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"White Noise Head amp kit" - Page 3

post #31 of 682
glad to hear it mike.

like most things there is no standard "plug it in and play it" design and each opamp based design really should be optimized for the individaul chip though i can't really say i blame opamp rollers for trying.

where most run into trouble is trying to put a high bandwidth part into a low band design and then expecting the same layout ,part orientation and bypassing/ground scheme to be optimal

The problem with some of these lightening fast chips as i see it is the attempt to mate them to slower buffer stages and that is just looking for trouble unless you limit the bandwidth of the gain stage ,and that kinda defeats the purpose of choosing the part anyway.


I like the size and like you have tried to jimmy projects into casing at least a size to small (more like size ten feet into size six shoes) and sometimes you just get lucky man,other times you just end up with a wrecked chassis looking for something to fill it
post #32 of 682
PF - from your second photo of the 5% populated board, there are obviously three 8-pin DIL locations. Two will be for op-amps (one for each channel -LM6171's or whatever) - what's the third one for? Is it another op-amp and if so, what does it do and should it be the same type as the other two? Confusingly, it looks like two of the locations are marked IC1, but I presume that's my eyes and one of the "1"s is really a "3". Good write-up - how's the burn-in going?
post #33 of 682
Quote:
Originally Posted by Alick
PF - from your second photo of the 5% populated board, there are obviously three 8-pin DIL locations. Two will be for op-amps (one for each channel -LM6171's or whatever) - what's the third one for? Is it another op-amp and if so, what does it do and should it be the same type as the other two? Confusingly, it looks like two of the locations are marked IC1, but I presume that's my eyes and one of the "1"s is really a "3". Good write-up - how's the burn-in going?
The two DIPs labelled IC1 look like they're in identical amplifier sections, and the third labelled IC2 looks like it's in the power section.
post #34 of 682
Thread Starter 
Quote:
Originally Posted by Alick
PF - from your second photo of the 5% populated board, there are obviously three 8-pin DIL locations. Two will be for op-amps (one for each channel -LM6171's or whatever) - what's the third one for? Is it another op-amp and if so, what does it do and should it be the same type as the other two? Confusingly, it looks like two of the locations are marked IC1, but I presume that's my eyes and one of the "1"s is really a "3". Good write-up - how's the burn-in going?
Hi Alick,

There are two IC1's on the board and one IC2. IC2 deals with the rail splitter and you can use an el cheapo opamp here such as an OPA134 or TLO71 or similar.

Either side of the board can be used for left channel / right channel so components are identified as, say, R1 on the left hand side of the board and R1 on the right hand side there are two of each components (one for the left and one for the right hand side) so if R1 is a 47K resistor then you fit a 47K resistor into both R1 positions on the board.

Hope that makes sense?

All the best

Mike.

PS: 24 hours of burn in under the belt and sounding superb...... I'm taking a few notes and will do a write up over the next couple of weeks.
post #35 of 682
i am curious pinksteroo .

a lot of brit gear seems to use a 24 volt power supply followed by a rail splitter for +/- 12 volts instead of a full blown bipolar power supply (creek,musical fidelity,this amp). Why is this man ?

just wondering out loud
post #36 of 682
Quote:
Hope that makes sense?
Perfect sense, thanks. I'll be placing my order as soon as you get the class A/LM6171 modded parts list up. Actually, I think I've figured it out anyway, but my modded list is at work. I'll wait for yours in case I missed anything. Did you fit the 22R resistors instead of the lamps?
post #37 of 682
Thread Starter 
Quote:
Originally Posted by Alick
Perfect sense, thanks. I'll be placing my order as soon as you get the class A/LM6171 modded parts list up. Actually, I think I've figured it out anyway, but my modded list is at work. I'll wait for yours in case I missed anything. Did you fit the 22R resistors instead of the lamps?

http://www.rock-grotto.co.uk/class%2...%20biasing.htm for the class A biasing.

To optimise the circuit for the LM6171 simply remove R4 ( 220R ) and jumper over its position on the pcb ( both channels obviously )

You'll also need to fit 2 output caps.... anything over 2.2MFD will do and they MUST be bi polar....... fit them between signal out and headphone socket (one for each channel) Choice of cap is down to you but I went for the first thing that came to hand..... 25MFD ALCAP bi polar electrolytic. you may prefer polyprops (I hate them) or polyesters but, as long as they are bi-polar, anything over 2u2 (2.2MFD) will suffice. I chose 25uF and the bass is toe curlingly deeeeep :-)

There's no need to fit the input caps (C1 2.2uF polyprops) and you can jumper over the pads but if you are going to use the LM6171's (highly recommended!!) then you "must" fit output caps (unless you can think of a better way)

Whether or not you choose to fit the LM6171's it's best to remove R4 (220R) anyway ....... Dr. White says " I originally included R4 (220R) because I'd read that it acted as a "stopper" resistor and improved stability in opamp plus buffer type circuits. In fact, in this circuit and with very fast opamps, it does exactly the reverse and causes the amplifier to oscillate. You must try the LM6171, its one of my favourites because the the wonderful clarity of the sound that it produces."

