Posted: 30 Jul 2007, 01:24
Hello again
I have re-designed the Demeter oscillator section of the tremulator schematic posted by Torchy, which is just a badly designed triangle wave.
First - I simulated the schaller oscillator in markm's heart throb tremelo, and found it to be a lot similar in design to the classic Fender 12AX7 oscillator (phase shift oscillator type), but realised with an NPN bipolar transistor. However the sine wave function is not very clean and I suspect it cuts the transistor off on it's negative sweep - SO - I simulated an opamp version which gave a very clean sine wave, BUT needed a triple ganged pot to shift the frequency of oscillation.
OKAY - I googled and came up with a National Semiconductors application note using LM101 and LM111 devices.
After several hours simulating and adjusting this, I came up with a damn near perfect pure sine wave oscillator that only requires a single ganged 50k linear pot to tune from slow to super fast.
Armed with this new oscillator schematic, I attacked the demeter board, cutting and moving tracks and replacing components etc.
I retained the LF 442 op amp and reduced the gain of the led driver that follows the oscillator to 13dB (was 27dB).
I plugged my guitar in and WOW, this tremelo is smooth as No sign of any choppiness or uneven - sounds almost like a leslie on very fast setting ( which is something I will be using this oscillator in in future )
I wonder if I should give Ry Cooder a phone call
ANYWAY - Enough raving - I will redraw the board layout and schematic etc. and post for all to build in the next few days - YOU will like it much better than the Heart Throb or stock Demeter versions.
Stay tuned
bajaman
I have re-designed the Demeter oscillator section of the tremulator schematic posted by Torchy, which is just a badly designed triangle wave.
First - I simulated the schaller oscillator in markm's heart throb tremelo, and found it to be a lot similar in design to the classic Fender 12AX7 oscillator (phase shift oscillator type), but realised with an NPN bipolar transistor. However the sine wave function is not very clean and I suspect it cuts the transistor off on it's negative sweep - SO - I simulated an opamp version which gave a very clean sine wave, BUT needed a triple ganged pot to shift the frequency of oscillation.
OKAY - I googled and came up with a National Semiconductors application note using LM101 and LM111 devices.
After several hours simulating and adjusting this, I came up with a damn near perfect pure sine wave oscillator that only requires a single ganged 50k linear pot to tune from slow to super fast.
Armed with this new oscillator schematic, I attacked the demeter board, cutting and moving tracks and replacing components etc.
I retained the LF 442 op amp and reduced the gain of the led driver that follows the oscillator to 13dB (was 27dB).
I plugged my guitar in and WOW, this tremelo is smooth as No sign of any choppiness or uneven - sounds almost like a leslie on very fast setting ( which is something I will be using this oscillator in in future )
I wonder if I should give Ry Cooder a phone call
ANYWAY - Enough raving - I will redraw the board layout and schematic etc. and post for all to build in the next few days - YOU will like it much better than the Heart Throb or stock Demeter versions.
Stay tuned
bajaman