Poor Man's Pultec EQP1-A Build Support Thread

[unklepablo]

Well spotted! Id originally done that on the input as well but id changed that and must have missed it on the output. Also the fuse should be on the brown live wire and not the neutral. Ill get it changed tomorrow and repost it.

Thanks again
Paul

 

[ruffrecords]

Well spotted! Id originally done that on the input as well but id changed that and must have missed it on the output. Also the fuse should be on the brown live wire and not the neutral. Ill get it changed tomorrow and repost it.

Thanks again
Paul

You might like to add screened cable from the EQ input to the switch and from the switch to the input connector.  Connect the screens together at the switch so there is a 0V connection all the way from the EQ in to the input connector. It is not strictly necessary as the input is likely to be relatively low impedance but  it is good practice.

Cheers

Ian

 

[unklepablo]

Well spotted! Id originally done that on the input as well but id changed that and must have missed it on the output. Also the fuse should be on the brown live wire and not the neutral. Ill get it changed tomorrow and repost it.

Thanks again
Paul

You might like to add screened cable from the EQ input to the switch and from the switch to the input connector.  Connect the screens together at the switch so there is a 0V connection all the way from the EQ in to the input connector. It is not strictly necessary as the input is likely to be relatively low impedance but  it is good practice.

Cheers

Ian

Ive updated my wiring diagram with a few more things and taken into consideration the input shield you mentioned. Hopefully this is better and will make a little more sense to people like me who are still learning.

Thanks again

Paul

 

[ruffrecords]

I just realaied you have pins 1 & 3 of  both input and output  XLRs strapped together and connected to chassis. You do not need to strap them together. Tie pin1 to chassis but not to pin 3. The signal 0V (pin3) gets connected to chassis via the power supply. You should also add a screened lead from the input XPR to the switch an connect its screen to the one going to the EQ input.

Cheers

Ian

 

[troubleous]

Hi Ian and everyone following!

I'm almost finished with my build but I have a peculiar problem with my mid board. Everything is working as expected, except when I turn the mid switch to 4K position, the sound cuts off completely.

I'm re-checking and re-checking the wiring (as per the Mid Hookup PDF), but I just can't figure out what the problem is. Probably something obvious that keeps missing my eye

I've also cut the traces from the mid board as instructed.

Is there anything obvious that comes to mind that could be wrong? Maybe someone has had the same problem before, no?

Cheers from Sweden!
/Jarkko

 

[ruffrecords]

If all the other mid frequencies work OK then it suggests to me that there is a short across the 4K capacitor. SOlder splash or faulty cap maybe. Try removing the 4K cap and see if it goes away.

Cheers

Ian

 

[troubleous]

Hi Ian!

I'll try removing the capacitor - though the problem is the same on both channels (building 2xmono unit here), suggesting me it's some stupid wiring error on the mid boards.

I'll let you know.

Cheers,
Jarkko

 

[troubleous]

Hi!

Alright, no change after removing 4K (C7) cap from both mid boards - the sound still cuts off when mid frequency is set at 4K and boost/cut is full on (rotary switch at pos 12).  Staring at the schematics + wiring guide and trying to figure out what could be wrong...

Any ideas?

 

[unklepablo]

I just realaied you have pins 1 & 3 of  both input and output  XLRs strapped together and connected to chassis. You do not need to strap them together. Tie pin1 to chassis but not to pin 3. The signal 0V (pin3) gets connected to chassis via the power supply. You should also add a screened lead from the input XPR to the switch an connect its screen to the one going to the EQ input.

Cheers

Ian

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?

The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

 

[ruffrecords]

If you are using  a Carnhill inductor with the built in metal clamp, this can sometimes short against on of the switch pins.

Cheers

Ian

 

[ruffrecords]

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

The mid boost cut switch is supposed to be a three position centre off type. This is required because the simple design of the mid EQ means that this is the only way it can be fully off.

My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?

The boost and cut are separate circuits.For the hi boost you just short all the inductor pins together and also short the hi Q pins together. Don't forget to fit the Qmax resistor 4K7. Did you use the Cpoorboost capacitor values?

For the cut, the only thing I can think of is you have the wrong value resistor for the 430 ohms just above and to the right of the the hi switch.

The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

The loss of low cut is unusual. Most faults I have come across tend to increase the lo cut rather than reduce it. If the other EQ lo cut works OK on both PMTGMU boards then the fault is clearly in the EQ board, but I cannot think what the fault would be.

