I recently got one for cheap, the moment I plugged it in, I noticed that it had excessive noise – a non-stop rustling sound, especially when the “Warmth” was turned all the way up. Google search turned up some threads and confirmed my suspicion that the PSU was not well filtered, and the PCB traces were not properly routed. In addition, running the 12AX7’s at 48V did not help its performance either.
Instead of doing some of the mods found at groupdiy, which involved replacing all the IC’s, and adding more local bypassing caps to the PCB. I decided it would be much easier to just scrap the stock PS PCB and replace it with a SMPS. At the same time, the tubes will run at HV with a DC-DC converter that I already have. And finally, the I/O PCB will be replaced with I/O transformers. The total budget for the above modifications should be less than $100, as I already have some of the parts on hand.
I got an idler turntable this weekend, it’s the ELAC Miracord 50H-II. It’s in pretty good condition except for the left channel RCA plug which was cut off, the arylic cover had some bad scratches on it, but otherwise, the mechanical condition was quite good for such old deck. The cartrige was junk, so I tried to put on a Shure M97 I had laying around, for some odd reason, I had to reverse the left hot and cold wiring, otherwise, it shorted out when the right channel was plugged in, weird! With the wires reversed, I was expecting some sort of L-R cancellation, but it played just fine, what was that about?!
The sound, even without any adjustment at all, no stylus alignment, VTA, etc., already sounded much better than the Technics SL-1200MK5G, so there’s something to the idler magic after all. I am mulling over whether to build a custom plinth for it or not. Since I like the way it sounds, I may just get some corner supports to replace the springs… we’ll see.
Today, I build a simple dufferential instrumentation amplifier consisting of TL072 and INA128. With it, I can now measure the impedance response of the OPT, choke, etc. The task is made simple by using the Syscomp CGR201’s built-in network analyzer function, which is set to sweep from 10Hz to 1MHz, and the voltages across the reference resistor (3.3k) and the primary winding the OPT are fed to Ch 1 and Ch 2 respectively. After exporting the resulting data to Excel, something like the following impedance vs. frequency plot can be plotted. From which, all the parameters of the OPT can be estimated.
I found some good MIDI tracks for New Order’s Bizzare Love Triangle, which could be great for remixing, so I used Bandstand and Audacity to create the individual tracks. The trick was to record the output from Bandstand with Audacity, after some fiddling around, this is the setup that I came up with, notice the routing via the Virtual Audio Cable in the Audacity settings below:
One of the neat thing that one can do with the Mackie 1640i, is using the Aux Send via Firewire to create a effects loop – just like with an analogue console (which it is), the only difference is no actual wiring is involved.
There are just a few steps required to do this:
- Press down the “Sends 1-6 to FW 9-14” button above the Aux SENDS pots.
- Create a channel in the DAW (I’m using Reaper), set its Input to any of the FW channels (9-14), depending on which AUX SEND you are using.
- Add the effect or effects that you want to the newly created channel, e.g., reverb, compressor, etc. Arm the channel for recoding, and set the Record Monitoring to On to hear or record the effect. I just set the output to the Main Mix, but you can always add it to a sub-group if desired.
- That’s it, just like with an analogue console, now you can control the level, EQ of the Fx by playing with the channel fader and/or the Aux Send levels.
- For those of you that want to get fancy, you can also automate the Fx by using the functions inside the DAW, but I’m happy just to twiddle with the knobs…
There were some recent discussion on the quality of the output transformer – vintage vs. modern, etc. It’s often been said that vintage Partidge OPT was hard to beat, but is it true? Pulling data from a couple of sources, I came up with the following comparison chart, it is pretty clear that there is indeed some truth to the Partridge’s legend… -3 dB at 80kHz!