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MBK 9th April 2007 05:54 PM

Symasym 5.3 "AAK model" builder's thread
Welcome! This thread is for all those who bought the PCB for Mike Bittner's Symasym 5.3, this PCB model designed and tested by "AAK", and organized / produced by "Ryssen". AAK's design implements several incremental changes, most notably very linear Toshiba output transistors (and drivers), a change also rcommended by Pavel Macura (PMA), and 50V rails instead of 36V. All this is done in a compact PCB design of 5x3", intended to mount on top of a 4x5" heatsink.

It is for all discussion related to the actual building process: BOM, components, modifications, testing, functionality, and eventually, one might hope, sound quality :D

Related threads and posts:

PCB group buy , with all PCB related complementary info in the first post of the thread. This round of the GB is closed, but another round may be forthcoming if interest keeps coming in strong.

AAK's design

Mike Bittner's original design

Pavel Macura's review and technical recommendations

Ryssen 9th April 2007 09:04 PM

I asked Ender Hoffman (roender) about changing the 2 input transistors to j-fets,and that shouldnīt be a problem.
Schema j-fet
Might be a problem if you use 2x50v DC though,as it says max 40v in the data sheet:Datasheet 2SK170 I donīt know how much voltage is over the j-fet .
Anyone know of a substitute?

mlloyd1 9th April 2007 09:59 PM


i don't know any conventional jfets that could be used "bareback" with 50v rails. however, there are some power jfets that several folks have been happily experimenting with, stimulated by a nelson pass project. sorry, i don't remember the drain-source voltage limitation of this device. also don't know how suitable it would be as an input device (have to check device capacitances, transconductance, etc.)

but even dropping the rails lower (for example) to 40v, for the 2sk170, reputable designers on this board strongly recommend cascoding to keep the drain-source voltage in the 10-15 volt range. the issues with not doing so would show in a search, i think.


Ryssen 9th April 2007 10:24 PM

They are I have a few of them. They only take 24v and input C is 1147pf compared to 2SK170 30pf.You mean to cascode with the LD1014?
The thing is,if I start to experiment with this they will probably blow up before I have switched the power on.. :xeye:
Never done such a thing.
And Iīm thinking of using 2x50v DC,maybee a little lower if I find such a transformer.

Ryssen 9th April 2007 10:44 PM

Here is sommething that looks like what Iīm searching for:
It is from Symasym Roender style
Maye it works,will se how much it differs from the orig schema.
Edit:Quite much...:scared: :scratch2:

Ryssen 9th April 2007 11:37 PM

This one can take 50v and has even lower input C 2SK117


pinkmouse 9th April 2007 11:40 PM

A link to the BOM would be handy. ;)

Ryssen 10th April 2007 12:50 AM

Cascoded input stage..


MBK 10th April 2007 03:40 AM

BOM link for AAK model

MBK 10th April 2007 04:13 AM

Some questions about the BOM
Due to the higher rails, and some design choices, some resistor values differ from the original Symasym. In some cases the reason was clearly given by AAK, in some I am not so sure whether the changes are a must, or if there is some flexibility. Here is a summary comparing component values other than the transistors, between Symasym 5.3 original ("5.3") and "AAK" BOM:

- base stoppers: R1, R3 AAK: 10R (5.3:1.2R); R8, R9 AAK: 100R (5.3: 22R). In the sequel thread, Mike Bittner said he used 22R for "speed issues", and AAK justified these values because they are like in the AKSA and other reputed amps. Is there a definitive answer to this question?

- thermal transistor T1 (BD139): R22 AAK 100R, 5.3: 470R; R23 AAK: 1k, 5.3: 2k; R24 AAK: 316R, 5.3: 499R. I would like to know whether this change has anything to do with the higher rails, or whether it was simply more convenient. I will be using pretty much AAK's BOM but with 36V rails only, so I'd like to know which combo is better for this case, the 5.3 values or the AAK values.

- R26 AAK: 150R necessary for thermal stability, 5.3: 33R

- output zobel: C18: AAK not in BOM but exists on PCB, 5.3: 47nF; R4: AAK 10R, 5.3: 4R7. I suppose the point is to maintain the same corner frequency, which would put the AAK C18 at 22nF.

- output inductor: AAK none, 5.3: 10R // a dozen windings of 0.6mm dia magnet wire around it. Optional?

- ground link R2 AAK: cannot find R2 on BOM and PCB, 5.3: 10R.
Is IGND and AGND tied or separate on the AAK PCB?

- emitter resistors for the input diff pair if reduced gain desired by increasing R30 to 1k: AAK: not on PCB, 5.3: R16, R19.

Additional comments that may be useful:

Pavel Macura, using the same output transistors as AAK, recommends C14 at 3.3pF and setting Iq at 150 mA for minimum distortion. He also used 220pF for C3, C4 (AAK and 5.3: 330 pF) and 0R15 for R27, R28 (AAK, 5.3: 0R2).

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