Cheers

Ian

 

[unklepablo]

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

The mid boost cut switch is supposed to be a three position centre off type. This is required because the simple design of the mid EQ means that this is the only way it can be fully off.

My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?

The boost and cut are separate circuits.For the hi boost you just short all the inductor pins together and also short the hi Q pins together. Don't forget to fit the Qmax resistor 4K7. Did you use the Cpoorboost capacitor values?

For the cut, the only thing I can think of is you have the wrong value resistor for the 430 ohms just above and to the right of the the hi switch.

The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

The loss of low cut is unusual. Most faults I have come across tend to increase the lo cut rather than reduce it. If the other EQ lo cut works OK on both PMTGMU boards then the fault is clearly in the EQ board, but I cannot think what the fault would be.

Cheers

Ian

I will double check the resistor near the high is 430 ohms and will wire the 2 boards seporatley to the suspect tube gain section to double check. I'm glad I used molex connectors now! Ill check the wiring again while i'm there. Also i'm getting a little hum around -60db but I assume thats due to it being unbalanced and without a lid on the chassis.

All these problems aside, what I have heard sounds great and it punches well above its price range. Looking forward to getting rid of all these niggles and moving onto the next one (1176 rev A).

thanks for all the advice

 

[unklepablo]

Ok so I changed the xlr wiring and the screen like you said and I got the gain stages working but I have a few issues:

When bypassed all is well and sounds really nice and 'tubey' but when I engage the eq the mid band seems to have around a 2db boot or cut (depending on mid switch position) at the lowest pot setting (fully ccw). 

The mid boost cut switch is supposed to be a three position centre off type. This is required because the simple design of the mid EQ means that this is the only way it can be fully off.

My high bands are not working properly. I get maybe 2db of cut when the pot is up fully cw but I dont get any boost at all. I'm not using a high inductor so your guide shows to short all the points where the inductor would gone and short the high Q. I've used hook up wire to short all the high inductor points together and Ive shorted the 3 high Q pins with some wire. Do I now hook these together with some more wire?

The boost and cut are separate circuits.For the hi boost you just short all the inductor pins together and also short the hi Q pins together. Don't forget to fit the Qmax resistor 4K7. Did you use the Cpoorboost capacitor values?

For the cut, the only thing I can think of is you have the wrong value resistor for the 430 ohms just above and to the right of the the hi switch.

The last problem is that one of my channels looses the bass cut when it is connected to the pmgmu stage, if I remove the eq and connect to my d/a converters with a preamp the bass works fine. It's strange because I have both channels wired the exact same way yet just the 1 has this issue.

I've checked all cap values and they all match up to the schematic. I cant see any shorts.

I'm getting there, slowing but surely.

Cheers

Paul

The loss of low cut is unusual. Most faults I have come across tend to increase the lo cut rather than reduce it. If the other EQ lo cut works OK on both PMTGMU boards then the fault is clearly in the EQ board, but I cannot think what the fault would be.

Cheers

Ian

I will double check the resistor near the high is 430 ohms and will wire the 2 boards seporatley to the suspect tube gain section to double check. I'm glad I used molex connectors now! Ill check the wiring again while i'm there. Also i'm getting a little hum around -60db but I assume thats due to it being unbalanced and without a lid on the chassis.

All these problems aside, what I have heard sounds great and it punches well above its price range. Looking forward to getting rid of all these niggles and moving onto the next one (1176 rev A).

thanks for all the advice

I've checked the hi resistors and they are 100% 430 ohms.  I didn't get around to removing the inductors and checking for shorts but I did rewire the suspect tube gain channel using better wires and crimped connectors for the switches. This seems to have fixed the problem and now the low boost is working fine. So that's most of my problems solved I just need to check for the shorts underneath the inductors and Ill have her all working.

I'm expecting my front panel to arrive back today or tomorrow complete with powder coating. Next Ill need to figure out how to use this water slide decal paper to do the silk screening. Either that or I may have it engraved, not sure yet.

 

[unklepablo]

Ive hit a wall with the high boost. I have joined all the pins where the high inductor would have been with wire links and shorted out the 3 high q pins together with a bit of wire. I get the high cut working fine now, however the high boost is not working properly. The pot I'm using is 47k(b) linear, yet it acts like a high pass filter. Im not sure what Ive done wrong as been over and checked the pot wiring, all cap values, resistors and everything appears to be correct. Ive removed the inductors (not an easy job) and added electrical tape (direct on clips) followed by card taped down again with electrical tape to stop the clips shorting out on the pins. Im getting close now but a little lost here about what I can do to solve the hi boost problem?

