SYMEF amplifier

[Nico Ras]

It is interesting that even at the massive amount of capacitance you say you have it is evident in the display that the square wave top and bottoms is not flat lines but is lower on the left that on the right, the higher frequency (middle) plot is better but still reveals a sag on the left.

It could also be an indication of you choice of input capacitor filtering the low frequency, try increasing it if you want to see if this is the problem.

Thanks for the pictures Routhun

 

[OnAudio]

Thank you all who have contributed your time, ideas, expertise and investment. We have many PCB ideas in this thread including Alexmm, Drowranger and this draft of the type 2 which I post for your scrutiny(the clean version has minor mods). I am hoping Terry will also share his new layout with us. All the best.

Comments very much welcome

 

[pinnocchio]

Thank you all who have contributed your time, ideas, expertise and investment. We have many PCB ideas in this thread including Alexmm, Drowranger and this draft of the type 2 which I post for your scrutiny(the clean version has minor mods). I am hoping Terry will also share his new layout with us. All the best.

Comments very much welcome

All I can ask for the new revision is that you first check the hole size with components before sending to fab. It was way too tight last time... Had to drill some and force components.

Thanks
Do

 

[OnAudio]

Thanks Pinnocchio. As you can see the holes for the input capacitor have been widened to accomodate bigger devices. The holes of the MUR120 have also been widened.

 

[pinnocchio]

Thanks Pinnocchio. As you can see the holes for the input capacitor have been widened to accomodate bigger devices. The holes of the MUR120 have also been widened.

Thanks!

 

[routhun]

One comment, with the power outputs located in the middle of the board, its very hard to mount them on the heatsink without access holes on the PCB.

Thanks,

 

[OnAudio]

Thank you Routhun. Yes this PCB is different, the power transistors, drivers, predrivers and bias transistor are all mounted under the board. They will first be mounted onto heat sink using a mounting document. Then the PCB shall be placed over them and soldered. Very compact. Measures 4 * 3.5. You could build a 7 channel amp with them

 

[bambadoo]

Slowly moving forward.. Doing som psu testing now...

I guess during the weekend sound will appear from some speakers.. Hopefully If my soldering skill has been up to the tast....

 

[OnAudio]

Hi Bambadoo, take your time Looking forward to your review.

 

[bambadoo]

Folks - I think we have a psu..
It consist of a 500v trannie. Encapsulated. Looks nice.. I only got hold of 35v secondaries.

Measures with no load 49vdc.. (a bit high but lets se how it goes. )

8 pcs. hfa08tb60 diodes. I couple of ampohm 0.0022 uf over each secondary and a couple of 7.5 ohm power resistors after rectification. I have to make some measurements when the amp is playing. Maybe these are unnecessary?

Yes and a couple of 2.2kohm bleeders.

 

[alex mm]

...... nice elco's , I think they are Elna Cerafine ......

 

[bambadoo]

They are.. Have had them for a long time no...

4pcs 18000uf - 63vdc. Sounded extremely good in an amp I made many years ago.

 

[OnAudio]

Folks - I think we have a psu..
It consist of a 500v trannie. Encapsulated. Looks nice.. I only got hold of 35v secondaries.

Measures with no load 49vdc.. (a bit high but lets se how it goes. )

8 pcs. hfa08tb60 diodes. I couple of ampohm 0.0022 uf over each secondary and a couple of 7.5 ohm power resistors after rectification. I have to make some measurements when the amp is playing. Maybe these are unnecessary?

Yes and a couple of 2.2kohm bleeders.

Almost there . I wonder what you will hear with the first few notes

 

[bambadoo]

Give me a couple of months and I will let you know

Beer now.. Cheers.. BTW.. The amp ready to be connected to speakers now for testing...

 

[OnAudio]

Connect the red wire to the red socket and the black wire to the black socket

 

[bambadoo]

Hehe - one channel playing That is one loudspeaker connected... Not my main speakers - yet...
So far so good... Extreme grip on the woofers....
Slight hum. Much more gain than my 300b amp..

I got 35Vdc on the rails... Will try to remove the power resistors in the psu..

 

[bambadoo]

Houston we have sound..

However with my main speakers (approx 97dB sensitive) the gain is just too much. I can barely touch the volume knob and it gets too loud.
I have to do something with that. Any suggestions?

Remenber I changed the input resistors some.. Not much but a bit..
And the input cap is 12uF.

Is it possible to bypass this BTW?

Soundwise - it got potential

Sorry about the really crappy pic..

I have not checked bias..
How to do this?

 

[OnAudio]

Thanks for the update Bambadoo. Cheers, you have first note ......Extreme grip on the woofers...

Is the slight hum gone ?

Tell me more about your preamp. The amp reaches full power with approximately 1.3 V input . Does your preamp have a sensitivity control ?

 

[bambadoo]

Yes I almost fainted when i played Lee Ritenour as the first note. Holy crap - I felt the bass note right in my guts..
No the slight hum is there but I am not so concerned about that. It is a cable mess right now

And how hot should the heatsinks be? I can barely touch it.. I guess a bit above 50 degrees C?

I an hear hum (some hiss) for approx 3m away.

My preamp is an Audio Note l3 line.. With hi-B output transformers... Slightly (read very) modified.

I guess it has more or less the same data as audio note m8 (since I use e80cc-6463) tubes ... And a 33:1 OPT after that..

Under is the data for AN M8
Gain @ 1kHz 18dB
Input Sensitivity (for 1V output) 126mV

My setup looks more or less like this. The QuadIIs are gone...

 

[OnAudio]

Thanks Bambadoo. Does your preamp have both a volume control and a sensitivity control ? What input voltage are you feeding the preamp ? It seems you will need to feed it that 126mV. If the preamp does not have a sensitivity control you will need an attenuator. Good job.