I am an old git, and with retirement during these times with enforced lock-down meant I have time learning and building things with Valves. So having built a Stereo amp I need to play things through it. Initially using Clementine from the PC decided on something else I could leave running, so picked Volumio on a recommendation, running on an old HP8000 headless computer and going direct from the line out works very well with no discernible noise. Would like to know what it can do better or what smaller units I could put into use. Tried a HP Thin client which worked for a while perfectly and then started to gave me noise as well as music, believe it could work on a raspberry pi?
I have to ask about these DAC cards, or Digital to Analog converters, the chips inside the HP 8000 (ALC261) already have 24 bit DAC’s at up to 192 KHz and are classed as high definition codecs, so what advantage would I gain using an external card? From what I gather the Pi DACs are also 24 bit?
I can imagine the RaspberryPi as standard may be lower but can not actually find specs on them, CD audio was only 16 bit at 44.1KHz sample rate so if playing CD’s converted to mp3 you can not improve going from 16 bit 44.1KHs to 24 bit at 192 KHz as you can not get more quality out from the original signal.
Many DAC chips included in PCs are indeed capable of very high performance, but once they are integrated into the digital environment of a PC which is not specifically designed to keep digital noise out of the audio chain the performance suffers.
A solution using a Raspberry Pi4 feeding an external USB DAC will deliver near state of the art performance. A HAT card will work quite well too but not as good as an external DAC. Look at the Audio Science Review website, for example this review of the Chinese made Topping E30
Available from Audiophonics in France with a 2yr warranty. This will outperform virtually any HAT DAC. Also it will allow you to use a heatsink case for the PI4 such as the one made by FLIRC which will keep the PI4 running cool.
A standard RPI4 power supply will almost certainly do the job well for the RPI4. You’ll need a 5V power supply for the E30. Don’t overspend here the E30 has got quite good filtering internally. There are many audio reviewers who profess to have ‘golden ears’ and say they can hear differences between different interconnects but don’t be fooled into buying expensive USB and RCA leads - Amazon basics are solid enough and no audible or measurable improvement will result from spending much more.
OK thanks for the comments, I can certainly vouch for some noise issues when I tried the Thin client as I could hear when the unit was accessing the flash drive as noise on the output, but thankfully this 8000 seems to be well filtered and quiet. At my age anything over 8KHz is getting hard to hear. I will see if there is a X86 section to ask question of before I spend a few hundred £’s on external DAC’s and Pi4’s.
I too am in the old git category. I can just hear 10-11kHz at high level.
I tried computer streaming a few years ago. It wasn’t a patch on my CD player - mid range clarity and freedom from distortion at low(ish) signal levels being the noticeable shortcomings. That was until I tried an external DAC.
A good external DAC will be better than the best CD player of even just 5yrs ago although the differences will be quite hard to discern except in measurement. But if your valve amps are high end (like push-pull ultra linear EL34 or KT88 pairs in the output stage) then the E30 could prove a worthy complement.
Not quite sure what you mean by computer streaming? I do not think am streaming anything, well over IP that is. The computer is playing the mp3’s which I believe in Volumio is using a program called mpd, the mp3s stored on a usb stick plugged into the PC, so not using any network drive etc. The web interface just allows me to control it.
As to the amp, well not EL84 or ultra linear either although it is using the Mullard 5-10 transformers, actually using TT-15’s using the Radford ST15 circuit for the basis, ended up with EF91, ECF82 and TT-15 per amp. The last time I did any measurements was during a test build state and I got a peak signal to noise reading of 74.6dB. The measured distortion on my last test with the amp was 0.2% at something like 5 Watts output. The power supply has been improved so perhaps I should do more measurements now.
So I doubt it true Hi-Fi by any standards, but it sounds good to my ears, I am not an audiophile by any means, it has just got me listening to music.
I will probably go down RasberryPi route in a while just to make the outfit smaller. So understanding options is good.
Cheers
Adrian
Just done a re-measure for the hell of it. Unfortunately my test set will not measure less than 0.2%, so that I will have to say, is the best I can measure. At 8.7 Watts (39.4 dBm) output just before I start to see limiting on the scope I get a distortion of 0.7%, so the new PSU has given me slightly more power output. Signal to noise at 75.4 dBm from peak, again the test reads a minimum of -36dBm noise level in with no input so that to peak level is the best I could say with any honesty.
