DRIP EQP1A Build @drip-eqp1a - Tumblr Blog

A shiny new back end :-)

For my second EQP Tat was kind enough to design me a customised rear panel for his case, and it really makes it look so much more pro than my Dymo labeller :-)

Actually , I had already built these units before I got the new panels from Tat, and had to pull off all the connectors, transformer and various turret boards , ugh :-( - don't make my mistake !!!

LISTENING TEST

Ok The moment of truth for me.

I now have to convince myself, and my wife for the money i’ve spent (or saved when comparing to say a Retro Audio), that this project is fantastic.

This project was financially directly competing with a much needed bathroom reno at my place - so it’s a tough one.

I put this through a range of really quick audio tests, sadly didn't have any vocal recordings at hand, but i put drums, bass, sax, synths, drum machines (my old Yamaha RX7), and it is nothing short of amazing !!

When bypassed, audio still runs through the valves, it simply bypasses the EQ section - and even that in itself adds a beautiful depth.

Where i was truly amazed was in the upper low and mid. This thing absolutely sings, it is as smooth as you want.

If you want to pull a knarley axe sound, like some of those tones from a foo fighters record - this will kill it !!

If you want to smooth out the front pickup of your nice SG and make it the jazziest tone you could get, i wouldn't go past this.

It is definitely beautifully fizzy in the top end, it will easily add air (so 10K and above) to anything.

I had the luxury of comparing a retro audio passive EQ, and i have to say this is better, by a long shot.

The retro was great, but what i like about this product is you can use it as a subtle EQ or you can use it as a knife and make it behave like an effects unit, as in you can crank shit up in ungodly ways to make things sound definitely abnormal, i just couldn't get that from the Retro.

Now i’m not taking anything away from Retro here, there all sorts of different tools for different jobs. It just so happens for me the Retro was just not in your face enough for me to shell out 3 to 4 times more than it cost me to build this EQ.

Naturally it’s dead quiet.

Its’a big case, and after 3 hours behind the console mixing and testing, it barely broke a sweat.

I’m being harsh now - but i would probably mostly relegate this unit to tracking and individual instruments WHEN in comparison to my Manley Massive Passive.

The Manley has amazing capability, and the top end of that EQ is something that is hard to get near.

The Pultec is a much better tool for tracking and mixing, perhaps as a parallel or 2 in a buss setup.

So this test is purely in the analogue domain. I had it jacked in via my patchbay to a single channel on my desk doing A B comparo’s.

As another test i set up a virtual FX loop in cubase, and ran the Pultec as an external plugin. Now D to A converters aside, the Pultec STILL did amazing things. It had no issue playing directly with the impedance of my sound card AND it had no issue with the hotter output of digital devices - I didn't have to use the attenuation dial at all.

As a bit of fun, i ran it side by side with a digital plug in of a passive EQ - Need i say more BUT, like the retro, different tools for different jobs.

I’m not a fan of side by side digital vs. analog testing, it’s just not even the same thing. The emulations are brilliant in their own right, i use them A LOT, particularly the TG ones - love em :-)

I also mix down a lot to 2trk tape. I have an Otari MTR 12MkII, i use 499 and usually bury the meters at either 15 or 30 ips , the tape can handle it, and i like its saturation.

Patched the left through the Pultec and right direct. then A B’d - and it made me want to mixdown AGAIN with the pultec in the chain !! (where does one stop)

But i only have 1 Pultec and i cant make a stereo buss, so i now need to build another, and get more rack space.

Ultimately it comes down to my ears - regardless of components or brands, and my ears LOVE this.

Hmm....there goes my bathroom reno.

IEC Socket

These parts are both available from Jaycar.

The addition of the rubber boot is a very neat but very safety conscious addition for 90 cents.

I use this in any mains powered project i’m doing.

Adding to that, pulling apart my other pro-audio gear from Neve (above), API etc - you’ll see the same best practice :-)

The lower picture is inside my 33609.

THE CROSS BAR

So the ugly aluminium cross bar here is my addition, i will be priming this with etch primer and coating in matte black.

