Paralleled EF86 mic preamps + opamap as input buffer all sound the same??

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renx

Well-known member
Joined
Jan 3, 2007
Messages
59
Location
Zagreb, Croatia
Hi to all,

I have designed a modular microphone which some of you may have seen here:

http://www.groupdiy.com/index.php?topic=44121.msg551606#msg551606

It is a mic in which you can exchange output transformers and a solid state module to get different sounds.

Then I wanted to design a mic which will have these three sounds simultaneously available as its outputs.
And So I did design and built it, but there was something very strange, at least to me - all of the outputs sounded exactly the same.

What I did was, I put the opamp balanced driver after the transducers biasing circuitry to transport the "untouched" signal to the PSU where I placed the opamp de-balancer.
The de-balanced signal was then sent to to two different EF86 preamps (different only by their output transformer) which were both buffered with opamps, and the same de-balanced signal was also sent to a opamp output buffer.
Everything is working nicely, beautiful sound, except all outputs sound the same, exactly the same.
When the ef86 preamps were connected to the transducer biasing circuit directly with no opamps in the middle the difference in sound was VERY evident.
I suspect that something is missing on the input of the ef86.

Here is the schematic:



schematic in pdf

http://www.mediafire.com/file/7zbgsp85sl7u8g7/s1.pdf

Any thoughts are very welcome.

Regards, Renx.
 
Well what about output transformer? Doesn't the output transformer have any influence on the sound especially in combination with the tube?
I am basically feeding the same signal to the same amps, but no difference even compared to the pure solid state output.

Regards, Renx.
 
It doesn't surprise me that the big change in sound is capsule connected to tube grid vs. capsule connected to opamp input
 
renx said:
Well what about output transformer? Doesn't the output transformer have any influence on the sound especially in combination with the tube?
I am basically feeding the same signal to the same amps, but no difference even compared to the pure solid state output.

Regards, Renx.
Have you made actual measurements? They may sound identical to you, but you may find that performance at high level and extreme frequencies may be different. If your auditive tests have been conducted with "average" signals, it is not a surprise they sound similar.
 
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