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LDB1 (Bridged-T drums) mods
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Paradigm X



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PostPosted: Thu Jul 30, 2015 10:24 am    Post subject: LDB1 (Bridged-T drums) mods
Subject description: Some confirmed, others could use some help with!
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All

So i finished up my LDB1 drum machine, and am now getting into some mods.

Richard c64 has been kind enough to give me some pointers, but thought id share what id got for discussion.

Ive attached a schematic showing what 'works'. EDIT updated to v2

edit:dont fit the '1u' cap, it doesnt work and kills the voice

OH decay is straightforward, and is as richard c64 has described in detail before (electro-music.com/forum/topic-55928.html). The same could be done for the closed, but wires and space are getting ridiculous so ive omitted.

The hihat filter works reall nicely, used a 1k pot. Would prefer a bit more range, but...

A lot of these circuits seem quite unstable, by virtue of their simplicity.

I tried to repeat the filter on the CL and SN, but they didnt work. Seemed to just oscillate. I tried the simple 'double the original value' for the pot, but have since tried a 1k* pot, which seems to work a lot better, albeit reduced range.

The Kick pitch is determined by r48, and doubling this to a 5k pot worked really nicely. But again, using 2k pots on the LT HT and WB didnt work. Maybe my 2k pots are ropey Laughing need to try 1k* pots later.

Another odd thing is there is some significant background noise/hum. guessing its either the wiring, or the 'wrong' value resistors.

things to try;

Id like more range on the hats filter, thinking a bigger pot will mess it up, based on the other voices, so maybe two more caps in parallel with c9 and c10?

Try to remove the self-oscillation on the toms.

Add the impact sound from the Drum Cookbook to the snare

Add a repeating trigger generator for the clap. Mickey said hed programmed that in and made little difference, so he removed. perhaps its been simplified just that little bit too much?

Add alternative (single supply) drum circuits - suggestions?

Separate white noise and pitched noise, for the hats. I tried a simple pot but it didnt work too well, may need to be buffered.

Might try to build a 'ride' based on Richard's circuits and the existing noise sources. The hats are excellent.

Cool, any thoughts appreciated, im hoping to get most of what i can done tonight, so hopefully can post some sounds.

Cheers, many thanks
Ben


*I ran out of 1k pots, so used 2k pots with a 2k resistor in parallel. Messes up the taper a little, but its free! Also, and i realised after the event, you can easily tack it over the pcb connections, save you desoldering all the wires...


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Last edited by Paradigm X on Mon Aug 03, 2015 1:40 am; edited 2 times in total
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Paradigm X



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PostPosted: Fri Jul 31, 2015 3:14 am    Post subject: Reply with quote  Mark this post and the followings unread

ok,

Ive updated the schematic in the first post.

The 1uf just kills the sound =/

Very odd, if i press a cap onto say pins 6 and 7 on the top, the noise vanishes. Solder to underside, and it kills the voice. Something odd in that area.

Reducing the pots value for the LT and HT has killed the oscillations, yay!

Still got the bloody background noise. Possibly all the wiring?

Ive attached a short demo playing with all the sounds.

My clap is still not working. Ive also got a boss HC2 clone which works on single supply power, might replace it with that, infinitely better sounding.

Built the impact generator but not tested.

Might add decay to the closed hihat as well, they are the star of the show and should make the most of that.

Realising that this is never going to be an 808 but a not bad 606 type machine. WIll try a few more things then wrap it up. If i can get rid of the noise ill be happy. Very useful box, especially with the midi and external triggers etc.

Cheers
Ben


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prgdeltablues



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PostPosted: Fri Jul 31, 2015 5:43 am    Post subject: Reply with quote  Mark this post and the followings unread

I've built a number of twin-T drum circuits from TH's Drum cookbook. Some have background self-oscillation noise, some not. I suspect it depends on circuit layout, etc - as TH says, these circuits are inherently noisy (after all, they are on the cusp of self-oscillation - the trigger kicks them into a short-lived oscillation). He suggests using a gate after the drums - I found that using an envelope follower (of the drum output) to drive the CV of a VCA, and adding a bit of DC offset to the CV successfully killed all the background noise, without affecting the drum sound.

