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Old 28th Apr 2019, 6:47 am   #821
Craig Sawyers
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Default Re: The Audiophoolery Thread.

All well and good, but the point is that this is indeed a professional application device, where you have knwlege of the dynamic range of the piece and can set the gain structure appropriately. Or push it through a compressor first.

And although fully featured and then some, it needs deep knowledge to set the controls appropriately, particularly the Q. So although a wonderful piece of gear, I'd argue that it is inappropriate in a domestic setting. And for a domestic device, where levels are around 0dBu of 0dBV the S/N is pretty average.

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Old 28th Apr 2019, 7:05 am   #822
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Default Re: The Audiophoolery Thread.

That means somewhere between 5 and 11dB between peak operating level and the opamps clipping point. This is not too bad considering the brick-wall limiting of ADCs. Just so long as the opamp's distortion hasn't risen significantly by the peak operating level.

David
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Old 28th Apr 2019, 8:05 am   #823
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Default Re: The Audiophoolery Thread.

Since the Maselec is made by Prism, they may resonably be assumed to have taken care that it doesn't get in the way of their convertors, and I've not found that it does.

I still think the Cello is neither fish nor fowl, and not half as useful as the set-up Quad used on the 44. Now that really does alter programme balance in a way useful in the home.
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Old 28th Apr 2019, 8:18 am   #824
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Default Re: The Audiophoolery Thread.

We must have had parallel thoughts. Back in the early 80's when I put a preamp together for my silly power amp, I reverse engineered the Quad 44 tilt etc controls from their published curves, and implemented them. I've lived with them for 30+ years and have found them very satisfactory.

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Old 28th Apr 2019, 9:08 am   #825
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Default Re: The Audiophoolery Thread.

Speaking with a friend a few years back, who worked in and had his own studio summed up recordings quite well.

The final release ultimately has to be all things to all people, one reason why 'we' use the Yamaha speakers with white cones. If it sounds ok on those, it'll likely sound OK in the home.

Looking around his studio, not only did you need an in-depth knowledge of the equipment, but you had to be good at juggling too!

Mark
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Old 28th Apr 2019, 4:07 pm   #826
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Default Re: The Audiophoolery Thread.

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Originally Posted by Ted Kendall View Post
useful as the set-up Quad used on the 44. Now that really does alter programme balance in a way useful in the home.
Accepted. I never had a 44, but for many years I had a 34 which had the same basic tone arrangement as the 44, but one more notch on the tilt (so +/-3dB rather than +/-2dB on the 44). I never used the filter nor the bass controls, but the tilt was a good way of taming over-enthusiastic mixing engineers work.
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Old 28th Apr 2019, 6:33 pm   #827
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Default Re: The Audiophoolery Thread.

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Originally Posted by ajgriff View Post
Please don't get your coat Terry. Your contribution is a refreshing piece of sanity and you should in no way be considered a second rate anything by any member of this forum.

Alan
Hello,

Firstly, I’ve put my coat back on the rack and I’ve laid down my hat

Thanks for the kind comments - my faith in the forum has been restored tenfold.

Being honest I’ve seen things in the darker recesses of the hi-fi industry that had me doubting reality.

Over the last 30 years I’ve had the privilege to closely work with one of the more charismatic characters in the hi-fi world, who is responsible for some innovative mechanical engineering and I’ve learnt a lot in those 30 years, but it can be interesting at times

Good audio equipment is about good engineering and listening to one’s efforts but not letting one override the other as there is a balance between what you hear and measure.

Regards
Terry
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Old 2nd May 2019, 11:19 am   #828
Craig Sawyers
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Default Re: The Audiophoolery Thread.

You got me thinking about the quad tilt circuit. There are two varieties. The Quad 44 has a rather complicated arrangement that was improved on in the 34. Fortunately the 34 service manual discloses the resistor chain in the controls.

For the tilt is is end stop resistors of 13k, and six 9.1k which go to the switch contacts.

Anyhow I put it into spice using the LM4562 model. The performance was a bit off the mark. The bass end peaked at 3.16dB on maximum tilt, and the treble end at 2.9dB. There was also a significant bass roll off (probably intentional) as a result of the 68nF capacitor from the slider to the inverting input of the opamp.

Anyway, you can get it pretty much bang on by changing C31 from 68n to 330n. Changing R53, R65 from 56k to 51k. And changing the end stop resistors from 13k to 18k.

Response attached.

The slight gotcha is that the capacitors need to be matched on each side - so the two 1nF and two 3.3nF. 1% is good enough. If they are in error by 10% typical it introduces a mid band hump of 0.4dB, particularly troubling in a flat response at zero setting. There seems to be nothing in the parts list that suggests they are close tolerance, but they might have selected them at Quad or specified selected parts from their suppliers.

