DIY audio: what are you building?

[aussievintage]

  On 01/04/2024 at 6:17 AM, Cope said:

While I can see the merit, I struggle to make sense of things at the best of times. I'd bamboozle myself pretty quickly trying the bird's nest method.

Expand  

 

you know, the method I personally find hardest to sort out, is when they line all the components all up  neatly on a turret board and sneak wires underneath between them,  and on down to a covered up valve socket  

[sleach]

Whipped up a pair of Markaudio MAOP 11 speakers using spare ply and powered by a pair of minidsp pwr ice amps I have had lying around. I anticipate adding a big bass unit to this. 

 

They do sound good! Not as sensitive as I expected. Bass is understandably ight in the small 20litre seaped cabinets, but pretty good to about 60hz. 

I anticipate adding a big bass units to this, leveraging the two way capabilities of the amps.

 

[Type 1]

Always fun to try new things!!

while i don’t do it, small fulrange with added bass I believe could be pretty good!

[Ian McP]

Mate of mine built these using the Mark Audio 7PHD

 

https://www.darcher.com.au/index.php?route=product/product&path=59_60&product_id=127

 

The box is a triple chamber bass reflex, I've heard these, very impressive bass from such a small speaker. The trick is designing the triple chamber series reflex to extend the bass.

AUD $649

Item Condition: Very Good

Shipping Options: Pickup available and you can audition.

Suburb or Town: Richmond melbourne

State: VIC

Payment Method: cash EFT

Reason for selling: Moving - Surplus to future

MARKAUDIO Speaker with 19mm silk dome supertweeter

In hand finished complex Solid (18MM ) Merbau series (3) chamber , reflex boxes .

Amenable domestic size 80cm H x 24cm W x 20 cm deep

Deep convincing fast , deep ( 42 Hz) bass due to complex TCSR  (triple chamber series reflex) tuned boxes -which also has the benefit of flattening and distributing the impedance curve for better amplifier loading. Ideal match for low power tube amplifiers 

 

Some of you will be aware of MarkAudio (Mark Fenlon, ex Goodmans designer , formerly of UK , then Hong Kong, lately Spain) famous for his superb full range  metal cone drivers , in the ilk of Ted Jordan  (RIP - famous Goodmans , Jordan Watts , Jordan designer )

Truly international design effort , European /iconic FR  design expertise , Japanese expertise in spiders , cones , basket , hand assembled just over the Hong Kong border with Southern China around ShenZhen

However to my ears, the much more  limited range of Markaudio paper cone speakers are the superb sonic gems of both ranges - clean , fast, efficient non fatiguing. The smaller cones are stiff and superlight and quick , in many respects outperforming the larger types 

In talking recently with the MAHK management, there is some agreement, the challenge being that the custom designed paper cones have minimum order quantities of 3000 pieces per size - a big investment for a niche, elite manufacturer  . 

The small 19mm silk dome supertweeter is added above 10Khz as single cone Full range FR drivers tend to beam a lot at successively higher frequencies for suboptimum  sound presentation.

These have been my recent personal speakers and sonically outperform very many of their commercial competition boasting many times higher prices 

Not for head banger music but superb for jazz/blues/vocal /pop at usual domestic volumes 

Limited audition available for serious buyers 

Pick up for Richmond Melbourne >

 

regards Ian

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Type 1]

Interesting project!

I would imagine that it sounded quite lively… Mark Audio drivers aren’t that big and Merbau timber Is pretty hard and dense..

Getting a great finish on Merbau could be a challenge!

He talks about a Triple chamber box…. I would love to know what is happening inside…. Clever box work really makes these “ badboys shine!!

Anyone going to tell us what Triple Chamber is?

[muon*]

Been thinking about rebuilding this Chinese 6SN7 tube pre amp point to point, but in the interim was looking at adding a safety ground from the IEC as it had none when it came, first I tried one connected to the transformer bolt in the red square, but this increased the bit of hum/buzz the pre has by 10 fold!

