Intact Audio

That's interesting, Gregg. Collins radio...I wonder why they went to the trouble? Question: do you remember the faders they used to have on control consoles in the 60's, with the ring of copper poles and the slider and the stepped attenuation resistors? Except the knob rotated smoooooooth as butter,...

That's very interesting. The other thing I see are the affected frequencies; for the LR, there are major changes in impedance from 100 Hz to 1 KHz - a crucial area of the spectrum - the LCR has already done with changing impedance by 100 Hz; 100 Hz and below is not at all a crucially important part ...

You're probably right; I do remember reading studies that suggested that phase shift wasn't very important. I suppose I was hoping that the majority of cuttings were made on one brand of machine with one "standard" reverse RIAA with predictable phase shifting; without that, I guess the onl...

Which brings up an interesting question:

the inverse RIAA that is used to cut the master with, what about phase shift?

It seems to me that a phono preamp should "undo" the phase shift built into the cutting EQ as well as the the frequency EQ's, no?

VB, Maturin

Dave, let me see if I understand you aright or if I have it all bolluxed up: the best way to terminate a mc cartridge is at the primary of the SUT (or at the output of the cartridge), and the SUT should then terminate into a very high impedance input amplification stage? I'm just trying to get the g...

Thanks. I didn't know about Ptplot, I'll look it up.

I'll also look at the LR thread; now that you mention it, I'd rather get rid of caps LOL.

VB, Maturin

Wow, this is killer. This is very close to the phono stage I wish to build. I would like to modify the EQ RIAA to eliminate the resistance, I think.

Question: what software are you using for the simulation and the distortion analysis?

VB, Maturin

Dave, I have a suggestion. Like most unsolicited suggestions, this means a lot more work for you than me LOL!! But, if you need help on this - I doubt you do - I will be happy to oblige. I cannot believe I never ran into inductive attenuators before, but wowowowowowwowoowow WHAT A GREAT IDEA!!!! Res...

Stephie, Thanks so much!! Now I have a new tool to use in LTSpice...heh heh heh. I have attached the waveform graph of U1anode vs U1screen. I can't figure out how to post a link that will display IN the post using dropbox; anybody know what I did wrong in the first post? Well, that was fun. Very Bes...

I am in awe of Dave's inductive volume controls - perfection. What I'm going to buy for my next project. This thread is just for the fun of it. I freely admit this circuit is a terrible idea...but it's MY terrible idea LOL. Actually, it's an old idea; using the screen to control gain - I just wanted...

LOL, I rather doubt I would learn something from you, Naz, but I appreciate the gracious gesture. Oh, good points - yes, the only thing the differential design does is eliminate common mode noise, my bad, I was being fast and sloppy. I first learned audio electronics in the 60's in radio, where a 60...

Thanks, Stephen. When you say lowish impedance EQ networks, I am not sure of the application, since the only EQ network I ever work with is RIAA for phono preamps. Is that what you mean, or something else?

Naz, truly nice work, both versions, the all-tube mu-stages and the using the cascoded DN2540's... ....I couldn't help wonder if going to all the trouble of using either design but in a fully differential manner might be a useful way to go cancel noise, power supply noise, and so on. I think that's ...

OK, I'll bite...just when I thought I'd seen everything...why are these resistors air-coils?

I'm not saying it's a bad idea, not at all, I just wonder why it's a good idea?

I presume, since you mounted them between wood discs, they must not get awfully hot LOL.

I'll be taking you up on this, Dave! I am designing an amp where there's no OPT - just hundreds of speakers in series in an array so that the impedance is high enough to be driven directly by a tube heh heh heh (yes, the output stage will be in the same cabinet as the speaker array; wouldn't want a ...

Dave, love your attitude. Couldn't agree more. The people who have always been the greatest impediment to the advancement of any field of knowledge are always the experts who think they already know everything...there's no substitute for "try it, see wha' happens!!" The Hubble Telescope ha...

very cool, thanks, Lars Question for everyone: for small signal work, including REALLY small signal work (mm or even mc cartridges, playback heads, etc - but not RF stuff), what is the advantage of a D3A over the EF86? The steilheit of the D3A is 35 mA/V, whereas for the EF86 it is but 1.8 mA/V, so ...

Ah, most excellent!!! Thanks!!

Are D3A's actually still available? Anybody know?

All these great D3A circuits and circuit ideas - but where to get the tube?

Some one recently pointed out to me the wisdom of using EF86's for small signal pentode work: "they're still in production"...Amen!!!

sbench: thanks for your comments. I will use that tip of inputting a .wav and listening...or perhaps viewing?...the output. I once did the following: I'd play a passage of vinyl, and take a photograph of the oscilloscope screen displaying the input to a stage at a certain point in the (classical) mu...

Re: screen regulation: well, in simulations, I just use a voltage source to the screen and bypass it to the cathode. I look at the data sheet for the pentode and the data sheet is usually pretty specific about what the screen likes to be at. Another sim short-cut would be to use a current source to ...

FWIW, one way to improve all the circuits in this thread is to regulate that screen; dropping down voltage to the screen from B+ with a bypass cap to cathode is in my understanding not the best way to run a pentode. But, in any case, a phono preamp circuit that rolls off at 20 KHz is not going to so...