A Welcome to EP For AudioGuru

[CDRIVE]

Audioguru, welcome to EP. Are you still as crotchety as you were on that other forum that I don't mention here?

For those of you that don't know Audioguru (AG), he's exceedingly proficient in audio design spanning from vacuum tubes to solid state but he has spent a lifetime honing the most abrupt, contrary, persona you can ever hope not to encounter. How y'all react to it will depend on you. For me it's always been a love hate emotion.

Chris

Mods, can you please correct my typo in the title?

 

[Arouse1973]

Yeah seen him on other forums. He seems alright
Adam

 

[CDRIVE]

Adam, I remember posts like this...

Nube:
Hi, here's my schematic. It should output 3W of audio but only puts out 500mW. Can someone tell me what I'm doing wrong?

AG:
You're circuit is crap!

Eventually AG would give the poor slug what he needed but not without AG's signature prologue. Heck, when he didn't open with one of those I thought he was sick!

AG, I hope you're taking this with the humor intended.... A 'Celebratory Roast'.

Chris

 

[Arouse1973]

LOL yeah I was joking
Adam

 

[CDRIVE]

Hi Adam. Actually I don't even expect AG to respond to this thread. He's a consummate ElectronHead that does not engage (I think he's Borg! ) in social commentary. On the other hand if you want to build an exceptional audio amplifier you can't go wrong picking his brain. His member name (AudioGuru) is not an embellishment.

I used to love busting his b!lls because there were never any retorts. It's like telling your PC you hate it and expecting a response!

Chris

 

[Audioguru]

I say it like it is. I uploaded my avatar now.

 

[(*steve*)]

I say it like it is. I uploaded my avatar now.

Perfectly reasonable.

But we prefer if you back up criticism with helpful advice.

 

[shrtrnd]

Sounds to me like Audioguru finally found the best website of its type on the internet.
It'll be good to have another high-quality, knowledgeable member here.

 

[KJ6EAD]

I'm glad you're here AG. I've been wanting to build a 741/747 based audophile quality headphone amplifier. Where should I start?

 

[CDRIVE]

Perfectly reasonable.

But we prefer if you back up criticism with helpful advice.

Unlike someone else we know (who's also knowledgeable) but is a word minimalist, who sometimes (most times) blurts out crap, AG is very helpful. He just doesn't have any tolerance for questions that he may consider 'Too Damn Basic'. Sometimes you have to prod the man to give it up .

I think most will find his Ebenezer Scrooge persona to be an acceptable door charge that must be paid if they want his help.

Chris

 

[CDRIVE]

I'm glad you're here AG. I've been wanting to build a 741/747 based audophile quality headphone amplifier. Where should I start?

OMG!!! I remember stuff like that! Talk about a Catalyst for a rant!!

Chris

 

[Audioguru]

The "general purpose" 741 opamp is about 48 years old. I made a headphones amplifier with one about 45 years ago and it sounded awful. Modern audio opamps are much better.

 

[CDRIVE]

Surely you're playing with me. You know you're being on your best behavior. Mentioning a 741 to you is like waving a crucifix in front of Dracula.

Chris

 

[(*steve*)]

Modern audio opamps are much better.

Hey @Audioguru, I'm in the process of designing a hybrid valve preamp using a small directly heated Soviet tube (1j24b). The intent is that it will be battery powered and built as a kit. I'm using a DSA to evaluate early prototypes for frequency response, gain, and distortion using a swept sine input.

Audio op-amps are being used to buffer the the input and output, provide a small amount of additional gain either before or after the valve stage, and to perform a voltage shift to set the tube bias. The tube is running in triode mode, without feedback, with a low (18V) HT, and an active load. Currently I am getting a gain of around 19dB flat (3dB) from 1Hz to 16kHz and a distortion of around 0.6%.

The active load is a constant current source with an impedance of around 500k. The grid bias is adjusted by essentially a very low frequency feedback loop to maintain the operating point (in early tests I have adjusted it manually).

A "distortion" control alters the gain before and after the tube to allow the amplitude of the signal into the tube to be changed with minimal change the overall gain.

This is the first real design I've done with tubes and I would welcome any hints you might be able to offer.

Mostly I am interested in any observations you might have as to any gotcha's for young players. My early results are in this thread, if you're interested.

If you are interested in giving a beginner some advice, I'll post the schematic in the thread I mentioned above. Currently I am 5376km from home (via road) so it may take a short while to get hold of it.

For those of you in small countries, yes, I am still in the same country and I'm only 2 states away from home.

 

[Audioguru]

My first amplifier used tubes and was a Heathkit about 53 years ago. It sounded good for a month or two then the distortion became noticeable. The MacIntosh amplifier clinic tested its distortion and found it to be about 20%! Replacing the tubes reduced the distortion for a month or two again and again. Some rock groups replace their tubes before each show!

About 50 years ago I sold my tube amplifier to an old geezer and bought an HH Scott solid state receiver that I still use today. It never produces distortion.

 

[(*steve*)]

It never produces distortion

I'm not a person who likes distortion. Unfortunately there are a large number of musicians who like "tube sound". My understanding is that running the valve at significantly lower than its rated power will yield longer tube life. This is largely an experiment for me, however the muso's seem to be getting excited.

 

[Audioguru]

Like a transistor with no negative feedback, a tube with no negative feedback produces even harmonics that are "musical". But added harmonics are distortion that should not be present.

Even harmonics are when one half of the waveform is squashed, either the positive going (usually) or the negative going.

I agree that a tube operating at low power will last long but it is not operating correctly and might produce more distortion than if it had its normal power.

 

[hevans1944]

I say it like it is. I uploaded my avatar now.

Nice avatar. And welcome to Electronics Point.

Thank you for responding to the noob who posted in this thread.

Hop