 

Funny enough I just connected it to the central PCB mount point in the red circle and it didn't increase the hum/buzz.

 

At least It's listenable now, all be it with a hum/buzz that is just audible when no music is playing.

 

I also changed the RCA sockets and input and output wiring, not shown in this pic. Tubes are NEVZ brown base 6N8S and rectifier is USA made 6x5GT.

 

Edited April 13, 2024 by muon*

[aussievintage]

  On 13/04/2024 at 10:18 AM, muon* said:

Been thinking about rebuilding this Chinese 6SN7 tube pre amp point to point,

Expand  

 

Great idea.  A circuit that simple should never need a PCB anyway .  

 

  On 13/04/2024 at 10:18 AM, muon* said:

but in the interim was looking at adding a safety ground from the IEC as it had none when it came, first I tried one connected to the transformer bolt in the red square, but this increased the bit of hum/buzz the pre has by 10 fold!

 

Funny enough I just connected it to the central PCB mount point in the red circle and it didn't increase the hum/buzz.

Expand  

 

Hmmm,  I'd be doing some checking for continuity to the metalwork.  The ground is for safety if you touch it, and if the hum pickup is reduced in the new position, that might be because it is not grounding properly.

[muon*]

  On 13/04/2024 at 10:24 PM, aussievintage said:

 

Great idea.  A circuit that simple should never need a PCB anyway .  

 

 

Hmmm,  I'd be doing some checking for continuity to the metalwork.  The ground is for safety if you touch it, and if the hum pickup is reduced in the new position, that might be because it is not grounding properly.

Expand  

It's not reduced compared to no safety ground connection, just compared to where I had it before, there is still continuity to the top plate metalwork.

[aussievintage]

  On 13/04/2024 at 10:34 PM, muon* said:

t's not reduced compared to no safety ground connection, just compared to where I had it before, there is still continuity to the top plate metalwork.

Expand  

 

Yes but the transformer bolt, the top, and (presumably) the PCB mount should all be connected solidly, so grounding to any point should produce about the same amount of hum, as the "loop" size for hum pickup is virtually the same.  Hence, when you said it was different between the transformer bolt and the PCB mount( - not concerned about the no-ground situation), I was a bit concerned.

[muon*]

  On 13/04/2024 at 10:39 PM, aussievintage said:

 

Yes but the transformer bolt, the top, and (presumably) the PCB mount should all be connected solidly, so grounding to any point should produce about the same amount of hum, as the "loop" size for hum pickup is virtually the same.  Hence, when you said it was different between the transformer bolt and the PCB mount( - not concerned about the no-ground situation), I was a bit concerned.

Expand  

I stand corrected, I check just now and yes you are correct.

 

Fixed now.

 

Will see how the hum is, I hope it is not huge

[muon*]

OK, hum/buzz still not any worse, and there is connection between earth pin and top plate. The top screw tat screws into the standoff had come a tad loose.

 

Cheers, Aussie.

 

I have no idea why it was much greater when connected to the transformer bolt.

 

 

Edited April 13, 2024 by muon*

[mwhouston]

On some very early tube power amp and preamp Id earth the top plate with the neg of the PS then take earths where required from the top plate. This didn’t work well and I got hum. It wasn’t until I not only earthed the top plate but also run individual earth wires to each part of the build that required it did I eliminated hum. I don’t do it any different now and very rarely will I get any hum.

 

You would think 2mm of sheet Al would conduct earths efficiently but not so. Additional earth wiring is required. 

[muon*]

Hum reduced even more now after chatting with Stephe.

 

Only a little now not heard from my 2m seated position.

 

[aussievintage]

  On 15/04/2024 at 9:19 PM, muon* said:

Hum reduced even more now after chatting with Stephe.

 

Only a little now not heard from my 2m seated position.

 

Expand  

 

You relocated, twisted, and ran an ground wire along the front panel power switch wiring?

