Hi All,
I have a Stanton DJF-1 that I'd like to tweak out a bit. Its a dual 4 pole filter with line and RIAA inputs. Runs at -10 unbalanced. What I hope to accomplish is basically reduce or eliminate the noise floor, and bring the output up to +4.
The RIAA input is based on an LM833 and comes straight out of National's application guide for that chip: http://www.national.com/an/AN/AN-346.pdf). The output of the RIAA amp and the line input both pass through the line input buffer (TL072) and on to the filter circuit.
From looking at the schematic, it looks like each filter has its own input buffer (again LM833) and output buffer (TL074). Is that correct? When you run the filters in parallel (notch mode) the output of the filter sections is summed using another TL072. When you run the filters in serial, the output of filter 2 acts a the final output buffer. But what's interesting is that the schematic seems to indicate that the output is DC coupled... Basically What I want to do is balance the final output with a step up transformer (1:4 ???). How do I calculate the output impedance of the circuit? What's an acceptable buffer output impedance to be able to adequately push such a tranny? Will the transformer's output impedance be too high?
Finally, would there be any noticeable benefit to replacing the buffer amps with higher spec'd parts? Of course I'm going to do the obligatory coupling cap upgrade/bypass.
Also, looking at the power supply, am I dumb or does this thing have two rails? There are markings for +-12V and +-VV... ??? Why would they do that when all the opamps in the circuit can be run off one rail? But anyway, 12v would be rather low for the opamps right?
Schematic attached. Thanks in advance!
Mark
I have a Stanton DJF-1 that I'd like to tweak out a bit. Its a dual 4 pole filter with line and RIAA inputs. Runs at -10 unbalanced. What I hope to accomplish is basically reduce or eliminate the noise floor, and bring the output up to +4.
The RIAA input is based on an LM833 and comes straight out of National's application guide for that chip: http://www.national.com/an/AN/AN-346.pdf). The output of the RIAA amp and the line input both pass through the line input buffer (TL072) and on to the filter circuit.
From looking at the schematic, it looks like each filter has its own input buffer (again LM833) and output buffer (TL074). Is that correct? When you run the filters in parallel (notch mode) the output of the filter sections is summed using another TL072. When you run the filters in serial, the output of filter 2 acts a the final output buffer. But what's interesting is that the schematic seems to indicate that the output is DC coupled... Basically What I want to do is balance the final output with a step up transformer (1:4 ???). How do I calculate the output impedance of the circuit? What's an acceptable buffer output impedance to be able to adequately push such a tranny? Will the transformer's output impedance be too high?
Finally, would there be any noticeable benefit to replacing the buffer amps with higher spec'd parts? Of course I'm going to do the obligatory coupling cap upgrade/bypass.
Also, looking at the power supply, am I dumb or does this thing have two rails? There are markings for +-12V and +-VV... ??? Why would they do that when all the opamps in the circuit can be run off one rail? But anyway, 12v would be rather low for the opamps right?
Schematic attached. Thanks in advance!
Mark