The Altman Attraction DAC

Paul Hynes · « **Reply #100 on:** 3 May 2007, 11:12 pm »

The HP 6227B power supply has been out of production for a long time and any unit you may pick up is likely to suffer from component aging (particularly electrolytic capacitors and possibly resistors). Because of this the reliability may be poor and the performance may be much worse than the original specification, which is not outstanding by modern standards. For reference the service manual including specifications is available on the Agilent website http://cp.literature.agilent.com/litweb/pdf/06227-90001.pdf

The transient response settling time is poor at 50 microseconds for settling to 10 mv. I would not use this power supply for any high clocking speed digital circuitry (digital to analogue converters for instance) as it would not be able to track the resultant load transient voltage fluctuations. The regulator error amplifier would cause the output voltage to bounce around (overshoot and ringing) causing distortion of the digital data stream waveforms leading to power supply induced jitter. The rest of the specs are not much better than typical modern three terminal regulators regarding noise and power supply line rejection. To be frank I think you would be better off with a standard car battery.

There is more to power supply regulator design than meets the eye at a quick glance. You have to consider how the regulator will behave under dynamic load conditions, and if it is mains driven, you also have to consider the power supply line rejection of the regulator circuitry. The regulator must continue to work all the way through the load’s frequency spectrum, anything less will degrade load’s signal integrity.

An old $3000 laboratory power supply may seem like a bargain for a few dollars but the cheapest option isn’t always the best option. Remember that you are the one who has to live with the resultant sound quality.

Paul Hynes

miklorsmith · « **Reply #101 on:** 3 May 2007, 11:16 pm »

Nice first post, welcome aboard!

What is your outboard 12v DAC solution?

Paul Hynes · « **Reply #102 on:** 3 May 2007, 11:29 pm »

Hello miklorsmith,

I’m not sure whether I should be indulging in self-promotion on the forum as it is forbidden in the forum rules though I am prepared to discuss general power supply issues. However it is late, well past my bedtime and I have to arise early tomorrow for a consultancy meeting. Sorry to be a party pooper. Will post further over weekend.

Paul Hynes

Russell Dawkins · « **Reply #103 on:** 3 May 2007, 11:36 pm »

Yes, welcome, Paul.

You might be the person to tell me if there is noise riding on top of the DC coming out of a battery.

I read years ago that nicads, at least, produced a (very high frequency) noise as a bi-product of the chemical process by which they create electricity.

A capacitor across the output was recommended and was what I used in a nicad power pack powering a microphone preamp. I never did experiment with the caps on and off (maybe I was afraid I wouldn't hear the difference!).

I wonder if you know anything about this and, if so, whether you are aware of noise produced by other types of batteries, such as lead-acid and nickel metal hydride.

I know there was always a presumption on my part that batteries produced pristine DC, so this came as a bit of a surprise to me. I have brought this to the attention of a manufacturer who makes DC powered amplifiers, but the information was basically dismissed.

Ben Duncan's notion that you are basically listening to your power supply as modulated by the music signal has always stayed with me, and that is why I remain curious about this seemingly trivial detail.

doug s. · « **Reply #104 on:** 4 May 2007, 12:11 am »

hi paul,

thanks for the info on the hp power supplies. i have used two different old hp power supplies for my origin live dc motor kit on my turntable, with excellent results - noticeable improvement over the stock power supply supplied w/the excellent o-l motor. a buddy of mine has had similar results. it's good to know that it may be different w/the altmann dacs. i queried altmann directly about it, (as well as redwine audio about using this w/their gear) & their opinion was that a lab-grade power supply would work fine, but may not be as good as a battery, which they both feel is likely to be the best possible solution.

regards,

doug s.

denjo · « **Reply #105 on:** 4 May 2007, 01:40 am »

Hi Paul
A warm welcome to the AudioCircle forum! I feel sure that fellow Circlers will benefit immensely form your knowledge, expertise and professionalims and perhaps come to a better appreciation and understanding of how a good power supply influences the performance of digital sources.