[muon*]

  On 15/04/2024 at 9:45 PM, aussievintage said:

 

You relocated, twisted, and ran an ground wire along the front panel power switch wiring?

Expand  

Just twisted the wires that were running to the switch and moved the run to the bottom of the chassis.

 

This seems to be where the hum is coming from.

 

Silly the way the PCB is designed with the signal out at that rear corner.

[muon*]

Still too much gain for me at 22db.

 

I have Nelson's H2 generator board to assemble and fit into my volume control box, I'll alter the resistor values in that so it is near zero gain, and see how that goes.

[aussievintage]

  On 15/04/2024 at 9:56 PM, muon* said:

Just twisted the wires that were running to the switch and moved the run to the bottom of the chassis.

 

This seems to be where the hum is coming from.

 

Silly the way the PCB is designed with the signal out at that rear corner.

Expand  

 

Yes, you are on the right track.    I might have run the twisted switch wiring tight up against the metal of the top - using it as a ground plane,  or used shielded wiring, or installed an internal metal shield to segregate it. - or even done away with the switch completely (and so kept all power wires well away from the circuit)   Just further suggestions.  Stop when it is quiet enough for you    

 

 

[muon*]

  On 15/04/2024 at 10:03 PM, aussievintage said:

 

Yes, you are on the right track.    I might have run the twisted switch wiring tight up against the metal of the top - using it as a ground plane,  or used shielded wiring, or installed an internal metal shield to segregate it. - or even done away with the switch completely (and so kept all power wires well away from the circuit)   Just further suggestions.  Stop when it is quiet enough for you    

 

 

Expand  

I did try it against the top plate, not as quiet.

 

Stephe also suggested doing away with the switch.

[aussievintage]

  On 15/04/2024 at 10:05 PM, muon* said:

I did try it against the top plate, not as quiet.

 

Stephe also suggested doing away with the switch.

Expand  

 

  These things can be "try it and see"  a lot of the time.

[andyr]

  On 15/04/2024 at 9:56 PM, muon* said:

Just twisted the wires that were running to the switch and moved the run to the bottom of the chassis.

Expand  

 

Yes, every pair of wires needs to be twisted:

• signal (if, like me, you don't use coax)
• DC +/-
• AC active/neutral.

 

Sometimes with AC wires, I'll thread them through a length of braided shield and unbraid one end of the shield, add a spade and earth it to the chassis earth bolt.

 

[muon*]

  On 15/04/2024 at 10:26 PM, andyr said:

Sometimes with AC wires, I'll thread them through a length of braided shield and unbraid one end of the shield, add a spade and earth it to the chassis earth bolt.

 

Expand  

I'm thinking of trying a braided shield covered in heat shrink, connected at the IEC ground.

 

Edit: due to the high gain, I'm looking at reducing the hum just for resale.

Edited April 15, 2024 by muon*

[aussievintage]

  On 15/04/2024 at 10:31 PM, muon* said:

Edit: due to the high gain, I'm looking at reducing the hum just for resale.

Expand  

 

You know there are plenty of ways to reduce the gain?  What does the schematic look like, do you know?

[muon*]

  On 15/04/2024 at 10:58 PM, aussievintage said:

 

You know there are plenty of ways to reduce the gain?  What does the schematic look like, do you know?

Expand  

 

Double sided black PCB is a pain.

[aussievintage]

  On 15/04/2024 at 11:18 PM, muon* said:

 

Double sided black PCB is a pain.

Expand  

 

A simple circuit so less to work with.  How about splitting the cathode resistor, R4,  into a simple voltage divider?  

[andyr]

  On 15/04/2024 at 11:18 PM, muon* said:

 

Double sided black PCB is a pain.

Expand  

 

Wow!  Can you possibly get a simpler circuit than that?

 

And does that count as 1 gain stage ... or 2?  (IE. does it invert the signal... or not?)