The placement is very deliberate.

My criteria was, i need to be able to see all components

I need to be able to swap out valves

It cant obstruct any components / headers

It needs to be safe

It’s a single piece of 3mm aluminium angle purchased from Bunnings for less than $5.

I cut it down to make 2 ears (left and right) which i could fold down and attach from the sides of the case.

I used 2 x M3 nuts and bolts each side, so you need to make the ears long enough to fit 2 small bolts.You could use screws if you wanted to, aluminium is soft enough for that.

You cant use 1 bolt because the angle will spin/flip.

You cant see them (that's deliberate), but i have 4 holes drilled across the lower edge so i can pass cable ties through to hold the wires inside the angle.

Whats important here is the cable ties DON'T put direct pressure on the high voltage wires. Remember this is carrying 240VAC direct from the mains AND 6.3VAC from the heaters.

This is done so i can pull the cable ties tight WITHOUT crushing the cables, they have a very small amount of play, which means they are less susceptible to rubbing through the cable sheath.

Adding to that, it has added quite a bit of rigidity to the case.

POWER WIRING

It’s a bit hard to tell from these photo’s but I've kept all my power wiring to one corner of the case.

The Power light is run off the 6.3vAC Heater supply, and as with the power switch, the wiring runs across my added cross bar, in the next post.

DRIP BYPASS SWITCH

I am getting toward the end of my blog here, as my EQP1A is now racked and in production.

One issue with the build was the bypass switch, and it was the only fault i had with my build from first power up.

The top picture is direct from the DRIP build manual, but it is incorrect.

Wire up your bypass switch according to the bottom picture and you should be fault free.

For reference, you are looking at the rear of the switch here, and the switch is the one specified in the DRIP build manual (Carling DPDT)

A note on these switches, unlike most DPDT switches, when the switch is in the DOWN position , the top and middle contact normally bridge. But in the case of this particular switch, when the switch is down, the middle and bottom contacts bridge.

You don't need to concern yourself with this, just follow the diagram BUT for continuity testing you might want to know how this particular switch works.

WHATS WITH C17 ???

OK, this is a mod i have chosen to do.

C17 forms part of a Zobel network, which in a very crude summary loads up the transformer to keep it’s inductance in check.

The original design called for a 270 Picofarad capacitor, the result is a darker sound, or a sound that i s true to the original Pultec design (see picture of original schematic from Pultec)

If you use a 500pF cap instead, you can achieve a brighter sound, crispier, i suppose is a way to describe it?

I’ve only put it in a simple mod, to give me a tone option.

I installed that orange header, ran a piece of Canare audio cable to a DPDT switch i put at teh back of the case near the XLR IN & OUT.

I put the 270pF on one side and the 500pF on teh other side, and i ca switch between the as a tonal option.

Why would i do that? Again, it’s only a tonal option, but if i want to track something that i want to be more present or raspier in the top end i can choose the bright setting (500pF).

It will be subtle no matter what, this is a passive EQ after all, and the effect of the EQ relies heavily on the reactance of the program material.

TESTING VOLTAGES

Now the EQ is fired up and on the test bench and nothing is burnt or busted lets test some voltages

Now work through the board with your multi-meter and test ALL the voltage test points across the board.

You’ll be starting with the transformer voltages. This is testing all the voltages that go to the board from the transformer wires (taps). The heater, the high voltage.

These are AC voltages - so set your meter. test them, make sure they are withing 5% of the stated value of the transformer spec. For example, if the heater tap on your transformer is rated at 6.5 Volts AC, make sure that you get somewhere near that (could be 7vAC or 6vAC), so do that for all AC inputs to the board.

NOW - the PCB. now here you are post the GZ34 or 6X4 rectifier - hopefully you’ve realised that post a rectifier you ar now in DC Volts land, not AC Volts :-), so switch your meter to DC Volts.

Start with the resistor marked ‘A’, work your way along the other resistors in that Pi network ‘B’ etc By the time you get to Resistor 6, you should be getting bang on 31 Volts DC.