Peter
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Paradigm X



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PostPosted: Fri Jul 31, 2015 6:34 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks. I might look at it again.

But i still cant understand how i can (repeatably) touch two pins on the IC with a cap and lose all the noise. But then soldering it on kills it?

Maybe its the socket (those crappy cheap ones).

Ive just bought a nice desoldering gun actually, its brilliant, removed a 16 pin box header no issues. While itll be a pain with all those wires, maybe i should replace the sockets with nice ones.

I will definitely give your idea some thoughts tho. What have you been using as an envelope follower? Ive got the NE570 book as well actually which has one in. could also use the CV for the VCF im planning ... Will be pricey for 8 voices tho.

feature creep is a killer.

Many thanks, Ben
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richardc64



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PostPosted: Sun Aug 02, 2015 2:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

C12 is a mighty strange place to affect OH decay, Ben. Why there, and not at the E.G. formed by C14, and D3?
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Paradigm X



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PostPosted: Mon Aug 03, 2015 1:27 am    Post subject: Reply with quote  Mark this post and the followings unread

whoops. you're quite right, that's where it is .

Schematic is wrong. Doh

Ill update it when i can.

Cheers
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Paradigm X



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PostPosted: Mon Aug 03, 2015 1:41 am    Post subject: Reply with quote  Mark this post and the followings unread

I have fixed the schematic based on richard's correction.
Thanks.
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Paradigm X



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PostPosted: Mon Aug 03, 2015 3:01 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, well major improvement in signal to noise. i replaced an opamp, whcih i actually now suspect wasnt seated correctly, and increased the size of the PSU decoupling caps, and the noise is loads better!

Also got Thomas Henry's impact sound generator working for the snare, which really adds a nice snap to the start. thank you very much mr Henry! cant post the schematics but theyre in the drum cookbook, which is well worth the money imo.

edit theyre the ones in the bass++ - a good read incidentally.

Have also got a tunable woodblock filter working. Replace r34 with a 1k pot, or a 2k with 2k in parallel. Just a 2k resonates.

And variable closed hat decay, changed c13 to 2u2 with the same pot configuration as the open hat.

Sounding really good now, with some nice variations available.

clap still isnt woring i have no idea why.

lost my little portable recorder but hoping to get another recording done tomorrow night. chuffed!

got a little mxr distortion+ pcb to go in, tested and working, going to mix it in parallel. and maybe a behringer vp1, have the three running in parallel.

cheers
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Paradigm X



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PostPosted: Tue Aug 04, 2015 3:09 am    Post subject: Reply with quote  Mark this post and the followings unread

NB

I just noticed in the Bass++ schematic, the output of the impact generator goes to the -ve input of the opamp. in the drum book, he suggests mixing it in via the +ve input, as its a positive going pulse.

I had to lift pin 5 of the opamp to stop it being connected to ground, and solder a bit of wire directly to the pin. Works fine tho!

...anyhoo...

One thing that is really confusing me is the grounding situation. From a standard 9v source, Mickey uses a TLE2426 rail splitter, which makes a 'virtual' ground halfway between V+ and 'ground' (Mickey calls 'ground' V-).

So the audio output is referenced to the virtual ground, so presumably oscillates +/-4.5v. So when i connect it to the output, isn't that referenced to 'ground' (i.e. V- in mickey' terms). Is that a dc offset of 4.5v?

So when i connect my little distortion pcb which just has V+ and ground connections, i.e. 9v, do i connect this to V+ and 'virtual ground', or V+ and V-? The dist pcb just creates a 'virtual' (wrong term i know) ground using a resistor divider like typical single supply opamp circuits.

But then all the 'ground' are floating anyway, as its powered from a (regulated) wall wart.

Any help figuring this out would be greatly appreciated. Its confusing the heck out of me!

Cheers
Ben
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prgdeltablues



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PostPosted: Tue Aug 04, 2015 5:25 am    Post subject: Reply with quote  Mark this post and the followings unread

The VCA I used was the MFOS Log/Lin, and the Polyfusion envelope follower, but that's simply because I happen to have those. Any VCA to which you can apply a DC offset should work, and any envelope follower with a fast following action too.

