Sound Quality Vs. Measurements

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Hi Matt . You use your hi fi exactly like me . Previously in my ramblings I said I want to make MP3 and You Tube better . After many blind alleys I am getting somewhere . Layers is the things you can have . The top end is a problem . I think better tweeters and super tweeters are justified to squeeze the most out you can . My Magneplanars are remarkably OK with MP3 . In fact the balance of your speakers is not a million miles different . Absolute detail is the difference as I guess anyone would imagine . These speakers to be built I hope are not too far adrift . As I said I will simply use the Maggies as reference to do it by ear to start .

I hope Pano will say something about the 902.539 15 inch as it might be an alternative to GRS for UK builders .

As for baffle . The basic idea is to decouple the baffle whilst not causing excessive movement of the drive units . I have been told by others that the Jamo is good . Jamo in UK was my friend John James ( Rep , recently Bose and was Goodmans ) . Jamo and QTC were about the same as far as hi fi shops were concerned . John always called in with no hope of selling to me ( not me , he would sell to me as he knew I would struggle to sell them ) . John said Jamo could do anything if they wanted to . He was right .

I will pop over with the mains chokes sometime . Also see if I can make some 2.5 mH + 1 R air cored for you ( 0.6 mm ) . Convinced that will work . I said to Matt I am convinced that 1R resistance in a choke is not a problem . That makes for more economical air cored .

As said it will take a year . Would be nice to have it flying before October .
 
DNA Sequence Speakers dipole open baffle woofer high efficiency point source array midrange tweeter treble loudspeaker

Here's Don's approach. By the way, I didn't authorize the adjectives about me, although it helped a maths friend in locating me. On the site, the products for headphone listening are entirely his own development.

Interesting , the part that should really be dipole (mid) isnt , and in such a small enclosure to boot ...

But :

For the tube "die-hard", a 10 tube (4 6SN7s and 6 6C45s), single-ended class A, zero-feedback, all triode active crossover is employed. Satellite highpass section is ultra quiet with very wide bandwidth. Uses over 400 parts including Audio Note copper foil capacitors. Note the double decker power supply! Black acrylic faceplate is custom laser engraved. Designed by legendary circuit genius Brad Wood. Includes bass level control for gain matching of different amplifiers.



When you're working with Legends , anything is possible .....:)
 
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Interesting , the part that should really be dipole (mid) isnt , and in such a small enclosure to boot ...

But :

For the tube "die-hard", a 10 tube (4 6SN7s and 6 6C45s), single-ended class A, zero-feedback, all triode active crossover is employed. Satellite highpass section is ultra quiet with very wide bandwidth. Uses over 400 parts including Audio Note copper foil capacitors. Note the double decker power supply! Black acrylic faceplate is custom laser engraved. Designed by legendary circuit genius Brad Wood. Includes bass level control for gain matching of different amplifiers.



When you're working with Legends , anything is possible .....:)
As I say, the legend shite was unauthorized by me, and I'm surprised it's still up. I found my anti-ego vaccines were still working when I saw it, fortunately.

We did make a circuit board though, that unit shown is not photoshopped. However, the last I had my hands on it the toroid had to be positioned slightly out of the box to make the hum acceptably low, I think mostly because of those absurd Audio Note caps' loop areas. Maybe he's played with that and fixed it. According to Thorsten even Qvortrup uses film caps now!

Also the low frequency boost signal chain with the SN7's has a lot of excess noise. And the bass level control needs to be a wirewound, as there was a turnon transient that eventually burns up low power potentiometers!

The mistake Don made was not banging on me harder to finalize the sand-state electronics, which sound just fine, with a 2134 for the bass and 2SK389 source followers for the mid-high highpass. It has some decent discrete I-source-fed shunt regulators too, quite adequately low noise. Those electronics were designed and built in a couple of days!

I admit the tube one does look impressive, and consumes a houseful of power, crazy excess. It sounded fine to me too.
 
Thanks for the measurements. :up: The Qts of your 15" is close to that of the GRS. It will react much the same way on baffle, I suspect.

Nigel, do you have any way to measure the output? Even an SPL meter?


What I will do is start by ear . As Matt said room effects are so important . My friend 3 miles away can help .

Talking to Matt yesterday I saw he uses an iron cored choke ( 2.65mH ? ) . He showed me an air cored one . $150 . I thought looking at it the thickness of wire was over the top . 0.6 mm might be OK if R < 2 ohms .


