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Old 17th May 2012, 09:42 AM   #5581
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Active and (at least) two subs, I couldn't agree more and have been running 4way actives for years.
Btw Billy Woodman (owner/founder of ATC) claims that the efficiency gain of active over passive is at least 3dB but depending on complexity of the passive xover can be up to 9dB.

When I first activated my Tannoys I gained exactly 3dB in the bass which uses a very simple 12dB slope. Tannoy even agrees with that as the power handling with passive xover in place was stated as 100w while the bare driver was clearly marked '50w max'.



PS: The german mags I remember reading back in the '80s were Audio and stereoplay.
Measurement galore and in the case of stereoplay all listening test were done in a reproduction of a typical average german living room. They even rebuild it on their stand at the IFA the 2 times I went.
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Old 17th May 2012, 10:19 AM   #5582
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Originally Posted by Joao@AltheaMusica View Post
Nowadays
Audio magazines nowadays appear to have a half-life period, as someone commented on a thread about Image Hifi at Holger's home page earlier this year.
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Old 17th May 2012, 11:07 AM   #5583
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Default Subs

One thing about subs and very low price . One can put the amp on the speaker and use the air to cool it . Naturally that reduces fidelity as it is the type of sub-woofer most of us deplore . However to have it for party mode is not so bad ( switch) .

No class D needed . G is fine ( or whatever people choose to call it now ) . Can switch off G rails if not in party mode / mood .

My friend John worked nearby Mr Woodman by pure chance . He moved into the building they also rented . My friend was even an audio engineer so benefited greatly .

D V V . Have you thought of using Douglas Self's Class A/C ( class G ) ? It would seem ideal for your application of active ? It is public domain in his book . I made a 4 transistor Class A/C of 8 watts 21 W ( 42 W 4 ohms ) for this very application . Just a bit of fun and now replaced with KT 88 anyway . Mine does not look like class C to begin with . It is very over biased class B . Not the same exactly but similar . If higher power I would have put in the zener diodes . Mine only needed a 80VA transformer in 8 ohm mode and 2 x 30 000 u F . It had very cheap almost silent PSU to VAS using a voltage multiplier and RC filter chain . Funny thing is I ran it below the maximum voltage as it sounded better even though I lost a few watts ( I used +/ - 20 V when + / - 25 would be optimum power wise and was available ) . It clipped more gracefully ( not soft clip , that is different ) . When going into class G ish B I include a small bootstrap to clean it up . I can not measure any transition into this nicer type of B after many adjustments . Not having Beta doubling effects at crossover point is no small deal .

Last edited by nigel pearson; 17th May 2012 at 11:11 AM.
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Old 17th May 2012, 11:13 AM   #5584
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Originally Posted by nigel pearson View Post
That is fascinating about FET's . Especially the information about common cheap FET's . That is already a useful range . My experiences with them has not been especially good . I use Exicon which were designed for audio use .

Do you have experience of UHF op amps ? Some even give audio specifications and are cheap , they even can work in conventional voltage feedback configuration if I remember correctly ? Normally 5 V operating so have to be used with imagination . Seeing as you know so much about UHF your opinion even if that you have none is useful .

Thank you in anticipation .

I am designing a Gu 50 amp for fun , what a nice tube and from Russia ( was Telefunken LS 50 ) .

D V V . 10 watt class A amp will have Gu 50 to replace KT 88 soon . No choice in this as my friend wants tubes . Me too now I have made it work . This is in the active set up .
In that speech by russian designer, the Ciss and Crss have not been addressed, and they add nothing good to properties of switching vertical MOSFETs.
I do not have experience with UHF OpAmps. Wide bandwidth is only a small part of whole story. In addition, I would say, that the only DIRECT benefit from VHF FETs at output stage is facilitating of proper operation of NFB. However, there are also positive by-products from using VHF transistors, like smaller and less varying capacitances, more linear Vgs-Id curves around 1A current. Similar (even better) starting conditions is provided by tubes, but the issue of output trafo put tubes down. Also, I believe, that good choke is a must in PS of good tube amp. From my comparisons, SS (usually low wattage )amp, with proper parts and specilal topology, wins over tube designs, since similar or less investments into properly composed "output cap" of SS amp give better results, than equivalent or higher investments into output trafo.