Mainly streaming from my NAS ripped (44k/16) and downloaded FLAC files (mix of 44k/16 and 96/24) but also listening to BBC on the 320k internet feed.
I too have built Mullard 5-10 amps back in the late 1960’s - I recall measuring approx. 0.1% distortion at 10W when I took it to the university lab to to check it out but I had to do a cancellation of the input signal with the amplifier O/P because the generator had around 0.3% THD - this was a technique recommended by the late Peter Walker of Quad fame for measuring high performance amps. I can detail it further if you’re interested.
The 5-20 is appreciably better and I made a couple of them before knocking out a few more KT88 50W amps for my musician friends!
I picked the 5-10 transformers as I thought if I made a mess of this one, I would go on to build it as the Mullard book and get some EL84’s. At the time, it was a case of what ever valves I had to hand as I was just getting back into the technology. I had stripped some ex-military Cold War radios as the aluminum chassis had badly corroded. So it left me with several EF91’s and a TT-15, the ECF82’s were cheaper than ECC83’s hence going for the Miller/Radford circuit, which is meant to be a better performer anyway. So it left me with the valve line-up as mentioned. The anode to anode for the TT15 should be 7K0 Ohm rather than 6K6 for the Mullard but it is close enough. And as the valve only has one screen grid connection, it stops me using the distributed load taps on the transformer, so the screen grid is fixed voltage.
OK on the 5-20’s I guess that was with EL34’s or KT77’s
OK on the streaming bit. I use a program called fre:ac (Linux) to convert the CD’s I have to mp3’s. I could probably use a better format then mp3, but doubt I would ever hear any difference.
I need to understand a few issues with installing from the Volumio x86 image as it wastes a lot of hard disk space that in theory I could use to store the music. So I need to fathom that small issue.
Most of my valve amps were made using WW2 admiralty transmitter surplus power supply components from Lisle Street (a street packed with electronics emporia back in the day). Fabulous quality c-core mains transformers in oil filled welded steel cases all unused and packed in waxed cardboard cartons. Had to pay top dollar for Partridge O/P transformers though
Around 1970 the supply of these surplus components began to dry up and anyway the best of transistor designs were beginning to beat the valve amps sadly
I have ripped my CDs using dBPowerAmp the full version of which isn’t free after the trial period. It provides meta tags for the tracks and album covers. Also does a checksum against the rip others have made of the same album and tries a more careful re-read of the CD if your rip doesn’t align. I ripped to FLAC for home use and then post processed to 320k for the car. Playing the 320k files on my home system I sometimes noticed that complex layered music sounds better in the FLAC version in a semi-blind trial with someone else doing the changeover. I’ve stuck with FLAC since storage isn’t that expensive now.
I am an old git at heart.
50 but have used power tools etc.
I thoroughly recommend trying FLAC quality.
You could just test one cd, I reckon you will notice the difference even if you can’t quite put your finger on the difference.
I am quite new to this whole digital malarky myself.
So take all that I say with a pinch of salt, I am very much learning.
It can be quite complicated, but that is mainly because there are so many different options and ways to do it.
You can do all sorts of budgets.
Indoors I am slowly trying to make a decent source using a pi.
In the garage I am just mucking about and cost and size is important.
In the garage I got a Pi zero (W) £10.
Plus a cheap aliexpress dac hat. (Not a lot about £10-15 I think)
I run volumio on that and can control that via my phone.
It connects to my wifi automatically and starts playing through an old amp out there.
I have been enjoying Radio Paradise which plays in FLAC.
Another thing I played with was a Khadas Tone Board.
Which is a separate DAC which I think is pretty good value for money.
About £80 I think it was.
That can be powered and fed data to via a single usb lead and feeds via rca to the amp.
PCs are pretty noisy (electronically).
Anyway, I noticed a huge difference with that from my pc.
(It can also have coax in)
(Just one of absolutely loads of DAC options out there. It is WAY better than my pc DAC and my 20 year old amp DAC)
Thus encouraged that my ears could tell the difference between flac and mp3 and so on, I am slowly playing with a Pi3B+. I will gradually imporve that as I go.
