Offset adjustment
Hi LC,
The offset of one channel is at 30 mV after half an hour. Can I adjust it by turning tr1 ?
Since I am about to press button 'add to cart', what would you suggest:
one SMPS3kA400 or two SMPS1200A400 ?
Congratulation for this great amp. !!!
Hi LC,
The offset of one channel is at 30 mV after half an hour. Can I adjust it by turning tr1 ?
Since I am about to press button 'add to cart', what would you suggest:
one SMPS3kA400 or two SMPS1200A400 ?
Congratulation for this great amp. !!!
An externally hosted image should be here but it was not working when we last tested it.
Very nice amp 😎. Regarding offset if the yellow RCA plug is connected to preamp the -34,3mV reading could be offset preamp added to offset FO (example offset pre -39,3mV + offset FO +5mV = -34,3mV). Input FO should be shorted under calibration and check.
Hi Theodosis
DC offset as you measured now can be result of DC component present at the preamp's output, adding itself to the First One output DC offset.
To check the cause, disconnect preamp from the amp and shorten the First One's inputs to see the real DC offset of amp itself. If it's in the range of +/-10 mV than leave it as it is, otherwise read the last chapter of the user's manual to correct it to zero. Output DC component is always measured or trimmed with amp's input shorted in this way we simulate zero DC present at the input and low impedance of the source, that's mandatory.
Buy two SMPS1200A400 and connect them as per sch in post #838.
Regards, L.C. 😉
OK, it was just not visible from the picture. So read the last chapter of the user's manual and trimmed it to zero. For that purpose TR1, TR2 should be used. In your case slightly turning TR2 in clockwise direction you should set it to zero. 😉
Or reducing the cap 10x on nc400 and then compare if the bass is the same. Just for testing purposes.
Let us know if anyone decides to try.
Igor
Hello,
Tell me if I am wrong : of what i understood use one or two SMPS1200A400 give almost the same SQ but using one gives less power. So if the power is the only issue why don't use one SMPS3kA400 instead of two SMPS1200A400 ? It gives more power and cost less (1*240€ vs 2*150€) ...
Is there any downside of using a SMPS3kA400 ?
Thanks
Tell me if I am wrong : of what i understood use one or two SMPS1200A400 give almost the same SQ but using one gives less power. So if the power is the only issue why don't use one SMPS3kA400 instead of two SMPS1200A400 ? It gives more power and cost less (1*240€ vs 2*150€) ...
Is there any downside of using a SMPS3kA400 ?
Thanks
Hi Voysto
No power level issue here, dual mono using two SMPS1200A400 simply gives better sonics. Look to the post #838 for the details.
The topology was tested in three systems with consistent results.
Regards, L.C. 🙂
With high quality source having low Zout of 30 Ohms or less, NC400 has no chance against First One on all audio spectrum.
With high quality source having low Zout of 30 Ohms or less, NC400 has no chance against First One on all audio spectrum.
i think <120ohm is fine.
I had the idea of re-using my 10K pots between DAC and FO. (like I do now with my Holton NxV amps) I already was in doubt whether or not this would work because of the rather low input impedance of the FO, but after reading previous posts I think I better look for a different solution...
Mark.
Mark.
Okay better spec always welcome and maybe pay back, but certainly you can give a try bits pieces you already have. That setup was approved over at VSSA thread, and input seems same (FO verse VSSA input rated by looking at FO pictures). Own experience <600ohm source into 10Kohm a 10K pot between can sound wonderfull.
I could try the SQ difference between 10k pot between DAC (approx. 50 Ohm output impedance) and FO in comparison with DAC directly. But if the outcome of this comparison is likely to be in favour of no pot, I will look for a solution in that direction.
In my DAC I can quite easily adapt volume control before line stage. 🙂
2 Pcs. SMPS1200A400 ordered up! 🙂
Mark.
In my DAC I can quite easily adapt volume control before line stage. 🙂
2 Pcs. SMPS1200A400 ordered up! 🙂
Mark.
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50ohm source to 10K pot is good spec, from what i know it's when turning the pot that you manipulate a little the low pass filter in FO input filter and thereby HF up in ? (>100-500Khz) area. This can be avoided by placing a buffer between pot and FO. Good building.
Based on the experience with VSSA (the same thing exactly minus the emitter follower drivers) passive volume is a definite no-no as far as sound quality goes. A 1k driving impedance also proved much inferior to 300ohms. I am also unhappy about this but the final result is very much worth some rethinking of the volume control/preamp.
Btw one of my FOs is also up and running - throughout the range improvement over the VSSA and especially in the bass region. Looking forward to try bridging soon.
Btw one of my FOs is also up and running - throughout the range improvement over the VSSA and especially in the bass region. Looking forward to try bridging soon.
Strangely, cannot get it running hum free with a shared between the channels linear supply... the strange part is that the VSSA had no probs.
No 3-rd wire ground connection, or chassis ground are used and the two channels are connected to the exact same points to the PS. Once the input grounds get tied together inside the preamp - hum. One of my preamps has a transformer coupled output which makes possible for separate left/right channel ground connections. Unsurprisingly, it is the only source which is entirely hum free with the FO.
My current setup is only meant to test if 4 modules are best utilised as a two channel balanced/bridged amp or a 4 channel bi-amp. Once this gets answered it will probably end up as a dual mono. Still, baffled and perplexed about the ground loop sensitivity.
No 3-rd wire ground connection, or chassis ground are used and the two channels are connected to the exact same points to the PS. Once the input grounds get tied together inside the preamp - hum. One of my preamps has a transformer coupled output which makes possible for separate left/right channel ground connections. Unsurprisingly, it is the only source which is entirely hum free with the FO.
My current setup is only meant to test if 4 modules are best utilised as a two channel balanced/bridged amp or a 4 channel bi-amp. Once this gets answered it will probably end up as a dual mono. Still, baffled and perplexed about the ground loop sensitivity.
