Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lauri on August 05, 2014, 10:24:37 am

Title: Octave down effect with tubes
Post by: Lauri on August 05, 2014, 10:24:37 am

I was trying to find out if anyone has ever made a octave down effect using tubes, but after searching the internets for hours I didn't find anything useful. So here's a circuit I put together and it works pretty well.

Schematic:
http://www.kolumbus.fi/~kp5188/musiikki/octaver.png (http://www.kolumbus.fi/~kp5188/musiikki/octaver.png)
First double triode is just a regular voltage amplifier and low pass filter. Second one converts the signal to square wave and the third one is a flip-flop circuit.

Sound sample:
http://www.kolumbus.fi/~kp5188/musiikki/octaver.flac (http://www.kolumbus.fi/~kp5188/musiikki/octaver.flac)

Title: Re: Octave down effect with tubes
Post by: eleventeen on August 05, 2014, 10:29:42 am

Oh yeah!! I made something like that (using tubes) when I was a kid. And a ring modulator, too. Trouble is...the sophistication and response time you can get with modern op-amps will probably devastate tube performance by any measure. Cool, though!!

Title: Re: Octave down effect with tubes
Post by: PRR on August 05, 2014, 09:08:09 pm

Very clever.

Title: Re: Octave down effect with tubes
Post by: EL34 on August 10, 2014, 09:45:47 am

Cool circuit!
Sounds cool too

Title: Re: Octave down effect with tubes
Post by: jojokeo on August 11, 2014, 02:56:00 am

Is this made as a stand-alone effect unit? I've did a bunch of R&D work on an old effects circuit that gives a bit of octave down called the Harmonic Percolator but it's much more subtle and actually more of a side effect of the circuit, not it's main purpose.

Title: Re: Octave down effect with tubes
Post by: tubeswell on August 11, 2014, 09:56:06 am

Awesome Lauri. Thanks for sharing.

Title: Re: Octave down effect with tubes
Post by: Lauri on August 12, 2014, 10:53:48 am

Quote from: jojokeo on August 11, 2014, 02:56:00 am

Is this made as a stand-alone effect unit?

Right now it's made on a test chassis. At some point I will either make an amp that will have it integrated in it or a stand alone unit.

Title: Re: Octave down effect with tubes
Post by: kagliostro on August 25, 2014, 03:23:36 am

Ciao Lauri

intriguing circuit  :smiley:

---

Which is the value of R1 ? Is it the "standard" 1M resistor ?

Thanks

K

Title: Re: Octave down effect with tubes
Post by: Lauri on August 27, 2014, 10:10:09 am

Quote from: kagliostro on August 25, 2014, 03:23:36 am

Which is the value of R1 ? Is it the "standard" 1M resistor ?

Yes it can be 1M or whatever you want the input resistance to be.

Title: Re: Octave down effect with tubes
Post by: kagliostro on August 27, 2014, 10:33:45 am

Thanks Lauri

K

Title: Re: Octave down effect with tubes
Post by: Lauri on September 02, 2014, 07:27:50 am

Here's the schematic and a picture of a stand alone octaver unit I built.
http://www.kolumbus.fi/~kp5188/musiikki/octaversch.png (http://www.kolumbus.fi/~kp5188/musiikki/octaversch.png)
http://www.kolumbus.fi/~kp5188/musiikki/octaverpic.png (http://www.kolumbus.fi/~kp5188/musiikki/octaverpic.png)

Title: Re: Octave down effect with tubes
Post by: kagliostro on September 02, 2014, 07:50:56 am

Thanks for sharing

I've a question for you

I see a pair of CF (U1A = ECC83 - U2A = ECC82) acting on a mix pot and a plate follower U2B = ECC82 as output

Why your choice was to ave a plate follower at the output instead of a CF ?

K

Title: Re: Octave down effect with tubes
Post by: Lauri on September 02, 2014, 08:08:04 am

With cathode follower as the output stage the output signal would be 180 degrees out of phase with the input signal. Which usually isn't a problem but I wanted the input and output to be in phase in case I use it in parallel with something else.

Title: Re: Octave down effect with tubes
Post by: kagliostro on September 03, 2014, 10:12:46 am

I understand, OK


Thanks for the answer


Franco

Title: Re: Octave down effect with tubes
Post by: Lauri on September 04, 2014, 02:30:53 pm

Here's another flip flop circuit that seems to work quite a bit better than the one in my earlier posts.
http://www.kolumbus.fi/~kp5188/musiikki/flipflop2.png (http://www.kolumbus.fi/~kp5188/musiikki/flipflop2.png)

Title: Re: Octave down effect with tubes
Post by: PRR on September 16, 2014, 12:15:30 am

> another flip flop circuit

Very ordinary.

But yes, grid-toggled is easier to slap than plate-toggled.

Tube-type is not critical. This specific plan has low-value resistors, so for a higher supply voltage you may need 12BH7 beef. But you could raise all resistances by a factor of 2 or 5 or 10 and use 12AU7. Would probably work with 12AT7 or 12AX7, real snappy.

R1 does not need to be scaled-up.

C2 C3 improve swithing time which might *not* be needed, or even best, for audio. I'd try leaving them out (save 12 cents and several solder joints).

D1 D2 could be 1N914-like small diodes; there's no need for 1 Amp parts here.