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Post by firebottle on Mar 17, 2020 19:14:32 GMT
Is that a thing? A Fire_blog? I've heard of a fire log. Any way up, I though it about time to start one. One of the on going experimentations is with different ways to control volume level, or to be more accurate how to provide loss less attenuation. My original KIN build included the ubiquitous (?) Alps Blue, only because it was cheap. I know there is the Alps Black and Noble pots that I believe are better but I don't have direct experience of them. The Alps Blue is used in a lot of preamplifiers, some at rather expensive price tags, but there are much better alternatives. There are even lesser quality pots that can be found in various kit, once such is this one:  This is marked up 'Alpha' and was in an expensive preamp  The owner brought an Alps Blue to fit instead. I took this pot apart and have never seen such worn tracks, as can be seen the wafer size is quite small. Even given that I did manage to reshape the wiper contact arms to track on unused areas of the wafers, so it is now usable again. The next up the scale is an Alps, but both channels are on a single wafer and tend to have a bit of a mis-match at low level, example:  This type of single wafer has different lengths of resistive element for each channel as one is inside the arc of the other, not that great. Now we get on to relay switched resistor ladder type attenuators, there are quite a lot of variants about, from cheap kits from China up to versions from Khozmo. A cheap kit from China such as this one gives very good performance for the outlay:  Cost under £30 but does need some assembly and soldering. The drawback for some people is that there are multiple relay contacts that the signal has to pass through. Although the relays appear to be 'small signal' relays there isn't any guarantee that the contact material is some sort of precious metal as used in the best ones. I haven't come across any problem due to relay switching in the ones I have used or modified though. Having multiple relays and pcb tracks does add a little capacitance to the signal path. |
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Post by firebottle on Mar 17, 2020 19:19:30 GMT
The next step for those not of a DIY disposition is a ready built relay ladder type, a few folks have bought these.  They can suffer from a little suppression of dynamics dependent on the synergy of the system, I have fitted a buffer on the output of a couple of units which cures this. I was looking for pics of one I had fitted a buffer to but can't find one. Building a little buffer is a piece of cake with miniature boards available from the usual suspects:  More to come ........ |
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Post by Bigman80 on Mar 17, 2020 19:40:59 GMT
Ha! Welcome to the blogging arena....I do think you missed an opportunity though.
Firebloggle is absolutely the best name for this lol
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Post by Deleted on Mar 17, 2020 20:21:47 GMT
“Around the Blog-Fire” would have been a funnier title.
It will be interesting to see how much I learn from this.
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Post by Bigman80 on Mar 17, 2020 20:52:32 GMT
“Around the Blog-Fire” would have been a funnier title. It will be interesting to see how much I learn from this. Excellent alternative name |
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Post by jandl100 on Mar 18, 2020 8:18:19 GMT
All this hardware attenuation is for wusses - to do it truly lossless you just need a really big room and you move your listening position, nearer or further from the speakers, to get the desired loudness.
Sorted.
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Post by Deleted on Mar 18, 2020 8:19:32 GMT
I hope you asked Alan before you changed the title?
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Post by firebottle on Mar 18, 2020 8:24:35 GMT
I changed it Kevin, all good.
I have added more detail to the original post.
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Post by Bigman80 on Mar 18, 2020 9:16:50 GMT
I hope you asked Alan before you changed the title? Tisk Tisk, Kevin We dont behave like that here lol |
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Post by Deleted on Mar 18, 2020 9:33:50 GMT
I just didn’t want to get in trouble with the creator of my pre-amp.
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Post by Bigman80 on Mar 18, 2020 9:40:45 GMT
I just didn’t want to get in trouble with the creator of my pre-amp. Lol....safety first |
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Post by sq225917 on Mar 18, 2020 12:17:59 GMT
Alan, most Alps Blue pots on ebay are fake, sit a £20 from Farnell down with a £6 from Ebay and the difference is obvious, better moulding, steel shaft and better channel matching. The Tkd Ko-on is my current favourite pot. I might have got a good un but the channel matching is 1% after the first few degrees.