Best Regards
Dennis

Paul Hynes · « **Reply #106 on:** 4 May 2007, 05:43 pm »

Miklorsmith

After further consideration I have decided to avoid direct promotion of any of my products on the forum. Others have posted my web address on the forum should you wish to investigate further, but it will be 4-6 weeks (hopefully) before it is updated. I want everyone to understand from the start that I am involved in the industry as a freelance design consultant, which is how I earn my living, and that my web site is basically a part time hobby at present. I will do my best to remain impartial during any discussions. Also please understand that some of the design work I have done is commercially sensitive and may be the subject of license agreements that preclude full disclosure of the technology used.

I am a music enthusiast, just like all who post on the forum and I see the discussion of individual’s findings with various pieces of equipment as beneficial to all.

Regards
Paul Hynes

Paul Hynes · « **Reply #107 on:** 4 May 2007, 05:44 pm »

Hello Russell

Batteries generate noise just like other components. The only way to stop this would be to reduce the temperature to absolute zero. Fortunately the noise is relatively low at room temperatures and often noticeably lower than typical regulator chips. The noise generated by batteries is wideband. I haven’t done any tests with respect to noise levels verses current flow but it is possible that increased current flow would increase current noise due to the increased chemical activity. The internal impedance of the batteries will dictate the absolute level of the noise at the output terminals and if the impedance rises with frequency so will the noise voltage. Adding a parallel capacitor would tend to reduce this noise by reducing the impedance at high frequencies.

In my search for power supply perfection, I conducted some performance trials on 12 A/Hr SLA batteries (medium capacity) in the early 1990's, using sine wave, square wave and pulsed loads. Most audio and digital circuits present a varying load to the power supply. The noise specs of a battery may well measure very well under static conditions, but add a varying load, and things change. Unfortunately, I didn’t do any dynamic noise testing at the time. My notes were left with a now extinct company I was consulting for at that time so I am unable to refer to them. The results, with the batteries I tested, were generally favourable for low frequency operation compared to typical mains supplies with three terminal regulators. Batteries rely on a chemical reaction to provide power and their transient response, at higher frequencies, like typical three terminal regulators (typical transient response of 5 microseconds with noticeable overshoot), is quite poor, so no real gains here. This is very relevant with digital loads. Batteries do remove mains born interference from the supply equation and typical three terminal regulated mains supplies are poor in this respect due to the regulators poor supply rejection (typically 70 dB at low frequencies but falling rapidly with frequency often starting barely above 1 KHz and being virtually non existent at 1 MHz). These regulated supplies also have poor impedance performance. Lack of mains interference, reasonably low noise and their better impedance characteristics are the reasons why batteries have been generally preferred against these general mains supplies.

Another point to consider is load transient induced noise on the battery terminals. If you have a power amplifier drawing a 5 amp transient through say 0.003 ohm (Red Top impedance specification) this will generate a signal related voltage fluctuation of 0.015 volts. This will interfere with the wanted signal (subject to the supply rejection ratio of the circuit under power, which is often not good, particularly at higher frequencies) and become part of the noise floor, which rides on the wanted signal. A busy signal with lots of different frequencies happening at once can really clutter up the noise floor, masking very low level information (you know, the bit that gives you all the subtle clues about how the instruments are played, the song is sung and the acoustic space is portrayed).

I can’t advise you on the relative merits of various battery types, as I have never conducted a specific test. I chose the SLA battery for the trials because I was after a low impedance supply and this type fitted the physical and electrical requirements at the time.