On grounding (apart from suggesting using a proper dual power supply), you need to bear in mind that even if your power supply is floating (like a battery) you may at some point connect it to equipment - active speakers say - which are referenced to mains earth. And digital chips don't like voltages below their reference 'ground' (Vss on datasheets). If you connected your 'virtual' ground to the 'ground' on your distortion pcb, then that circuit would be seeing a signal going from +4.5V to -4.5V, but would not have a power connection below 0V. It won't be happy. If you connect the virtual ground of the drum circuit to the virtual ground of the dist circuit, you'll avoid that problem, but could have problems with one virtual ground not actually being at the same relative voltage (or, put another way, you'll have two different V+'s, which if shorted together....


That may confuse further! Hopefully others can explain better.

Peter
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Paradigm X



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PostPosted: Tue Aug 04, 2015 7:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Peter

Trying to understand what youve written, if i wire V+ V+, 'ground' to ground, and 'virtual ground' to the point on the distortion pcb, that should balance everything?

A proper bipolar PSU would be ideal, but the LDB1 has pics limited to around 5.5v, i already blew one set by overvoltage. I would have to quite significantly redesign/rewire the board, adding a 78l05 or similar. The rail splitter design works fine as a standlone, but not ideal for modding/adding.

Many thanks

Regards
Ben
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Paradigm X



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PostPosted: Thu Aug 06, 2015 3:43 am    Post subject: Reply with quote  Mark this post and the followings unread

hmm.

Clap is stil not working, but can now hear a little 'pff pff' every time a trigger is received, so i must be close, short or a cold solder joint.

Regardless, the clap was not the most inspiring sound ever (sorry Mickey) so have built a Boss HC2 handclap clone PCB. Missing a couple of parts but will order today, hopefully. I was getting bored of fiddling with the LDB1 so had a change of scenery. Smile

This thing is the opposite of the LDB1, 7 (!) ICs and loads of passives for a handclap. Sounds great tho. and includes all the mods. Schematic is attached for interest. It also has a digital noise out, so intending to use this as an alternative for the hats Very Happy

Anyway, the output of the HC2 is referenced to 'ground' (V-), as is the distortion. Maybe i should reference the output of the LDB1 to v- as well?

Ill just try a few things. I generally prefer to know/think i know what im doing before i go messing, but i guess i cant hurt anything. Just dont want to blow those PICs again with a short or something.

Cheers
Ben


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Paradigm X



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PostPosted: Thu Aug 06, 2015 2:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

heres another demo with some tweaking. basic presets running, not got as far as programming it.

my little recorder has no line in level, and some idiot didnt put an output volume on it yet Laughing so it clips in places.

sounding really good tho, im chuffed.

Edit: at around 2:20 i add the impact tone, does add a nice snap to the snare, can overdo it tho, was over doing things for the demo. Also i was recording it in my garage/workspace, via old computer speakers so couldnt hear anything below about 340hz or so ! Laughing

cheers
ben


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prgdeltablues



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PostPosted: Fri Aug 07, 2015 6:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi

i'm not familiar with either of the circuits, and trying to explain grounds and virtual grounds ain't easy! I wouldn't want to give wrong advice. Personally, from what I understand, I would treat your V+ as V+, your V- as Ground, and use DC blocking caps around anything that uses a so-called virtual ground. So I'd put a big cap (electrolytic) on the output of both circuits, also a largish (100k) resistor to Ground. If you look at most guitar pedal circuits you'll find this sort of arrangement, them being battery powered.
Peter
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Paradigm X



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PostPosted: Fri Aug 07, 2015 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for bearing with me Peter.

There is an output cap on the LDB1, which i guess blocks the dc.

Ive been trying to rationlise it, and the output of the LDB1 is presumably intended and works for plugging it into other gear. So it shouldnt be an issue. And wired internally, id only use one wire anyway (?)

I shall try a few options. Chance are itll just work! and ive been worrying for nothing.