Last edited by VladimirK; 17th May 2012 at 11:15 AM.
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Old 17th May 2012, 11:19 AM   #5585
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Thank you . I think it is not a fruitful avenue of research as 5 V is very limiting . However - 86 dB distortion for MC stage and 0.9 nV costing $3 is what I have seen ( dual op amp SMD ) . That was for intermediate video functions . Not UHF really . Made by LT and I suspect similar to audio op amps . Sorry I forget the number if asking .

I only did a tube amp to please a friend . Up to now I have no design experience of them . Your words would be my words on that subject mostly . I do notice a holographic effect with tubes ( a type of distortion perhaps ) . My transistor amps do not have it nor others I listen too ( No way Krell has it to my ears ) . I reject tube amps that sound romantic or nice . I do not think a tube amp has to sound that way . Transformers are as you say exspenive . Also $1 capacitor is superior to $100 transformer . That is true .

Transistor amps that have similar distortion as tube amps do not have the holographic effect ( they have some of it I must say , not identical if looking identical ) . I don't think it is microphony ? Analogue tape recorders have similar distortion . They do not have the holographic effect either . However tube analogue recorders do ? The latter effect is less noticeable and I only mention it becasue I suspect tube analogue tape recorders are better . They have comparable overall distortion as tape distortion dominates in that . I assume we go into the red when saying that and good quality tape heads .

Last edited by nigel pearson; 17th May 2012 at 11:45 AM.
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Old 17th May 2012, 11:25 AM   #5586
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Personally I use fairly high-powered class AB bipolar amps made by MC2 Audio.

That said in a phone call to one of the designers I was told that in a domestic environment it is very unlikely that the amps ever leave class A operation.
Probably true as I use a total of around 900W/ch in amps.

You can never have enough headroom IME and small (ie less than 100w) ss amps are the worst.
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Old 17th May 2012, 11:48 AM   #5587
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That sounds like my type of amplifier . Why not have amps like that ? C Audio were fun in the old days it is said . I know someone who tried to sell it as hi fi in another form . It was rejected because of him not the product . The reviewer was reluctant to give it back .

Last edited by nigel pearson; 17th May 2012 at 11:50 AM.
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Old 17th May 2012, 11:50 AM   #5588
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Originally Posted by dvv View Post
Odd you should say that, Nige, you are one of the very, very few who think so.
You obviously haven't been following the right threads here on diyAUDIO.
Multiple subs has been the subject heated debate.
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Old 17th May 2012, 11:51 AM   #5589
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I think we may have a winner! Whoever said IM might cause the irritation on my EL34 amp could be right. (Anthony?) There is a little ringing on resistive and reactive loads, but it doesn't look like much more than 1/2 a dB. That might still be annoying.

But IM is bad and gets worse on a reactive load. Interestingly, harmonic distortion is a little lower on a speaker load than on a resistor. Maybe an impedance thing. I'll post charts in a bit.
IF this is a feedback tube amp, probably a pentode? <---EDIT: this idiot can't read! ha.

You might consider altering the fb network so that it does *not* try to make the response flat all the way out to 20kHz. If the iron itself is not flat out there, then using the FB to make it flat always introduces ringing and other "icky" sonic byproducts... you might want to live with a bit of rolloff, it will likely sound better. Also strap the pentodes (if that is what they are) for triode.

Alternately just mod the sucker for very low or no fb and be done with it...

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Old 17th May 2012, 12:03 PM   #5590
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Hey Bear. Yeah, I think it has pretty heavy FB, as the overall gain isn't outrageous and it's pretty flat out to 35KHz. It does have a Triode mode switch, which I neglected to test. I like the idea of messing with the FB and will give it a try. I'll be tickled pink if I can make it sound better AND measure that difference.
Thanks.
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