Paul Hynes

Paul Hynes · « **Reply #108 on:** 4 May 2007, 05:45 pm »

Hi Doug S,

Originally my main concern about the HP supply was one of component age and reliability but when I checked the specs to see what the performance could be like I was disappointed. Please remember that my speciality is power supplies. For 27 years I have measured, tested and listened to the effects of a vast number of power supply types and configurations including very similar circuits to the HP. Certain measurements correlate directly to perceived sound quality an transient response is one of the big ones. A specification of 50 microseconds to settle to 10 mv is not good for fast signal circuitry but in your application it may not be the dominant parameter. It is good that the HP supplies you acquired were in a condition that allowed an improvement over the stock supply. That doesn’t mean that it is the best you can do for your DC motor but I have to admit it is a low cost solution.

Regarding absolute performance, it is all a question of degree. A power supply may well measure and spec well under static conditions. How it behaves under dynamic conditions is more important. The faster the load changes the faster the power supply transient response needs to be. The lower the impedance the less the interaction with the load.

Regarding the Origin Live DC motor. The original stock power supply was a simple and basic solution to the power requirements of the motor. Your results with the HP supply are not surprising as it is very easy to improve on the stock supply, indeed Mark offers a higher spec supply for upgrade purposes. I also used to provide my own high spec power supply for this motor for my friends and old customers.

Batteries do make good power supplies but improvements are possible with everything and a lot of people are not keen on the hassle factor with batteries.

Regards
Paul Hynes

Paul Hynes · « **Reply #109 on:** 4 May 2007, 05:46 pm »

Hi Dennis,

Interesting times. No pressure then? Seriously, thanks for the welcome. Thanks for your feedback on the Sanders amplifier. Will talk next week.

Regards
Paul

audiotone · « **Reply #110 on:** 4 May 2007, 09:09 pm »

Quote from: Paul Hynes on 4 May 2007, 05:44 pm

Hello Russell

Batteries generate noise just like other components. The only way to stop this would be to reduce the temperature to absolute zero. Fortunately the noise is relatively low at room temperatures and often noticeably lower than typical regulator chips. The noise generated by batteries is wideband. I haven’t done any tests with respect to noise levels verses current flow but it is possible that increased current flow would increase current noise due to the increased chemical activity. The internal impedance of the batteries will dictate the absolute level of the noise at the output terminals and if the impedance rises with frequency so will the noise voltage. Adding a parallel capacitor would tend to reduce this noise by reducing the impedance at high frequencies.

Another point to consider is load transient induced noise on the battery terminals. If you have a power amplifier drawing a 5 amp transient through say 0.003 ohm (Red Top impedance specification) this will generate a signal related voltage fluctuation of 0.015 volts. This will interfere with the wanted signal (subject to the supply rejection ratio of the circuit under power, which is often not good, particularly at higher frequencies) and become part of the noise floor, which rides on the wanted signal. A busy signal with lots of different frequencies happening at once can really clutter up the noise floor, masking very low level information (you know, the bit that gives you all the subtle clues about how the instruments are played, the song is sung and the acoustic space is portrayed).

Paul Hynes

Hello Paul,

your comment is interesting stuff...
I placed some black gates accross the input terminals for the power supply and hear a very different sound...
Bass seemes less "congested" and I have the impression that details comes alive...
But some listeners keep saying there is something there that should not be there (????)...
I always thought it was more detail but I am not shure anymore that's true...

So I made a new set of power cables without the BG's only with some thicker wire (2,5mm2), nothing special, just wire I had available.
Now the "congestion" thing is gone and I have (almost) all the details I was looking for...

I am confused...is it the running in of this amp (about 800 hours) that made it better or is it the thicker wire...I do not know...

I guess no power supply or battery is perfect...

Russell Dawkins · « **Reply #111 on:** 4 May 2007, 09:36 pm »

audiotone,
By introducing two variables you have made it impossble to know if the difference you are hearing is the result of the thicker wire or the removal of the caps. Have you tried the thicker wire with the caps?

By the way, I asked you about whether you heard a difference with and without the caps because I wasn't sure why you were using the caps in the first place - most people seem to use them as short term power storage, not battery noise filters.

