The Grung Buster Project

[Ian Mackenzie]

Okay,

We have had some fun posting our grungy experiences....mostly amplifiers.

So I figured its time to de grung all you wonderful formites with a new project.

Every now and then a really great idea or invention comes along, they are often very simple.

This invention will have a bigger single impact on the sound of your JBL's than anything you have done before!

And you can make it your self and enjoy the satisfaction of hearing it go!

I will be presenting simple but unique amplifer project over the next month or so based on the super class A amplifier I have built and referred to from time to time.

The project can be scaled in size to suit particular needs and level of experience. From a small toaster to a furnace.

It's fairly easy to make and the subjective performance will astound you.

I will be supporting the project with pcbs on request, matched parts and detailed technical assistance.

To be continued.

[scott fitlin]

About how big and how much would a 100wpc@4ohms be? And can this amp be done with an input sensitivity of 3/4 volt?

[Ian Mackenzie]

Hi Scott,

Thanks for your interest.

I have not done any costings recently so I will let you know. Most of the cost is in the heatsinks and power supply.

The size of such a device would be like a 3 unit rack size amplifier but much heavier (mono blocks).

Suggest you hire the movie "The Forbidden Planet". The immense power of such an amplifier is breathtaking.

Sensitivity can be set to suit any level. The input should preferrably be balanced and I propose to include a unbalanced to balanced class A preamplifer line stage.

Ian

[Ian Mackenzie]

Scott,

Based on your power requirement the approx cost;

Semiconductors $150
Heatsinks $150*
Transformers & $300*
Capacitors

This is an indication only and you would need to check pricing from local vendors. The final cost will also depend on your individual approach to construction and your application.

Such a project would take some time to source parts, construct and commission and you would acquire many new skills and an appreciation of this kind of amplifier. There is also the self satisfaction and the results that would compare favourably to any amplifier at any price.

Amplifers on this scale tend to be conservatively designed and parts rated accordingly.

Here is a gallery showcasing some recent diy efforts.

http://www.passdiy.com/gallery/alephx-p3.htm
http://www.passdiy.com/gallery/alephx-p2.htm

Of course not everyone needs a monster from The Forbidden Planet, and all you may require is a 30 watt amplifier to bi amp your 4430/4435 or a 75 watt (8ohms) version to bi amp your 4343 etc and use a conventional amplifier for the bass.

So I intend to provide templated options for the above power levels, but if you have specific needs I am happy to consult.


Ian

*There is a tendancy to use less volume with such a very dynamic & high resolution amplifiers because you can hear significantly more information even at low level.

[boputnam]

Originally posted by Ian Mackenzie
This invention will have a bigger single impact on the sound of your JBL's than anything you have done before!

Lovely Karen...!!

Oh, sorry - wrong Thread...

[Ian Mackenzie]

I doubt if she or her husband would appreciate that!

Karen for those who are unaware, is the DIY Diva at Passlabs.

No love letters please, Karen is married with 3 daughters.


Ian

[Ian Mackenzie]

As to the program for rolling out this project, some description and story behind the design is in order and then a step by step plan of how to build it is in order.

Firstly, some background.

This amplifier is a diy version of the most recent technology from the Nelson Pass company Passlabs. Diyaudio forum guru Grey Rollins designed the circuit based on the Pass patents and presented the amplifier on the Diyaudio.com Passlabs forum some 24 months ago.

The design is protected by several patents but this version can be constructed for diy purposes on a not for profit basis. In fact over a 1000 diy pcb boards have been made world wide.

Sufficient numbers of this diy amplifier have now been successfully built and tested that with some careful attention to detail, the average constructor can attempt and commission the project with only a minimum of test equipment. No less used in tuning a bass reflect enclosure!, an audio ocsillator, multimeter and low voltage DC bench power supply.

I conceptual terms, the amplifier is solid state (FET) pure class A but its topology is termed balanced single ended. The earlier Aleph patented current source and the more recently patented Super Symmetry (su) have been mixed to create an amplifer with the velvet smoothness of SE Class A, but with the brilliant dynamic contrast of that Su X delivers.

For the technically minded, the amplifier uses only a small amount of feedback to make the balanced function of the amplifier perfectly symmetrical, thus enabling 100% cancellation of all distortions without resorting to the more commonly used negative feedback.

