DIY thoughts of the day

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karatestu
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Re: DIY thoughts of the day

Unread post by karatestu »

Thanks for updating us on your progress Simon. Do you listen solely to classical music ? And do you think it has swayed which direction you have gone in with your speakers ?

I ask because many say there is no imaging when listening to classical music in a concert hall and that reflected sound waves dominate over direct to a point where you can't pick out where the various musicians are placed. I have heard that Shahinian speakers were designed mainly for the replay of classical and they are poly ? directional (but not true omni's). Don't know how well they image..

I couldn't comment personally as i have never been to a classical concert in my life and imaging is not high on my agenda. Those that value image above all else on diyaudio seem to be into controlled directivity with horns , compression drivers and very large wave guides. It's the ultimate in point & squirt with room reflections (image killers) reduced to a minimum.

Regards, Stu
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Simon Hickie
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Re: DIY thoughts of the day

Unread post by Simon Hickie »

Hi Stu. I listen to many genres. Currently listening to Neil Ardley's Kaleidoscope of Rainbows, one of a tiny number of jazz albums in my library. Imaging is one of those things I like, but not at the exclusion of tonal balance etc. The beauty of OBs and DML panels is that room modes have far less influence than P&S speakers combined with the better imaging than semi-omni.

Cheers

Simon.

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Re: DIY thoughts of the day

Unread post by karatestu »

Why do we have so much gain through our systems only to attenuate it so much with the volume control ? Of course we need headroom and scope for sources with lower output voltage. NVA systems are not so bad in this respect as there is no active preamp with gain but even so maybe there is too much gain in the power amps.

It can't be good for the signal to noise ratio if say a CD signal is attenuated so the signal level is that much closer to the level of noise in an amplifier. That amplifier then amplifies the signal and the noise. Everything adds noise, every stage of amplification, buffers, equalisers, DSP, anologue active crossovers, cables, dodgy connections and joints. At what level does this become audible.

It's even worse if you have really efficient speakers over 100 dB. Some could probably get away with having very little voltage gain but current gain is needed on the end. So how to lower gain , get rid of excess and improve our signal to noise ratio.

Run your power amp flat out with no attenuation before it. Put the volume control in the speakers. That sounded good to me until i realised that we may be passing the power amp too much voltage, overloading it and it would be clipping. Not good. Suppose it depends on power amp sensitivity and the voltage level given out by your sources. Also very inefficient working the amp hard and then attenuating it after.

Design the amp input stage so it accepts more voltage before full output is reached . No, still inefficient with the amp working hard.

Modify our sources to lower their voltage output. But then we are decreasing their signal to noise ratio and amplifying it.

A balance is needed through the system chain. Attenuation (volume control) before the power amplifier is probably unavoidable to get best results. We dont want to overload amplifiers causing distortion and clipping. We need some headroom. We can still lower amplifier gain and use less attenuation.

How do we reduce amplifier gain. Well that requires some heavy duty redesign work. Lower voltage gain in the VAS stage - over my current pay grade i expect. Play with the feedback resistor (lower it's value) and so increase the amount of negative feedback (which reduces gain). Sounds good to me as increased levels of negative feedback can be good for distortion and linearity. But the whole thing can become unstable if not designed properly. We don't want the feedback turning positive and causing oscillations. Oh dear my amp has melted.

Why bother i hear you say, sounds like unnecessary work and a bit of a nightmare.
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Re: DIY thoughts of the day

Unread post by TheMadMick »

Oddly, I had an exchange with SavvyPaul about attenuators. He was of the opinion they robbed the dynamics from the music (or something like that).

Having -20dB attenuators between my source and amp, which previously had improved SQ, I took them out. Result - not a lot. There was little change. However, I have used both Rothwell and GoldenJacks and the latter do seem to give a rather harsh edge to the sound. I prefer Rothwell.

It may not be what you do but how you do it?

Like you, it's a bit above my pay grade.
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Re: DIY thoughts of the day

Unread post by savvypaul »

TheMadMick wrote: Mon Dec 09, 2019 9:43 am Oddly, I had an exchange with SavvyPaul about attenuators. He was of the opinion they robbed the dynamics from the music (or something like that).

Having -20dB attenuators between my source and amp, which previously had improved SQ, I took them out. Result - not a lot. There was little change. However, I have used both Rothwell and GoldenJacks and the latter do seem to give a rather harsh edge to the sound. I prefer Rothwell.

It may not be what you do but how you do it?

Like you, it's a bit above my pay grade.
The Rothwells are addressing the symptoms of your problem (input overload) but not the causes (high sensitivity / gain in your active preamp). I used Rothwells (and Russ Andrews attenuated interconnects) when I had a Sugden a21aS2 integrated amp. Without the attenuators, I couldn't get the volume control past 9 'o' clock...it gave me more adjustment (addressed the main symptom of the problem) but caused a further problem by sucking the life out of my music.

With an NVA passive pre / power, most of my listening is done between 10 - 2, depending on the efficiency of the speaker, giving plenty of subtle adjustment, with no need for Rothwells. A passive removes components that, IMO, don't need to be there. IMO, you are adding components (the Rothwells) that don't need to be there, to fix problems caused by other components that don't need to be there (a high sensitivity active gain stage).

In your current set up, if you can reduce the output voltage from your digital source, it would be worth trying.
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keepitsimplestupid
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Re: DIY thoughts of the day

Unread post by keepitsimplestupid »

A pre amp attenuates the signal and noise equally, so running the pre quiet is only an issue if your power amp has poorer noise performance than the pre, as you're adding extra noise vs what an unattenuated source would have presented.

The best active pre amps can be quieter than a passive.

Most/all power amps are fixed gain so theres nowt you can do about it anyway, other than buy a stellar low noise power amp. Mines -110db and as such a rare beast, most are mid -90db.

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Re: DIY thoughts of the day

Unread post by TheMadMick »

Does anyone know a pin compatible low gain valve for 6SL7's. My pre-amp section has 6SL7's and I might be able to reduce the gain by fitting such valves (should they exist).
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Re: DIY thoughts of the day

Unread post by Ali Tait »

Equivalents here-
http://tdsl.duncanamps.com/show.php?des=6SL7

Very useful page for valve info.

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Ali Tait
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Re: DIY thoughts of the day

Unread post by Ali Tait »

Better if I put this page up. Just put the valve type you're interested in, in the box-
http://tdsl.duncanamps.com/tubesearch.php

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Re: DIY thoughts of the day

Unread post by Ali Tait »

TheMadMick wrote: Wed Dec 11, 2019 10:46 am Does anyone know a pin compatible low gain valve for 6SL7's. My pre-amp section has 6SL7's and I might be able to reduce the gain by fitting such valves (should they exist).
Don't know what you are using it on, but you should be able to sub a 5751 using an adaptor like this-
https://www.angela.com/tubeconversionad ... intop.aspx

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