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Old 30th January 2013, 08:43 AM   #8321
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Mobius loop again ( should have been my nom de plume ) . At the twist point we get the Nyquist point . Visually I do see a feedback amp as being like that .

I recently built a unique application of a bootstrapped VAS . I could not use a CCS as it a power engineering application and requires nearly 100% positive feedback ( 96.4% ) . The hum levels were atrocious ( and of absolutely no importance ) . Has anyone had poor noise performance from bootstraps ? It is not talked about . Looking at my results it seems logical they would . This further endorses regulated power to the VAS ( shunt ) . Also the tail resistor is then a possibility rather than a CCS , as one of us said it might behave better at HF ( fas 42 ? ) .
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Old 30th January 2013, 05:01 PM   #8322
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Quote:
Originally Posted by nigel pearson View Post
Mobius loop again ( should have been my nom de plume ) . At the twist point we get the Nyquist point . Visually I do see a feedback amp as being like that .

I recently built a unique application of a bootstrapped VAS . I could not use a CCS as it a power engineering application and requires nearly 100% positive feedback ( 96.4% ) . The hum levels were atrocious ( and of absolutely no importance ) . Has anyone had poor noise performance from bootstraps ? It is not talked about . Looking at my results it seems logical they would . This further endorses regulated power to the VAS ( shunt ) . Also the tail resistor is then a possibility rather than a CCS , as one of us said it might behave better at HF ( fas 42 ? ) .
(Bold & underlined by DVV)

This is an assumption most open to discussion. A resistor afrter a zener is preferred by the audio industry for cost reasons only. Those same manufacturers will do it right on their more expensive models.

As we had the opportunity to see here some time ago, somebody posted his own test of 10 or so CCS types tested for PSRR, clearly demonstrating numbers from 38 to 82 dB. Kinda BIIIIG difference, don't you think?

Somebody else mentioned the fact that this is outside the NFB loop, so it it what it is, no subsequent corrections. While I cannot pretend to know just how audible this is per se, I am ruled by the logic that everything matters, that effect included. The most difficult thing ever, in any field of technology, was to make a well balanced product.

Because of this, I am not very keen on all-in-one power amp chips and prefer those which require external power devices. The key reason is that in such a case, I can use fully electronically regulated power supplies for the chip and separate unregulated supplies for the output stage.

In case of a discrete CCS, the transistor separating the zener voltage from the input stage rules supreme no matter what anyone says. Preferably two transistors in a cascode topology, and still more preferably with a FET separating the BJT from the supply line (but because of generally low FET voltages, this usually requires an extra resistor, zener diode and filtering capacitor. Thank God I am not the industry.
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Old 31st January 2013, 08:27 AM   #8323
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I wonder how many very boring / competent amplifier out there might be improved by simple PSU upgrades ? Fit a larger toroid transformer and upgraded capacitors . Next a few tweaks to the power amp VAS supply . Graft 4700 uF next to output transistors . If knowing virtually nothing about electronics this should be possible and rewarding. If space allows use the old transformer to power the VAS etc (and preamp section if an all in one design ) . Rotel told me that their cheapest amplifier was simply a smaller transformer ( I think I recommended it and they did it about 1985 ) . It sounded very different ( anemic ) !

I might tell a sad twist to that story . Comet was where I bought my Akai AA 8080 receiver when aged 15 ( 1971 139 ) . Comet probably launched the reborn Rotel of Stan Curtice and Tony Morpath . When I had a shop I used to send students to Comet to buy a Rotel amp ( RA 820 Silver ) ,then return to me to buy the rest ( 10 % student discount and all cables supplied ) . I was so impressed I phoned Rotel and became a dealer . I was I think the only independent then who sold it in the UK ( 1980 ) ? Comet were like Walmart , most shops wouldn't touch it if sold there . I didn't give a dam if it made money directly as it made money for me selling other things . Truth is it did make money and Rotel liked having an enthusiast to talk to who got involved with circuit design .

My shop closed in 1997 . Student grants were cut and parking became impossible . My little shop turned over 400 000 at the peak and 210 000 when we closed . Even by UK standards it was a small shop . It cost 38 000 from the profit just to open the door per year .

Comet ( all UK ) closed about a month ago . Rather than them being competition we shared business , the manager was astonished and I am sure he sent me twice what I freely sent him ! We both noticed if recommended by the other usually the sale was made . It was like the film Miracle on 34 th street ( 1947 ) . Opposite the shop was Pizza Hut , it was a prime secondary site . Also Jessop's the top photographic chain . Jessop's also have gone just after New Year .

I am told John who took the business I lost now has to do 1000 000 to survive ( Oxford Audio Consultants , I presume still there ) . No wonder we have no hi fi industry . Talk about the vampire drinking the blood of their cash cows .

