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Old 3rd September 2013, 05:27 AM   #741
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Ryan, I have sent you the LTSpice - model of the SYMASYM per EMail.
Maybe it can assist debugging your problem.

Best regards - Rudi_Ratlos
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Old 3rd September 2013, 09:38 PM   #742
potepuh is offline potepuh  Slovenia
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Some weeks ago I finished my SYMASIM amp. Still to finish the case but it sounds superb... It is a litlle diferent the power suply is +-43V, the zeners are 39V and for CAP multiplier i used BD139/140. Bias procedure was easy 2SK 170BL matched 10mA. MP1-MP2 24,0mV, DC offset 0,2mV and 0,3mV.

Then I soldered the second pair and enjoyed the music...

I noticed that the amp is running a bit hot, ok its summer the room temp was 28C....

Yesterday I separate my test heatsink and noticed that one chanel is much hoter. 57C on mosfets and 49c on the heatsink, the other 43C mosfet, heatsink 37C. today I measure again the MP1-MP2 points on the hoter chanel I have 49,5mV and the colder 39,6mV, Dc offset is 0,3mV on the hoter and 0,2mV on the colder. the amps idles around 280mA the hoter and 220mA the colder. Input is shorted when I measure.

Do I have to readjusted the trimpot again?
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Old 4th September 2013, 02:36 AM   #743
RKH is offline RKH  United States
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Default Ooops update #1

Reminder of the problem: I had loud static output after returning to my amp whilst letting it play unattended. I wasn't around when things went awry.

Here are some of the measurements I made:

As a precaution, I checked that there were no shorts between transistors and the heatsink. All was fine.

So then I powered up the PSU...
- Rails:+/- 38 VDC (unloaded, my mains fluctuates a lot, and my rails are in the 37-38+ range). I have +/- 25VAC primary transformer.

Then I powered the Amp board:
With input grounded:
- Vtp1 to Vtp2 is 24 mV
- Vdc across output 18 mV

Any ideas? Is it possible that because of my higher rail voltage, the front end regulation was toasted?

I have Rudi's LTSpice sim (Thanks Rudi!) , but I do not have an immediately easy way to run it. So, I don't have voltages to check yet.

Thanks
Ryan

PS: Yes, I have tested the amp with another pre-amp and set of speakers, so I know that the problem resides with the amp.
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Old 4th September 2013, 02:42 AM   #744
RKH is offline RKH  United States
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In a previous post, I believe Rudi suggests to re-set the bias after adding the second set of output transistors. In my case (TO-3) I found that I needed to adjust the bias a little bit... on the order of a couple of mV, after adding the second set of TO-3s. Nothing dramatic.

If I am incorrect or have mis-understood, please let me know.

Quote:
Originally Posted by potepuh View Post
Some weeks ago I finished my SYMASIM amp. Still to finish the case but it sounds superb... It is a litlle diferent the power suply is +-43V, the zeners are 39V and for CAP multiplier i used BD139/140. Bias procedure was easy 2SK 170BL matched 10mA. MP1-MP2 24,0mV, DC offset 0,2mV and 0,3mV.

Then I soldered the second pair and enjoyed the music...

I noticed that the amp is running a bit hot, ok its summer the room temp was 28C....

Yesterday I separate my test heatsink and noticed that one chanel is much hoter. 57C on mosfets and 49c on the heatsink, the other 43C mosfet, heatsink 37C. today I measure again the MP1-MP2 points on the hoter chanel I have 49,5mV and the colder 39,6mV, Dc offset is 0,3mV on the hoter and 0,2mV on the colder. the amps idles around 280mA the hoter and 220mA the colder. Input is shorted when I measure.

Do I have to readjusted the trimpot again?
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Old 4th September 2013, 06:54 AM   #745
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Ryan, if you have activated the onboard-CAP-multiplier (if you did not set the jumper-cap), the zener diode delimits
the frontend-voltage to 36VDC. You need not worry then.
Moreover: 38VDC is not a voltage to worry about.

I recommended to adjust the quiescent current / BIAS with only one MJ21196 / MJ21195 being soldered to minimize the dammage,
in case you have done a error while soldering the PCB.
It is then required to do the adjustment once more, after you have soldered the 2nd pair of MJ21196 / MJ21195.

The usage of LTSpice is very simple. Download the current version, open the SYMASYM.asc file that I sent you,
and then click on the icon "RUN" on the toolbar.
Position the cursor on any component / track on the schematics and click to plot the voltage, amount of current, ...

According to my experience a crackling noise has to do some with a mechanical error (f.e. a short between the ALU profile
and the output transistors, something getting hot after a while, ...).

I hope that you are able to find the error.

Best regards - Rudi_Ratlos
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Old 9th September 2013, 06:54 AM   #746
yoyoy is offline yoyoy  Philippines
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HI,

im planning to build a bass amplifier(with 2x8" speaker), and i saw this thread, reading all the post i think this is a good amplifier, but now im not sure if i can use it to my bass guitar, and it does not have a pre amp...

can i use a 24-0-24 trnasformer?

and also i cant understand the different kinds of capacitor that was use in the symasym,
thats why im confused to which should i use...
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Old 9th September 2013, 03:26 PM   #747
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Yoyoy, I do not know the requirements that a bass guitar amplifier must have.
The SYMASYM is a Class A/B amplifier, and it does not have a pre-amplifier onboard.

About capacitors: there have been some questions about the value of the input capacitor C1.
The job of C1 is to block DC voltage. You can take any value from 3.3F - 10F for C1.

You can of course use your 24VAC - 0 - 24VAC transformer.

Best regards - Rudi
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Old 9th September 2013, 07:18 PM   #748
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Default Previous version PCB's for the TO-3 SYMASYM

Does anyone have two or more of the previous version of the TO-3 SYMASYM
PCB's. I missed the last group buy. Let me know.
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Old 11th September 2013, 08:36 AM   #749
dadod is offline dadod  Croatia
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Quote:
Originally Posted by Rudi_Ratlos View Post
@mcds: the PCB-layout already includes CAP-multipliers to provide smooth and stable voltages for the frontend, and the CAP-multipliers
are doing a very good job.
@Rephil: I measured my TO3s with a collector current of 100mA (adjusted by the CCS of my test-rig).
The main function of the input capacitor is to block DC voltage.
I myself am using a 3.3F Vishay MKT.

Best regards - Rudi_Ratlos
Rudi, strictly speaking this is not cap multiplier but a regulator with no feed back and with stable utput voltage. A cap multiplier output follows slow changes of the input voltage.
BR Damir
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Old 11th September 2013, 09:25 AM   #750
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You are of course right, Damir.
I am using a very simplistic implementation of a CAP-Multiplier.

It has 2 jobs to do:

- 1st: to generate a smooth and stable frontend voltage (and it does this quite well - but can even be made better, f.e. by a shunt)
- 2nd: to restrict the frontend voltage to +/- 36 VDC to not destroy your preciously matched differential input amplifier (f.e. 2SK170)

I am currently thinking about adding a "cross-distortion minimizer" (Douglas Self calls this: "XD - Technology" (Chapter 11 of his amplifier - cookbook).

I know that he has a patent pending upon his idea.
If any moderator is reading this post: may I talk about this improvement (?) in plain text or am I not allowed?

Best regards - Rudi_Ratlos
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