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Hi!

Welcome to my DIY audio forum.

Cheers
Per-Anders Sjöström

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#31
Power supplies / Re: SSR01 => unregulated DC in...
Last post by peranders - April 06, 2022, 07:44:50 PM
For inspiration you can check how SSR04 is designed.

Important for design: What is the max current consumption of your amps?
#32
Power supplies / SSR01 => unregulated DC input ...
Last post by kunlun121 - April 03, 2022, 07:30:17 PM
Hi Per-Anders,

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...
#33
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by W1DAN - February 13, 2021, 01:57:44 AM
Hej Per Anders!

I would like to increase the gain about 6dB. Would I increase R51 to do this?

I am using a MM cartridge and the preamp is working pretty well (still have an issue with the right channel DC offset without input termination).

Thank you,
Dan
#34
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by W1DAN - February 01, 2021, 02:57:29 AM
Per Anders:

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!!

Cheers,
Dan
#35
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
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?

On to the RIAA section!

Thank you,
Dan
#36
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by peranders - January 31, 2021, 04:26:35 PM
If you use the keywords "emitter follower oscillation", I'm sure you can find something.

I think you can put that aside and try to get the RIAA stage to get working properly.
#37
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by W1DAN - January 31, 2021, 02:43:40 PM
Per Anders:

Each transistor is mounted between 0.6cm to 1cm above the board.

I thought being an emitter follower, which normally having gain less than 1, could not oscillate?

Thank you,
Dan
#38
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by peranders - January 31, 2021, 07:14:43 AM
Emitter followers can oscillate under certain conditions although it's much easier with power mosfets. How near the pcb have you mounted the transistors?
#39
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by W1DAN - January 30, 2021, 11:31:54 PM
Per Anders:

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. :-)

Dan
#40
Phono RIAA amplifiers / Re: QSXM2 troubleshooting!!
Last post by peranders - January 30, 2021, 09:07:17 PM
If you turn off the power, do you still have the oscillation? For being an oscillation with BC transistors I think the frequency is very high. 1-10 MHz seems more natural.