When the shop was doing OK the UK was 60% non productive ( not making things ) . Now I guess 90 % ( UK = Greece with banking safety net ) ? In 1997 I went into manufacturing and never looked back . I was forced and also told a white lie at my kids school . When a teacher was having a go at my boy I said it's not surprising as I am an inventor and he is used to an eccentric life style . I never regretted that forced change of life . It has made me many friends and I have seen the world due to it . Never had any money and I guess I never will ? I am try to pass through the eye of needle without volunteering I guess ?
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Old 31st January 2013, 08:54 AM   #8324
dvv is offline dvv  Serbia
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Quote:
Originally Posted by nigel pearson View Post
I wonder how many very boring / competent amplifier out there might be improved by simple PSU upgrades ? Fit a larger toroid transformer and upgraded capacitors . Next a few tweaks to the power amp VAS supply . Graft 4700 uF next to output transistors . If knowing virtually nothing about electronics this should be possible and rewarding. If space allows use the old transformer to power the VAS etc (and preamp section if an all in one design ) . Rotel told me that their cheapest amplifier was simply a smaller transformer ( I think I recommended it and they did it about 1985 ) . It sounded very different ( anemic )! ...
In my experience, quite a lot of so called budget amps will benefit from beefed up power supplies. Some more, some less. When any one of my friends decides to refresh his gear, the first thing I tell them is to carefully investigate whether installing larger caps is possible, and if so, to go for them.

Sometimes, it's also necessary to change the bridge rectifier, so it can handle the eadded capacitance.

Several times, the power transformer had also been changed, but that's very rare as usually there's not much spare space, or if there is, the basic device is simply not worth the trouble and expense. I mean, if you own a 30 WRMS Technics, what's the use of investing more than its purchase price into beefing it up?

Why even consider it? Usually, for one of two reasons. Sometimes the owner is most attached to a device and will not give it up for any reason. Secondly, even in the budget sector, you occasionally come across an uncut diamond, so to speak, a design which you would never expect to find in that price bracket. Toshiba R45 comes to mind, exactly such a product, designed and made MUCH better than its price would lead you to believe. Its only real failings are a ridiculously small power transformer and a U shaped piece of aluminium which acts as the "heat sink". Both can be changed for better without too much hassle, resulting in an integrated amp purchased for a princely sum of € 35 (app. $50), requiring about €100 (app. $130) for the whole list of works (new power transformer, new proper heat sink, new caps up from 8,200 to 15,000 uF, new output devices, etc, all of which will make it play music like a modern integrated amp about 7-10 times its total price.

You won't have a remote, but you will have the music. Who knows Toshiba's transistors better than Toshiba?
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Old 31st January 2013, 09:31 AM   #8325
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My dad has a Kenwood ( Trio ) 10 W receiver . It is out of this world good . The power supply looks to be for a train set . I studied the design and feel it must be a 30 W design chopped down in price . The FM is astonishing , as is the build quality . The sound is fantastic apart from obviously low power . The tone controls in the power amp ( nice ) . Nothing in the power amp would say it is less than 50 W . This receiver was sold when 10 W was already below acceptable . I bought it by listening and being totally amazed . Stranger still it drives LS3/5A which are considered to need 100 W ( 500 transient was said by a BBC designer , Meridian 105 is very good ) . I remember the Kenwood raising the roof on Proms night . It can be clipped without any distress to itself or speakers .

It would be a No 1 for an upgrade . It has the space . I think a 250 VA toroid is where to start . They are cheap at Rapid Electronics and CPC . Caps after . Good to hear the progress in stages .

Toroidal Transformer 230v Single Primary 225va 0 15v 0 15v ( a guess for a 10 W design , A Japaneses 10 W was often 20 W ) ??
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Old 31st January 2013, 10:50 AM   #8326
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Quote:
Originally Posted by nigel pearson View Post
I remember the Kenwood raising the roof on Proms night . It can be clipped without any distress to itself or speakers
This is indeed the mark of a sound design. Plenty of music material which sounds to be of a high order is in fact badly clipped, but I doubt if anyone can pick it at normal levels. For example, that YouTube clip I linked to some days ago, of a live percussion band vs. speakers has a tremendous amount of clipping ... in the speaker section? No, in the initial "live" capture!!

How many people can hear that happening ...?

Frank
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Old 31st January 2013, 11:13 AM   #8327
dvv is offline dvv  Serbia
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Ooooooh, this is totally off topic, but I just have to share it ...

An hour ago, the postman brought me my quarterly fix of CDs from Amazon.com, and this contains the triple CD/DVD package "The Traveling Wilburys".

There's a leaflet supplied, with very well natured and humorous writings of several people, all of whom are signed as per their "academic" titles, one of which is:

Professor "Tiny" Hampton is currently leading the search for intelligent life amongs rock journalism at the University of Please Yourself, California.

:-)))))))))))))))))))))))))))) Caustic!
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Old 31st January 2013, 12:53 PM   #8328
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Our ears clip also in a very similar fashion . Very bad news if so as SPL is very high . I speculate that compression that does similar things as our ears goes unnoticed ?

Here is a tip . Belgians add cocoa to mediocre coffee ( and others I am sure , also coffee to chocolate cake ) . It makes it taste like better quality coffee , yet the cocoa is not obvious . Better quality coffee with it added is often too soft and does taste of it . I am sure hi fi has similar tricks of perception which don't always work . Multiple caps can be less good than one posh cap . Like the coffee sometime multiple is rather good .

I do wonder if Kenwood had done something rather wonderful by de-tuning a more powerful amp ?
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Old 31st January 2013, 01:11 PM   #8329
dvv is offline dvv  Serbia
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Nige, are you are trying to reinvent old principles?

Question: How do you make an excellent 100 WRMS amp?
Answer: You make a good 150 WRMS amp and call it 100 WRMS.

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Old 31st January 2013, 05:34 PM   #8330
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It is the reverse of short changing a customer . Often German cars go faster than claimed . How frustrating ( not ) .
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