Dynacord Input Cards.

[hans a]

I had 4 cards from an Eminent 2 that i racked and tried to record with. The result was ok. I tracked my band jamming and while i got sound it lacked any depth.

I was wondering if it is a problem of the ouput section being not made as an output stage.. If someone would be willing to take a look at the schematic i would be happy.
Br H

 

[hans a]

Schematic.
To be clear. Im missing a bit of bass response..

 

[jensenmann]

You did rack the input card only? Where did you get your output signal from? 2a or 3a?

Assuming there´s no output stage added to these cards then both outputs have a way too high output impedance. You´d need at least an output driver circuit which can drive the input impedance of the next piece of gear.

 

[hans a]

So, i need an output transistor and an output resistor?
Is this whats called a current-to-voltage converter?
Br

 

[hans a]

Im pretty sure i took the output from 2a, and im pretty sure that i took it before the 220k resistor since it sounded louder to me.

 

[hans a]

Could i change the resistor value (from 220k) to something smaller, or will that mess with the circuit impedance?

 

[abbey road d enfer]

So, i need an output transistor and an output resistor?
Is this whats called a current-to-voltage converter?

No; it's a buffer. However you may not need it.
You could try replacing resistor R119 with a much lower value, like 1k. Then take the signal from it (point 2a). You should note a significant increase in level.
Lack of bass may also be a sign of electrolytic capacitors needing replacement (particularly C110, 114 & 115).

 

[hans a]

Thank you!
I will try this swapping R119.
Also the el caps are tantalum but i might not matter maybe?

I'll do some testing and report back if something sounds rad.

 

[abbey road d enfer]

Thank you!
I will try this swapping R119.
Also the el caps are tantalum but i might not matter maybe?

Tantalums usually don't loose capacitance, so that may not be the culprit.

 

[hans a]

I was wondering about maybe putting a transformer on the input. The inputs are quite sensitive.
I was thinking if i could go for a lundahl 1531 in 1:1 maybe. Or is there any benefit in 1.5:1 or something similar. Any loss in high end is ok. But any gain in bass would maybe be beneficial. Any qualified input maybe. These sound actually ok. The distortion is quite pleasing and they are bouncy and lively sounding in a way.

 

[abbey road d enfer]

I was wondering about maybe putting a transformer on the input. The inputs are quite sensitive.
I was thinking if i could go for a lundahl 1531 in 1:1 maybe. Or is there any benefit in 1.5:1 or something similar. Any loss in high end is ok. But any gain in bass would maybe be beneficial. Any qualified input maybe. These sound actually ok. The distortion is quite pleasing and they are bouncy and lively sounding in a way.

If you put anything that's more than 1:1, you may have headroom problems. Transformers will not help boosting bass, anyway.

 

[hans a]

Ok! Thanks
I added a resistor as proposed. At 100 Ohm i clipped at near 0 in Logic.
I had some 300 Ohm so i took those. The sound is actually ok.
But i still find the input a bit sensitive. Even for SM57. At half a full turn on the potentiometer there is distortion and hitting the roof. The gain is set after the first stage. Im thinking of putting a resistor on the input to change the sensitivity.

 

[abbey road d enfer]

Ok! Thanks
I added a resistor as proposed. At 100 Ohm i clipped at near 0 in Logic.
I had some 300 Ohm so i took those. The sound is actually ok.
But i still find the input a bit sensitive. Even for SM57. At half a full turn on the potentiometer there is distortion and hitting the roof. The gain is set after the first stage. Im thinking of putting a resistor on the input to change the sensitivity.

According to the schemo, the potentiometer is a dual that controls both the input gain and the output level. The input section has a gain of about 32dB; it should be capable of handling an SM57 in most circumstances. However, the output section has also 24 dB gain. So the total gain here is close to 60dB. An SM57 delivering its nominal level of 1.9mV will result in 1.9V at the output of the second stage, but in common usage (close vocals, snare drums), an SM57 delivers about 10 times that, which puts the output close to the maximum possible output level.
Now, if you add the output stage, that has about 23dB gain, the overall gain is close to 80dB. So something must be turned down. I would think with the pot at mid-rotation the overall gain would be about 40dB, which is correct for handling a dynamic mic.

 

[hans a]

Ok! Thanks for explaining I will look at the schem and see if theres a place to start looking at around the second stage. I tracked some drums, and did some a/b with my interface (d-pre), there was more high end on the Steinberg but thats ok.

Ok, yes, ive mostly pushed it with drums and some yelling into the mic since i found it distortion. Maybe some normal tracking to see if they are useful (with some a/b with the interface to see whats missing in the lowend)

 

[hans a]

Took a look at it. I have only basic understanding of the concepts. But if the second stage is to blame for 'overloading' the output stage maybe one could increase the 330 Ohm emitter resistor. Maybe it would make for asymetric clipping and if so adjust the collector resistor also. But is there also a feedback resistor that one could increase?
Another thinking was to adjust the output decoupling capacitor to increase impedance but that was some chancely thoughts. Dont know if it works.
I think the second part of the first dual potentiometer is a kind of attenuator that the whole Eminent used as an AUX tap. Not sure tho.
Br H

 

[abbey road d enfer]

Took a look at it. I have only basic understanding of the concepts. But if the second stage is to blame for 'overloading' the output stage maybe one could increase the 330 Ohm emitter resistor. Maybe it would make for asymetric clipping and if so adjust the collector resistor also.

You don't have to do that.
We didn't discuss it but I assumed that you have the connection between the negative pole of C102 and ground, as indicated on the schemo.
Actually gain can be adjusted there. Inserting a 1.2k resistor results in10dB less gain, open circuit in 25dB less gain.

Another thinking was to adjust the output decoupling capacitor to increase impedance but that was some chancely thoughts. Dont know if it works.

Certainly not. That would introduce errors in frequency response that you don't want (less bass).

 

[hans a]

Thank you for the explanation once again. I will have to check that connection. And also try with a resistor. Br H