Cheers
Ben
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Paradigm X



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PostPosted: Mon Aug 10, 2015 1:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Im such a plonker sometimes.

I didnt even think i could use croc clips, i was worried about all the other wiring before knowing it would work, but just thought i could temporarily try...

I have wired up a mixer for the dry, distortion and phaser.

The HC2 clap clone is finished but not tested it yet.

I did try the BD decay mod, adding a pot by C35 (see attached). Didnt work tho Sad just got white noise and a bandpass filter. Any ideas? Must research further.

I have also since tried adding a 'harmonics' pot a la CGS Drum Synth. Not had chance to try yet. Edit, hmm, ive got two back to back diodes, ken only used one. Interesting, all the clippers ive seen before use 2...

Also done loads of boring wiring up output jacks etc... Got the digital noise from the HC2 as an alternative to the LDB1/110 noise source too.

Was going to add trigger mutes, but Mickey has cleverly already done this in software, saves 8 switches and 16 wires! (every little helps). Its getting really fragile, wires keep breaking now. These projects are a nightmare, mechanically.

Volume controls for all would be great, but poss un-needed if using separate outs.

Ran out of time after that, so hoping to put it all together this week.

So, TO-DO list reads

Test and install HC2
Wire up the two FX and check all working.
Wire up the output jacks
Possibly add wasp filter to output, if I have enough room

cheers


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Skrog Productions



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PostPosted: Mon Aug 10, 2015 9:53 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Ben

Im looking forward to see your case & panel , I like the sounds so far , keep battling on with the build Smile


Dave.

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Paradigm X



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PostPosted: Mon Aug 10, 2015 11:33 am    Post subject: Reply with quote  Mark this post and the followings unread

I....er.....yeah.

Laughing

it was only going to be a temporary enclosure while i figured out all the mods. now im wondering if it is worth rewiring all those switches yet again....

Cheers
Smile


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Paradigm X



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PostPosted: Tue Aug 11, 2015 1:23 am    Post subject: Reply with quote  Mark this post and the followings unread

OK, well one of those nights Mad

Realised id wired up the mixer completely wrong (+ input to opamp instead of negative).

Broke several wires moving the pcbs around

Finished up the HC2 but 3 of the voltages are wrong

So lots of frustration for no gain.

I really make the most work for myself with these projects. Sometimes im so jealous of the eurorack kits with no wiring.

But im stubborn enough to keep going Laughing will be the best little drum machine, built to my needs.

Excuse the monologue!
Cheers
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PostPosted: Tue Aug 25, 2015 3:19 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello!

Well, had a mad few weeks with work, and trying to get this sorted. Spent ages on the hardware/physical side of things. Find this side of things really hard. Wires keep breaking with movement too which is a real pain, might just hotglue them all... Mad

Got the clap working, sounds great. Distortion pcb just makes a horrible noise, worked before. Ho hum. Blew a tle2426 rail splitter so spent ages debugging mixer before i realised. Waiting on pots for the phaser. Just last night figured out why the bass drum decay wasnt working, by checking richard c64's notes yet again (thanks again!) so can try that. Resonance described for the filter (R11) is understood to be equivalent to decay for the drums, so shall have a play with that.

Still have a spare trigger so might make a 110esque cymbal. Also might build a little expander/noise gate from the NE570 cookbook (T Henry), theres a bit of background noise.

So not much concrete progress but have troubleshot (shooted?) most of the problems. Hoping to get this wrapped up soon.

Cheers
Ben
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PostPosted: Wed Aug 26, 2015 6:43 am    Post subject: Reply with quote  Mark this post and the followings unread

[grunt]

My suggestion for Bass Decay was based on the Resonance control of the WSG filter, which puts a pot in series with the cap at the ( - ) input of the op amp. (C34 in the LDB.) Although I'm not sure it makes a difference, if I said to put it in series with C35, I apologize.

Another possibility is to put a cap -- as much as 1uF -- in series with a pot in parallel with R47. The range of Decay may turn out to be small, and there'll likely be interaction with the Tune pot.

The sample above sounds real good, Ben.


