Poor Man's Pultec EQP1-A Build Support Thread

[johnnyscotch]

Understood, thanks gents!

 

[dirtyhanfri]

Hi

I've been some time with my Poor man's pultec unused, lot of things happened lately... Well, I fired up the unit yesterday, and it was not working properly, I opened it today and noticed the tubes were not glowing as usual, so I turned the power off, took out the tubes and with power on measured voltages. HT read 344V DC, and between H1 & H2 I had 7V AC. With the tubes on their place it's the same, also disconnecting the wires going to the Tube Make up Gain pcb.

I think 344V is too much for HT, IIRC that should be around 250V, right?

In the transformer secondaries I got 250V AC, as expected, but at the cathode of the diode before the first 1K resistor I got 344V DC. The resistors looks and measure ok, the PSU is properly grounded, any of the caps looks bad, and anything smell bad when I turn it on.

Any ideas on what to look for?

Thanks in advance

 

[dirtyhanfri]

I replaced the diodes and the 100nF cap in the PSU and now have 315V in HT.

I plugged it on and tested the sound, without the output transformers, the first channel doesn't sound, anything, on the second channel I got sound both  with the EQ In & Out, but with EVERY switch I turn I got a loud POP, this didn't happen before...

Will check the wiring and all the usual, this little is giving me a lot of headaches...

EDIT: Also tried swapping the tubes, and the same channel doesn't sound.

 

[ruffrecords]

First you need to get the tubes glowing. If they are not glowing they do not draw HT current and the HT will go up to about 344V. I suggest you carefully check your heater wiring first.

Cheers

Ian

 

[adeptusmajor]

Hey guys, just wanted to share my (almost) completed 2 channel Poshman build. I picked up a broken Altec 1606B as a donor chassis and a handful of knobs for free at a hamfest last year, around the same time I purchased the boards from Ian. I was determined to make these work for this project, so the layout is pretty much based around the space constraints of the super shallow folding chassis and the front panel real estate of the control knobs. Backwards as hell, I know, but I saw it as a fun challenge to just work with what I acquired. It's tight and the front panel is a bit crazy but it works, kind of.

I went with a low-mid and high-mid control, with Chrion's inductors. I didn't even use the mounting holes for Chrion's daughter boards, just let the wiring kind of hold them in place naturally, seems totally secure that way. Sowter transformers, Amperex tubes, caps are mostly Wimas, values recalculated for US pot values. The wiring on the front panel is kind of messy. I just laced the wires around each other as I started wiring it up, it was looking nice at first but started to get out of control as more wires were added. It doesn't seem to be adding any noise so I may or may not clean it up later.

The EQ sounds great, it's nice and quiet and the low and mid controls sound particularly huge on everything I have tried thus far. I haven't had a chance to use it in a mix yet, but looking forward to it. At some point I'll do some tests and see how close the frequencies are. But my ears are telling me that they are pretty accurate.

I'm a bit embarrassed by the current state of the front panel, but I took a picture anyway. I printed out a design from front panel designer and used it to cover the Altec panel and provide a rough drilling template so I could test fit and get this thing up and running. You can't really see it because my printer is low on ink, but the controls are all color coded to make a little more sense out of the somewhat obscure layout. The design has been cleaned and prettied up quite a bit from what you see here and I'm ready to get a panel made when funds allow.

And on that note - I love the quality and look of panels from Front Panel Express, but pricing this one out on their software is getting up towards $300 at this point, which is a bit ridiculous. I would appreciate it if someone could recommend a place that could produce similar results as FPE with more reasonable pricing, if that exists. I would love to finish this thing up and give it the look that it deserves.

Anyway, thanks to Ian for the great project and to Chrion for offering the inductors which work flawlessly and beautifully. This one is definitely a fun and useful addition to the toolbox. Not to mention I learned quite a bit on this build.

 

[ruffrecords]

Well, done. It is really pleasing to see the finished results of your designs. Post another pic when the front panel is done.

Cheers

Ian

 

[lymix]

hi,
i built an EQ inspired by the Poorman and DIYgallery.de's EQP-1A, with a few customization
I added semi-parametric middle range correction, switchable into a notch, and with 12 selectable frequencies from 240 to 10kHz.
Each of the 5 bands are switchable, and there is a main bypass
I used bourns inductors for the mid section, and panasonic caps. Resistors are 1% vishay
The output amps is from the EQP-1a, i just changed the resistors to have 0dB gain but a highr max level input (+22dBu) now
I plan to add transformers for in and outs, probably an engraved front panel

(THANKS A LOT to the developpers of the initials projects, and to the forum for the many help/infos i got)

it's quite messy inside, i have to study connectors and strips for next project... it's the second one

no pcb inside, all components wired

 

[duantro]

I'm almost finished gathering parts for this awesome project! Thanks for all of your hard work Ian!
Could someone more knowledgable let me know if these transformers would be a good fit for this?
Lundahl LL1521 (high impedance input, 1+1:2,28)
Lundahl LL1524 (bal output, 1+1:1+1)

Cheers.