To assist in providing detailed background information I shall use hyper links where possible. There have been dozens of threads and thousands of posts on the diyaudio.com forums regards this particular amplifier, so please do not stray from the marked trail or you will get lost in hyper space.

Go to this link for official background information on the X Aleph project. http://www.diyaudio.com/wiki/index.php?page=Aleph-X

[Ian Mackenzie]

Okay,

At this point if you are interested in the project, you are probably saying what power level do I need and how do I scale my project .

I anticipate everyone has their own idea of how much power they think they need, but practicality, cost and degree of competence must be considered.

So to rationalise this issue I plan to present 2 power levels which should suit most members needs and slot in nicely for some typical JBL bi amplifed monitors. The powers levels chosen will also enable construction without being overly expensive while also being practical.

The power levels will be 30 watts (8 ohms) for the 4430/4435 biamplification of the HF horn and other 2 way HF applications, and a 75 watt 8 ohm version for bi amplification of the 4343/4345 and 4350 monitors and the smaller JBL monitors.
(Both versions can be adjusted to operate in a 4 ohm load to product the same or proportionally higher power output).

Some of you may dissmayed at the modest power levels here compared to your industrial pro amps but I assure you the dynamic qualities and high resolution of these amplifiers are sufficient for the highest level of musical enjoyment.

I will provide an Excel spread sheet calculation for scaling both versions two interested members.

I do not propose to publish the actual circuit design here for reasons of potential patent infringment but I can email to those seriously interested or it can be located in the above hyperlink.

Next week I provide an overview for the basics of contruction for the project.

Here is a glimpse of a finished X Aleph project!http://www.passdiy.com/images/gallery/ax-p5-f3.jpg



Ian

[Ian Mackenzie]

Okay,

The design calculations for both versions have been completed using an excel spreedsheet.

I will start presenting the kit this weekend by building up the higher power version myself as this will be shipped to the USA when completed for one lucky member.

The concepts and design are common to any scale in the design so you can follow the basic steps.

I will start be looking at the PCB, this can be either made by your self following some simple instructions and a few basic tools, or I can provide it perhaps or I can refer you to a supplier..

Making you own pcb is the fun part so keep your eye on this thread.(its easy)

I will then provide a parts list, followed by instructions on stuffing the pcb(s), assembly and mounting of power fets on the heatsinks, assembly of the power supply, guidance to fabrication of a chassis, and testing.

To be continued.

Ian

[Guido]

Thanks Ian!

I'll follow for sure...

[Ian Mackenzie]

Well you will be busy for a while, but cosy when you are done.

They do burn off a bit of heat....keep your pussy nice and warm in winter.

Ian

[Ian Mackenzie]

The beginning.........................


Here I will discuss some pre design aspects of the project and an introduction to Class A.

Quoted from Erno Borbely........World authority of Class A amplifiers, former director of Engineering for Dynaco and the David Hafler Company.

"The quest for class A starts here. Many listening tests have proven that amplifiers working in "pure"class A sound better than those in class AB. Users report an improvement in low level details and ambience as the bias current increases. They normally attribute this to the fact that the active devices (bi polar or mosfets) are operating in their linear region, without abrupt nonlinearities or turn-on/ turn off delays.

Equal weight is put on the current capability of class A amplifiers. By definition they are high current amplifiers and they are capable of driving difficult speaker loads better than class AB amps.

The definition of "pure class A" can be very different from one manufacturer to another. Often this is nothing more than marketing hype, the question of current is probably enough up to 1 watt, but nothing more.

The definition of Class A is simply that the device always conducts current and never goes into cut off. This is especially important to keep in mind when you consider the output stage, where large currents flow. Looking the output stage of most amplifiers, the push pull, complementary emitter-follower or source follower stage. In such an amplifier, the peak output current in class A is equal to twice the idle or bias current."

In preparation for the project it is necessary to specify the DC bias current conditons for these Class A amplifiers.

In order to do this we need to look at the load conditons represented by the intended speakers.

This afternoon I measured the impedence of the JBL 4345 system and then the midrange high frequency section as used in the bi amplified mode.

