz and a good max dissipation for SOT89.
Would there be any performance advantage in using these when compared to say the BCP53/56 compliments?
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Old 5th November 2012, 04:48 PM   #1985
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Originally Posted by kgrlee View Post
Thanks for this hitsware. So Ro = 1/hoe

So my crude estimate of 20R for 1n4148 is in the ballpark and so is the 'cure' .. tweaking the simple current mirror resistors.
_______________________________

I propose to yus gurus SPICEing that we also do a more stringent load test

3.162Vp 20kHz into 15R. OPA configured as Voltage follower

This is from NwAvGuy: O2 Headphone Amp

I'm having difficulty getting the various contenders to show THD above -140dB on a 600R load which implies no sensible real life results with a 24b soundcard. It will also show up important 'CMR' effects.

It's already showing up some of the BJT models at high currents.
_______________________________

BTW, IMHO, even with seriously PITA matching, I think we will need tweak pots for offset and maybe for Iq. The first guys who build a breadboard get to pontificate on this.
If you need a low impedance load then maybe you should consider the FET output stage used by Mr Cordell.
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Old 5th November 2012, 05:25 PM   #1986
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Scott, I'm really interested what you think about my little baby?
At first glance this looks fine.
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Old 5th November 2012, 05:28 PM   #1987
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(although not very well matched)
I'm sure they would work in the circuits we are discussing. Pesky holes and electrons!
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Old 5th November 2012, 06:54 PM   #1988
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Originally Posted by scott wurcer View Post
At first glance this looks fine.
Thank you Scoot...btw, Sansui-Rush opamp can/could be converted into a Rush-Rush opamp in a sec with similar DC/AC performance.
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File Type: pdf Rush-Rush Opamp.pdf (19.3 KB, 150 views)
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Last edited by aparatusonitus; 5th November 2012 at 07:03 PM.
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Old 5th November 2012, 08:56 PM   #1989
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Quote:
Originally Posted by aparatusonitus View Post
Scott, I'm really interested what you think about my little baby?
Sonitus, will you oblige us with your LTspice file so us wannabe SPICE gurus can have a play? Also your Rush-Rush version?

Quote:
Quote:
I propose to yus gurus SPICEing that we also do a more stringent load test

3.162Vp 20kHz into 15R. OPA configured as Voltage follower
If you need a low impedance load then maybe you should consider the FET output stage used by Mr Cordell.
On 2nd thoughts, 210mA peak may be a bit too stringent. c2240/a970 & bc556/546 are only 100mA. 4401/3 are OK but I was trying to get a series of tests for the contenders which didn't need too many special devices in special places. Special i/ps are unavoidable.

Got a link or sketch of Cordell's output stage accessible to beach bums?

Low loads aren't a problem if you are prepared to use medium power devices like the original 990 or even just 4401/3.

Scott, did you get your breadboard up & running?

My contention about offsets is that you may need tweak pots to avoid Volts of offset rather than mVs even with loadsa device matching. But this is just from SPICE so the breadboard man has the last (??) say.

Last edited by kgrlee; 5th November 2012 at 09:14 PM.
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Old 5th November 2012, 09:45 PM   #1990
PHEONIX is offline PHEONIX  Australia
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Hello kgrlee,

What is your desired ultimate spec THD into 15R @ 20KHz @ 3.162Vp that you seek to attain.

Regards
Arthur
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