Mcandmars ramblings \ build thread...

[Paul Joppa]

We did once get a bad batch of "431" chips - they may have been fakes, or factory rejects - that were very noisy. Hard choices there - resistor/capacitor is always quietbut you can hear the cap, resistor alone risks high frequency drive to the power triode, LEDs can be noisy (the predecessor of theHLMP-6000 was measured to be very quiet - but long ago), chip regulators such as the 431 can be noisy (the specs on the major brands say they should be relatively quiet, but fakes and rejects abound) ..

Thanks for the kind words guys, feeling much better now - I'll probably be pretty occasional on the forum over the next few weeks!

 

[mcandmar]

I did a little research and found a few sources who claim the On Semi LM431A measures the quietest so i ordered a few different brands from Mouser to see. Using the highly scientific testing methodology of a pair of Grado RS1 headphones on my head i found the TL431's were actually considerably quieter than the On Semi, Fairchild, and Ti LM431's.  Unfortunately it still wasn't good enough with a constant white noise in the background.

I found some test measurements which noted the LM431 performed much quieter when set for higher voltages, i assume that is due to the resistor added between the reference and cathode. The test report measured the LM431 noise in the 20uv range, when configured to 5v it measured down around 3uv, vs a selection of red LED's that all measured under 1uv.  It seems to me that adding the two resistors across the 431 would defeat the purpose of using the 431 in the first place, and similarly adding bypass caps would do the same so i came to the conclusion it just wasn't going work and threw in the towel.  Frustrating really as there was clearly better high frequency response and lower distortion while using it.

So back to the HLMP/500r sting, i did one final frequency response plot with the stock 1.27k resistor and sure enough the HLMP helps the high end response.  Its kind of a half way point between the stock resistor and LM431, but more importantly its completely silent.

Before i close the door on the LM431 idea i should point out i am using very sensitive Grado headphones, the noise may not be audible with less sensitive headphones or speakers so it may work perfectly fine in other setups.  As always, please report your findings

 

[ZacharyP]

I have been following this thread like trial and error gospel ever since I submitted my order for the sex 2.1, great job to all who contribute and especially mcandmar for sharing all the fun with us!

My kit and c4s kit should be arriving within a couple of weeks and I've already gathered some mundorf Supremes (2.2uf, and 0.1uf for parafeed and interstate caps respectively), two triad chokes, some 100r resistors for heater supply, and all I'm waiting on now is for my mind to finish an internal debate over a goldpoint or this; http://www.diyaudioblog.com/2011/03/elma-stepped-attenuator-populated-with.html?m=1

Anyway I plan to build the kit entirely stock (except for the attenuator just to make wiring it up easier).  Almost all of my listening will be with Alpha Dogs headphones and a set of speakers I'm building with my father's friend (the speakers are rated 8 ohm too I believe, maybe 4 though). 


First question, if anyone has experience with any of the Fostex mods, ZMF or MrSpeakers Mad Dogs, etc. should I wire for 8 or 4 ohms?  Any help would be greatly appreciated.  I'm leaning towards 8.

Second question:

In what order should I implement the upgrades and modifications if I wish to enjoy each individual change as much as possible?  Would putting the c4s in first only make all the changes brought by capacitors that much more transparent, or does it have an opposite effect?

Thanks for reading guys!

 

[mcandmar]

Glad to be of help, sorry about your wallet

I would start with 8ohms, i've stuck with that for a variety of different headphones, and since your planning on driving speakers that would make 8ohms an ideal setting.

As always, build it stock first, then move onto the Bottlehead options, impedance switch boards, then the C4S.  Basically you want to get all that up and running before you start adding in custom parts to the mix.

As for the upgrades, the capacitors will give you the most immediate change, but i would would fit them last as they limit access to the rest of the circuit around them and its all too easy to ruin a nice cap by hitting a hot soldering iron against it.

Also resist the urge to chuck all the parts in at once, best to use it for a while so you can fully appreciate the differences each change will make.  Enjoy, and keep us posted!

 

[ZacharyP]

Glad to be of help, sorry about your wallet

I would start with 8ohms, i've stuck with that for a variety of different headphones, and since your planning on driving speakers that would make 8ohms an ideal setting.

As always, build it stock first, then move onto the Bottlehead options, impedance switch boards, then the C4S.  Basically you want to get all that up and running before you start adding in custom parts to the mix.

As for the upgrades, the capacitors will give you the most immediate change, but i would would fit them last as they limit access to the rest of the circuit around them and its all too easy to ruin a nice cap by hitting a hot soldering iron against it.

Also resist the urge to chuck all the parts in at once, best to use it for a while so you can fully appreciate the differences each change will make.  Enjoy, and keep us posted!

I never really shared any pics of my old Crack's internals, I can definitely work with tight spaces after stuffing that headphone amp!

I attached some different shots of it between mods, without the capacitors mounted with zip ties of course, much neater in the box.  Mounting the choke at an angle to the transformer resulted in absolutely zero hum.  Dunno, I tried to follow my Morgan Jones amplifier design text to lead me.  For my first time with a soldering iron since my freshman HS electronics course (22 now) I think I did a decent job with the crack.  Now time to move on and keep improving.

