Expensive signal caps extinguish bass?

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FlexQ

FlexQ

Member
Joined 2008
Hi Guys

Im just here for a fast question.

I have build the first part of a pa150W gainclone.

Noninverted with 20x amplification, 10k input resistance, and this little bugger.

http://img23.imageshack.us/img23/5669/dsc01243r.jpg

However, when it is mounted, the bass sems to be gone - and not out in the loudspeaker, unfortunetly.

So my question is, how can that be?

I tried just as a test to use a 1uF wima cap, it doesent sound good, but it has all the bass that the Jensen cap seems to have lost.

Hope someone can give an explanation.

FlexQ
 
FlexQ

FlexQ

Member
Joined 2008
Nuuk said:
0.7uF is too small a value. It is obviously forming a high-pass filter with the input resistor. Try using at least 2.2uF. ;)
Click to expand...

With 10k input resistance it should form a highpass filter at 22Hz.


Dr.EM said:
Yes, just parrallel it with your 1uF WIMA cap, should do fine:)
Click to expand...

I will tryk that, will return when tested :).

Btw, the cap is made for tact audio, has been sitting in the input of a pre amp at the cost of around 20.000$ :p.
 
FlexQ

FlexQ

Member
Joined 2008
pacificblue said:

Right. -3 dB at 22 Hz and attenuating up to 110 Hz. Do you use Ci? Tuned to what frequency? How do those two filters add up?


Maybe. What was the input resistance of that Tact Audio preamp?
Click to expand...


There was 2 flaws in my theory ;P

the first one was me thinking i knew all about that circuit, and the second that this cap is used in another type of circuit.

So right now i am using another cap ;)

It sounds good, all three amps playing right now.

I am currently playing it up against NAD 214, and it suck quite a bit in relation to detail - but it has a tighter bass. But that could be because of that input-cap.

any suggestions to which i could use instead of?

FlexQ

EDIT: Here is what happens when one doesent have a place to work ..... dinnertable-invasion ;).

http://img223.imageshack.us/img223/3269/image063.jpg

And of the pride:p

http://img10.imageshack.us/img10/5996/image064r.jpg
 
FlexQ

FlexQ

Member
Joined 2008
analog_sa said:
FlexQ

The fact that a capacitor is expensive or used in expensive equipment means very little. Is it properly broken in? Still, is it very difficult to raise the input impedance to 100k? Assuming it's a non-inverting amp.
Click to expand...

I will try it as soon i come home :).

AndrewT said:
if your input impedance (Zin) is 10k then I would suggest you try >=9uF as the DC blocking cap to hear what it sounds like.
Click to expand...

I might have one lying around, i will try it :)


pacificblue said:
Original heatsinks.
Click to expand...

yeah, did not have any heatsinks so i just used what i had lying around. Not quite enough, but fine for testing purposes :)

Does any of you have any suggestions to what type of DC blocking cap i might use?

Thanks
 
FlexQ

FlexQ

Member
Joined 2008
Brainfart ... just sat at my desk at work, and suddenly i realised what i have been doing.

The circuit is the same. However, i didnt have any 200k resistors so i used 1k/20k to set the amplification.

But, if you use such low resistor value, it will cut way up in the middleband.

So, i got my hands on some 10k and some 200k, and my 0.7uF jensen cap suddenly worked fine ;).

I forgot all about the virtual ground the signal sees into from the input.

at the in+ and in- there will always be a virtual ground. So in relation to the signal the input/gain resistor has a he*k of alot to say.

So i solved my own problem, it took some time, but it came :p.

Now it is playing just about fantastic. So tomorrow i am going to start burnin :D ... :hot: :hot: :hot: :hot: :hot: :hot: :hot:

Have a nice evening guys.
 
A

AndrewT

R.I.P.
Joined 2004
Hi,
an inverting topology, with negative feedback, uses the series input resistor as the Zin to the virtual earth point at the -ve input pin.

A non inverting topology has a very high input impedance and Zin is set by the resistor from +ve input to ground that carries the input offset current and allows the amp/opamp to work properly. The +ve input pin is not a virtual earth.
 
FlexQ

FlexQ

Member
Joined 2008
AndrewT said:
Hi,
an inverting topology, with negative feedback, uses the series input resistor as the Zin to the virtual earth point at the -ve input pin.

A non inverting topology has a very high input impedance and Zin is set by the resistor from +ve input to ground that carries the input offset current and allows the amp/opamp to work properly. The +ve input pin is not a virtual earth.
Click to expand...

Exactly, and i am using the inverting input as input ;)
 
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