Helios 69 tube EQ support

[ruffrecords]

Someone just asked me where the support thread is for my Helios 69 EQ in its various incarnations and I realised there isn't one. So here it is. Ask away.

Documentation can be found under the DIY tab of my web site:

http://www.customtubeconsoles.com/diy

Look in the Helios69 folder.

Cheers

Ian

 

[dogfaceaudio]

Thanks for putting this thread up. I've put together a list of all the components, but it needs to get checked. In particular I'm not sure the Grayhill switches are the right type. I was going to go with 1% 1/4W Metal Film resistors, and Wima Film capacitors. Should I go with Polypropylene or Polyester for the capacitors? What type of potentiometers should be used for the 22k and 50k, should they be conductive plastic or will any type work? I used the schematic posted under the Poor Man's Pultec for the 2520 gain makeup circuit to make a quick board to amplify the output of the Helios69 v2 board. Not sure if I got the potentiometer position correct though.

Helios69 EQ Parts List

Capacitors:
0.56nF - x1
1nF - x2
1.5nF - x2
2.2nF - x2
3.3nF - x2
4.7nF - x2
6.8nF - x1
10nF - x4
12nF - x1
15nF - x2
22nF - x6
33nF - x2
47nF - x1
68nF - x2
100nF - x1
270nF - x1
0.18uF - x1
0.68uF - x1
2.2uF - x1

Resistors:
470ohm - x1
3.3k - x1
5.1k - x1
8.2k - x1
15k - x1
22k - x1
24k - x1
33k - x1
56k - x1
100k - x1
180k - x1

Other:
VTB9042 - x1
VTB9043 - x1
DPDT Switch - x1
22k Linear Potentiometer - x1
50k Linear Potentiometer - x1
Grayhill 71BDF30-02-1-AJN - x1
Grayhill 71BDF30-01-1-AJN - x2

 

[ruffrecords]

I have checked your component lists against the schematic and the build document and they seem to me to be 100% correct. My original Helios 69 board was designed some years ago at a time when the documentation I provided was somewhat less comprehensive than it is today and I simply updated it for the minor mods I made for the V2 board. I will add a BOM to the documentation .

Quarter watt metal film resistors are what I would recommend.

WIMA caps are OK but you need to be very careful to get ones that are not too fat. Many of the smaller value caps are quite close together on the PCB and the fat WIMAs will not fit. Dielectric type does not really matter. Any film capacitor rated at 50V or more will be suitable. I generally used Panasonic or EPCOS. All the caps have a 0.2 inch lead spacing. Most of the Helios 'sound' comes from the inductors.

For the pots. any type will work. I generally use Alpha or OMEG or ALPS. Modern carbon pots are very good so plastic film types are generally not essential unless the EQ is going to get a lot uf use.

There is an error in your gain make up schematic. The 470K should be connected from the DOA + input to 0V rather than in series with it as in your schematic.  I would also recommend adding an output capacitor with a bleed resistor and supply decoupling capacitors. . There is a more detailed schematic for a TL072 in the MK2 poor man's Pultec folder which is equally applicable to a DOA:

https://drive.google.com/file/d/0B_n67A1hN3qtQ2I4blMzTEE4Y00/view?usp=sharing

Other than that I think you are good to go.




Cheers

Ian

 

[dogfaceaudio]

Did I pick the correct Grayhill potentiometers? I'll spend some time making a Mouser cart for the BOM over the weekend.

 

[ruffrecords]

Did I pick the correct Grayhill potentiometers? I'll spend some time making a Mouser cart for the BOM over the weekend.

Yes, I checked the Grahill numbers; they are correct. Of course, they are switches not pots.

Cheers

Ian

 

[ruffrecords]

A quick note about the two pots. The PCB is laid out to accept OMEG 16mm plastic track pots but just about everybody who has built this board has mounted the pots off board in order to space out the controls better which is why I originally said the type does not matter.

Cheers

ian

 

[ruffrecords]

I have just added a new version of the build document to the web site. It is Helis69V2EQIss0.2,pdf which you will find in the Helios69 folder under the DIY tab od my web site:

http://www.customtubeconsoles.com/diy

Cheers

Ian

 

[dogfaceaudio]

I redid the 2520 gain schematic, it should be correct now. Any suggestions for the 47uF capacitor type? Did you use the PC16BU (http://www.omeg.co.uk/pc6bubrc.htm) potentiometers from OMEG? It looks like 5mm distance between each pin on the PCB. Thanks.