Planning a much cleaner build this time; starting with the wooden base.  An extremely light burgundy stain followed by a linseed oil finish, cream white top plate (if I can find a powder coated to do it) with claret/red wine accents to match my Alpha Dogs.  Will definitely have to try to make a thread 1/100th as useful as yours!

 

[Paul Joppa]

Generally any change that increases resolution (i.e. most of the good ones) will make the next change easier to hear. So the optimal strategy in my mind is to go with the biggest effect first, so that the more questionable "upgrades" get the best chance of making a difference.

 

[ZacharyP]

Generally any change that increases resolution (i.e. most of the good ones) will make the next change easier to hear. So the optimal strategy in my mind is to go with the biggest effect first, so that the more questionable "upgrades" get the best chance of making a difference.

I think I'll 'fit' the larger mundorf Supremes just to make sure the c4s board won't cause issues and/or how to solve potential issues, then I'll build it stock, add c4s, then solder in the Supremes where I previously fitted them.

Thanks everyone!  Best support community by far.

 

[ZacharyP]

Has anyone here ever used an Elma attenuator?  Have a line on one populated with kiwame resistors but it's 50k.  Will there be any issues with that?  My source will be a Schiit Modi 2 uber

 

[mcandmar]

Elma make the switching part, for example the Goldpoint attenuators use the Elma switches, but add their own PCB's and resistor layouts to make the complete attenuator.  Anything using Elma switches gets a thumbs up from me.

There are different types of attenuator, main ones being series and ladder.  Personally i don't like the idea of series attenuators as you end up with a whole string of resistors in the signal path, where as with ladder style there is only ever two resistors in the path creating a divider. Easy to spot the difference as the ladder style have double the amount of resistors.

Then there are resistor choices, much like brands of coffee or beer everybody will have a preference. Kiwami are carbon resistors, i think they are carbon film as opposed to carbon comp.  Personally i find them a little soft sounding, rounds the edges off and makes things all smooth and cuddly.  Where as metal film i find to be more transparent so you don't notice them.  I've always use Dale RN series resistors in signal paths and attenuators for that reason, but again that's just my opinion, i may be completely wrong about that.

I believe 50k will work fine, especially with something like a Modi driving it as it will have been designed to drive 20k-50k loads.

 

[ZacharyP]

Thanks.  It's an Elma switch populated with thru hole kiwames.  The slight soft sound, or rounding off shouldn't be an issue because I tend towards neutral-bright sound preference.

The attenuator in question:

http://www.diyaudioblog.com/2011/03/elma-stepped-attenuator-populated-with.html?m=1

Thanks again!

Still part of me wonders if the series goldpoint with and resistors for under $180 shipped is the better choice.

 

[mcandmar]

Dunno.  Depends on how much you are getting the Kiwami one for.  From what i have read many people dont like the SMD resistor versions of the Goldpoint, i remember Doc B expressing a dislike for them too so stick to through hole resistor attenuators.

Personally i think these are the best value, proper ladder style unlike the current Goldpoints and uses Dale resistors. http://www.ebay.co.uk/itm/assembled-dale-24-step-copper-axis-attenuator-volume-control-100k/281664997434?hash=item41948ac83a 

You can also buy them unassembled if you are a sucker for punishment. BTDT, and swore never again.

 

[Grainger49]

Ladder attenuators keep a constant impedance to the source.  It approximates a pot with none of the drawbacks of a pot. 

I, personally, would not consider any other configuration.

 

[ZacharyP]

Dunno.  Depends on how much you are getting the Kiwami one for.  From what i have read many people dont like the SMD resistor versions of the Goldpoint, i remember Doc B expressing a dislike for them too so stick to through hole resistor attenuators.

Personally i think these are the best value, proper ladder style unlike the current Goldpoints and uses Dale resistors. http://www.ebay.co.uk/itm/assembled-dale-24-step-copper-axis-attenuator-volume-control-100k/281664997434?hash=item41948ac83a 

You can also buy them unassembled if you are a sucker for punishment. BTDT, and swore never again.

Biggest issue with that is the ship time can be horrible.  I'd hate to have the kit arrive next week sometime and then I spend a month waiting for the Dale resistor ladder attenuator because I have looked at that one.

Anyone have any extras? 

 

[ZacharyP]

What is the necessary wattage rating for the 100r heater supply mod?  1/2 watt?

 

[mcandmar]

Yes at a minimum as they will be dissipating approx .4watt.

 

[Grainger49]

Then a one or two watt would be nice to keep the heat down.  heat is an enemy to all components.

 

[ZacharyP]

Then a one or two watt would be nice to keep the heat down.  heat is an enemy to all components.

My thoughts exactly.

 

[ZacharyP]

For those who have installed the c4s, would it be beneficial for me to install the nylon standoff before I populate the terminal strip?  It looks like it'll be a tight fit, removing the nut among the diodes, wires and resistors, and If it saves me from a later hassle then it's worth it.

Thanks for reading!

 

[Grainger49]

It is easier.  You might also get some soldering iron burns on the standoffs while installing components.  Those burns won't compromise the standoff it will just look bad.

 

[ZacharyP]

It is easier.  You might also get some soldering iron burns on the standoffs while installing components.  Those burns won't compromise the standoff it will just look bad.

Well we don't build amps to stare at standoffs

Thank you Grainger!