'The Secret of Tube Amplifiers Revealed - and much more!'

[kikey]

Interesting new book:

http://www.diyaudio.com/forums/vendors-bazaar/157787-secret-tube-amplifiers-revealed-much-more.html

www.current-drive.info

I know that high output impedance can be a good thing when it comes to creating a good guitar sound, but this book seem to take the discussion to higher level 

What do you think?

[teemuk]

He seems to market the topology like it's a new thing though it's been known at least since 1950's and used in various solid-state amplifiers since mid 1960's - most often in instrument amplifiers due to mentioned deficiency of introducing a very non-linear frequency response.

Also, designing a good current amplifier is a rather complex task due to numerous issues such as requirement for high output voltage swings with great current demand - practically equaling a requirement of very high power amplifiers. I also discuss some of these topics in my book.

[phatt]

Hi kikey, short answer,, BTDT,,, next please

IF and it's a mighty big if I walked into a music shop and the moment I played a SS Amp with CDrive my brain went WOW man this must be Current Drive,,
Then I'd be looking deeper but it did not happen for me.

Yes it does technically improve things but sonically on stage at a live gig with everything cranked you will never notice it,
Use of such slick ideas won't make you famous.  
I tend to leave all that out there ideas for the HiFi set.
Guitar amp hobby geeks are a little crazy but those HiFi chaps are on another planet :duh
my 2 cents worth.
Phil.

[joecool85]

Guitar amp hooby geeks are a little crazy but those HiFi chaps are on another planet :duh
my 2 cents worth.
Phil.

I agree entirely.

[J M Fahey]

Hi Kikey, thanks a lot for the link.
I'm *sure* the book is very interesting, and worth reading.
*I* would read it and I'm sure I will learn a couple good things, no doubt.
Download Teemu's book, it's very well written and interesting .

[Joe]

With any technology there is an equation of cost, usability, and performance which is solved over time. Cost is the predominant factor, and it affects the audio industry like any other. From a practical standpoint I'd say "no", but a current amp might make a good DIY project.

Of course phrases like "the FATAL FLAWS of voltage drive" are always entertaining.

Something related here (kinda technical):
http://www.essex.ac.uk/csee/research/audio_lab/malcolmspubdocs/J12%20Distortion%20reduction%20MC%20current%20drive.pdf

Teemuk's book (starting at page 87) also offers a good introduction to the differences between the amplifier types.

[kikey]

Thanks for the replies and the link 
Nice to see that we have open minded people on this forum.

Here is another current drive link:
http://www.lenardaudio.com/education/13_guitar_amps_3.html

I find current drive an interesting approch for a guitar amp.
Some Peavey and Vox designs are clearly inspired by current drive.
Many tube amps (without nfb) are basically current drive.
I suppose many classic speaker models are designed for high output impedance(?)

I find rowdy_riemer's 'CMOS amp' an interesting and simplistic approch for current drive.
http://www.ssguitar.com/index.php?topic=1177.0
I am working on an amp inspired of rowdy's amp. 

Have you seen other current drive projects on this forum?

Best Regards

[phatt]

Hello kikey,

If it interests you I've built a lot of these things and had little success.

The best I ever got was experimenting with a small noname amp.
By running the mains (primary) through a 40Watt light bulb did wonders for the compression.

This allowed the *clean channel* to sound much more like a  compressing output stage of a tube amp.
Like a vast majority of SS amps the clean is *Super clean* and the drive has vastly to much distortion.
There are few SSamps that produce that *middle ground rattle* that Valves do so well.
You need to trial a few different wattage light bulbs to get more or less
compression.

BTW don't try this trick on Amps with a whole lot of switching circuitry as
things may well go all haywire once the light bulb starts to sag the supply.
Do it with simple Amp designs, preferably really simple discrete component types.
My best guess is that chipamps have to many current source/mirrors an all the fancy hi fi tricks. They maywell be *To accurate* You need chaps like Teemu and J M Fahey to explain the indepth stuff.

Re the Lenard stuff,, Very good ground work on your part and it's well explained.
My beef with these chaps who know so much more than little ol me.

***They never bother to show a *REAL LIVE TEST*.
ie a shootout between Valve an SS

I do not doubt their ability to understand the maths but in all my testing of
things that make these claims very few have ever really worked as implied.

I cite my Maxiverb Reverb circuit as example;
My desire to build a simple Spring Reverb took me on a wild and wooly roundabout.
The Overwhelming Opinion on driving Reverb transducers was to use *Current Drive*.

An being only a novice I could only assume it was me making all the mistakes. I would probably qualify as being the builder of nearly all the reverb circuits on the net, as well as what circuits I found in books. :duh

10 years latter I built my Maxiverb stand alone Reverb.
Finally I got one that delivered the sound,,, an guess what?
YEP **Voltage Driven**. which just leaves most C drive circuits sounding like toys. (Listen to my PhabbTone Demo Clips,, the reverb is on *1* 8|)

I can only assume the Cdrive maths they use is correct BUT there is something missing in their equations.
Armed only with limited knowledge all I can come up with is this observation.
Current drive or not *Without voltage not much can happen*.

Re The 90% increase to the speaker mentioned on Lenard page might not be talking about *What you Hear*, in other words it might imply to the novice that you get almost *double the wattage*,,, (or SPL is doubled).

I don't think that is what is meant but I'm not the expert.

In all my experiments with these ideas there is a drop in output power or SPL.
Again,,I'm not the expert and may have missed the *Oh I see bit*.
Don't get me wrong Kikey,,I'm quite happy to give you all that I learnt from
experamenting with such ideas.
If you have an idea in your head that you can't let go of,,
then just *DO IT* and damn what others say.
I had to do that with my reverb and that's hard to do when all the experts point the other way.

Sadly that lil' amp with the light bulb is long gone,, I sold it but I may have some schematics down in the shed. Having moved twice since then I can't promise much.
have fun, Phil.

[rowdy_riemer]

I find rowdy_riemer's 'CMOS amp' an interesting and simplistic approch for current drive.
http://www.ssguitar.com/index.php?topic=1177.0
I am working on an amp inspired of rowdy's amp.

Awesome!!! Let me know how it turns out.

[phatt]

Kikey and rowdy,, Re http://www.ssguitar.com/index.php?topic=1177.0
I don't think that circuit would be current drive?
Anyone care to elaborate,,,Headscratch?
Phil.

[rowdy_riemer]

I'm not claiming it is. I'm just glad someone is interested in doing something with the design. All it really does is allow you to vary the negative feedback, so with little feedback, the damping factor is low, possibly making it sound a little more like a tube amp with no negative feedback. When the speaker impedance is low, it will load down the amp a bit limiting the current through the speaker, but there is, of course, no active current control.

[kikey]

Awesome!!! Let me know how it turns out.

Thanks rowdy ! 
Do you have any sound clips available from your experiments?

My idea is lower the quiescent current and use temperature compensation.
This would make it possible increase the supply voltage.
Since there will be very little nfb I will need a dc-servo.

There is, of course, no active current control and its not true 'current drive'.
But thats the charm with it, I think that makes it more simplistic and 'tube like'.

How many times have you heard "ss-amps are super-clean and clips ugly"?
I think this is one way to change that and thats why I find this idea so interesting.

[rowdy_riemer]

I posted some sound clips, but apparently the links do not work any more. I'll fix the links and let you know.

[rowdy_riemer]

Ok, I've reposted the sound clips.