I'm in the process of putting all this info and tweaks together Alick and will be uploading everything to my website shortly (hopefully by this time next week) so please bear with me

I haven't yet fitted the resistors in place of the lamps and really don't think it's necessary...... they are there as a form of protection and to remove them would make the amp less bullet proof. I'll leave them in the circuit for the time being and remove them once I've finished fine tuning things :-)

By the way, if you fit the LM6171's, always ensure that your headphones are connected when you power the amp up.... Dr. White explains: "The only way you can get instability using LM6171s with my headamp is if you switch on with no load, i.e. no headphones plugged in. This eventuality can be guarded against by wiring dummy load resistors on the headphone socket - they get switched out as soon as you plug in the headphones."

Hope that's enough for you to be getting on with Alick

All the best.

Mike.
post #38 of 682
Thread Starter 
Quote:
Originally Posted by rickcr42
i am curious pinksteroo .

a lot of brit gear seems to use a 24 volt power supply followed by a rail splitter for +/- 12 volts instead of a full blown bipolar power supply (creek,musical fidelity,this amp). Why is this man ?

just wondering out loud
It's a secret British recipe passed down through the generations........ I'm afraid you'll have to remain in the dark on this one Dr. White may be able to answer your question and I'll pass it on to him.

All the best.

Pinkie. (pinksteroo?)
post #39 of 682
Quote:
Hope that's enough for you to be getting on with Alick
More than enough - thanks a lot. I'll get ordering then...
post #40 of 682
Thread Starter 
I've got a varied selection of bipolar caps and can send you a couple. Be warned......... I'm not a polypropelyne lover and find non polar electrolytics to sound more "honest" to the event........... polyprops may "measure" up but IMO they impart a rubbery signature to the sound.


I've got a couple of 25uF ALCAPS, two Bennic 12uF's, a couple of ANSAR 12uF supersounds (huge) and a few Nitai 100uF bipolars. If you're a polyprop convert then the Evox / Rifa 250V are a good cap.

Enjoy building the amp Alick and be sure to report back with your impressions..........

All the best.

Mike.
post #41 of 682
I might just take you up on the very generous offer of the Alcaps Pinkie - thanks. I'll let you know when I've got the rest of the kit and am ready to build. I've a feeling I might want to experiment with the class A mod in and out to see if the advantages of class A outweigh the need for the output capacitors. You suggested the improvement was marginal?

Cheers again

Alick
post #42 of 682
Thread Starter 
Quote:
Originally Posted by Alick
I might just take you up on the very generous offer of the Alcaps Pinkie - thanks. I'll let you know when I've got the rest of the kit and am ready to build. I've a feeling I might want to experiment with the class A mod in and out to see if the advantages of class A outweigh the need for the output capacitors. You suggested the improvement was marginal?

Cheers again

Alick
Output caps are essential with the LM6171............ no need for any caps with the AD8610 OPA627 etc. Trust me, the LM6171 is the way to go......... "astonishing" is one word to describe the improvement.

Pinkie.
post #43 of 682
Thread Starter 
Quote:
Originally Posted by rickcr42
i am curious pinksteroo .

a lot of brit gear seems to use a 24 volt power supply followed by a rail splitter for +/- 12 volts instead of a full blown bipolar power supply (creek,musical fidelity,this amp). Why is this man ?

just wondering out loud
This is all I could get out of Dr.White at such short notice but I trust it answers your question Ricksterooni?


"The points that rickr42 makes about fast opamps and buffers are quite correct - you can't just fling together any fast opamp and any old output stage and expect them to work. You have to design with high speed in mind, and do a compatable pcb layout. I think there are going to be an awful lot of disappointed people buying AD8065s on adaptors and expecting them to be general purpose drop in replacements for all opamp circuits.
As to the 24V plugtop plus rail splitter, the rationale goes like this. Plugtop regulated supplies offer very good performance for very little money. If you have high impedance headphones you need a decent output voltage from your headamp. Plugtop power supplies don't normally come in split rail versions - they are available but expensive. The highest commonly available voltage from a regulated plugtop supply is 24V. So use a 24V supply and rail splitter to get +/-12V.
My headamp will work with a conventional split rail psu giving anything from +/-6V to +/-18V and there is a separate connector on the pcb for this purpose. To use a split rail psu you just unplug the rail splitter opamp and connect power to the three pin power connector. The WNA headphone amplifier sounds better when powered from a really good split rail supply, like my cascode power supply or a Jung type supply, rather than a plugtop psu. Good split rail power supplies are expensive and you're into diminishing returns territory here. Headamp plus plugtop gives you most bang per buck; whilst headamp plus good split rail gives you best performance regardless of cost. Pay your money and take your choice!


Regards, David"

Hope that answered your question Rick?

Mike.
post #44 of 682
Quote:
Hope that answered your question Rick?
absolutely ,thanks mike.

I was mainly just curious . I guess it just comes down to economics and circuit complexity like most things in audio and choices need to be weighed as to where can you cut and still produce something good .

and i agree 100% with that actually
post #45 of 682
Quote:
I think there are going to be an awful lot of disappointed people buying AD8065s on adaptors and expecting them to be general purpose drop in replacements for all opamp circuits.
another good point i agree with totally
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