Also I still notice when I engage the mid switch from cut to boot it always seems to be slightly boosted by maybe 2db (pot at lowest point ccw). Is there anyway to stop that, or is it just the way the design is?

Thanks
Paul

 

[ruffrecords]

Ive hit a wall with the high boost. I have joined all the pins where the high inductor would have been with wire links and shorted out the 3 high q pins together with a bit of wire. I get the high cut working fine now, however the high boost is not working properly. The pot I'm using is 47k(b) linear, yet it acts like a high pass filter. Im not sure what Ive done wrong as been over and checked the pot wiring, all cap values, resistors and everything appears to be correct. Ive removed the inductors (not an easy job) and added electrical tape (direct on clips) followed by card taped down again with electrical tape to stop the clips shorting out on the pins. Im getting close now but a little lost here about what I can do to solve the hi boost problem?

i just had a look at a bare PCB and I just realised there is one pin of the inductor you should not short to the others. This is the pin labelled G which would connect to the metal frame of the inductor. This pin is connected to 0V so it will seriously mess up your EQ if shorted to the other pins.

Also I still notice when I engage the mid switch from cut to boot it always seems to be slightly boosted by maybe 2db (pot at lowest point ccw). Is there anyway to stop that, or is it just the way the design is?

Thanks
Paul

That's the way the design is - it was a compromise. As I mentioned before, the mid boost/cut toggle switch should be a 3 position type with a centre off position so when the mid EQ is not needed it is really off.

Cheers

Ian

 

[unklepablo]

Ive hit a wall with the high boost. I have joined all the pins where the high inductor would have been with wire links and shorted out the 3 high q pins together with a bit of wire. I get the high cut working fine now, however the high boost is not working properly. The pot I'm using is 47k(b) linear, yet it acts like a high pass filter. Im not sure what Ive done wrong as been over and checked the pot wiring, all cap values, resistors and everything appears to be correct. Ive removed the inductors (not an easy job) and added electrical tape (direct on clips) followed by card taped down again with electrical tape to stop the clips shorting out on the pins. Im getting close now but a little lost here about what I can do to solve the hi boost problem?

i just had a look at a bare PCB and I just realised there is one pin of the inductor you should not short to the others. This is the pin labelled G which would connect to the metal frame of the inductor. This pin is connected to 0V so it will seriously mess up your EQ if shorted to the other pins.

Also I still notice when I engage the mid switch from cut to boot it always seems to be slightly boosted by maybe 2db (pot at lowest point ccw). Is there anyway to stop that, or is it just the way the design is?

Thanks
Paul

That's the way the design is - it was a compromise. As I mentioned before, the mid boost/cut toggle switch should be a 3 position type with a centre off position so when the mid EQ is not needed it is really off.

Cheers

Ian

I removed the wire link to the G pin and it is all now working in full, it sounds great!

I'd missed where you said about the mid switch having a centre off position. That makes perfect sense now. I just used an spdt which is why I always get the mid bump. I will get one ordered soon as I can.

I did eventually finish my wiring diagram and used it to get the wiring right in the end. Ive attached it in case any one new to switch wiring (like me) can save some time.

1 tip I will give about the switch wiring is that I found it much easier to use crimped spade connectors and heat shrink make the connections solid. Soldering direct they would just snap off while I was working around them.

Thanks for all your help, Ive really enjoyed the whole process. It seemed much easier than my 1st build (GSSL). I think thats mostly down to your support here Ian

Cheers
Paul

 

[johnheath]

Ian

Sorry if this has been asked before, but what are your opinion on ceramic capacitors in this project… compared to the film capacitors. I guess there would some space to save if using ceramics… and some money as well?

Best regards

/John

 

[ruffrecords]

Ian

Sorry if this has been asked before, but what are your opinion on ceramic capacitors in this project… compared to the film capacitors. I guess there would some space to save if using ceramics… and some money as well?

Best regards

/John

Generally speaking I would not recommend ceramic capacitors in EQ circuits because they can be microphonic.

Cheers

Ian

 

[johnheath]

Thanks Ian

Straight forward answer is something I like =)

Best regards

/John

 

[troubleous]

Hi everyone!

Happy to report finally finishing my dual channel build. Extremely pleased with the sound and will definitely build another one asap

Many many extra thanks to Ian for answering my stupid questions and giving great advice along the way!

Attached a photo of the finished unit.

Cheers!