That's a pity. I hope it doesn't affect the charity too much.
The BOM update has converged to
R14, R25, R26, R27, R103, R104, R105 and R106 become 2 kohm +/- 1 %, 0.6 W metal film
RV1 and RV2 either stay as is (Bourns 3386P-1-502LF) or become Bourns 3296Y-1-502LF, depending on whether one prefers single or multiturn
The PCB needs no update, as both options for RV1 and RV2 fit in the present footprint.
The BOM update has converged to
R14, R25, R26, R27, R103, R104, R105 and R106 become 2 kohm +/- 1 %, 0.6 W metal film
RV1 and RV2 either stay as is (Bourns 3386P-1-502LF) or become Bourns 3296Y-1-502LF, depending on whether one prefers single or multiturn
The PCB needs no update, as both options for RV1 and RV2 fit in the present footprint.
Good idea! What’s the height underneath your board? I’m trying to match the chassis with my other ones.
Thanks Marcel. It will be fine as I will do the ride next weekend so as not to let down my sponsors. The situation is a bit annoying as it was just a puncture, so I fitted a brand new replacement inner tube and fixed the punctured one but I couldn't get the tyre to re-inflate and expended both of my CO2 cartridges trying - turns out the valve core wasn't inserted properly at the factory so the CO2 came out as quickly as it went in. C'est la vie!
Thanks, I'll update the Digikey part numbers on the BOM/shopping cart that I'm working on for the GB.
I used 50mm stand-offs to mount the PCB. My chassis has an internal height of 70mm so, allowing for the PCB, I have around 18mm of space above the board, which is fine for the majority of the through hole components.
I derived a mechanical drawing for all the stand-off holes, valve holes etc. if that would be useful? I'll wait until I have fitted my chassis top plate before making it available though - just in case I made a mistake.
I've used my free afternoon to do some more experimenting around noise reduction and have had some success. I switched the bottom valves with the outside top valves on the opposite channel - no significance in that other than I know what I swapped to where - I re-centred the potentiometers, I was brave and set HQP volume to max and played my favourite 32 minutes of silence. The noise was clearly audible at first and I was able to do the initial trim from in front of the DAC but then with careful adjustment I was able to get the noise right down. I was able to get to a lowest noise point on both channels without fully rotating either of the poteniometers and I think I have achieved a marginally lower noise floor (difficult to be sure with only my ears for measurement). I certainly can't hear the noise from my listening position and it is just a quiet static/hiss with my ear close to the drive units. I've heard a lot worse noise in some people's system from hums/buzzes - with nothing playing my system is 'silent'.
I know I'll use multiturn potentiometers when I build a second Valve DAC as it is really easy to over-adjust with the single-turn ones, the tiniest tweak with the screwdriver can have a quite noticable affect.
I've not touched RV3/4 at the moment.
Ray
I know I'll use multiturn potentiometers when I build a second Valve DAC as it is really easy to over-adjust with the single-turn ones, the tiniest tweak with the screwdriver can have a quite noticable affect.
I've not touched RV3/4 at the moment.
Ray
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OK, so I tried the 'AMSDM7 512+fs' modulator in HQP, which obviously involves swithching to DSD512.
Firstly, just changing to DSD512 without changing any other settings resulted in a slighly higher noise floor but still not audible in my listening position. Switching to 'AMSDM7 512+fs' I couldn't hear any change in the noise floor.
Firstly, just changing to DSD512 without changing any other settings resulted in a slighly higher noise floor but still not audible in my listening position. Switching to 'AMSDM7 512+fs' I couldn't hear any change in the noise floor.
Maybe it would help people if I try to quantify what I'm talking about regarding my noise floor experimenting/tweaking as i don't want all the posits about it to give the impression that its a problem. I'm afraid my attempt isn't very scientific as I have no measuring facilities other than my ears.
I've attached a table of sounds and their associated relative levels in decibels (I feel something is missing - distance - but we'll go with it as is).
Fortunately I have a couple of benchmarks because;
I played some solo violin music and set the volume level to correspond with my recollection of an actual violin being played - again not terribly scientific - but perhaps 95dB.
Without adjusting the volume I then played some 'silence'. From my listening position I could have been listening to a leaf falling i.e. to me it was inadible at perhaps 10dB.
Sorry I can't do any better than that but maybe it is useful? I should add that my ears are well past their prime as I'll be 63 next month.
I've attached a table of sounds and their associated relative levels in decibels (I feel something is missing - distance - but we'll go with it as is).
Fortunately I have a couple of benchmarks because;
- my partner plays the violin and I've heard her play in the house lots of time so I know how loud a violin sounds.
- I've never heard the sound of a leaf falling but I do hear leaves rustling.
I played some solo violin music and set the volume level to correspond with my recollection of an actual violin being played - again not terribly scientific - but perhaps 95dB.
Without adjusting the volume I then played some 'silence'. From my listening position I could have been listening to a leaf falling i.e. to me it was inadible at perhaps 10dB.
Sorry I can't do any better than that but maybe it is useful? I should add that my ears are well past their prime as I'll be 63 next month.
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Great. Although it can be used at 256, it is recomended at 512. Afaik this setting never results in a lower noise floor, but helps with certain ISI related problems (like lack of or bad settings of RTZ function).
I thought you had that problem because you said you were experiencing noise problems that vanishes as soon as the music signal got high enough.
What a bummer for the charity event, good thing is it left you with enough "air" to test all these things;-)
For the tube spirit, I wonder if it's a good idea to use this tube voltage regulator board to power the Valve DAC? It can output maximum 400v/100mA and a dual sets of regulated heaters, quite handy. Seems overkill but I love tubes. 
The chassis will get really large but it's not a problem for me.
The chassis will get really large but it's not a problem for me.
For the tube spirit, I wonder if it's a good idea to use this tube voltage regulator board to power the Valve DAC? It can output maximum 400v/100mA and a dual sets of regulated heaters, quite handy. Seems overkill but I love tubes.
Why not? I have used regulated supplies for the B+ (actualy B-) and filaments, although I didn't try the onboard power supplies so can't tell you if it made any difference. My HV regulator is a '21st Century Maida Regulator' and the filaments is just a conventional linear power supply. I am also using a LDO ultra low noise regulator for the 5V supply.
BTW, on the PCB the six valves are connected in parallel so the regulated filament supply requirement is 6.3V @ 1.8A and it needs to be floating.
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