Craig
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File Type: pdf Quad mod response.pdf (86.2 KB, 275 views)
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Old 2nd May 2019, 11:24 am   #829
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Default Re: The Audiophoolery Thread.

Actually disconnecting the switch slider at zero gives a flat unity gain response, determined by the two 820k resistors.

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Old 2nd May 2019, 11:40 am   #830
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Default Re: The Audiophoolery Thread.

Interesting,

When I did my preamp, I liked the shapes of the plots Quad advertised, so I just synthesised four passive networks to give those shapes, with an attenuator for the flat position. I never did find out Quad's implementation.

David
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Old 2nd May 2019, 12:51 pm   #831
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Default Re: The Audiophoolery Thread.

For completeness, this is the original Quad tilt response

Craig
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File Type: pdf Original Quad 34 tilt response.pdf (86.3 KB, 247 views)
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Old 2nd May 2019, 2:48 pm   #832
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Default Re: The Audiophoolery Thread.

I swapped op-amps (at a theortetical level, that is). The LM4562 is a superb low noise opamp, but is discrete transistor and has a significant input current. Given the relatively high resistors, it generates 10-20mV offset.

Quad used the old and iffy audio performance TL071, which is FET input and has input current in the few nanoamps range. They made the right choice in that regard.

So I substituted the modern FET op-amp, the OPA2134, and confirmed the offset voltages were all down in the tens of uV range. Again just Spice at this point.

Craig
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Old 2nd May 2019, 10:43 pm   #833
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Default Re: The Audiophoolery Thread.

Hang on a minute..... the last few posts aren't about audiophoolery, they seem quite rational


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Old 3rd May 2019, 1:17 am   #834
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Default Re: The Audiophoolery Thread.

Quite a few have been.
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Old 3rd May 2019, 1:55 am   #835
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by Radio Wrangler View Post
When I did my preamp, I liked the shapes of the plots Quad advertised, so I just synthesised four passive networks to give those shapes, with an attenuator for the flat position. I never did find out Quad's implementation.
I think that Quad used the Baxandall modification of the Ambler tone-balance circuit. But as it is more about sound audio engineering than "audiophoolery", I have taken this item to a separate thread for more detailed exposition. See: https://www.vintage-radio.net/forum/...47#post1142147.



Cheers,
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Old 3rd May 2019, 7:34 am   #836
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Default Re: The Audiophoolery Thread.

Quote:
Originally Posted by Herald1360 View Post
Hang on a minute..... the last few posts aren't about audiophoolery, they seem quite rational


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Old 3rd May 2019, 6:37 pm   #837
Craig Sawyers
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Default Re: The Audiophoolery Thread.

Latest iteration of the Quad tilt circuit. The dominant noise source is the resistors, which are all rather high, and probably chosen so that the weedy output current capability of the TL071 would not be overtaxed, particularly since it also drives the balance control and the input to the filter circuit.

So the tilt pot goes to 10k instead of 54.6k. Everything else scales.

C40/45 18nF
C41/46 5.6nF
C51 shorted
R51/52/63/64 16.9k
R53/65 9.31k
R54/66 150k
End stop resistors 3.3k

Frequency response is the same as before for all 7 settings of the tilt switch.

Noise signal to noise is -107dB to -110dB depending on the tilt setting. Output noise is about 4uV. Both on a 20kHz bandwidth. That is a quiet circuit!

Distortion is just over 8e-5%, which is what the OPA2134 spec sheet says.

Time to build it, I think.

Craig
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Old 4th May 2019, 12:01 pm   #838
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Default Re: The Audiophoolery Thread.

We seem to be straying a long way away from audiophoolery which I always assumed was to be found in the farther recesses of the internet until I read this in the pages of the current issue of HiFi Plus:
"...the vast majority of [phono] cartridges use magnetism to convert the mechanical groove energy into an electrical signal. One characteristic of these magnetic devices is a lack of LF and excess of HF output, so they require something called RIAA equalisation in order to deliver a 'flat' response."
This was written by Paul Messenger, a doyen of British hi-fi reviewing, in a piece on a phono stage. Unbelievable that after so many years in the business he does not know how LPs are made. Not surprising that it appears in a magazine founded by Roy Gregory who pontificates about LP equalisation but has no idea of how it works.
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Old 4th May 2019, 12:09 pm   #839
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Default Re: The Audiophoolery Thread.

Good heavens. That is bewildering ignorance for Messenger, who I've met several times and has always seemed to be on the ball.
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Old 4th May 2019, 12:27 pm   #840
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Default Re: The Audiophoolery Thread.

Detailed technical knowledge leading to high quality technical analysis doesn't sell well as the market is so limited.

Alan
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