Poor Man's Pultec EQP1-A Build Support Thread

[ruffrecords]

Love the logo!!!!

Cheers

Ian

 

[kante1603]

...and I love chickenheads!

Congrats,have fun mixing with it!

Udo.

 

[dirtyhanfri]

...and I love chickenheads!

Congrats,have fun mixing with it!

Udo.

Love the logo!!!!

Cheers

Ian

Thanks to both, some friends use to call me Cheaper for it's english meaning (long story ) and I decided to use it for my buildings

For sure, I'm having lot of fun with it

 

[funkymonksf]

Ian,
I accidentally ordered 4x 470uf 400v caps for the tube gain stage PSU. Apparently I should of ordered 220uf. Will it have a significant effect if I use the 470uf caps or should I just order 4x220uf caps?

Thanks,
Brice

 

[ruffrecords]

Ian,
I accidentally ordered 4x 470uf 400v caps for the tube gain stage PSU. Apparently I should of ordered 220uf. Will it have a significant effect if I use the 470uf caps or should I just order 4x220uf caps?

Thanks,
Brice

They will be fine. The original design of that PSU uses 470uF caps but that has enough smoothing to power an entire mixer. That's why I reduced the values to 220uF for the EQ as it only uses a couple of tubes. All it means it your HT will be even smoother than usual. You may well find that when you switch it off, the HT takes quite a long time to discharge (through the heater elevation resistors). Just be aware of this whilst you are constructing it else you might get a shock from the charge stored in the capacitors.

Cheers

Ian

 

[rmaier]

...and I love chickenheads!

Congrats,have fun mixing with it!

Udo.

Love the logo!!!!

Cheers

Ian

Thanks to both, some friends use to call me Cheaper for it's english meaning (long story ) and I decided to use it for my buildings

For sure, I'm having lot of fun with it

Very cool build! I really like the look of the logo and labels. How were they done?

Ralph

 

[funkymonksf]

I had a feeling it'd be okay but I never would take a chance with such a high voltage PSU or any PSU for that matter! Thanks Ian for the quick response. As soon as get my omeg pots from Germany I can finish this thing!

-Brice

 

[dirtyhanfri]

Very cool build! I really like the look of the logo and labels. How were they done?

Ralph

It's all photoshop work printed in a vinyl sticker. Cheap and nice.

 

[ruffrecords]

Very cool build! I really like the look of the logo and labels. How were they done?

Ralph

It's all photoshop work printed in a vinyl sticker. Cheap and nice.

Do you use those vinyl stickers you can get in A4 sheets and print onto in a regular ink jet printer?

Cheers

Ian

 

[dirtyhanfri]

No, I get it done with a plotter in a artwork shop

 

[ruffrecords]

Chicago Dave has kindly donated his colour 3D hook up diagrams for the poor mans EQP1A and also for the mid cut/boost mod. I have added them to the first post in this thread:

http://www.groupdiy.com/index.php?topic=44213.msg553036#msg553036

but the are also now on my mini web site along with all the other documentation for this project here:

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

Thanks Dave.

Cheers

Ian

 

[funkymonksf]

Great work Dave! You made it almost too easy!

 

[wave]

It's my pleasure to help out! I think Ian deserves all the credit. he has given us  a great project.
Now if I could just get the rest of my parts...

Dave

 

[dirtyhanfri]

Hi

I realised yesterday that my unit doesn't work propperly.

In one channel, the Low cut switch acts like Hi cut. In pos 1 to 5 of the switch it doesn't seem too bad, I can't hear it cutting lows, maybe just a bit, but when I go above pos. 5 it starts working as a LPF, lowering everything above 2K. The Boost switch seems to work fine. The other channel works nicely.

I've rechecked the wiring between switches and it looks fine, the same in both channels, so I can't figure what's going on.

Another thing I noticed (I think by the OEP transformers) is a soft fall in frequency response above 10K, It's nice, usable in mixes.

Actually I can use it, because I never go as far in cutting lows, actually, I use the whole eq in a very subtle way, sometimes just bypassing the eq and runing the whole mix in it, and I really like it.

 

[ruffrecords]

Hi

I realised yesterday that my unit doesn't work propperly.

In one channel, the Low cut switch acts like Hi cut. In pos 1 to 5 of the switch it doesn't seem too bad, I can't hear it cutting lows, maybe just a bit, but when I go above pos. 5 it starts working as a LPF, lowering everything above 2K. The Boost switch seems to work fine. The other channel works nicely.

I've rechecked the wiring between switches and it looks fine, the same in both channels, so I can't figure what's going on.