 

[ruffrecords]

I'm almost finished gathering parts for this awesome project! Thanks for all of your hard work Ian!
Could someone more knowledgable let me know if these transformers would be a good fit for this?
Lundahl LL1521 (high impedance input, 1+1:2,28)
Lundahl LL1524 (bal output, 1+1:1+1)

Cheers.

You will probably get away with using the LL1521 at the input. You will need to reduce the gain make up to compensate for the transformer gain but that is not a problem. It does mean the input impedance of the EQ will look like 2500 ohms rather than the 10K is should. If your gear is happy driving that then it should be OK.

The LL1524 is not really suitable at the input  - its impedance is too low. As an output transformer it is intended to be driven by negative impedance semiconductor circuit so if you intend using a DOA or op amp gain make up stage it should be OK but it is not suitable for use with my  tube gain make up stage.

Cheers

Ian

 

[duantro]

Thanks Ian. I'll just order some Sowter's, like you designed this for. No reason to save a few pennies and cause a headache.
Cheers!

 

[ricothetroll]

Hi,

It seems to me that according to this schem...
http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png
...the worst case scenario is Zin ~ 50k (domined by hi boost pot + hi cut pot, with lo boost pot = 0) for freqs not affected by the EQ. Where does the 10k come from ?

Best regards.

Eric

 

[ruffrecords]

Hi,

It seems to me that according to this schem...
http://www.ianbell.ukfsn.org/pics/PMEQP1-AMKII.png
...the worst case scenario is Zin ~ 50k (dominated by hi boost pot + hi cut pot, with lo boost pot = 0) for freqs not affected by the EQ. Where does the 10k come from ?

Best regards.

Eric

The input impedance varies with frequency.  The worst case is when hi boost  and cut pots are both at max then at some high frequency the caps are very low impedance so the effective  input impedance  is little more than the 4K7 resistor in series with the 470 ohm resistor. You are right that at unboosted frequencies it is closer to 50K.

Cheers

Ian

 

[MatthisD]

I'm almost finished gathering parts for this awesome project! Thanks for all of your hard work Ian!
Could someone more knowledgable let me know if these transformers would be a good fit for this?
Lundahl LL1521 (high impedance input, 1+1:2,28)
Lundahl LL1524 (bal output, 1+1:1+1)

Cheers.

The LL1521 works fine with the Poorman EQ. With the primaries and secondaries in series the ratio is 1:1.14 so primary impedance with a 10K load on the secondary is 7.7K and approx. 1dB of gain minus losses.

 

[duantro]

I've finished my eqn pair, and when I get some more free time, i'll be ready to focus on wiring up these gems. I'm doing a poshman dual mid version, with Crion's inductors, and Sowter transformers. When connecting mid boards, do both lo mid and hi mid bands connect at the same place as stated in the schematics for the one midband?

 

[ruffrecords]

I've finished my eqn pair, and when I get some more free time, i'll be ready to focus on wiring up these gems. I'm doing a poshman dual mid version, with Crion's inductors, and Sowter transformers. When connecting mid boards, do both lo mid and hi mid bands connect at the same place as stated in the schematics for the one midband?

Yes, they do. You just have to make sure the frequency selections in each band do not overlap.

Cheers

Ian

 

[duantro]

I think troubleshooting my pm670 has made my brain into mush. I can't seem to wrap my head around how to hook up ChrioN's inductors to the Modified mid board fix. Can someone shed some light or draw connections to this image?

 

[ruffrecords]

I think troubleshooting my pm670 has made my brain into mush. I can't seem to wrap my head around how to hook up ChrioN's inductors to the Modified mid board fix. Can someone shed some light or draw connections to this image?

#

I would offer to help myself but I have not used one of Chrion's inductors yet. I am sure there are others here who have though.

Cheers

ian

 

[duantro]

Thanks Ian.
I think I understand where the pins for Chrion's inductors are.
Red dot is zero and clockwise is tap 1,2,3, etc with the ground pins on the outside.

I'm confused at the pcb fix. I understand that I don't need to cut any traces. I think I do not need to connect the little corresponding numbers with a jumper.
Am I correct that the letters "S,B,D,E,...on the boards" would have originally mated with "Tap 0,1,2,3..."
If so then the inductor connections 0,1,2,3,... goes to the little numbers in the "fix photo", except 0 =screen, correct? And would it be best to use the number outside of the caps?

The new Screen pad appears to goes to cut/ boost switch.

So....where would the newly labeled "ind" go to?


I hope you can follow all of this, as I'm getting confused just reading it back ???


edit: Chrion discontinued his pcbs so I'll just be soldering wire direct to the pins.

 

[ruffrecords]

I'll get a board out tomorrow and have a look. It should just be a case of hand wiring it to the right holes on the PCB.

Cheers

Ian

 

[adeptusmajor]

I used Chrion's inductors, I do remember having a bit of a kludge to make it work. I remember having to fly some cap leads due to more frequencies being connected to a given tap than what the pcb had allowed. I just followed the schematic and used or reallocated the pcb traces where possible. I'll try to get it out and have a look again sometime, I need to troubleshoot some ground/hum issues that have surfaced anyway.

Chrion's inductors sound awesome in this circuit, BTW.