As a reference, i built mine with eth Hammond 240V transformer and the GZ 34 rectifier. My voltages on the test points BEFORE R6, were around 15-20V DC higher than stated on the board. This is fine. Test point 1 states 355V, but mine read 378V. I chose not to mess with the resistor values prior to R6, because R6 and every other test point along the PCB into the amp and EQ stages we absolutely bang on. I’m happy for the power supply to run a bit hotter.

In fact given time, as components wear in and valves become less efficient, i’ll most likley see those values drop anyway.

If you’ve used DRIPS recommended components, you’ll be safe, they are quite well OVER spec’d for the job.

FIRST TIME POWER UP

OK, so now all your components are in.

All POTS and SWITCHES wired in.

Power transformer is wired up, and you’ve done all your continuity tests and earth/gnd tests? in that you don't have any shorts from a High Voltage to the chassis or anywhere.

Ok great.

If you have access to a mains RCD (in line) safety switch, i suggest you plug the EQ power cable into that. This will save you in case you’ve missed a short to a high voltage line somewhere.

Turn on the power point then turn on the EQ.

The RCD is still in operation ? OK, that's good.

Use your multi meter to test for AC voltage on the case. You want to make sure that between earth and the case there is NO voltage there. THE RCD should have tripped BUT don't trust it fully.

No voltages? great.

If they are new valves, you’ll hear the sound of TING TING (like someone tapping the valves with the end of a spoon) That’s normal - it’s the valves heating up.

Now it’s time to run through the test points on the PCB (detailed in the above post)

It’s been running now for a few minutes right? and there is no smoke or flames :-) - OK you are in a good space.

FRONT PANEL POWER

Wiring the front panel is a small challenge, if you want to keep best practice in mind and safety.

The power inlet (IEC Socket), line power terminations and headers are all on the opposite side of the PCB to the power switch and power light on the front panel.

I have seen some builds where the power cable is installed diagonally across the top of the board, some under the PCB, and some right around the interior perimeter of the case - none of these appealed to me. I want to be able to see my 240Volts, i want it to be away from my audio path, and i want any of its’ potential free space radiation to be away from any of my valves and components.

And mostly, i wanted the wires to be secure, in the event that through extreme conditions, the sheath might wear off and make the case live !!

So i created my own cross bar in the middle of the case to carry the wires for my switch and light.

This add rigidity to the case straight away. 2nd, being right angle aluminium means i can hide the cables under the right angle BUT i i can still inspect them. I can also brace them.

The power switch in the DRIP build manual suggests a toggle switch, but the panel screening is for a rotary switch - i used this part for the rotary from Mouser ( http://au.mouser.com/Search/ProductDetail.aspx?R=HS13Xvirtualkey63300000virtualkey633-HS13X )

POWER WIRING

Lets start with the iEC socket.

if you are using the case from DIY Racked, you will find the IEC socket with the built in fuse will exactly in the cut out, easily purchased from Jaycar.

Not essential, but best practice, buy the rubber boot that goes over the rear of the IEC socket in the case.

For 90c from Jaycar, it adds a significant degree of electrical safety, i have posted the picture toward the top of the blog.

The power switch and power light are on the diagonally opposite side of the case, so posted toward the top of this blog is the cross bar i made to get high voltage to the other side of the case with out compromising safety and access to the components on the PCB.

I chose to use a large gauge wire for both the power switch and light.

I pulled apart a bunch of old IEC cables i had. Stripped off their black sheath and used the blue and brown wires to feed the globe.

I also pulled apart some 240v 10A electrical cable, the stuff you find in the walls of your house. Stripped off the white sheath and used the black and red to feed the power switch.

I twisted both into pairs.

I find the best way to do this is start the twist by hand, say 5 or 6 twists.

Then put that twisted end into your cordless drill.

Hold the loose ends, and put a bit of tension on the wires WHILE starting the drill at low speed.

Keep pulling the wires with a bit of tension to make sure you get a nice even twist.

