REDD EQ, Helios 69 and Dick Swettenham

[salomonander]

Best Girl ever. This is a fraction of what she did. she literally matched hundreds of them.

 

[ruffrecords]

Jakob, can you send me some full resolutions pics of this build so I can get Pierre to add them to his gallery of my projects?

Cheers

Ian

 

[salomonander]

Jakob, can you send me some full resolutions pics of this build so I can get Pierre to add them to his gallery of my projects?

Cheers

Ian

problem is my camera. this is high resolution mode but i have some friends over for the match tomorrow night and im certain that one of them has a smartphone with better cam. ill send you some pics then.  unless im too devestated in case italy kicks us out of the tournament - as usual

 

[salomonander]

these sound amazing. especially with a v72 as gain makeup. i tried neves and gmls as well and while i like it, there is something really special when powering them with the old telefunkens. the high end is pure butter.
i do have a slight hum issue which i have to trace down. i did use the output transformers unshielded wire - ill replace that first.

edit; i think i chased it down. looks like i miswired the marinairs - fed 0v to a wrong pin. its clean now.

 

[ruffrecords]

I see Italy AND Wales both got kicked out. Will France beat Germany tonight???

Alons y!!

Cheer

Ian

 

[UffeK]

Would the G-Pultec gainstage be suitable as gainstage for the REDD EQ?

http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif

Thanks

UffeK

 

[ruffrecords]

Would the G-Pultec gainstage be suitable as gainstage for the REDD EQ?

http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif

Thanks

UffeK

Yes it will. You might need to add a preset pot between the EQ output and the amp input to set the overall gain to unity - a 470K pot will do it - but otherwise it should be ideal.

Cheers

Ian

 

[UffeK]

Thanks Ian
I really appriciate this.

I consider building the EQ as a stereo pair, and consider the pros and cons with tube vs transistors as booster.
No doubt the tubes will have a small say on the sound, but here we are only looking for the flavor from the filters(chokes caps and resistors), right?

I consider two alterternatives for step one:
1) - Simply use my EF86 based Ampex MX 10 as booster
        https://www.gearslutz.com/board/attachments/geekslutz-forum/148250d1260800659-post-xformer-pad-mx10-ampex_mx-35_schematic.gif

2) - Do a stereo version of the the TL072 amp you also suggest.
        Here I was wondering if this simple little amp based on the TL072 would be a suitable MKI alternative:
        http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k2572_rev2.pdf
        Perhaps modded with an OPA2604 for a more tubey sound.

Could I have your thoughts, please?

Thank you, Sir

UffeK


 

 

[ruffrecords]

I consider two alterternatives for step one:
1) - Simply use my EF86 based Ampex MX 10 as booster
        https://www.gearslutz.com/board/attachments/geekslutz-forum/148250d1260800659-post-xformer-pad-mx10-ampex_mx-35_schematic.gif

This has more than enough gain but unfortunately the EF86 has no drive capability so as soo as you connect it to a 10K line input you will lose a lot of level and distortion will become significant. If you want a single tube gain make up you could use my poor man's tube gain make up stage.

2) - Do a stereo version of the the TL072 amp you also suggest.
        Here I was wondering if this simple little amp based on the TL072 would be a suitable MKI alternative:
        http://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k2572_rev2.pdf
        Perhaps modded with an OPA2604 for a more tubey sound.

For the correct high impedance input and best noise performance you need to use a non inverting op amp configuration. The  little amp you refer to is configured as an inverting type which is not really suitable. I guess you could cut tracks and wire link it to convert it but it is a lot of trouble to go to. Perhaps there is something similar which is non inverting? The circuit you need is not complex so you could always build it on Veroboard.

Cheers

Ian

 

[UffeK]

Thanks Ian.
Sometime during the reading on REDD EQ and RS127, I found an article on the Siemens W295B.
I also got the this plugin from Soundtoys for free:
http://www.soundtoys.com/product/sie-q/
-which is modeled after the W295B.
Comparing the functionality + the fact that the W295B has both the input and output transformers as well as the booster amp, got me thinking that this might be an alternative not too far from the real EMI thing.
Long story short; I found a fine set of these for sale locally for less that the BOM I made for the EMI project, and I decided to buy.

These old Siemens EQs sound absolutely fantastic, especially the high shelving is really nice. No harshness at all.
Comparing the Plugin to the real deal, I must say that they did a really good job at capturing the sound of the hardware, but the hardware has more of the hard to describe pleasing the ears factor, which is probably because of the the transfomers.

Here is a diagram for comparison:
http://audio.kubarth.com/rundfunk/getfile.cgi?f=H%2C30W-S0Q-%234Y.5%5DW%2BW-I96UE%3BG-%3F%3DS%28Y-6%29%3F%3CV-H96UA%3D%26EC%2BG%21D9%40%60%60%0A

Thanks

 

[ruffrecords]

The W295B is interesting but quite different to the Helios and REDD EQ. Looking at the W295B schematic it is clear that the treble and bass boost/cut are straightforward Baxandall style EQs that rely on negative feedback. The topology of the mid EQ is very similar to one of the API EQs. I uses a passive circuit for cut and a negative feedback one for boost.

