Poor Man's Pultec EQP1-A Build Support Thread

[ruffrecords]

Thanks Ian.
Im really impressed by the sound of this project.

Just tried a female vocal track and it just shines!

however tried a BYPASS switch and it really needs a PAD.

One more question do you think its a good idea to make the Hi section or Low section switchable??

Here's a pic of the recommended way of doing a bypass, including the required pad.

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/EQSystem.png

The 470K pot is just one way of setting the overall gain to unity. You can change the gain of the make up amp. In your schematic you asked about the cap across the 470K. You don't need one.

Can you clarify what you mean by making the hi or lo section switchable? Do you mean changing the pots for switch pots or do you want to switch the hi or lo section in or out?

Cheers

Ian

 

[3nity]

no i meant just to be able to bypass the low section or the hi section?

 

[JohnWatkins]

The peak at 20Hz looks like it might possibly be the resonance of the output capacitor with the primary inductance of the transformer

I'll have some time this afternoon to work on this.  Is there a recommended remedy?

Thanks, John

 

[ruffrecords]

The peak at 20Hz looks like it might possibly be the resonance of the output capacitor with the primary inductance of the transformer

I'll have some time this afternoon to work on this.  Is there a recommended remedy?

Thanks, John

Depends on the transformer but you either try to move the peak below the audio band  by increasing the outout capacitor or make the peak smaller by lowering the Q of the resonance by adding a series resistor. Which transformer are you using?

Cheers

Ian

 

[JohnWatkins]

The transformer is an Antek AS-05T240.  I believe Dave Wheeler used the same one.  I wonder if he's had this issue.

 

[ruffrecords]

The transformer is an Antek AS-05T240.  I believe Dave Wheeler used the same one.  I wonder if he's had this issue.

Sorry, I meant the output transformer not the power transformer.

Cheers

Ian

 

[JohnWatkins]

Oh, sorry.  It's the Sowter that was recommended.

 

[ruffrecords]

Oh, sorry.  It's the Sowter that was recommended.

No problem. That probably explains the 3dB bump around 20Hz. If you are using both the 4.7uF output caps and the transformer primary inductance is about 10 Henries then the resonance is around 16Hz. The simplest solution is to increase the output cap to say 47uF. Try a 47uF 400V electolytic. That will move the resonance well below 10Hz by which time the amplifier output will be falling off rapidly anyway. Another solution is to use a 10K:10K transformer instead which will raise the inductance and lower the resonance. A third alternative is to use the output unbalanced.

To be honest, this amplifier stage was never designed to drive a transformer which is why I have always said not to load it with less than 10K.

Cheers

Ian

 

[JohnWatkins]

Got it.  Thanks for the tips and explanation.  I've got it racked up for a project now, but I'll try those solutions at the next opportunity. 

 

[ruffrecords]

Got it.  Thanks for the tips and explanation.  I've got it racked up for a project now, but I'll try those solutions at the next opportunity.

I still don't know what is causing the apparent HF drop off.

Cheers

Ian

 

[JohnWatkins]

I decided to live with it and just compensate by giving it a little bump all the time in that range.  It's only a db and a half and goodness knows I'm not going to run out of boost capability.  Trying to strike a balance between learning as much as I can as I go and not spending a year on one project.  Gotta move on at some point. 

 

[ForthMonkey]

Is this possible to use something like this for gain stage?

http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323

 

[ruffrecords]

Is this possible to use something like this for gain stage?

http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323

Unfortunately this will not work. It is a simple stereo cathode follower so it has unity gain and we need a good 20dB of gain for the EQ.

Cheers

Ian

 

[ForthMonkey]

Is this possible to use something like this for gain stage?

http://www.ebay.com/itm/Tube-6N3-Buffer-Audio-Preamplifier-kit-Pre-AMP-AMP-kit-DIY-/130814272291?pt=US_Amplifier_Parts_Components&hash=item1e75236323

Unfortunately this will not work. It is a simple stereo cathode follower so it has unity gain and we need a good 20dB of gain for the EQ.

Cheers

Ian

Thank for reply.

 

[dirtyhanfri]

Hi

I´d like to add 2 mid bands to my first Poor man´s build, my holidays gift, and when searched for the Chrion´s thread selling the Inductors It´s just gone!

Where can I get inductors suitable for this project?

 

[ruffrecords]

Hi

I´d like to add 2 mid bands to my first Poor man´s build, my holidays gift, and when searched for the Chrion´s thread selling the Inductors It´s just gone!

Where can I get inductors suitable for this project?

I have no idea what has happened to Chrion. Anybody?

The poor man's mid was designed to use Carnhill inductors. There is an error on the PCB that means some tracks need to be cut and links added for them to work. The document describing the frequencies you can get with each inductor type is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/PMmidfeb12.pdf

and the document describing how to do the inductor fix is here:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/PMEQP1A/MIDPCBfixv2.pdf

Cheers

Ian

 

[dirtyhanfri]

Great! Thanks for the answer, I'll start looking them

 

[ilfungo]

Hi
I'm working on  a P2P Redd47 and I want to ad a poor man's mid in same case as a Channel strip.
Which transformer can I use between Redd 47 out and poor man's mid in?
I can insert the eq at some point of the channel, rather than later?
THANKS!!!

 

[ruffrecords]

Hi
I'm working on  a P2P Redd47 and I want to ad a poor man's mid in same case as a Channel strip.
Which transformer can I use between Redd 47 out and poor man's mid in?
I can insert the eq at some point of the channel, rather than later?
THANKS!!!

The short answer is yes you can insert it in part of the chain but you need to add another stage of amplification. This was discussed in detail on one of the REDD 47 threads but I cannot remember which one.

Cheers

Ian

 

[mikeyB]

Hi Ian - can the poorman make up amp be used with a standard pultec filter network - ie 600ohm.
someone is asking me if i can convert a diy chip amp to a tube output, but want to leave the filter circuit (based on the original) intact.
Wil the tube makeup circuit work ok with the original filter impedance?

Thanks in advance