Interestingly, in the normal passive mode the 4345 system presents a load of around 4.5 ohms from the bass to midrange frequences and then rises through the HF region.

I then measured the system in biamp mode, the midrange and HF both measured around 8.0- 9.5 ohms and then increases in the HF region.

The low impedence of this system and most likely the 4343 and 4315 monitors suggests why some amplifers would not give good or best performance in passive mode while bi amp mode being a much easier load for the amplifier also gives better performance.

To determine the bias current we use several formulae to arrive at the peak voltage and peak current.

For example if we want 75 watts into 8 ohms:

The RMSvoltage = V(P x R ) where P =75 and R =8

Equals 24.49 V RMS.

This is the equivalent of 34.64 volts peak. So the supply voltage must be a minimum of 34.64+-.

I Bias = 1/2 VC/R load where VC =34.64 and R=8
Equals = 2.165 A

The output stage will deliver a peak current of 2 x I Bias =4.33 amps before leaving class A, which is the equivalent of 3.06 amps RMS.

The class A output power into 8 ohms is

Po =Vrms x Irms = 24.49 x 3.06 = 75W.

In the next post I will apply these bias requirements to the actual design using an excel speedsheet

Ian

[Ian Mackenzie]

Here we have some specific design requirements for the amplifier.

The attachment file is a screen capture of an Excel 5.00 spreadsheet (If you would like a file copy pm me).

The overall idea is to balance a variety of criteria based on a few facts and some certain known assumptions. Then apply some practical experience to get a workable design. I have built 5 similar amplifiers and they all work very nicely.

In the above thread we looked at a known speaker load and came up with some minimum output requirements for the amplifer to operate in pure class A.

The spread sheet below is a neat and convenient way to flesh out the amplifier key operating parameters. Output power into 8 ohms or higher impedance in this instance, DC bias current, supply rail voltages, number of output devices, power dissipation etc.

I worked several simulations framed by the desired output power, the known power dissipation and thermal ratings for a given size heatsink equivalent to 2 x 0.25c/watt.

To round out the design we have to allow for practical losses. To cover losses 20% more bias current was added to the above formulae ensuring complete class operation right up to full power and beyond giving 5.20 amps DC bias current.

As this particular class A design uses an (ccs) active current source that shares 50% of the AC Current Gain (Patented by Neslon Pass) the amplifier DC bias current conditons are a bit more realistic for practical design amplifier of this size.

As the current source is actively sharing the ac current gain the load effectively seen by the amplifier is a negative impedance twice that of the speaker. ie 16 ohms.

The target of 75 watts output is a conservative operating conditon and the power dissipation of 200 watts for one channel conveniently fits the heatsink K/w ratings I have on hand of 2 x 0.25C/watt.

Heatsinking is a major design factor for class A operation and cannot be overlooked. I will refer to this in more detail later in the thread. By the way, we normally use sufficiently large heatsinks that fan cooling is not required. That way the ambient noise from even the quietest fans does not mask the resolving power of the amplifier.

Ian

[Ian Mackenzie]

In this instance, we are not concerned about driving an impedance lower than 8 ohms, however this graph illustrates the amplifier has sufficient reserve for more power into lower impedances.

In the event an individual constructor wishes to operate a lower or perhaps higher impedance load, the design can be revised for that application.

Ian

[Ian Mackenzie]

This aspect of the spreedsheet deals with more the business end of the amplifier. Heat as mentioned above and effective ways to get rid of it must be managed.

The design uses the rule of thumb that 25c above ambient , or 50C is hot to touch but not that hot as to cause pain or user damage. This is a known threshold in that 55 c is almost too hot to touch and 60Ci s even more so. None the less the amplifier will survive under these conditions day in and day out until the Sun cools and becomes a Red planet with an afternoon glow!

Just think, in the middle of your North American winter you will be able to come home after work, crack a can of beer and enjoy a nice warm listening room after a short warm up.

The output devices are an IRFP240, rated at 150C junction temperature. In this design we use 12 per channel based on the above mentioned heatsinks. The design is conservative and can be revised for even lower junction temperatures by using 16 devices per channel if required! (These devices are particularly tough, unlike your garden variety plastic Bi polar transisters in many consumer amplifers)