John Curl's Blowtorch preamplifier

[PMA]

He apparently did.

 

[Steve Dunlap]

Thanks OS. I will have a look.

I notice Steve has disappeared. Why am I not surprised?

I'm old and frail. I sleep occasionally.

 

[PMA]

This is without global NFB:

 

[Steve Dunlap]

Hi Steve (Dunlap),

I've been real short of time as of late. Did you post those designs here? I didn't read your Krill thread yet, but you have peaked my interest. I didn't care much for the sound of early Krell product. I haven't heard any later ones.


-Chris

Hi Chris.

One of my early designs is posted in the Krill thread.

My designs have nothing to do with Krell. I chose the name as a humorous take off on Krell. The design I posted was for a small (physically) amp that sold for under $1000 per pair (they were mono) and delivered stable power into reactive loads. Krill is about as far from Krell as you can get.

 

[Steve Dunlap]

Well then your measurement system or technique is probably duff.


Cheers,
Glen [/B]

Well of course it is. I got results you don't believe.

 

[PMA]

This is without global NFB:

And this would be the competitor 😉 :

http://stereophile.com/images/archivesart/407MXRFIG09.jpg

 

[Steve Dunlap]

Glen ,I told andy that I don't have that anymore , since I was most
jealous and frustrated by it. Simulate it yourself, but don't use his input stage.. use what you know is best. This seems to
be like apples and oranges ,as I still am not not sure whether
he (steve) was referring to just the krill current stage or
the whole design (or some unknown mystery design).

I am absolutely objective and would love to gnaw on
that unknown design..
OS

I am talking about amps I built using a modified Krill current stage. As I have pointed out, since it runs open loop, you can play around with any voltage gain stage you want. I stated there was nothing special about the one I posted.

You don't really think I got 400W with no voltage gain, do you.

 

[GK]

Well of course it is. I got results you don't believe.

Yup

 

[scott wurcer]

Re: Multi Layer Ceramic Cap measurements

Getting a balance at these ratios (CMRR of 10,000) at the higher frequencies is very difficult. The differences from the reference cap ( A Component Research film and foil Teflon in a plastic case with pure copper non-magnetic leads) is very small.

We actually got much better than you can do with a 7A22 at audio frequencies with the discrete setup. At best around 120dB CMRR @ 20kHz.

 

[syn08]

I'm old and frail. I sleep occasionally.

Good. Meantime, we got an extra zero and extra 19KHz. Now we are going somewhere.

Could you once and for ever clarify those numbers:

Distortion: [insert number here] [insert units here] at frequency [insert number here] [insert units here] and output power [insert number here] [insert units here]

 

[1audio]

Re: Re: Multi Layer Ceramic Cap measurements

We actually got much better than you can do with a 7A22 at audio frequencies with the discrete setup. At best around 120dB CMRR @ 20kHz.

Geez, my 7A22 is all discrete.

John mentioned a particular opamp, I'll get one from him and build another fixture. At 20 KHz 120 dB suggests an exceptional balance in the associated components. And a small stray component could throw everything off. 1 part per million is very difficult to get in a stable way, suggesting 10 uV in 10 V.

 

[andy_c]

It will be in my "WWW" in 12 hours using better devices
with good models (no ON's). (directory .... frugalamp\other)
edit: its there now .. original and just OPS

Thanks!

Edit: Corrected files are attached. Q12 was reversed and there were some syntax errors in the model files.

 

[andy_c]

I have to nit-pick here. Since gain bandwidth product is equal to the unity loop gain frequency times the closed loop gain, a GBWP figure means rather little unless you know what the closed loop gain is.

You're right of course. I was thinking of a comparison of two amps with equal closed-loop gains.

 

[PH104]

Demian --

I have an extra AD524 or so to donate if John Curl does not have any spares.

 

[Steve Dunlap]

Good. Meantime, we got an extra zero and extra 19KHz. Now we are going somewhere.

Could you once and for ever clarify those numbers:

Distortion: [insert number here] [insert units here] at frequency [insert number here] [insert units here] and output power [insert number here] [insert units here]

I really don't see how I was misunderstood.

Distortion (THD) at twenty thousand Hz - 0.005%

Output power at 8 ohms - 400W

Distortion measured (not simulated) at rated power of 400W at 20KHz was 0.005%.

 

[Steve Dunlap]

Now that I have your attention, I will ask again.

Have any of you used LDRs in volume controls or as switches. What were your results and/or impressions.

I have not used them in these applications so I have no opinion. What I have read indicates they are both wonderful and very bad for these applications.

 

[PH104]

Steve -- Have you seen the thread "Lightspeed Attenuator a new passive preamp"? LDRs are discussed there.

 

[Steve Dunlap]

Steve -- Have you seen the thread "Lightspeed Attenuator a new passive preamp"? LDRs are discussed there.

Yes, I have seen that thread. I was hoping someone had measured the distortion that LDRs are claimed to introduce.

 

[jan.didden]

Now that I have your attention, I will ask again.

Have any of you used LDRs in volume controls or as switches. What were your results and/or impressions.

I have not used them in these applications so I have no opinion. What I have read indicates they are both wonderful and very bad for these applications.

Hi Steve,

I have experimented with LDR attenuators for audio many years ago. I abandoned them, never looked back because they were unacceptably noisy. As an attenuator they were doing OK closed loop. I used a DC component on the signal to linearize the control law, which worked like a charm, but the noise! Especially at low levels.
IIRC I used VACTEC units (LDR & LED), not sure the company even exists still.

Jan Didden

 

[PH104]

VACTEC does not exist anymore. Audio Research used to use their LDR/LEDs as series/shunts in the SP-6 preamp for output attenuation and were later found (or at least believed) to degrade the sound.