DIY thoughts of the day

A place for DIY project discussions.
NSNO2021
Posts: 733
Joined: Thu Jul 04, 2019 1:06 pm
Location: Industrial waste lands of the north west
Has thanked: 341 times
Been thanked: 269 times
Great Britain

Re: DIY thoughts of the day

Unread post by NSNO2021 »

karatestu wrote: Fri Mar 12, 2021 12:42 pm Duct tape did the job, I doubt it will last but I got my welding done :grin: Just wrapped some around the rollers that feed the wire into the hose. Lets see how long it lasts before I have to replace the duct tape :lol:
You can take the boy out of the farm but you can't take the farmer out of the boy 🙂

Bodgetastic 👍
These users thanked the author NSNO2021 for the post:
karatestu (Mon Mar 15, 2021 1:55 pm)
Modified Airlink BPS 3110S with LDA DC filter, modified Rega Planar 8 with Apheta 3, LDA MCJ3 phono, NVA P90 SA MK2, FW Aleph J mono blocks, Cambridge Audio CXC, Denafrips Pontus 2 DAC, Mano Ultra2 streamer, Cisco switch, Audio Technica ATH 70 cans, Cubix MMXXI & NSNO W48.5 speaker cables

User avatar
r3xj0hn570n
Posts: 120
Joined: Fri Jun 25, 2021 4:54 am
Has thanked: 21 times
Been thanked: 76 times
Norfolk Island

Re: DIY thoughts of the day

Unread post by r3xj0hn570n »

karatestu wrote: Thu Mar 11, 2021 5:29 pm
Then we get on to the expensive bit which is stepped attenuation. Some of the prices are eye watering for the kit and ready built versions. Some of the resistors are very pricey especially the Audionote silver tantalum non magnetic jobbies. Can't afford them. I don't want a kit or ready built for reasons I will explain later so had a look at switches first. One or two pole ? That would mean choosing between stereo and mono. I can't decide yet, still torn in two about that. Do I want two volume controls? Could be handy for any balance problems I suppose but two mono switches cost more than one stereo switch.
Having done more than a bit of experimentation on this, can i suggest you avoid silver plated contacts that aren't sealed from the outside atmosphere. Silver oxide might be conductive, but it's still worse than hard gold plate. Grayhill make great switchgear.

No, you don't want 2 volume controls. It's awful, even when ganged together, unless you do it like this, in which case you loose simple balance control.
vol.jpg
vol.jpg (87.25 KiB) Viewed 593 times
While you are at it, you might as well buffer the output from the volume control. I use an uber linearised emitter follower (zero gain) after a switched attenuator in my preamp. You wouldn't want the input bias current from, say a BC182 flowing back into whatever volume control you've chosen. That just causes all sorts of issues, especially long term and the DC output voltage wanders up and down the volume control position, causing high sensitivity speakers like mine to flap about alarmingly.

Cheers, Rex
These users thanked the author r3xj0hn570n for the post:
karatestu (Sun Jun 27, 2021 7:14 am)

User avatar
karatestu
Posts: 4966
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1154 times
Been thanked: 672 times
Great Britain

Re: DIY thoughts of the day

Unread post by karatestu »

I haven't bought a stepped attenuator yet, been too busy faffing about with speakers and power amps :grin:

As to introducing a buffer is concerned- I would only do it as a last resort . Adding components goes against my less is more philosophy (which I borrowed from RD).

If I ever did use one it would have to be as simple as possible and unity gain as you suggest Rex :grin:
DIY inspired by Richard "The Doc" Dunn RIP

User avatar
r3xj0hn570n
Posts: 120
Joined: Fri Jun 25, 2021 4:54 am
Has thanked: 21 times
Been thanked: 76 times
Norfolk Island

Re: DIY thoughts of the day

Unread post by r3xj0hn570n »

karatestu wrote: Sun Jun 27, 2021 7:23 am I haven't bought a stepped attenuator yet, been too busy faffing about with speakers and power amps :grin:

As to introducing a buffer is concerned- I would only do it as a last resort . Adding components goes against my less is more philosophy (which I borrowed from RD).

If I ever did use one it would have to be as simple as possible and unity gain as you suggest Rex :grin:
Yeah, most of the time less is more, but occasionally more is more. Here is an abbreviated version of my voyage.

I 'discovered' high efficiency drivers. Ones that have obvious frequency response issues yet make most others sound quite sleepy.
The main issue with these drivers is that they make everything MUCH louder, including things we don't want, like noise, hum and switching noise. So i embarked on a journey to minimise this. Now NVA amplifiers are pretty quiet in most respects, but that damn volume control (direct coupled cermet) caused me no end of headaches. It was fine with normal speakers, drove me nuts with these ones. I'd turn off the amp and vigorously wind the knob up and down to make the things temporarily quiet, but within weeks it was noisy again and the simple act of altering the volume caused massive cone movement. WTF? It sounds amazing as long as i leave the volume alone?

Anyway, i noticed that there was a rather large amount of DC present on the outputs (I was using an AP70 at the time), so investigated. There isn't anything to adjust on these amplifiers, so to cut a long story short, it ended up being caused by unequal currents through the differential input pair. The base of these transistors needs have the same DC operating conditions at all times. Differences in the AC current are reflected in the output and that's the way it's meant to work, but differences in the DC current are also presented to the output. OK so what is causing this difference? A different resistance to ground it what finally dawned on me. The input bias current is flowing back out through the base resistor, into the volume control wiper and down to ground. THIS is what causes the volume control to become noisy and whenever you adjust the wiper position, you are adjust the DC operating conditions of HALF of the input pair. Result, DC offsets all over the map. Not enough to worry a normal speaker, but enough to cause craziness in mine.

