Simulation - Pass MF-12 MOSFET Quasi Comp (Original) Modification for HK Citation 12

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A matched pair makes a lot of sense for the diff pair but is not critical and it seems that even HK went to 2N5087s in later production - not sure if they matched them. Any similar high beta part with VCE >= 50V and Icmax = 100 mA should do. BC556B or C are also good choices:
Product Folder - BC560 - PNP Epitaxial Silicon Transistor, Fairchild Semiconductor - Global Leader in Power Optimization

There are some low cost duals still out there but most are in tiny modern surface mount packages such as the SC70-6. BC857s:
Product Folder - BC857S - PNP Multi-Chip General Purpose Amplifier, Fairchild Semiconductor - Global Leader in Power Optimization

Or Diodes Inc. IMT4, also in a very tiny package:
http://www.rohm.com/products/databook/tr/pdf/imt4.pdf

2SA1349 is in a normal size package but is getting hard to find:
users.ece.gatech.edu/~lanterma/sdiy/datasheets/transistors/2SA1349.pdf
A member has them:
http://www.diyaudio.com/forums/swap-meet/143997-fs-toshiba-2sk389-gr-2sa1349-gr-2sc3381-gr-14.html

If you buy standard parts like BC556Bs packaged on tape there is a good chance that they came from the same lot and if so will be very well matched.

Then there is always the LM394, and similar MAT02 and SSM2210, that you can read more about here:
http://www.diyaudio.com/forums/solid-state/107404-simulation-je-990-op-amp-deane-jensen.html
 
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Pete,

Thanks so much for all the info. and help you have provided me. It certainly has been a learning experience for me!

The 2N5551's came on the tape reel, so they should be pretty close.

I was able to create my schematic in LTS. I started from scratch instead of modifying yours. I figured I would learn more and how to better use LTS if I created my own schematic.

I believe everything is correct except for the three CCS's; which I used the diode symbol for and the variable BIAS resistor. Could you help me get those symbols correct on the schematic? Thanks again for all your help and time!!!!!!!!!!!
 

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That looks good Mike!
Should there be a resistor in series in the top rail?
Check your diode polarities, is there a band on the case
of the diodes, that is the bar in the schematic symbol.
I don't know where to get the correct symbol, you can
search online for LtSpice library add ons, or at the LtSpice
group on Yahoo. You could just make the component
designator start with CR instead of D.
 
Pete,

I was wondering if you know of any visual learning aids that might be available. For example, I am a visual learner. I need the hands on, visual experience to really grasp things. Let's use my circuit for example. I would love to see a tutorial that depicts the circuit, shows moving, colored lines to illustrate the voltage/current flowing through it. It would show the VAS stage, the differential stage, the power supply circuit. You would be able to see what is happening (using moving colored arrows) when different conditions occur. Such as when the amp is sitting idle and when the amp receives an input signal. Do you know of anything like this? It could also be done to show how components interact together or as a very basic introduction to a single component. Just curious about your thoughts on this.
 
First download my simulation files for the Quasi version, then also download the comp version. You need the spice library file that I only included in the quasi version. Then load either one into LtSpice and hit the run button. Click on a net to see the voltage plotted as if on a scope, over a component to see the current through it. Hover over a net and look in the lower left corner and it will give you the idle bias point with no signal input. The comp version is close enough to yours to get a detailed understanding of what is going on.
 
My current power supply filter caps are 17000uf 50v each. The original schematic calls for 6000uf 50v caps. Are 17000uf caps necessary, and if not, what is the lowest uf I could use without hurting the performance of the amp? I was thinking about replacing these as I am sure they must be over twenty years old.

I think it was Nelson who said on here that too much power supply capacitance is like having too much money - well said! The only issue is stressing the bridge rectifier and dimming your lights on power up if the power transformer is very stiff. If it has enough resistance then that will limit the peak current on initial startup.
 
Very nice thread. I have build an amp before but I'm interested in downloading the software and doing this project as well.
Has anyone built the amp? I would like to see some photos and build one myself!
This will be a very nice little amp, a true classic piece of history.
Well done by Mr. Pass.
 
Indipendent power supply

Hi,
Before chopping the PCB Tazz made with no return back, I would like some help to go in the right direction.

Many thanks and Happy 2017

Vito
 

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that show me a completely new perspective, I intended just sent cleanest power supply to the front end, but the FIRST WATT is the place to be !!!!
I've calculate the RC filter to not let drop the Voltage too much....
Thank you to take time to give a look if it's a good interpretation of your words!!!
 

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