AU D7 Amp. What does "Linear A DD/DC" mean

raj1008

New Member
Hi everyone,

I have had a Sansui AU D7 since 1982. It works great. But I have always been wondering about what Linear A DD/DC mean? It is printed on the face plate. Could someone enlighten me please?

Raj
 
DD/DC, The DD stands for Diamond Differential. The DC, just a guess could be Direct Coupled???

Greg
 
AU-D7 Integrated Amp
1981-1983
80 W/Ch @ 8 ohm
20-20,000Hz @ < 0.02% distortion
Damping Factor: 200 @ 1kHz
Slew rate: 220V/uSec
Amplifier bandpass: DC-300kHz +0dB, -3dB

(translated from German)

The remaining specs (e.g. phono) are about the same as the AU-D5.

However, one thing I didn't know as I researched this question is that the AU-D7 came in 2 flavours; the (B) and the (S) meaning, I assume, the 'black face' and the 'silver face'.


Paul (SanuiSan DB-man) :D
 
You guys are fantastic.

Greg, I read the catalogues on the link you showed me. What i understand is that Linear A DD/Dc is for zero distortion. Is what it is all about or am I missing something?

Raj
 
Don't rightly know as I'm just an amateur vintage home audio guy that just started about 7 or 8 months ago.
 
Well, DD/DC is a whole lot of salesmanship brought about by the audio wars of the 70's.

Everyone was scrambling to find newer and 'better' ways to build audio circuits and the big bugaboo (they thought) was distortion.

So, along comes 'direct coupled' amps that could pass a 0 Hz signal :D and a bandpass that extended almost into the RF regions :rolleyes: and.. and.. and.

Well, Sansui DD/DC is just one more thrust at building something that would capture the hearts of the buying public. So back in 1978 Sansui Introduced the "Diamond Differential DC (DD/DC) Circuit". They claimed that it reduced the total harmonic distortion to 0.008% and boosted the frequency response from DC to 500KHz!! Well, at 500 KHz my ears tend to be sizzling :dunno: so it's anyones guess as to how much better the actual AUDIO frequencies were handled.

Perhaps some of the techs here can pass on some comments as to the quality of the audio in these DD/DC amps. Did it actually sound better?


Paul
 
I have had this set for over 20 years. Practically grown up with it! I was 7 when my dad bought it. We teamed these up with two pairs of Altec Lansing Nine Series II speakers http://lansingheritage.org/images/altec/catalogs/1978-home/page04.jpg they blow the house down!

Despite the fact that I had the speakers reconed and Amp rebuilt ( blew one channel. Sansui had a service station in India which did a pretty great job), I dont find any distortion at any volume. Its awesome. I cant imagine that they built anything better than this but apparently after seeing you guys talk about better things on this forum I am in awe.

BTW how would these work as home theatre systems? I guess they would be better than any new fancy setups apart from the fact that they are stereo sounds and not 5.1. Any ideas?

Raj
 
Hi Raj:

I saw your question last night (before there were any replies) and I was going to answer it then, but apparently just at that moment, there were some problems with this site's server's and I couldnt post the message.

Anyway, The DD/DC stands for Diamond Differential/Direct Coupled. Supposedly, the "Diamond" terminology comes from the idea that when the circuit is drawn out on paper, it resembles the shape of a diamond. The DC refers to not using coupling capacitors in the signal path from the power amp section to the speakers, for what is theoretically claimed to then offer purer audio sound quality. If ALL coupling capacitors are eliminated, the DC is then said to be a reference to the terminology known as 'direct current' amplifier and the amp can uniformly amplify down to DC (O hz frequency).

Linear-A refers to the particular design used in the AU-D7 (and AU-D5 models). Since Class A amplifier designs tend to be inefficient because their transistors are always on, it eats up alot of power whereas Class B designed transistors do switch on & off but in doing so, while they do save power and minimize heat gain, give rise to large amounts of switching & crossover distortion. Thus, Linear-A was Sansui's design used in these models which combines the advantages of class A & B, but without their disadvantages.

The bigger, more powerful models in the AU-D Line, AU-D11 and AU-D9, are different from the D7 & D5, and use a circuit design called "super feed forward", its a sortve play on words, instead of feed-back, its feed->forward :)

As for specs on the AU-D7, a service manual is suited more toward repair, though there are specs contained therein. The AU-D7 brochure (or the D5 brochure) would be the best source of explaining the amplifiers features and would also provide the specs.

I have an AU-D7 by the way. And yes, it was offered in two color options, black and silver, and the same applies to the matching tuners, the TU-S7 and TU-S5.

B/F
 
I think that one of the primary objectives of the DD/DC circuit design was to reduce TIM distortion by increasing the slew rate and decreasing rise time in the amplifier and phono sections. THD was already low enough, but transient response was what the Sansui engineers were after, IMO.

RobV
 
Beatlefred, that was awesome. You really know your stuff.

RobV, wow. What did that mean! I have no clue what you just said. It sounded like you very not happy with the set???

I was wondering how the set would sound hooked up to a DVD player as a home theatre.Zero distortion.

I know that there are only stereo channels on this, but we have two sets of speakers and perhaps if we add a subwoofer it might just do the trick. Any views guys?

Raj
 
The AU-D7 was built before the era of home theater/surround sound systems, so it doesnt have any video inputs for you to be able to connect a VCR or DVD players' video signal output to it.

One of the things you can do, is get something like a Sansui AV-77 processor which you can then connect as an interface between the vcr and/or dvd to the AU-D7, thus you can watch movies and amplify the audio sound with the AU-D7. However, this setup does require making alot of connections with cables- atleast it did when I was using it with my AU-D7 to watch tv, vcr, and dvd on my computer.

I had a Sony STR-D990 receiver I bought new in '93 and decided to use that instead of the video processor. So, I just simply run a Tape Output from the Sony to the Aux input of the AU-D7, and thus I am able to derive the benefit of the Sony's video jacks but still be able to use the AU-D7. By the way, I am able to watch tv because my computer's video card, ATI All in Wonder card (still using the same one I bought new in '99) has a built in tv-tuner. Thats not a big deal anymore but certainly a nice feature to have, why buy a video card without one?, I say.

B/F
 
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