I ended up putting a wima MPP cap after the pot's wiper, which immediately solved the issue and i couldn't hear any issues with that (which was a relief, as i hate the sound of electrolytic caps). I stayed like that for a while, then i replaced the cermet pot with a switched attenuator, which is much better, but i'm not all that taken with only having 24 or so different volume steps. I like to keep the maximum volume presented to me under strict control, too loud and my ears distort the sound, too soft and i feel like i'm missing out. Anyway...

I moved onto an active crossover (begone foul passive crossovers), and so ended up using a separate box for volume and switching, now driving 3 power amps, so 1/3 the AC resistance, 3 times the load. Now i could just adjust the input impedance of all these amplifiers, necessitating much phaffing about with the DC operating conditions of the input pair, or i could just buffer the output of the volume control, which would also have the effect of presenting a nice DC bias on the output capacitor. Much easier to buffer the output. I eventually hit on a buffer composed of 4 of the same transistors, 3 of which are linearizing the other one. It's zero feedback and only one stage long. It sounded better when i installed it and when i tried to measure it, distortion and noise when down compared to loopback conditions (which just means that what i was measuring it with could be better).

As always, YMMV.

Cheers, Rex
These users thanked the author r3xj0hn570n for the post:
NSNO2021 (Mon Jun 28, 2021 7:54 am)

User avatar
karatestu
Posts: 4966
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1154 times
Been thanked: 672 times
Great Britain

Re: DIY thoughts of the day

Unread post by karatestu »

Interesting story Rex. Luckily (or unluckily) my heavily doped drivers are nof particularly sensitive. Unless a problem becomes audible I will be in blissful ignorance :grin: At the moment I don't have any audible problem when changing volume. Mostly because I can't change volume :lol: due to having a soldered two resistor potential divider in each channel.

Did I mention I was a practitioner of minimalism :lol:
DIY inspired by Richard "The Doc" Dunn RIP

User avatar
karatestu
Posts: 4966
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1154 times
Been thanked: 672 times
Great Britain

Re: DIY thoughts of the day

Unread post by karatestu »

Today my little AP20 finally got it's new TKD volume pot :dance: Just in time for Christmas :guiness; . It's tiny this thing.

Here's the original before surgery

Image

Here's the old green one and new TKD 10k next to each other. You will notice the pins are much closer together on the TKD and the threaded section of the shaft is not as long.

Image

I bent the middle pins a bit to make soldering the wires on easier.

Image

Here is the TKD in place. Anybody putting this pot in please be aware that the threaded section of the shaft is only just long enough to get the nut on. I had to remove the washer and file off the tiny bit which sticks out that usually goes in an indent to stop the pot spinning.. Anyway, it's in and very secure

Image

All soldered and ready to go.

Image

Just going to listen to it now :epopc:
These users thanked the author karatestu for the post (total 2):
Ithilstone (Sun Nov 14, 2021 6:10 pm) • savvypaul (Sun Nov 14, 2021 10:44 pm)
DIY inspired by Richard "The Doc" Dunn RIP

User avatar
karatestu
Posts: 4966
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1154 times
Been thanked: 672 times
Great Britain

Re: DIY thoughts of the day

Unread post by karatestu »

It sounds very good I must say. More detailed than the last one. The action feels superb, I can't stop playing with it :shifty:

The channel balance at low volume is superb. That was the only problem with the old one.

Recommended
These users thanked the author karatestu for the post:
antonio66 (Sun Nov 14, 2021 8:58 pm)
DIY inspired by Richard "The Doc" Dunn RIP

Vinyl-ant
Posts: 590
Joined: Sat Jul 01, 2017 12:51 pm
Location: South yorkshire
Has thanked: 0
Been thanked: 168 times
Contact:
Great Britain

Re: DIY thoughts of the day

Unread post by Vinyl-ant »

The 2cp601, great pot. The 2cp2511 big brother to it is superb, double the price though and certainly wouldnt fit in there
These users thanked the author Vinyl-ant for the post (total 2):
Ithilstone (Sun Nov 14, 2021 6:11 pm) • karatestu (Sun Nov 14, 2021 6:57 pm)
I am (barely....) in the hi-fi trade
Status: Manufacturer
Company Name bte designs
Www.bte-designs.weebly.com

User avatar
karatestu
Posts: 4966
Joined: Sun Jan 08, 2017 4:40 pm
Location: North Yorkshire
Has thanked: 1154 times
Been thanked: 672 times
Great Britain

Re: DIY thoughts of the day

Unread post by karatestu »

Vinyl-ant wrote: Sun Nov 14, 2021 4:51 pm The 2cp601, great pot. The 2cp2511 big brother to it is superb, double the price though and certainly wouldnt fit in there
Yeah, I'm well pleased with it. It has been a nice little upgrade for the little AP20. Silver wiring next I think

I may give the 2511 a go in something else that has more room.
DIY inspired by Richard "The Doc" Dunn RIP

User avatar
savvypaul
Posts: 6690
Joined: Tue Oct 11, 2016 7:14 pm
Location: Durham
Has thanked: 1048 times
Been thanked: 1119 times
Contact:
Great Britain

Re: DIY thoughts of the day

Unread post by savvypaul »

We are testing a couple of modified versions of the TKD pots for our new integrated amp. Let me know how you get along with it in your AP20, Stu.
These users thanked the author savvypaul for the post:
karatestu (Mon Nov 15, 2021 6:20 am)
I am in the hi-fi trade
Status: Manufacturer
Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

Post Reply