[sdiy] pining for old oscilloscope (weird LFO's)

[anthony]

Today I'm really needing to look at LFO waveforms on my scope and this 60 
MHz doesn't want to do it. I mean it CAN do it - it just seems liek the 
phosphors are way to fast to be of much use. At around 8 Hz I can see a 
square wave and sine wave shape quite plainly albeit faintly. I think my old 
Heathkit would have been FAB for this.

I'm looking at various stages of the LFO waveform of my DOD R-870 
Flanger/Doubler. Tweaking this unit is becoming problematic because the LFO 
seems to be a sinewave ultimately derived by a squarewave oscillator which 
shapes it with a big cap and a resistor (integrator).

The problem is that trying to use this as a normal flanger is very 
unsatisfactory because it doesn't make long sweeps. It just doesn't sound 
"right". And this being a rack unit I have a ton of parametrs to tweak and 
none of them sound right when trying to gert a flanger sound. However, 
chorus and vibrato are superb. But I've been having bad luck getting the LFO 
speed to go faster. At first I had a problem with the LFO ticking, but I 
matched some resistor pairs for a couple of voltage dividers related to this 
circuit (and the regen) and that fixed several problems.

I actualy think it's probably pointless to bother with the flanger part 
because this unit has an MN3005 for the doubler part and that's where I 
spend most of my time. It's like having a Boss DM2 with all the controls of 
a Boss BF2 and more (or maybe I should say like a DOD 585 and a DOD 575...). 
I like the analog delay sound so much more than digital (and I really really 
like the way my Digitech PDS2000 sounds). I just wish it had 2 or 3 MN3005's 
instead of just one.

The way the clock works is kinda screwy too. I think using an SAD512 and an 
MN3005 together is a bad idea. They realised that they should send the 
single-phase clock to the SAD512 before it gets divided by 2 for the MN3005, 
but the SAD512 divides its clock by 2 as well. So really although it looks 
like a 20kHz-400kHz clock is going to the 512 it's really only a 
20kHz-200kHz clock. That + the sine waveform = not a good flanger. I 
wouldn't gripe except I don't have a usable flanger that I like. I have been 
considering making a Bad Stone clone because stackign up a lot of BBD 
effects almost always results in clocks interfering no matter how hard I 
try.

BUT what would be a good way to get this kind of LFO to go faster AND make 
smoother slow sweeps?