KISS

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Colin Wonfor
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Re: KISS

Unread post by Colin Wonfor »

Dr Bunsen Honeydew wrote: Wed Dec 13, 2017 5:17 pm Stop thinking Naim think, you will just get confused. Not a clue why they go on about inductance, it is high cap that kills unfiltered amps.

As far as I am concerned I want LOW everything L,C and R. and stupidity. Naim think was mostly bollocks as Les will tell you. Linn then copied it with even less understanding than Naim.
How odd I have just done a blub on the subject on another forum, CAP KILL AMPS check 1/2*3.142*f*c note as the F goes up the C come down bang dead bits, smoke and joy lovely. And guess what music is not one f it is lots of f,s and harmonics of f , now we are in deep doo doo.
So we also will note that current a voltage will be out of phase and it changes also see "J" Notations. So this screw up the feed back and we are in stability hell, and more smoke cool.

Amp designs are simple if you never turn them on in the real world that is.

So Doc good on yer luv it
It can be done so imagine it.

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karatestu
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Re: KISS

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Not had a lot of time for tinkering of late :( but have done a little bit of experimenting with some old power amp boards. :grin: Since I now have some very nice and low capacitance LS6 speaker cables I thought I would have a mess about removing filters.

First off removed the input coupling caps which block DC (filter the very low frequencies down to DC). In to some stunt speakers which I had listened to before removing the caps. This was a very nice improvement :guiness;

Next off was to remove the output zobel network's return to 0V at the power supply. I left the cap and resistor in, just broke the circuit. Listening right now and checking heat sink temperature now and again. The sound has improved again and there are no audible oscillations or anything. Heat sinks are the same temperature they were before disconnecting the zobel. Only thing is a very quiet hum which is audible when no music is playing and volume right up. Will have to investigate that - I am using frame transformers for the amps so it is probably down to them and some untidy wiring - I hope.

Next up to try is taking the signal out to the speakers from before the output inductor and parallel damping resistor. Don't want to remove them from the pcb as that is a pain in the arse and they should not affect things when out of circuit I hope.

Mostly positive so far and no fireworks :dance:
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karatestu
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Re: KISS

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I suddenly realised why I have a low level hum with this stunt set up - the stunt speakers are each 12" from my BMU. Doh :doh: :doh: :doh: :doh:

I have done the wiring to take the signal from before the output inductor and parallel damping resistor and the amps are warming up whilst I go make a cup of tea :grin: . Going to connect to the stunt speakers and put on some choones when I get back. :epopc:
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Re: KISS

Unread post by karatestu »

Listening now and it sounds very nice :guiness;

Going to give it a few tracks before changing over to my little cuboid semi Omni's (without the big bass cubes).

Heat sink temperature is very low - about the same as it was previously. All good so far :grin:
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Re: KISS

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Switched to my little semi Omni cuboid 3's and listening to Stevie Wonder Songs in the key of life.

I am enjoying the new presentation very much but there are some things which are different in my system whilst trying out these amps filter less. I am using some older Avondale amp boards and not the ones I have in my usual 4 mono blocs. They are essentially the same but older and have different output transistors. Also not using the big bass cubes for this little experiment as I only have 2 old amp boards to try - don't want to mess with the 4 new amp boards. Also these stunt amps don't have a separate psu for their front ends like my usual amps.

Even so, I can make some observations through listening after ever filter removal. I have only just put my little cuboid 3's in to the chain as I did not know if the amps would be safe. So far (using my ears not test equipment) they seem to be completely stable and heat sink temperature has not changed.

My filter less amps now sound more like my AP20 but not the same obviously as they use a different design. There is much more openness to the sound like everything can breathe. Much more like real music. Cymbals in particular are shimmering like I have not heard them before. The only gripe I have is that high frequencies seem to have gone up in level - the tweeter seems louder than it has done previously. Not sure why that has happened. So most of the initial change seems to be in the mid and high frequencies although I am sure there are some changes to the bass. I need more listening time. I am definitely tapping those toes and being moved by the music. There is clearly more detail, dynamics and music to be had with out the filters (input coupling cap, output zobel and inductor.

Time will tell if it suits the topology of these particular amps. I am certainly having a lot of fun finding out :dance:

Stu
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Re: KISS

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Hooked up one of my usual amps (front end with own psu) to the big bass cubes and bass has been restored :grin: I think my comment earlier about the treble output being higher no longer applies. Can't fault it now. :guiness;

Alfi, get your soldering iron out :lol: :lol: :lol:
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Re: KISS

Unread post by Alfi »

karatestu wrote: Tue Feb 06, 2018 5:03 pm Hooked up one of my usual amps (front end with own psu) to the big bass cubes and bass has been restored :grin: I think my comment earlier about the treble output being higher no longer applies. Can't fault it now. :guiness;

Alfi, get your soldering iron out :lol: :lol: :lol:
You'll have to lead me by the hand through it all Stu :-?

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Re: KISS

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Alfi wrote: Tue Feb 06, 2018 7:45 pm
karatestu wrote: Tue Feb 06, 2018 5:03 pm Hooked up one of my usual amps (front end with own psu) to the big bass cubes and bass has been restored :grin: I think my comment earlier about the treble output being higher no longer applies. Can't fault it now. :guiness;

Alfi, get your soldering iron out :lol: :lol: :lol:
You'll have to lead me by the hand through it all Stu :-?

Alfi.
If you want to try it then i would be happy to. The way i have done it means that only one compnent needs to be removed and a wire link installed in its place. This is the input coupling cap (dc blocker). It is an orange bc128 10uf cap on my older boards. The zobel can be rendered non operative by pulling the spade connector that connects the zobel (labelled 0V next to the output spade) to the power supply 0V. The output inductor can be missed out by soldering a wire into a spare hole under one of the output resistors and running that to the positive speaker outlet on the back panel of the amp. The wire that goes to the output spade connector needs to be removed first. And voila.
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Re: KISS

Unread post by Alfi »

That sounds simple enough even for me Stu..

Would you say your NCC200 mono's now perform as well or better than your AP20?


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Re: KISS

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Alfi wrote: Tue Feb 06, 2018 10:50 pm That sounds simple enough even for me Stu..

Would you say your NCC200 mono's now perform as well or better than your AP20?


Alfi.
Hi Alfi,

I wouldn't go that far but the gap in musicality between the two has been closed dramatically. I have larger transformers on the NCC than the AP20 and they are mono blocks - this brings other things to the party.

The NCC200 being a quasi complimentary design :roll: has a certain sound to it ("rip" as Les would describe it) which can not be fully tamed unless it is changed to a complimentary output stage. Les' new NCC220 (Qudos) boards do use a complimentary output stage and do away with this "rip" artefact all together :guiness; . The reson being that a diode (the baxandall diode) is dispensed with along with a resistor or two and it is this baxandall diode that is said by Les to be the guilty party.

I am planning on getting a couple of pcb's from Les to build my own NCC220. The layout and design has hardly changed at all and NCC200 boards could be modified to NCC220 spec fairly easily. Half a dozen resistors change value, a resistor and diode are removed and the output transistor on the negative side of the board is changed to a PNP. All the rest stays the same (input stage, LTP, VAS and driver stage) apart from the bias transistor is moved to enable attaching it to the heat sink between the output transistors. This could be done with flying leads and enables the bias current to be ramped up from 38mA to around 150mA. More heat on idle but the rewards are worth it i believe.

Would be easier to buy a couple of A20's though. But where is the learning in that ?

Stu
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