Author Topic: Sansui AU111 Valve Amplifier  (Read 22576 times)

Offline Moog

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Re: Sansui AU111 Valve Amplifier
« Reply #30 on: July 20, 2011, 01:33:11 AM »
I think those little men doing hand stands & flip flops in your avatar are scaring him away.... :D


-F_D
OK! OK,  I Might need to retrench these "men in white coats" and install a new avatar. ;D ;D
I was impressed by Hendrix. His attitude was brilliant. Even the way he walked was amazing -

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Offline Ampdog

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Re: Sansui AU111 Valve Amplifier
« Reply #31 on: July 20, 2011, 02:59:25 AM »
I do not think the 'early' ones in this case were the 3300nF couplers;

Oops! Not 3,3F, only 300nF originally!

And yes, those (C67-R87) do appear to be the governing RC (referring to one channel only. The -3dB frequency for those is about 5Hz, while the other RC (R77-C71) cuts at 0,8Hz.  R71-C63 are also in the mix at 3.5Hz, but their phase shift rolls back to 0 at lower frequency.

Then the output transformer: I cannot now find where I noted down its inductance; I believe the -3dB point for UL only was about 10 Hz. But one must realise that the local cathode feedback of about 3 times pushes this down to about 3 Hz. All in all, technically, all these roll-off points are rather close together; it requires simulation to get the final frequency/phase plots, which I will not go into at this stage - I myself have not done it at the time.

To return to the point of the 300nF coupling capacitors (C67 - C70) then: I would not increase the value although I replaced with 330nF at the time. Since all these roll-off frequencies are quite low, those Cs could safely rather be decreased to 220nF or even 180nF. If one wants to stay close to the original of 300nF, I would go for 270nF, not 330nF. So not 'sacrosanct', as you asked.

A final remark: I did say that the 'early' roll-off is rather done earlier in the loop circuit. The reason for doing it here with the final coupling capacitors is likely because of the realtively low values of R87 - R90, ruled by the maximum allowed grid resistance forced by using fixed bias. This roll-off is normally done by making C71, C72 small, but then C67 - C70 would needed to have been some 2,2F at least, and that would have been expensive and bulky in the days of the design.

Edit: PS added: The practical way of testing whether any l.f. instability is threatening would be to do a frequency response run down to an octave below the relevant frequencies and looking for a hump in the response. This is difficult here as we are talking of going down to some 2 Hz, which is not common with the usual audio signal generator. Ambitious DIY-ers could build something doing say 0,5Hz - 20Hz, but a stable circuit is a little more complex than one might think.
« Last Edit: July 20, 2011, 03:07:01 AM by Ampdog »
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Offline TheMooN

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Re: Sansui AU111 Valve Amplifier
« Reply #32 on: July 21, 2011, 08:48:46 PM »
Thanks you for your considerations on this question A-D , this point , together with your recommendations on tweaking the performance of the AU-111 comprise some Valuable Research and Much Appreciated .   

Offline TheMooN

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Re: Sansui AU111 Valve Amplifier
« Reply #33 on: September 23, 2012, 12:07:32 PM »
Good Morning Folks .

I would appreciate any opinion regarding a loony plan I have been mulling over .
Whilst reading through the AU-111 manual I paid a little more attention to the various connection configurations open to the Au-111 owner and it would appear to me that I might be able to slave a second AU-111 to a Master Au-111 using the middle connection option that I have out lined in red on the attached image of  page 9 ~



The second image shows ( In a somewhat badly drawn cartoon diagram format ) what I am babbling on about at the 2 x amplifier point and also the main reason for my plan which would be to
re- sum together the + and - output from 2 x Au-111 into a single pair of speakers , the pre amp signal from the Master , fed into the Amp section of the Master as normal , and also via a Y splitter at the connection point of Pre and Main Amp sections on Master ,  fed directly into the Main Amp section Only of the Slave , Attenuation should , I believe , be controllable for both Amps via the Vol control on the Master !!!



Feasible Folks ? or  :nutter: :fuse:       

Offline ludo

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Re: Sansui AU111 Valve Amplifier
« Reply #34 on: September 23, 2012, 01:31:50 PM »
 :stop: :nono: :stop:

Using the same signal to drive the inputs of numerous amplifiers is fine, BUT:

If you sum the outputs of the amplifiers back together by simply connecting the output wires as you have in your drawing, you will have a fire.
If it 's going vrot, put it on the buffet ! - Fats

Offline Family_Dog

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Re: Sansui AU111 Valve Amplifier
« Reply #35 on: September 23, 2012, 07:24:10 PM »
Yep, not a good idea. But you could split the mids and lows as per the picture in the manual, going to different speakers via a high/low filter.


-F_D



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Offline TheMooN

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Re: Sansui AU111 Valve Amplifier
« Reply #36 on: January 03, 2013, 01:18:35 PM »
G'day Folks . I hope you won't mind my pulling this one out of the Shorts Drawer again  :)

If I might inquire of AD , I have been wondering , Re the AU-111 units upon which you have worked,  did you leave the original VR1 /VR2  in situ , replace same with a better quality pot (Not easy to source )  , or perhaps even removed it entirely from the circuit ?
As I tend to run and leave that particular control at max clockwise I have been considering whether I might as well go the latter for one less pot in the signal path .