That's a pity, especially as one channel works OK. I guess the next thing to check is the components on the boards of the channel that does not work. If the lo cut starts to act like a hi cut then that sounds like a wiring error with the capacitors not connected in parallel with the low cut pot as they should be.

Another thing I noticed (I think by the OEP transformers) is a soft fall in frequency response above 10K, It's nice, usable in mixes.

That's interesting. I have not heard of that before. One way to check is to turn all the boost and cut controls fully anti-clockwise. This should give you a near ruler flat frequency response. If you then switch between EQ in and EQ out, there should be no difference in sound.

Cheers

Ian

 

[wave]

Hi

I realised yesterday that my unit doesn't work propperly.

In one channel, the Low cut switch acts like Hi cut. In pos 1 to 5 of the switch it doesn't seem too bad, I can't hear it cutting lows, maybe just a bit, but when I go above pos. 5 it starts working as a LPF, lowering everything above 2K. The Boost switch seems to work fine. The other channel works nicely.

I've rechecked the wiring between switches and it looks fine, the same in both channels, so I can't figure what's going on.

Another thing I noticed (I think by the OEP transformers) is a soft fall in frequency response above 10K, It's nice, usable in mixes.

Actually I can use it, because I never go as far in cutting lows, actually, I use the whole eq in a very subtle way, sometimes just bypassing the eq and runing the whole mix in it, and I really like it.

I imagine that when you use it like that (eq bypassed) that you're getting the nice "tubey" sound from the gain make up stage and the iron? Did you use Ian's tube make up PCB?

Dave

 

[dirtyhanfri]

That's a pity, especially as one channel works OK. I guess the next thing to check is the components on the boards of the channel that does not work. If the lo cut starts to act like a hi cut then that sounds like a wiring error with the capacitors not connected in parallel with the low cut pot as they should be.

Maybe I've reversed the caps in the low board? Meaning, using boost caps as cut and viceversa?  I'll check the wiring anyway, it's a bit complicated so surely I'm overlooking something... Thanks for the advice!

That's interesting. I have not heard of that before. One way to check is to turn all the boost and cut controls fully anti-clockwise. This should give you a near ruler flat frequency response. If you then switch between EQ in and EQ out, there should be no difference in sound.

Cheers

Ian

Sorry, I explained myself bad, there's no difference in the sound bypassing the EQ with no boost or cut, I 'm reffereing to the whole unit sound, in logic studio channel eq analyzer it's a very soft fall, looks kinda natural, I didn't get surprised when I saw it (I've built a La-4 last year, using an OEP output transformer and it was about the same IIRC)

I imagine that when you use it like that (eq bypassed) that you're getting the nice "tubey" sound from the gain make up stage and the iron? Did you use Ian's tube make up PCB?

Dave

Yes and yes, but not sure if I would call tubey to the sound, I suspect the output transformers have a lot to do here, and I'm not a tube expert, but yes, it's really nice. I 've grown in digital, and now, when I hear this (and his partner my new gssl) is like "that sound" I couldn't get before, soft highs and big basses, having a really fun time now, this place is great!

 

[dirtyhanfri]

Hi

Today I had a bit of time to mess around with my unit.

I was thinking about what Ian said about the caps in parallel with the switch, so I looked the wiring and it was ok, then I put the low boards out of the front pannel and saw C12 was wrong, look the pic...

Ooops  ;D

BTW, my unit looks a bit noisier, I got a measurement program for mac, and it measured noise at -72 & 66 db's around 50Hz, I think it can be improved with some nicer wiring...

 

[ruffrecords]

BTW, my unit looks a bit noisier, I got a measurement program for mac, and it measured noise at -72 & 66 db's around 50Hz, I think it can be improved with some nicer wiring...

Because of the relatively high impedance output from the EQ you need to take care of signal wiring and use screened wire as indicated on the hook up diagrams. You should also try to keep them as short as possible.

Cheers

Ian

 

[ruffrecords]

I just had an order from someone who wanted to do separate frequency switches for bass boost and cut so he could also get 12 frequencies on each instead of the six in the regular poor man's. I had a look at the PCBs and the Lorlin switches and it looks like it can be done quite easily. The 12 way Lorlin has  a single wiper connected to the A pas on the PMEQP1A PCB and it will connect to caps C1 thru C12 as is goes through its 12 positions. The capacitor common for the first 6 is T1 and for the second six is T3 so you just strap these togher for 12 positions.

I have no idea if anyone else wants to do this but I thought it was worth passing on.

Cheers

Ian