John Curl's Blowtorch preamplifier part II

[Pano]

Thanks John.

 

[31697B]

I can understand the Grado dig, the headphones are subjectively and measurably too bright. But Magnapan? What would cause those users not to appreciate the problem?

HF ringing? I measured the early ones to have a treble peak which rings. Dont know if they do in current models.

-RNM

 

[Pano]

The Tympani III or similar, you mean?

 

[31697B]

Any earnest suggestions on the 'optimum' IC general purpose, but great sounding IC?

Try the LT1468 ... my Go-To opamp now. But havent listened to it... just for its ability to work extreamly well... measured.... in many different apps.


THx-RNMarsh

 

[SY]

So are you talking about line amps, and if so, what gain, swing, and load range? Volume control resistance? Setting design parameters comes first.

 

[31697B]

The Tympani III or similar, you mean?

yes.... with the seperate tweeter strip.

-RNM

 

[john curl]

Thanks Richard, that's a start!

 

[31697B]

So are you talking about line amps, and if so, what gain, swing, and load range? Volume control resistance? Setting design parameters comes first.

yes, only Line levels. a good universal opamp IMO. But do not know how it would perform in audio..... app. Something to try.

 

[Pano]

yes.... with the seperate tweeter strip.

I remember those from demos, but don't remember the ringing. Quite possible I didn't notice it. But that was what, 40 years ago? Now I only remember what they looked like. 🙂

 

[31697B]

Regarding the comment ... a lot of recording uses the 5532/4..... and there are an awful lot of bad sounding recordings,also. Not saying the 5532 is at fault but it doesnt mean a thing to say that. . But may be musically entertaining never-the=less. And, with so much compression used, who can tell?


THx-RNMarsh

 

[31697B]

I remember those from demos, but don't remember the ringing. Quite possible I didn't notice it. But that was what, 40 years ago? Now I only remember what they looked like. 🙂

I bought s/n 1 of DRA Labs MLSSA .. actually before they were DRA Labs.... You cant see it with a freq respponse test of the speaker.... it appears reasonably flat. and the grill cloth tended to smooth the freq response graph. Transient tests showed it. I still have that file somewhere on an old 486 computer.


THx-RNMarsh

 

[abraxalito]

Any earnest suggestions on the 'optimum' IC general purpose, but great sounding IC?

LM144, except its been out of production for years. Fails on your voltage noise spec but ultra-low current noise.

 

[hitsware]

LM144, except its been out of production for years. Fails on your voltage noise spec but ultra-low current noise.

High Voltage !
I once made an amplifier with LM344 for front end with
Hitachi lateral mosfet follower stage .....

 

[abraxalito]

Yep, the High Voltage is very much part of the LM144's appeal - up to 80V total supply. LM344 is its commercial younger brother, not quite as high voltage though (68V). Did you run your amp bridged?

 

[Waly]

TI/National
OPA827
OPA211
LME49710
LME49880

AD
ADA4627
ADA4898
AD8597
AD8610

LT
LT1115
LT1128
LT1792

MAXIM
MAX9632

These are all singles, but many have dual versions.

Yes, most are in SMD cases, none has a class A output stage, resistors are made out of dirty sand (doesn't matter some are thin film, dirty sand is still around), they don't have large open loop bandwidth, etc... etc..., shortly, none of these is good enough for you.

 

[DPH]

I'm probably going to launch into using the OPA1652 as my do-all OPA of choice. SOIC8 or SOIC14 for the quad. Biggest weakness is it's not going to drive low impedances well. Inexpensive to boot.

 

[abraxalito]

TI doesn't have any qualms about its low impedance driving capabilities - check their application in fig41 of the DS.

 

[DPH]

John Caldwell, in one of the headphone threads notes this about the OPA1652 for low impedance drive:

Also, the three-stage topology of the OPA1642 preserves high-frequency linearity better into low impedance than the two-stage folded cascode topology of the OPA1652. But if the load impedance is above about 2kOhms, this really isn't a factor.

Non-issue for most applications, but I'll trust him to know the ins and outs of that chip. 🙂

 

[abraxalito]

Fig41 shows a load impedance considerably below 2k.

 

[bcarso]

I've been studying the 1642 et al. recently. Consider Fig. 30 on the datasheet. There must be a capacitor lurking in there that makes the open loop output impedance rise at low frequencies --- and yet it doesn't affect output current capabilities. Does look like a very nice part, the 5nV/sq rt Hz is good for JFET op amps, and of course very low current noise for most apps.

I worry about heavy loads transmitting thermal deltas to input stages, despite how exquisitely the layout has made the effects symmetrical. So for serious stuff I like to get the heavy lifting off chip, or at least to another chip. For real audio material this consideration is alleviated by the low duty cycle.