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Post by firebottle on Mar 18, 2020 12:58:26 GMT
Yes I had heard there are fakes, fortunately I haven't come across any. I am not saying the Blue is a poor pot in terms of matching, they are generally very good. The problem is any pot isn't 100% transparent, I appreciate many will not have heard the difference but it is there when better alternatives are put into use. Which leads me nicely to stepped attenuators. I replaced the Alps Blue in the KIN preamp with a quality stepped attenuator (SA) and the difference was marked, much better detail and transparency. The problem really with cheap SA's is that they are based on 21/23 or 24 step switches and don't offer enough fine steps. The problem with expensive SA's is just that, they are expensive. However it is debatable that there is anything better than the Khozmo or Acoustic Dimension.  This is the Acoustic Dimension SA in my preamp, it takes more room than the Alps Blue but fortunately it is electrically a straight drop in. More to follow. |
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Post by macca on Mar 18, 2020 13:04:34 GMT
Stepped attenuators seem to be universally regarded as the best, can't say I have ever had a problem with the steps being too far apart but suppose it will depend on the partnering kit to an extent.
But what about digital volume control? Okay no good with an analogue source but for digital source would seem to offer the best of all worlds?
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Post by Bigman80 on Mar 18, 2020 13:14:22 GMT
Stepped attenuators seem to be universally regarded as the best, can't say I have ever had a problem with the steps being too far apart but suppose it will depend on the partnering kit to an extent. But what about digital volume control? Okay no good with an analogue source but for digital source would seem to offer the best of all worlds? Are you referring to a Digitally controlled Analogue chip? Such as the PGA211A? |
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Post by firebottle on Mar 18, 2020 13:14:27 GMT
Some implementations of digital volume control are exceedingly good, but only if done lossless. Having a greater bit depth helps but there is a Leedh algorithm that is truly lossless. See here darko.audio/2018/05/kih-57-a-lead-on-leedh/ |
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Post by Deleted on Mar 18, 2020 13:16:59 GMT
Yes I had heard there are fakes, fortunately I haven't come across any. I am not saying the Blue is a poor pot in terms of matching, they are generally very good. The problem is any pot isn't 100% transparent, I appreciate many will not have heard the difference but it is there when better alternatives are put into use. Which leads me nicely to stepped attenuators. I replaced the Alps Blue in the KIN preamp with a quality stepped attenuator (SA) and the difference was marked, much better detail and transparency. The problem really with cheap SA's is that they are based on 21/23 or 24 step switches and don't offer enough fine steps. The problem with expensive SA's is just that, they are expensive. However it is debatable that there is anything better than the Khozmo or Acoustic Dimension. This is the Acoustic Dimension SA in my preamp, it takes more room than the Alps Blue but fortunately it is electrically a straight drop in. More to follow. Did you need to move anything around? As my holiday is probably cancelled, and Brexit means I probably won’t be able to insure my toy car, I will probably buy the SA at the end of the month, assuming I don’t get infected before. |
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Post by macca on Mar 18, 2020 14:13:54 GMT
No, I mean controlling volume entirely in the digital domain.
I'm asking not telling as I've really go no idea.
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Post by Bigman80 on Mar 18, 2020 14:14:41 GMT
No, I mean controlling volume entirely in the digital domain. I'm asking not telling as I've really go no idea. Ah I see. |
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Post by firebottle on Mar 18, 2020 14:33:49 GMT
Kevin, yes I had to move the phono section back by 10mm to avoid fouling.
However there is another approach that I have been investigating that is a lot cheaper.
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Post by Deleted on Mar 18, 2020 14:44:14 GMT
I shall wait a bit then....