I got a Linear power supply, a reclocker and then a dac on top.
Next i will think about speakers, then amp.
Eventually i would love a valve amp. But I have a lot of learning to do before that. I am a complete noob at electronics.
I also will probably set up an old Hard Drive as a nas.
I guess I just like using thin client computers, they are fan-less so quiet and can also be used as a small PC, I have a dual core one heading my way soon.
I may try the idea of copying a CD to flac or wav or to some other lossless system. I do know that mp3 files are compressed so you will loose some quality with it, it is just so universal for any device.
If the data on the CD is encoded at 16 bit 44.1KHz PCM then it really makes no difference to my thinking if you re-encode with a lossless codec it in a higher sample rate and higher bit rate. Any errors/aliasing/jitter etc you have on the disk will still be there when you re-encode it.
I believe that DVD’s and Blue Ray have higher bit and sample rates as standard.
The 44k/16 on the CD probably started life as a higher bit rate output from a high quality ADC in the studio. Then the signal was digitally filtered with a sharp cut off low pass filter to remove any signals above 22.05kHz (such as from cymbals etc) then re-sampled to 44k1 safe in the knowledge that that no alias products exist in the CD transcription.
When your DAC reconstitutes the original audio signal we need the output to look closest to the signal seen at the input to the studio ADC - i.e what the studio engineer heard. Just outputting the samples as a set of analog steps doesn’t fulfil this - some DACs called no oversampling (NOS) do in fact do this but the mathematics of the stepped waveform shows a significant high frequency droop and also outputs ultrasonic interference which analog filters cannot remove. So most DACs digitally up sample to produce interpolated data between the 22 microsecond CD samples. This removes the frequency droop and pushes the ultrasonic interference further up to frequencies where the interference can easily be filtered by analog low pass filters without affecting the 0 to 22kHz frequency response. The ultimate filter of this type has been developed by Chord Electronics but is probably a bit of an overkill
As regards jitter this can come from 2 sources firstly in the quality of the ADC in the studio and secondly in your DAC and the stability of the clock used to put data into the DAC. A USB DAC has its own clock and the jitter from such a DAC is dictated by the freedom from jitter of the clock chosen by the DAC manufacturer (a lot better than any computer clock) and so often the USB DAC is preferred.
Doing your own upsampling is possible if you are not convinced that the DAC manufacturer is doing a good job (most are just fine!) and your DAC has the capability of taking in a high bit rate signal like 8X 352k samples/sec. SOX on a PC is a candidate software here perhaps. Or BruteFir installed on a Raspberry Pi 4 might be suitable but this would need some understanding to get right.
Yep.
I would definitely wear ear defenders more.
I don’t have much ringing, just a gentle background noise. I am fortunate.
Still, got to be worth a go eh?
I can tell the difference between 320k and flac when bluetoothing it to the van radio from my phone and driving around.
It is somehow a bit less tiring… or something.
I was amazed i could tell.
I couldn’t explain or pinpoint the actual difference.
I know because I hadn’t realised I had accidentally downloaded at 320k and was driving around disappointed that it didn’t sound as good as the day before and I was blaming my imagination.
Bluetooth audio adds another layer of compression so not sure what damage it might do to an already compressed file - it isn’t transparent like WiFi.
But FLAC files are the way to go for most home audio these days with Bluetooth best used for casual listening.
Even the wider bandwidth AptX Bluetooth has compression
To be fair there are optional codecs for Bluetooth audio which do not add compression. These weren’t in the original spec but have been added later as I understand. You obviously need both transmitter and receiver to support these modes and for this to be enabled. AptX can be arranged to be lossless if setup correctly. On your phone this may not be the default. A recent phone would probably have the capability but car audio evolution doesn’t move at the same pace. There’s a lot about Bluetooth on the web.
I’ve built a player using Pi 3, IQAudio DAC with headphone- and cinch connectors and a USB HD containing my CD collection in .FLAC format and Volumio as software (https://volumio.org/). The Pi has no moving parts (except the HD) and the noise is none to speak off.
