Poor Man's Pultec EQP1-A Build Support Thread

[ruffrecords]

I see...It can't drive transformer.

A properly designed DRPP will drive a transformer but the circuit you posted with a 24V supply most likely will not.

OK.I have last question.

Is this possible impedance balancing with this circuit?

It should  possible be but to do this you first need to know the output impedance of the circuit.

Cheers

Ian

 

[ForthMonkey]

There is SRPP out impedance calculator.But i can't understand.

https://dl.dropboxusercontent.com/u/91809016/SRPP.xls

In my circuit

Rk=300 ohm
RL=100K

I have no idea other values.

Or is there any way to calculate SRPP out impedance?

 

[ruffrecords]

Difficult to say anything about the spreadsheet without any accompanying explanation. Where did you find it?

What it does show is that output impedance gets lower as gm gets higher. Higher gm occurs at higher currents. Your circuit with its low HT inevitably results in low current which means a relatively high output impedance.

I know you have been using spice. Spice can be used to simulate output impedance by feeding an ac voltage source into the output and measuring the resulting current. The output impedance is the voltage divided by the current.

Cheers

Ian

 

[ForthMonkey]

Difficult to say anything about the spreadsheet without any accompanying explanation. Where did you find it?

What it does show is that output impedance gets lower as gm gets higher. Higher gm occurs at higher currents. Your circuit with its low HT inevitably results in low current which means a relatively high output impedance.

I know you have been using spice. Spice can be used to simulate output impedance by feeding an ac voltage source into the output and measuring the resulting current. The output impedance is the voltage divided by the current.

Cheers

Ian

I don't remember that where did i found it.

But...

I used a way to find output impedance.

"I'm estimating output impedance of nodes by attaching an AC 1A current source to the node of interest, and conducting a small signal AC analysis to see what voltage is produced.  By Ohm's law, the voltage at that node in V corresponds to the impedance in ohms."

There is a way.He says like this.

http://wombatamps.blogspot.com.tr/2011/11/on-output-impedence-of-cathodyne-phase.html

When i try this,i'm getting this result.Output impedance is 2K...

http://i.hizliresim.com/BRDE2g.png

Did i do right?

 

[ruffrecords]

That looks good to me but R2 contributes 470 ohms of the output impedance so I would try it afain without R2.

Cheers

Ian

 

[ForthMonkey]

That looks good to me but R2 contributes 470 ohms of the output impedance so I would try it afain without R2.

Cheers

Ian

Thanks in advice!

I remove R2.Now result is 1.5K.Is this okay?Can i make impedance balancing?And how?Cause there is no series resistor to output.

But i think i need to add 1.5K resistor cold pin to ground.

 

[ruffrecords]

But i think i need to add 1.5K resistor cold pin to ground.

Correct.

Cheers

Ian

 

[ForthMonkey]

But i think i need to add 1.5K resistor cold pin to ground.

Correct.

Cheers

Ian

Big thanks!

Now i will use only 10K:10K input transformer. Or 600:600?

 

[ruffrecords]

X

Now i will use only 10K:10K input transformer. Or 600:600?

I recommend using a 10K:10K input transformer.

Cheers

Ian

 

[ForthMonkey]

By the way i'm building solid state gain stage like Lang PEQ-2.Actually it's different but it's based Lang.

You can check...

http://groupdiy.com/index.php?topic=58126.msg739932#msg739932

 

[G-Sun]

Could I easy combine the EzTubeMixer preampsection with the PMEQP1A with the mid boost/cut in one unit?

 

[ruffrecords]

Could I easy combine the EzTubeMixer preampsection with the PMEQP1A with the mid boost/cut in one unit?

Yes. The 3 band Pultec PCB is pretty much exactly the PMEQP1A with a mid band on one PCB (with different switches) and is designed to be used with the EZTubeMixer preamps.

Cheers

Ian

 

[G-Sun]

Yes. The 3 band Pultec PCB is pretty much exactly the PMEQP1A with a mid band on one PCB (with different switches) and is designed to be used with the EZTubeMixer preamps.

Thanks! How would I typical mount the pcbs in such a build?
The preamp vertical, the others on the case bottom (horizontal) in a 3U case for one channel?

 

[ruffrecords]

Yes. The 3 band Pultec PCB is pretty much exactly the PMEQP1A with a mid band on one PCB (with different switches) and is designed to be used with the EZTubeMixer preamps.

Thanks! How would I typical mount the pcbs in such a build?
The preamp vertical, the others on the case bottom (horizontal) in a 3U case for one channel?

Most of the rack mounted builds using the EZTubeMixer that I have seen have  the preamp have it mounted horizontally. Easier to trouble shoot that way but there is reason you cannot mount it vertically in a 3U case.

The poor man's EQP1A and mid  board mount directly to the front panel via the  switches on them.

Cheers

Ian

 

[G-Sun]

Most of the rack mounted builds using the EZTubeMixer that I have seen have  the preamp have it mounted horizontally. Easier to trouble shoot that way but there is reason you cannot mount it vertically in a 3U case.

The poor man's EQP1A and mid  board mount directly to the front panel via the  switches on them.

Thanks! And then it's the makup-gain after the pulteq, right?

 

[ruffrecords]

Thanks! And then it's the makup-gain after the pulteq, right?

That's right and a 10k:10k transformer at the input.

If you are doing a pair of EQs in one box then you could use the twin line amp card for gain make up. It has two amps and positions on the PCB for two input transformers.

Cheers

Ian

 

[G-Sun]

That's right and a 10k:10k transformer at the input.

If you are doing a pair of EQs in one box then you could use the twin line amp card for gain make up. It has two amps and positions on the PCB for two input transformers.

Ok,  are (2ch) 2x preamp 2x PM Pulteq with mid doable in a 3U case?
And output-transformers are needed, right?

Thanks!

 

[ruffrecords]

That's right and a 10k:10k transformer at the input.

If you are doing a pair of EQs in one box then you could use the twin line amp card for gain make up. It has two amps and positions on the PCB for two input transformers.

Ok,  are (2ch) 2x preamp 2x PM Pulteq with mid doable in a 3U case?
And output-transformers are needed, right?

Thanks!

Yes they are.

Cheers

Ian

 

[ilfungo]

Hi
I need just some suggestion...
I've inserted the eq without make up gain and without transformers in Pro Tools track and all is ok ( I think).
My noise in pro tools with this configuration is -94db
Is this ok?
But, when I use makeup gain ( tube or ic's version) my noise go up to -65  ( no transformer) I want to use it on my amek m2000 ( unbalanced input)
I've cheked all the connection and tried all  but with no luck
It's normal this noise level?
THANKS!!!.... ???

 

[ruffrecords]

Hi
I need just some suggestion...
I've inserted the eq without make up gain and without transformers in Pro Tools track and all is ok ( I think).
My noise in pro tools with this configuration is -94db
Is this ok?
But, when I use makeup gain ( tube or ic's version) my noise go up to -65  ( no transformer) I want to use it on my amek m2000 ( unbalanced input)
I've cheked all the connection and tried all  but with no luck
It's normal this noise level?
THANKS!!!.... ???

The PMEQP1A needs to be fed into a high impedance. Pro tools will probably load it with 10K which is far too low but does explain why the noise is low.

With a tube or semiconductor gain make up you should achieve an output noise level much better than -65dBu. The EQ needs to be built into a screened box and screened cabling needs to be used as indicated in the hook up diagrams in the documentation. If you do this the noise should be much lower.

Cheers

ian