Quick question:
I had my FSP configured for 43dB gain with 68R R2 and 5k6 R13. I have now reconfigured the input stage to accommodate low output MC carts by populating Q1 and Q2 (Idss for the quad at about 11.7mA), populating R2 and R3 with 5R and changing R12 to 1k2. I also added a nice fat RN65E 100R input loading resistor.
I haven't fired it up yet, and the bias setting is still unchanged from the previous configuration. What can I expect when I connect power to the circuit? Should I just fire it up or should I change the VR2x setting to lower Rail+ just in case?
I had my FSP configured for 43dB gain with 68R R2 and 5k6 R13. I have now reconfigured the input stage to accommodate low output MC carts by populating Q1 and Q2 (Idss for the quad at about 11.7mA), populating R2 and R3 with 5R and changing R12 to 1k2. I also added a nice fat RN65E 100R input loading resistor.
I haven't fired it up yet, and the bias setting is still unchanged from the previous configuration. What can I expect when I connect power to the circuit? Should I just fire it up or should I change the VR2x setting to lower Rail+ just in case?
Attachments
Haven’t had time to do any further experiments, apart from turning the scope on and having another quick peek in between chores. It seems where I have set up the scope there is quite a lot of ac interference. Just moving the probe around the bench can pick up anywhere from 50 - 200 mV. This is with the all other equipment turned off. So I moved the power board you can see in one of pictures away and this helped, although there is still ac in the air. I see what you mean by lab work arounds Salas. Dealing with low voltages like those from a moving coil cart must require a very hum free environment. I’m on a mission to clean up my bench and try reduce all the noise.
Yesterday afternoon, with much patience, I managed to bias the newly configured MC phono stage. It took about three hours of fiddling (open lid, change setting, close lid, wait for circuit to settle, repeat). In the end I got the two channels to show the same behaviour, almost as if they were tracking. During measurement the TP1-TP2 voltage varied from 3.58V to 3.62V, depending on ambient temperature and air current or even breathing in the circuit's general direction.
The good news is that the circuit is dead quiet. With the volume all the way up and my ear next to the speaker, I can barely discern if the phono stage is switched on or off. Having the PSU in a separate enclosure and having a shielded, generously oversized toroidal transformer definitely paid off here.
I only had time to listen to two records, but I can already say that I like what I'm hearing. I'll see if I can pull some numbers from the phono stage in the coming days (gain, S/N, THD, THD+N, maybe an FFT).
The good news is that the circuit is dead quiet. With the volume all the way up and my ear next to the speaker, I can barely discern if the phono stage is switched on or off. Having the PSU in a separate enclosure and having a shielded, generously oversized toroidal transformer definitely paid off here.
I only had time to listen to two records, but I can already say that I like what I'm hearing. I'll see if I can pull some numbers from the phono stage in the coming days (gain, S/N, THD, THD+N, maybe an FFT).
Attachments
After few months of construction, Salas FSP is ready tested and with chassis and I decided to share this nice Phono with all of you.
Great. Congratulations
How do you like it? What gear is in the rest of the audio system except those shown?
Great. Congratulations
How do you like it? What gear is in the rest of the audio system except those shown?
Technics SL-Q2 / Denon DL-301 MC
FSP MC High Gain
Borbely Class A line Amp (DIY)
Electrocompaniet, The Two channel Audio Power Amplifier (DIY)
Quad ESL57
The silver unit on top of the Line Preamp is an Esoteric E-03 Phono Preamp (SRPP ~$6000) which I use for test/compare my FSP
I really like the FSP phono a lot, it's been a while since the last time I listen to LP (15years maybe) so it was a come back to analogue sound.
After little tuning and break-in period for both Phono and Cartridge it turns out
very nice with powerful dynamic sound with very nice tone , extended stage specially on the front to back, and nice musicality. Compared to the $6000 Esoteric is by far more musical, maybe less dynamic, but E-03 is Very clinical in comparison it's sounds like a bad first generation CD Player
Also I almost forgot, DEAD Silent
Bravo Salas!!
Thanos
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Hi Lampes, nice work, I’m really impressed. May I ask what enclosures you are using. I have been working on my own enclosure made from birch ply ant Aluminum sheet but had an unfortunate accident with a drill bit recently. I’m ok but the enclosure looks terrible. I’m thinking maybe buying something like yours may be money well spent. Thank you 
I have a question about using 2sa970 vs bc560c. The build guide says the "970
is more linear if you can get it". I was not able to find any 970BL, but did manage
to buy some 970GR and found a pair with Hfe just over 350.
The guide also says "the more Hfe the better".
Since BC560C's range is 420-800, I might be able to find parts with significantly
higher Hfe than the 970 pair I have.
Any thought on whether it's better to use high Hfe BC560C than the low Hfe 970gr?
Thanks,
Dennis
is more linear if you can get it". I was not able to find any 970BL, but did manage
to buy some 970GR and found a pair with Hfe just over 350.
The guide also says "the more Hfe the better".
Since BC560C's range is 420-800, I might be able to find parts with significantly
higher Hfe than the 970 pair I have.
Any thought on whether it's better to use high Hfe BC560C than the low Hfe 970gr?
Thanks,
Dennis