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PostPosted: Thu Aug 27, 2015 2:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey richard

Thanks for replying again!

Still not used to smiley spock!

Yes, i was trying with a pot between C35 and the output of the opamp - not a bother. Assuming i did it right, it really didn't work - just got constant filtered white noise.

I figured out my mistake finally by looking at the filter on your 110 page again - R11 is resonance. I have some 2m pots so was going to try to swap R47 with that (and add a limiting resistor). But also have another option to try now.

Many thanks! Decay on the BD (and maybe toms) was my last 'mod' desire, rather than just chucking in more pcbs and more wires Laughing

Work and family are all a bit hectic now, but i will give these a shot when i can.

Many thanks, Ben
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Paradigm X



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PostPosted: Thu Aug 27, 2015 12:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

richardc64 wrote:
Although I'm not sure it makes a difference, if I said to put it in series with C35, I apologize.


I missed this first time round. Please dont apologise! Youve been more than helpful ever since i started building !

I actually double checked the examples you sent and they do seem to suggest either side would work.

Ive wired up the pot and cap in parallel now so just off to test. Also figured out why id blown the tle which is nice. wiring it up like the data sheet seems to work much better Laughing

Cheers, all the best.
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PostPosted: Fri Aug 28, 2015 1:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Alas, didn't get a chance to try last night, but did take a couple of quick phone snaps.

Im quite proud of the ways its been installed - all pcbs and pots on the 'front panel' and the other gubbins in the tin, so easily separated. Relatively easily, that is. It seems to be a trade off between too many wires, and no room for manoeuvre.

Bank holiday weekend this weekend!


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PostPosted: Tue Sep 01, 2015 9:44 am    Post subject: Reply with quote  Mark this post and the followings unread

OK. So bank holiday turned into a bit of a family/boozey holiday, so not much progress.

Blew up a 330uf cap installed the wrong way, fecking loud! Most impressive noise ive got recently Laughing

Digital noise from the clap PCB works as an alternative noise source, but is quieter, think i can boost with a couple of resistors (non-inv buffer). Might try it on a pot as well.

The decay mod above (pot+cap) kind of worked, it affected the pitch a lot; and didnt seem to go much longer, only shorter. Hard to hear on my crappy speakers tho. Cant hear much in the low range, so will try to record. Getting the basic tone to go longer, with the same mods would be fine.

Ken's drive mod didnt seem to do a great deal. Maybe try 3x diodes in series, or abandon.

But the main issue ive not got is hum, seems to be grounding related. aS I feared Mad Mad

Trying to cobble together these 'fake' ground circuits is proving troublesome.

The LDB1 uses a TLE2426 rail splitter, which works fine for itself. Ive modded it far beyond its intentions so cant complain. As im trying to add additional opamps, i thought Id add an additional tle for that, as it only has a 20ma current output. But i need to connect the grounds together to make the hum disappear/reduce. As they're based on the same 9v supply, i thought the ground(s) would be the same. Connecting these shouldn't be an issue. BUT;

The handclap is then based on the ground being created by a 5.1v zener! (asymmetrical) Yet another ground! If i connect all these together, somethings going to go wrong (?) two at 4.5v and one at 5.1v.

But surely im only connecting via patch leads internally, as opposed to external patch cables? as in if it works in the real world, it shoudl be ok wored internally.

I could remove the zener and the other resistor and use the other grounds as the ground, i guess.

As it stands the clap wont mix into the LDB1s mix in, at U1 pin 6.

Can i ask a couple of super basic queries while im here;

Ive assumed that the output of the mixer (u1 pin 7) is a 'buffered' output, so i can connect multiple outputs? I have 3 wires coming out now, after c37, feeding the mixer (dry), phaser and distortion. Do i need to buffer these further?

Also, ive only used a single wire from the output, should i use screened signal + screen cables? I was trying to avoid connecting the grounds... if so, grounds at both ends or just one?

Are stripboard mixers and that amount of wires always going to be intrinsically noisy? So hard to tell if 'normal' or wrong.

So still a long way to got.

Many thanks
Ben
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