Don’t go too hard, you don't want to break the wires.

Reverse the drill a bit to let off some twisted tension, then do it back up again.

Once you release the tension from your hand and the drill, the wires should stay nicely formed :-)

THE FRONT PANEL

Oooh, the unenviable task of , cutting, stripping ,measuring, heat shrink, cable ties !!

There is a lot of work in wiring, don't under estimate how long this will take you, and don't rush it.

You can of course wire this any way you like. There are plenty of pictures on Google images that show how people have wired front panels.

I have chosen to wire mine with a central loom, with 4 branches, one at each end and two in the middle.

So general best practice rules. Always use shielded cable. Use cable that has an earth or ground wire, and that will usually be in the form of a bare wire running inside the sheath.

Cut of any un-needed wires in the sheath you don't need BEFORE you put heat shrink on each end. And yes for the best job heat shrink both ends.

I went to the trouble of labeling each cable and putting clear heat shrink over that. It certainly makes it easier when you are making the connections to the green headers AND should you ever have to pull the unit apart for service, much easier to put back together. - A $20 Dymo labeller from Target and $3 for a length of clear heat shrink.

I chose to leave a little extra length on my wires, to allow for any movement or mistakes :-)

Using the central loom concept means you use a little more wire between your pots/switches than wiring direct from the POT to the board. Certainly a purest would say that the shorter the length the better, BUT it makes no audible difference at all.

The other reason for this approach apart from best practice, was i referenced the inside of all my other great outboard gear, Neve 33609, Manley Massive Passive, 1176, Mellinia etc - proper neat functional and safe wiring will forever override the need to save a few centimeters of copper.

TRANSFORMER WIRING

With all of these, you’ll be inserting the wires from under (the bottom) of the PCB and soldering on the top, where you would normally mount components.

Where it’s logical, twist the wires coming out of the transformers into pairs.

In the above example, I've chosen the AMP Input transformer, and you can see from my orange squares I've drawn on the picture, I’ve made pairs of wires.

The inductor transformer, doesn't really have any logical pairs, so just loom that which ever way suits you.

Again, when you strip the wires on the transformer, try not to pull at the wires going into the transformer, you don't want to break any off inside the transformer.

Where possible use a proper wire stripping tool, and use your fingers to take up any tension before it gets to the transformer.

Always tin your wires with solder before you insert them into the PCB for soldering.

CAPS AND TRANSFORMERS DONE !!

You can work this in which ever order you would like but i have built out the board this way:

Non-polar caps first (that’s be the brown ones and the white ones)

Electro Caps (start with the little blue ones near the 12AX & AU valve sockets) then move on to the taller ones in the power-supply section.

Again as with all electrolytic caps, please ensure you validate twice you have them installed with the correct polarity.

Next the very sexy SOWTER transformers. These transformers come with 2 nuts on the mounting thread at the bottom of the transformer. You need to leave one nut on the transformer thread, left screwed up flush with the body of the transformer. The 2nd nut will be used to tighten and secure the transformer to the board. Use a firm pressure to tighten these, not so much you make the board creak and groan, but enough so that you cant spin the body of the transformer around with your fingers.

Then cut the wires with at least 10cm of length. You can leave the full length if you want, but it might be unwieldy to loom the wires.

MOUNTING CAPS AND TRANSFORMERS

Now that you have all your low level components mounted on the board (which are primarily, Jumper, Resistors, Valve sockets and headers - in that order) , you can begin to install the caps and transformers.

Hi guys,

In the build manual for the EQP1A vers. 1.0, there is no reference to jumper the ground plane.

PLEASE ENSURE YOU JUMPER THIS - VERY IMPORTANT.

What this does is makes the top of the PCB a grounded shield.

Noted by the yellow highlighted section in this picture, simply place a jumper between the 2 holes and solder, as you would with any other jumper on the board.

I have confirmed this with Greg at DRIP :-)

#eqp1a #jumper #drip #drip eqp1a #drip jumper #drip eqp1a ground earth jumper

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