Both the Helios and REDD EQs are passive thoughout and just need a gain make up amplifier to restore the insertion loss.

The fact that you like the sound may mean that the exact topology is not important as you might think.

Cheers

Ian

 

[tommypiper]

...4ch reddd using marinair on inputs, mullard caps throughout, dons Induktors for mid cut and carnhills on the outputs. ...Cheers Jakob

Nice build!  Can you share how you are wiring the transformers?  Which carnhills are you using on the outputs?

 

[surfkat]

Did anyone ever build this board into a 500 module? I read through the thread but did not see any. That is what I want to do, with a DOA make-up amp and transformer I/O. Just wanted to see if anyone else had managed to get all that into a 500 slot.

 

[ruffrecords]

Did anyone ever build this board into a 500 module? I read through the thread but did not see any. That is what I want to do, with a DOA make-up amp and transformer I/O. Just wanted to see if anyone else had managed to get all that into a 500 slot.

The standard board is too tall to fit in a 500 series module but the 3U version is only 100mm square so it should fit in OK. I am sure someone added a JLM 500 series interface board to one to make it into a 500 series module but I cannot remember who it was.

Cheers

Ian

 

[tommypiper]

Ian, I believe you mentioned that both these EQs need to be loaded 100k.  I'm thinking to build them stand-alone, and plug in outboard make-up gain amps from other boxes via XLRs.  What kind of transformers would I use to allow the EQs to interface with the outside world?  And what types of amps will create the correct load?  (I have Neve type Marinair / Carnhills, if you want to explain how to wire those, as an example...  ) thanks much.

 

[ruffrecords]

Ian, I believe you mentioned that both these EQs need to be loaded 100k.  I'm thinking to build them stand-alone, and plug in outboard make-up gain amps from other boxes via XLRs.  What kind of transformers would I use to allow the EQs to interface with the outside world?  And what types of amps will create the correct load?  (I have Neve type Marinair / Carnhills, if you want to explain how to wire those, as an example...  ) thanks much.

On the input you need any good 10K:10K input transformer. Something like the Carhnhill VTB9071 would do. Its data sheet shows how to wire it up.

The output needs to be loaded as lightly as possible and anything above 100K should be OK. If you want to use an external gain make up amplifier then perhaps the safest approach is to add a DI transformer like the Carhnill VTB9072 wired  144K:250R. Again, the Carnhill data sheet shows how to wire it like this.

This will give you balanced inputs and outputs. The EQ loss is about 15dB and the DI transformer loss is about 27dB giving a total loss of 42dB to be made up by your external amplifier.

Cheers

Ian

 

[tommypiper]

... the DI transformer loss is about 27dB giving a total loss of 42dB to be made up by your external amplifier.

Cheers

Ian

That's a steep loss on the output transformer just to have it balanced. 

What is the input impedance into the second tube on your Classic mu follower?  (I believe it's 1M, based on the grid resistor?)  So I could insert the EQ there.

To make a world-facing Line In on that second stage, what transformer would you suggest?  Since we already have very high impedance...  Thanks!

 

[ruffrecords]

That's a steep loss on the output transformer just to have it balanced. 

It is but that's because the EQ is not designed to be used that way

What is the input impedance into the second tube on your Classic mu follower?  (I believe it's 1M, based on the grid resistor?)  So I could insert the EQ there.

Yes, that is just the sort of input to load the EQ with. The input impedance will be close to 1M

To make a world-facing Line In on that second stage, what transformer would you suggest?  Since we already have very high impedance...  Thanks!

I am not sure I understand the question - I thought you wanted to connect the output of the EQ to it.

Cheers

Ian

 

[tommypiper]

Right, I understand putting the EQ in its own box not ideal...

I am not sure I understand the question - I thought you wanted to connect the output of the EQ to it.

Cheers

Ian

Was still thinking if I had the EQ in its own box, without the DI transformer, will it work to connect to the Classic?  Keep in mind there would be the 10k attenuator there, so does that change the load from 1M to 10k?  And what kind of Line Input transformer do I need -- does the 10k attenuator change that? 

I would need a Line In transformer on the Classic to be able to interface other line inputs... could you please link to the Carnhill transformer?  My browser can't get past their splash page to see any products.

Another option I'm thinking... add the BA 283AM output stage on the EQ.  Do you know what the input impedance is on that output stage, by chance? 
Thanks!

 

[ruffrecords]

Right, I understand putting the EQ in its own box not ideal...

Was still thinking if I had the EQ in its own box, without the DI transformer, will it work to connect to the Classic?  However I would need a Line In transformer on the Classic to be able to interface other line inputs... could you please link to the Carnhill transformer?  I can't get past their splash page.

You could add a switch to connect the input of the second stage of the classic either to the EQ output or to a line input transformer. The EQ input would then be unbalanced high impedance (just what the EQ likes) and the line in would be 10K balanced.

You can download the Carnhill Design Guide from audiomaintenance:

http://www.audiomaintenance.com/acatalog/Input_Transformers.html

Another option I'm thinking... add the BA 283AM output stage on the EQ.  Do you know what the input impedance is on that output stage, by chance? 
Thanks!

No I am afraid I don't know that but it is probably not high impedance enough.

Cheers

Ian