 

[ruffrecords]

I redid the 2520 gain schematic, it should be correct now. Any suggestions for the 47uF capacitor type? Did you use the PC16BU (http://www.omeg.co.uk/pc6bubrc.htm) potentiometers from OMEG? It looks like 5mm distance between each pin on the PCB. Thanks.

The schmatic looks correct to me. The 47uF should be an aluminium electrolytic rated at not less than 50V. The value is not critical.  The higher the better. 47uF gives a -3dB point of just under 7Hz with a 600 ohm load. If you will be feeding it into a  10K load then it is fine as it is.

The PCB footprint is designed for the PC16ECO type from OMEG:

http://www.omeg.co.uk/e16typ1.htm

but I do not normally mount the pot on the PCB as it makes the front panel layout a little cramped. If you have the space I would recommend moving it off the PCB to the side of the associated frequency select control much like the original Helios 69. In that case you can use and size or style of pot you like.

Cheers

ian

 

[dogfaceaudio]

I put together this Mouser cart: http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=6d539e4e30

Some of the caps will need to be mounted on the bottom of the PCB to get everything to fit. It looks like an SPST switch is needed for the EQ bypass? I think I missed that on the first BOM. The 22k and 50k potentiometers are perhaps a bit overkill, and I didn't include headers for J1/J2 as I'll be wiring those straight to 1/4" jacks.

 

[ruffrecords]

I put together this Mouser cart: http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=6d539e4e30

Some of the caps will need to be mounted on the bottom of the PCB to get everything to fit. It looks like an SPST switch is needed for the EQ bypass? I think I missed that on the first BOM. The 22k and 50k potentiometers are perhaps a bit overkill, and I didn't include headers for J1/J2 as I'll be wiring those straight to 1/4" jacks.

As I mentioned earlier, you need to watch out for WIMA caps being fatter than usual. There are plenty of suppliers so there are always alternatives that will fit. And yes, you do need a SPDT switch for the EQ in/out. I'll add that to the docs.

Cheers

Ian

 

[dogfaceaudio]

Populated the PCB, only one of the caps had to be installed on the back side.

 

[dogfaceaudio]

Ended up melting the plastic on two caps while soldering in the back side one, hopefully I didn't destroy anything.

 

[ruffrecords]

The possibility of melting caps is another reason to look for alternatives to the fat WIMAs. They are very robust and I have not had one fail because of this. An alternative, if you have plenty of height above the board. is to extend the length of the connections to the capacitor with tinned copper wire. Can be a bit fiddly but better than melting caps.

Cheers

Ian

 

[dogfaceaudio]

Should the 3.3k pot in the gain stage schematic be linear or log? Should the pot be conductive plastic, or does it not matter?

 

[ruffrecords]

Should the 3.3k pot in the gain stage schematic be linear or log? Should the pot be conductive plastic, or does it not matter?

You are refering to the new Helios 69 EQ with built in gain make up. The 3k3 pot isshould be a mumlti-turn trimpot. It should be a linear type (I don't think anyone makes a log trimpot). If you look in the documentation it gives 2328406 as the Farnell part number.

Cheers

ian

 

[dogfaceaudio]

Got the 2520 gain stage PCBs in the mail yesterday, just need to order the parts. I mistook the trimmer part in the schematic for a potentiometer. I'm going to try using a 3.5k linear pot with a 50ohm resistor in series to ground and see how well it works to adjust the output gain.

 

[dogfaceaudio]

Got the switches and wired them up, just need to finish the gain stage. I didn't see any mention on the schematic of an input or output transformer, so I'm guessing that I can just run an audio signal straight into the input?

 

[ruffrecords]

Got the switches and wired them up, just need to finish the gain stage. I didn't see any mention on the schematic of an input or output transformer, so I'm guessing that I can just run an audio signal straight into the input?

As you know it is a passive EQ and needs a gain make up stage. You already have the 2520 board for this purpose. The output of the EQ goes to the input of the 2520. You can then run the EQ balanced or unbalanced - which is up to you. For unbalanced (for example inside a mixer), you feed the signal into the EQ input and take the output from the 2520 output. For balanced operation there are several options. At the input you can just use a 10K:10K transformer or you can use an electronic balanced to unbalanced converter. At the output you can just connect a suitable transformer to the 2520.

Cheers

Ian

 

[groselicain]

Ian,

      Forgive me for asking again if you've already answered this elsewhere, but how much makeup gain is required for this? Thank you very much.