A speculation if I am allowed ? I have never liked active speakers much . Years ago I suspected that the drive units were unsuited to proper active use . Instead bi-amplifying is better . My thoughts are this . The bass choke usefully divorces the amplifier from the speaker . It is exactly like the choke between Audio and Digital is some equipment . This should especially help a feedback amplifier . I would call it a Watershed . This is not to say an energy store as a choke is is not without problems ( do people put reverse didoes on valves ? ) . Wanting a choke on the cheap I hope to use a series resistor . I then fashion the output as I want . If the damping factor is < 3 I suspect it will avoid ringing ? Thinking in mechanical terms . If damping is too stiff it usually is undesirable . Surely electrical damping also ? If a capacitor is used in parallel the damping can be restored higher up if thought desirable ( I doubt it will be ) . Phase shift is a problem and I hope the alleged omnidirectional qualities of bass allow it . They must if a 4 x 2 baffle can give bass . If not the energy would be determined by the 2 foot alone .

Conjecture . Ultra low distortion amps I have disliked simple required 2 R in series with the speaker ? Must buy an Audiolab / Sony ( joke ) . Sony TA5650 and 1010 were OK . As was Lentek . How can Lentek become Audiolab ?
 
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Believe me, with that driver on the size baffle you'll use, you want >10mH to make it right. Forget air core in this position, use a good iron core. It won't be cheap.

Or if you can experiment with active, try a 1st order low pass and slide it around from about 40Hz to 100Hz. That should put the woofer fairly flat down to Fs and also roll it off near 200Hz. Trust me, that's what works.
 
I think it will have to be active and use a series resistor to stop the coupling being too tight .

Worth a try .

I have been planning to build some amps for ages now using 55 - 0 - 55 AC transformers I have . One is 1000 VA . I have some 4700 uf 100 V I can bank up . I have even thought of some ECC 82 driving Darlingtons . 150 V is probably OK with ECC 82 driven from a CCS . 10 mA to drive the outputs . Loop feedback .

I might get lazy and use these in bridge . They are more than OK to get it working . I have an old PA amp chassis they would drop into .
http://www.diyaudio.com/forums/power-supplies/169601-velleman-200w-amp.html
 
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This is an idea . I have said 1 nF for VAS cap as one doesn't know without trying what it would be . GBWP needs to be 130 kHz . Reducing gain to 10 helps . The amp isn't high Z input . Some tweaking required as calculations assume op amp . Bootstrapped input perhaps ? 60Hz was discussed , thus 60 Hz . Linear phase filter .

The output filter is whatever is found and might be Zobel .

Just saw the price of the Velleman module . Maybe not . The were cheap in the past . Maybe it comes with heat sink ?
 
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With a rough idea of bootstrap . As luck would have it a LTP is offering an ideal solution . If kept below 100 % it should be safe . I didn't calculate it so doubtless it can be bettered . 100 K input should be OK . If gain is lowered the values change in the filter components . Usefully as the noise levels can decrease . 75 K in series is a bit high and will not be shunted by preamp low Z . Admittedly there will be no HF to worry about .

The output resistance can be anything required . 2 R seems about right following theory . Damping factor 16 is considered where it is unlikely any real advantage going higher ( Martin Colloms ? Discussing Naim NAP 250 and it's 0R25 output resistance . Hi Fi Answers circa 1981 ) . Damping factor 3 was said on speakers with paper roll surrounds to be where critical damping occurs ( 1950's Wireless World with measured evidence and apparatus ) . At 2 it is suggested resonance is seen ( EPS ) .
 
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I just remembered I did a turntable PSU of 21 V rms output ( Gyrodek ) . It used the power amp as a 55 Hz filter ( between 50 and 60 Hz , good for either ) . No stability problems using 68 pf VAS cap . I seem to remember amp was low gain and inverting ( 4.5 ? R in = 3K3 and 1 uF as subsonic filter ) . 6 pole total fed from a 74HC 4060 square wave ( 3.2768 MHz crystal ) . The final 2 poles the amp . Distortion total better than - 60 dB ( - 65 dB I think ) . That's about as good as Isotek's Genesis that does the same job . That requires 150 Hz to be - 50 dB down ( f3 = - 9.5 dB ) . It is a dam shame I didn't make a few more PCB's . Without the oscillator it would have been OK for this job . Even though only 1.7 V bias ( LED ) it showed no distortion in it's range . The 15 inch unit would be using the same range more or less . 3 x 1N4148 and a resistor will bias it well enough ( 2.3 V I would guess ) . 40 Vrms bridged .

2R is about where I expect it to be with output resistance .

This was how it looked except gain .
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Anybody know these ? Whilst I doubt the use of IRFP240/9240 as a great idea the CfbP input is intriguing ! I suspect it is even a pair for this money . As I am not thinking it will be the best amp I ever had it should be OK . The voltage rating suits the case and PSU I have . Also the heat sink .

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http://www.vishay.com/docs/91239/sihfp924.pdf
http://www.vishay.com/docs/91210/91210.pdf

If lucky a variation of the old Hitachi like here . It has a bipolar like bias system as it is more like a bipolar transistor when low Ron .
Schematic & Wiring Diagram: Audio Amplifer Circuit 230W With MOSFET IRFP240,9240
 
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For Dvv . The late Jim Bongiorno's 1985 circuit for bridged bridge ...