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Post by firebottle on Mar 18, 2020 16:16:10 GMT
Are you referring to a Digitally controlled Analogue chip? Such as the PGA211A? Funny you should mention that, it is the subject of investigation. With my long time involvement in electronics I was still under the impression that analogue multiplexers or chips that included them were very inferior, with very imperfect 'on' resistances that were far from linear with varying signal levels. How things have come on now with modern CMOS processing  . The Burr Brown digitally controlled analogue volume chips PGA2310/2311 have staggeringly low published distortion figures of 0.00002% I have acquired a slightly older ready made volume control unit from Mshow:  Construction is reasonable but one omission is a mute relay, as there is a pronounced click at turn off. This is the internal shot after certain modifications:  To glean the ultimate performance from these chips needs consideration of the operating conditions with regard to noise and impedances. Both regulators feeding the supply to the chip have been replaced with low noise regulator modules and a buffer stage has been fitted driving the input pins.  The buffer stage can be seen in the foreground and the mute relay has been fitted directly to the output sockets. The unit came without a remote control but I have been able to adapt one to work. Performance you ask? Stunning, really transparent  |
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Post by firebottle on Mar 18, 2020 16:32:12 GMT
Leading on from the Mshow experiments I ordered a new unit along the same lines, this time under the Weiliang Audio name. It is from China of course so availability now may be a bit delayed due to the current situation.  The pcb is very well done with some quality caps fitted, Elna and Silmic. It also has a mute relay included on board. I have fitted a buffer stage which improved on the as built performance but am still waiting to receive some low noise regulators. Compared to the Mshow it is only a few percent behind, hopefully with low noise regulators fitted it will have equal performance. The soundstage and spacial clues come though exceedingly well, this is in use at the moment. |
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Post by Bigman80 on Mar 18, 2020 17:14:12 GMT
I think it's only fair to give a nod to the fella who kicked off the thinking about this approach........me lol
Just kidding, The real instigator was Tony of Coherent Systems.
After his visit, i was particularlty taken with the spatial presentation and the almost boundless soundstage his Liquid Music preamplifier delivered. We chatted about the approach he had taken and one of the things i felt were of interest was th fact his preamplifier used a Digitally controlled Analogue chip. Now, obviously Tony isn't using off the shelf bits and designed his own DCAC.
Hoewever, China being the home of everyhthing electronic you can imagine, Alan identified the Weilang as interesting.
Inbetween this being ordered and arriving, the Mshow popped up on ebay and Alan snapped it up.
Funnily enough, i was there when this arrived and straight out of the box it delivered an alarmingly familiar experience of what happened when Tony put his preamplifier into my system. And before someone suggests otherwise, NO i am not saying it is as good lol
It just delivered a similar effect in Alans system, that Tony's had in mine. Just to a slightly lesser magnitude.
So go and buy one now?
Well, not quite.
The modded Mshow didn't fare quite as well in my system vs the Neurochrome from a tonal perspective. I felt it sounded slightly rolled off Vs the Neurochrome. However, when we substituted the 286 in for the 686, it sounded a little sharper. This investigation is far from over but it shows great promise as a volume control, regardless of price.
It's been a bit of a mad project but i have a few ideas i'd like to try but i have other things to sort out first, like a Torroid PSU for the 686.
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Post by jandl100 on Mar 18, 2020 17:37:54 GMT
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Post by firebottle on Mar 18, 2020 18:11:35 GMT
Yes they are, that's the one I bought.
A couple of modifications raises the performance even more as stated.
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Post by firebottle on Mar 19, 2020 11:52:54 GMT
Subwoofer maintenance, who knew? I realised I had some spare OCC speaker cable so I though 'why not upgrade the cable on the sub?' So I upended the sub to disconnect it and found lots of web, spider sort.  During dis-connection I found a loose terminal, plus the legs weren't that tight either. Those of a certain speaker persuasion might recognise where the legs came from. Upon removing the baffle I discovered the culprit:  There were a few dead carcasses as well as more spider web so the live one went outside and the rest up the vacuum. After the clean up:  |
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Post by firebottle on Mar 19, 2020 11:57:23 GMT
The cabinet insides had a quick wizz of the vacuum as well.  The cable was duly fitted to the sub amplifier connector, I have used an unusual gold pin locking connector, only because I had it when I built the amp.  All reconnected with some new spade terminals soldered to the other end:  Now all back in action. |
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Post by Bigman80 on Mar 19, 2020 12:15:49 GMT
Spiders....urgh
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Post by jandl100 on Mar 19, 2020 12:18:36 GMT
Yes, it's surprising how downward firing subwoofers accumulate spider webs.
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The owner brought an Alps Blue to fit instead.
. The Burr Brown digitally controlled analogue volume chips PGA2310/2311 have staggeringly low published distortion figures of 0.00002% 