I thought, given the refined nature of the Altman DAC, that if this phenomenon were ever audible it would be here.

audiotone · « **Reply #112 on:** 4 May 2007, 10:08 pm »

Quote from: Russell Dawkins on 4 May 2007, 09:36 pm

audiotone,
By introducing two variables you have made it impossble to know if the difference you are hearing is the result of the thicker wire or the removal of the caps. Have you tried the thicker wire with the caps?

By the way, I asked you about whether you heard a difference with and without the caps because I wasn't sure why you were using the caps in the first place - most people seem to use them as short term power storage, not battery noise filters.

I thought, given the refined nature of the Altman DAC, that if this phenomenon were ever audible it would be here.

Russell,

your first point: absolutely true...I will add the BG's later on.(first listen for a longer period)

about the reason why I added them...see higher. I was not thinking about noise or anything at that time...I just wanted to solve a problem and I know what the black gates did in my tube preamp and poweramps.

anyway...I am not shure yet how this will end...with or without the BG's.
For the moment it is without and looking good, but I will try to put the BG's on the thicker wire in the near future...

But with or without the BG's this is the finest sounding piece of equipment I have ever listened to!

Paul Hynes · « **Reply #113 on:** 4 May 2007, 10:40 pm »

Hello audiotone,

Placing capacitors across a power supply will modify the power supply impedance curve. If you have a power supply with a flat output impedance through the audio band the interaction with the signal circuit will be similar for equal amplitude signals at any frequency within this band. Now fit your capacitor across the supply. The capacitor’s impedance curve is not flat. Disregarding inductive effects and ESR for the moment, the impedance of an ideal capacitor drops at the rate of 6 dB per octave. The composite impedance of the power supply impedance in parallel with the capacitor impedance is no longer flat and the resultant interaction with equal amplitude signals is no longer even-handed through the audio band. Where the impedance has been lowered the most, you will hear less low level distortion and noise from the power supply interactions, and you will perceive this as an improvement. Where the impedance has been lowered the least will now stand out slightly as the power supply interactions will be relatively higher. The difference with the capacitor is quite clear to hear on a transparent system and could be perceived as an overall improvement until you begin to recognise the tilted distortion response. Of course less transparent systems make it harder to hear these effects. Real capacitors have non-linear impedance curves that vary with different constructions and therefore have different audible effects on the power lines hence one reason for the preference of one type over another. Removing the capacitor takes you back to the even-handed distortion response, which you may prefer.

Also remember that the power cables connecting the power supply to the load are part of the impedance equation. Gets complicated doesn’t it. It gets worse when you power more than one signal circuit from the same supply, but more on this topic another day.

The perfect power supply would have zero impedance from DC to light frequencies. I haven’t met one yet.

It’s getting late and I am tired, so if that lot above doesn’t make sense, let me know and I will have another go tomorrow.

Regards
Paul

audiotone · « **Reply #114 on:** 4 May 2007, 11:00 pm »

Hey Paul,

makes sense...
Improvement in some regions...but can get worse in other regions...

At least I know there is nothing wrong with my hearing.

How would you connect these two devices to one battery?

Paul Hynes · « **Reply #115 on:** 5 May 2007, 10:56 am »

Hi Audiotone

You probably won’t like this but I would be disinclined to connect two or more circuits to one power supply (unless it had zero impedance or the circuits drew an absolutely constant current) if I was after the finest performance from my equipment. Even then I would be very careful because grounding interactions can mess the performance up.