I thought bridged bridge was a bridged amp with the power supply centrepoints of each half of the bridge driven from the outputs of another bridged power amp?

It would be complex to build, the power supplies of the "inner" bridge have to float, and the input signals have to be level shifted. But something similar has been done commercially, I forget the manufacturer though. The scheme had a high quality class A output stage with low supply voltages in order to keep the power dissipation reasonable. The centre point of the + and - supplies was connected to the output of another, lower quality, class AB amplifier with high supply rails. The transconductance of the class A amplifier prevented noise and distortion from the lower quality AB amplifier from reaching the output.
 
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I thought bridged bridge was a bridged amp with the power supply centrepoints of each half of the bridge driven from the outputs of another bridged power amp?

It would be complex to build, the power supplies of the "inner" bridge have to float, and the input signals have to be level shifted. But something similar has been done commercially, I forget the manufacturer though. The scheme had a high quality class A output stage with low supply voltages in order to keep the power dissipation reasonable. The centre point of the + and - supplies was connected to the output of another, lower quality, class AB amplifier with high supply rails. The transconductance of the class A amplifier prevented noise and distortion from the lower quality AB amplifier from reaching the output.
Pretty much me too, bridging bridged.

If floating power supplies were easy and cheap many things become possible, but the dream of economical modularity often falls short.
 
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Forgive this old drawing of my Hitachi based amp revamped . In 2004 I put blobs everywhere . The feedback is still a question . A potential divider on the speaker I guess will do . As long as it has a representation of the output the exact amount is unimportant , that can be tweaked . If so it will then work as a power op amp when asked . As elegant as the Crown amp is it would spoil what I want to do .

This amp has a few virtues the books fail to realize . Slewing is symmetrical . Especially so if equal loads on both VAS . The driving current and input inpedance of the VAS is a nicer than average compromise . BC546/556 are nice devices .

3 diode biasing like TDA 2050 type devices is fine at LF , can be improved if wanting 50 kHz + . 100 R bass stoppers no doubt should be added . For a commercial Darlington maybe not .

27 K tail resistor is a better choice than some think . CCS if preferred .

Choice of devices is what my useful box has ( i.e . 0R33 ) .

Floating PSU is not important . Keeping speaker current out of the ground is .

Any recommendations welcome .
 
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Looking at my PA amp chassis it is a better one than I thought . +/- 50 V ( 53 V today ) . I have theses bits . No PCB so it will have to be kept simple . I have in the past built this exact amp just to know how good it would be . The distortion is very low ( yes ) . At LF the bootstrap isn't strictly speaking necessary . 10 uF polyester will be doing a good job as it is about at that point the contribution of the bootstrap becomes obvious . DC offset from notes was 5 mV . This will give 100 watts 8 R and 150 watt 4 . The PSU is 500 VA .
 
Forgive this old drawing of my Hitachi based amp revamped . In 2004 I put blobs everywhere . The feedback is still a question . A potential divider on the speaker I guess will do . As long as it has a representation of the output the exact amount is unimportant , that can be tweaked . If so it will then work as a power op amp when asked . As elegant as the Crown amp is it would spoil what I want to do .

This amp has a few virtues the books fail to realize . Slewing is symmetrical . Especially so if equal loads on both VAS . The driving current and input inpedance of the VAS is a nicer than average compromise . BC546/556 are nice devices .

3 diode biasing like TDA 2050 type devices is fine at LF , can be improved if wanting 50 kHz + . 100 R bass stoppers no doubt should be added . For a commercial Darlington maybe not .

27 K tail resistor is a better choice than some think . CCS if preferred .

Choice of devices is what my useful box has ( i.e . 0R33 ) .

Floating PSU is not important . Keeping speaker current out of the ground is .

Any recommendations welcome .

Nige, I don't think BC series will do as sufficient drivers for Motorola TO-3 series, 250W trannies.

At higher powers, their Hfe is reduced to 20 or less, you do need some powerful drivers for them. MJE 15030/15031 spring to mind ...

Just a thought.
 
Hi DVV . Doubtless that's right . For 100 watts it is a maybe . I wish I had some Hitachi PCB . It is nailing the DC and AC feedback loops . I suspect I can only have one . Will it behave ? It might just as the Vbe and diode voltages will match . A 4 transistor Widlar current mirror would help ( same as mine with extra two device and opposite made into diode ) . What I am saying as the current mirror is highly matched it might by ohms law alone force DC symmetry . Equally a double DC feedback path could work . It could be double inverting in the sense as both sides would look the same .


DVV . Just for you . I will get drummed out of the boy-scouts for this one .

http://www.diyaudio.com/forums/soli...-self-wants-your-opinions-24.html#post3583352
 
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