I have been keeping myself amused of late with a little cap rolling in the pre-amp section and have just installed a couple of V-Cap teflon 0.047's on which I shall report back on when they have a few more hours on the clock .

RGDS

     

Offline Ampdog

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Re: Sansui AU111 Valve Amplifier
« Reply #37 on: January 08, 2013, 02:05:16 AM »
Apology MooN,

Read that only now.

Gee - I cannot recall! I did look up the schematic just now but could not find a physical picture of the amplifier. Are those pre-sets at the back or front-panel controls? They pre-set the input gain; I am not sure why as everything remains in the original ratio.

Anyway, to answer your question: If you find the main volume control managable i.e. not too 'sensitive', you might as well remove those - just add a 470K resistor in place to common. Then you must just know not to have inputs so high that you hardly advance the main volume control for comfortable volume. There are stages after VR1 and VR2 but ahead of the main volume control that might then be overloaded. (I am thinking of some CD-players with their >1V output signals; not sure whether such is still the case. If so it should be an easy matter to 'equalise' everything with resistive dividers at their respective inputs.)
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline King_Julian_S

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Re: Sansui AU111 Valve Amplifier
« Reply #38 on: January 09, 2014, 10:46:16 PM »
Hi

How good are these amps in general ?
I see high end got one for 16k and that is 4 more then a pair of demo Isis mono's...
Non audiophile music lover...

Offline Ampdog

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Re: Sansui AU111 Valve Amplifier
« Reply #39 on: January 10, 2014, 04:37:03 AM »
King_J_S,

More of a question: Do you mean R4K more than the Isis pair, or 4x more? I take it to be the former.

My limited comment: I must confess to not knowing the Isis, but think that it is a power amplifier only. The '111' is a complete stereo amplifer, tone controls, filters and phono stage included. That makes it about as versatile as anyone would want. (The pre- and power amplifiers connect via external links so that they may be used independantly.) Also, it was the only amplifer from several brands I have refurbished that met its specs accurately.

The usual question will be how it sounds, and you will know by now that I cannot answer that as everyone will have a different opinion (my own ears are sadly not nearly up to judging standard any more). I am not familiar with the Isis design, but found the '111' design impeccable. It is one of a very few amplifiers where the power amplifier uses a UL output stage in the cathode feedback mode like the classic Quad II, which has a real edge over other topologies. When refurbishing I only exchange two electrolytic caps of rediculously high value for polyesters. To be more critical, one also re-positions a few high temperature resistors away from nearby capacitors and such - but that was not your question.

Whether all of this is worth R16K I cannot tell, not nearly being familiar with what second-hand stuff fetches - others will have to inform on that. I do know there is a certain snob-factor, making e.g. Leak TL-12s go for up to R30K which they are certainly not worth (not saying that there is anything wrong with them).

Let us hope for more definitive comments from others. 
Audio must be the only branch of engineering where lack of basics' knowledge is considered a superior form of wisdom. (Anon)

Offline King_Julian_S

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Re: Sansui AU111 Valve Amplifiers
« Reply #40 on: January 10, 2014, 08:03:40 AM »
Thanks AMPDOG.

Yes , sorry ... That is 4k more...

I've seen the Isis and it is a beauty.
Designed by mr Hobkirk...
Yes ... Isis is also only a mono power amp set...KT88 based.

I know the question is subjective ... I.e.Does it sound good...
Just wondered what makes it special .. And I think you have answered most of it in this thread...
Good and solid build I would say....

Tx again good sir...



Non audiophile music lover...

Offline Kent Kassler

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Re: Sansui AU111 Valve Amplifier
« Reply #41 on: January 10, 2014, 08:05:48 AM »
No it is not worth 16k(or anything close to that amount) ;)
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Offline King_Julian_S

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Re: Sansui AU111 Valve Amplifier
« Reply #42 on: January 10, 2014, 08:09:47 AM »
Tx Andre...

So ... It is most probably like AMPDOG said... a certain "snob factor" then...

Man ,,, how I wish they can make you (Andre) the minister of pricing on everything on our country....
As long as they keep you far away from our salaries.... Lol

Non audiophile music lover...

Offline Kent Kassler

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Re: Sansui AU111 Valve Amplifier
« Reply #43 on: January 10, 2014, 08:12:10 AM »
The man behind the Isis amps lived down the road here by me....he has since moved a bit further away.....he still has some new pairs available but at 3x the price of that pair.I was offered a pair to listen to at the shop but this has not happened as yet.I lost the gentlemans number.(Hi-phibian can you help again,sorry)....of course most know that Alan Hobkirk was the builder.....if the pair being offered are as described then the price is very good.
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Offline Kent Kassler

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Re: Sansui AU111 Valve Amplifier
« Reply #44 on: January 10, 2014, 08:14:43 AM »
KJ,if you type "Isis" in the search column of the opening page.....we discussed the amp and some pics were up at some point not too long ago.
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.