As an example let’s look at the Red Top Battery. Make no mistake this would be a fine power supply and would easily beat a typical three terminal regulator solution. If you connect a power amp and a DAC to it and then play the music there will be some low-level signal current interaction at the common point (at the battery terminals) of the power supply. A 5 amp transient current draw from the power amp through the 0.003 W impedance of the battery will generate a 0.015 mv fluctuation across the battery terminals. Lets assume you have a signal circuit (this could be a DAC or an active line preamp) with a supply rejection of 60 dB with respect to the frequency of the transient. The 15 millivolt noise fluctuation breaks into the signal line at 15 microvolts and is amplified by the gain of the power amp say 26 dB (around 20 times). The noise is now 300 microvolts (around 96 dB below the maximum signal delivered to the speaker with a bridged power amp on a 12 volt battery) in amplitude. This becomes significant with respect to the low level information of the music because it is a considerable percentage of its amplitude and the sum of the two is what you get (the noise will ride on the signal). The problem becomes much worse if you add a vinyl preamp to the equation, as the system gain factor is much higher.

If you were to use a separate battery for the power amp and one for the circuit feeding it, the noise induced by the 5 amp transient on the power amp battery would not be fed to the previous circuit and therefore not amplified. Net result, a quieter system with much less power supply noise inter-modulation.

I’m in a rush, so I haven’t checked the maths, however practice backs up theory here, and with a transparent system, all will be plain to hear. Separating the power supplies makes very noticeable improvements in performance. It also makes the grounding of the system a lot easier to implement, which is beneficial to the sound quality.

Paul

audiotone · « **Reply #116 on:** 5 May 2007, 11:44 am »

Hey Paul,

could not sleep last night...
my brain was processing your comments.
Two separate batteries was already on my to do list.
The BG's are not the way to go as I can hear and as you explaned...

The noise "riding" on the battery comment made me think about the Bybee purifiers...
Altough I cannot explane why these things work (there was a time I would simply reject such voodoo stuff), but I must say it is more than suggestive.

I had 4 of these connected to my speakers.
I have put them now on the plus and minus psu connection of the dac and amp.

first impressions:
they do change things for the better...the sound gets so real it is frightening.
I will listen to it some more...

What a beautifull day...the sun is shining...(its a shame to stay inside, so I will not...)

Tony

Paul Hynes · « **Reply #117 on:** 12 May 2007, 03:44 pm »

audiotone

Hello Tony,

Today I have been thinking in more depth about our last few posts regarding power supplies, without the distractions of work, and decided I had missed out a potentially important piece of information for upgraders. It concerns the use of standard three terminal regulators for powering sub-sections of a DAC (Monika). The DAC was battery powered (12V) with 3 LM78L05 regulators. One each for the DAC chip, the digital interface chip, and the re-clocker circuit. The three regulators were upgraded with high performance regulators providing a very worthwhile improvement in all things musical.

The battery is useful for removing mains artefacts from the audio equation, however, you will never see the full performance of the circuit under power with standard three terminal regulators in the power supply. They are just not fit for purpose. They are noisy, have lousy transient response ( typically five microseconds), and have virtually no supply isolation above 1 MHZ (some are worse than this). Their poor impedance characteristic allows a considerable re-action voltage to appear on the supply particularly at higher frequencies. Check out the manufacturers specifications to see the relevant figures.

Using standard three terminal regulators with digital circuits clocking at speeds over 1MHz is a waste of time, as they are not functioning properly at these frequencies. Their non-linearity and noise also messes up lower frequency analogue circuit performance. For correct high frequency operation the regulators must be designed to work properly at these frequencies. This means wide frequency response with a vanishingly low load transient settling time and output impedance.

Enjoy the sun.

Paul

anubisgrau · « **Reply #118 on:** 13 May 2007, 01:33 pm »

what is the output impedance of altmann attraction DAC?

i am wondering are there are any issues driving passive preamps?

denjo · « **Reply #119 on:** 13 May 2007, 01:44 pm »

Hi Anubisgrau
I am driving my Altmann via Bent Audio's TAP TVC passive preamp and find that the combo is just excellent - no issues with insufficient gain or anything like that. I think much will depend on the source that is fed into the Altmann. I am using a SB3 which feeds the Altmann (2 volts I think) and the internet radio is plenty loud. As for the ripped CDs, there are some recordings that have to be cranked up somewhat but most are fine.

Hope this helps!

Best Regards
Dennis