Last post by kunlun121 - April 03, 2022, 07:30:17 PM
I'm trying to figure out how to best provide unregulated DC power to the SSR01 boards. I am using a toroidal transformer and a basic discrete full wave bridge rectifier with some smoothing caps before the SSR01.
I'd like to know how much smoothing is necessary. Or better, the minimum amount of smoothing I can get away with. Can you advise about the minimum total size of the smoothing capacitance required for optimal operation of the super regulators? Or would you advise to maximise smoothing capacitance given the available space on my boards?
The application at hand is the 30V version I ordered the boards for. I want to use it for a minimalistic phono stage, so the load is pretty insignificant. But I'd like to know this number for different voltages / applications too. Is there relatively straightforward way of calculating that for different voltages? What are the relevant variables in determining the minimum smoothing capacity?
Thank you for looking into this.
BTW and off-topic: please find some other way of ascertaining that I am not a robot. These letter combination images are impossible to read, also for a living breathing if ageing human in need of reading glasses...
Last post by W1DAN - February 01, 2021, 02:57:29 AM
The RIAA stage came up fine for the left channel. On the right channel RIAA section I still have some offset on the output when the preamp has 10mv at TP1. For now I inserted a 10UF capacitor in series with R93, and the main output DC is now fine.
On the preamp DC servo amp IC1, when my test oscillator is set to 20hz, I see a sine wave on the output pin 6, as well as a little at C9. Would this AC audio correction signal "subtract" the from the main signal low frequency audio? Either way I added 10uF across C9 to make the correction voltage pure DC.
I'm listening to the preamp now-sounds clean. I will then look for the cause of the right channel DC offset and eliminate the audio coupling capacitor.
Good progress this weekend! Thank you again for your assistance!!
Last post by W1DAN - January 31, 2021, 05:34:59 PM
Hi Per Anders:
Adding 330PF capacitors directly at the base of T35 and T36 (paralleling C17 andC18 except close to the transistors) reduces the oscillation at the output of the preamp section without affecting the frequency response at 20KHz. Earlier I tried an 0.1uf capacitor and 10KHz was attenuated by more than half, so that was no good.
I am wondering if the physical distance of C17 and C18 to the bases of the emitter followers allows the oscillation?
Last post by W1DAN - January 30, 2021, 11:31:54 PM
The oscillation goes away when the power is turned off.
Definitely coming from the preamp sections, not the RIAA stages. I lifted R50 to separate the gain stage from the emitter followers. The oscillation appears at the emitter follower section. I confirmed that C103 and C104 are 100nF.
I also am a radio ham and broadcast engineer, and work on RF on both my radio hobby and at work, but there with slightly higher power of 88kW. :-)