REDD EQ, Helios 69 and Dick Swettenham

[ruffrecords]

I am down to the last two REDD EQ PCBs. If it looks like there is a demand I will order another batch.

Cheers

Ian

 

[goetzmd]

The Neutrik specifications are confusing  to say the least. It says "NTL1 is a line transformer intended to balance amplifier outputs for line driving up to +24 dBm". The it says it can drive 6V rms into 600 ohms at 30Hz which is just over 17dBu. The strange thing is the primary inductance is a whopping 150 Henries and the primary dc resistance is 100 ohms. YThis says to me that this is really intended as a 10K:10K line input transformer.

Thanks, Ian. I checked: on the Studer EQ this things is the input transformer…

Has anybody another idea for a small size output transformer?

Mouser-BOM
This contains all resistors and capacitors for 2 units:
http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=58a092f82a

Cheers,
Goetz

 

[ruffrecords]

Jensen and Cinemag both do a smallish (just over one inch cube sized) 600:600 output transformer but it is only good to about +8dBu.

edcor do the PC600/600 which will do 5V rms which i +16dBu but I cannot download the data sheet to se how big it is.

Cheers

Ian

 

[goetzmd]

Thanks, Ian! The Edcor looks good. I'm slowly getting the basic parts. I'll build your boards first and go from there…

Since Farnell sells the single value inductors only in bags of 5 I have some spare parts to give away:

If you're building a stereo pair, live in Europe and send me a pm, you'll get for free:
2 x 1 mH
2 x 2.2 mH
2 x 3.3 mH
Already gone – we have a winner!

Cheers,
Goetz

 

[ruffrecords]

Thanks, Ian! The Edcor looks good. I'm slowly getting the basic parts. I'll build your boards first and go from there…

Cheers,
Goetz

I just found these little gems:

http://www.triadmagnetics.com/catalog_template.php?productCategoryId=47

They are available from Farnell. I just bought some of the 10K:10K 0.1W types for use in a VU meter buffer. When I tested them their primary inductance was over 30 Henries at 100Hz and their response was just 0.5dB down at 20Hz. 1KHz distortion at +18dBu was just 0.05%. And the are really small.

For your application the 600:600 one might be more appropriate:

http://uk.farnell.com/triad-magnetics/ty-145p/transformer-audio-0-1w/dp/1610411

Cheers

Ian

 

[letterbeacon]

I'm also thinking about squeezing a REDD EQ in a 500 format. I would like to use a DOA to make up the gain after the EQ. Is it as simple as taking the gain stage and surrounding resistors and capacitors from the circuit below and using it after the EQ?

I plan to use the triad OT recommend in the post above.

Any help would be much appreciated!

 

[letterbeacon]

I just found these little gems:

http://www.triadmagnetics.com/catalog_template.php?productCategoryId=47

They are available from Farnell. I just bought some of the 10K:10K 0.1W types for use in a VU meter buffer. When I tested them their primary inductance was over 30 Henries at 100Hz and their response was just 0.5dB down at 20Hz. 1KHz distortion at +18dBu was just 0.05%. And the are really small.

For your application the 600:600 one might be more appropriate:

http://uk.farnell.com/triad-magnetics/ty-145p/transformer-audio-0-1w/dp/1610411

Cheers

Ian

It's more than likely me misunderstanding the specs, but don't they only go down to 200Hz?

 

[ruffrecords]

It's more than likely me misunderstanding the specs, but don't they only go down to 200Hz?

You are right, the spec says they only go down to 200Hz. that's why I was only considering using it for a VU buffer. They are so cheap I thought it was worth buying a couple just to try out. I was pleasantly surprised at their measured performance. In particualr, they have a nice high inductance which is the main determinant of low frequency response. At 30 Henries, this represents an impedance of  3770 ohms at 20Hz which, even with a 600 ohm source gives a 20Hz loss of only 1 dB.

Cheers

IAn

 

[letterbeacon]

Ian, I sent you some pics directly. Hope you got them.
Here's one for your listeners ;D
2 channels of Ruff Helios EQ mastering version all stepped controls. 
Solid State Pultec output circuit- 2520 opamp with a quadfilar transformer.
Run a few mixes with it.
Beautiful
Recycled rack case - decals mounted on 12 gauge aluminium front panel.
good enuf.
Thanks for the great project.
Kelly

Is there anywhere I can see the other pics that Kelly sent? I'm planning something similar and would love to see how he's laid out the inside of the unit.

 

[anjing]

You can find a gallery of different projects build from Ian's pcb'shere:
http://theworldin35mm.com/projectgallery/
Kelly's Eq is there.

Regards,
Pierre

 

[letterbeacon]

Perfect, thank you!

 

[Rocinante]

Hey all,
So im collecting parts for a stereo or dual mono helios 69 in a 1u using Ian's pmtgmu and ht-350 supply. I will be using 6gc7 tubes as well as the antec toroidal ive read others have used.
I have just a few questions I'd like some clarity on.
Thanks in advance.
So I'm probably doing a stepped gain switch using 1 pole 12 pos lorlins in place of the pots and using grayhills like they were intended and was wondering if the non-shorting type were okay to use?  Its all they have at digikey and I am trying to somewhat consolidate my purchases (and yes I know capi carries them).
I was also hoping on using edcor 10k/10k in and the 600/600 ohm output xfmrs and would like to hear some opinions on how they are since they seem to get mixed reviews.  Maybe sowter in and edcor out or vice versa?
And finally concerning inductors are there single inductor alternatives to the Carnhill vtb 9042 and 9043?
If the carhill inductors are a necessary component for the helios 'sound' id rather not diminish anything and will just suck it up but if I could save a buck or two that would be pretty helpful.

Ive pretty much gotten everything laid out using the wealth of info over on the poor man's pultec thread and parts are just beginning to come in so id really appreciate your thoughts.
Oh and Ian thank you very much for designing and supplying these boards.  Your contributions to this community are inspiring. You're a genius man.

 

[ruffrecords]

So I'm probably doing a stepped gain switch using 1 pole 12 pos lorlins in place of the pots and using grayhills like they were intended and was wondering if the non-shorting type were okay to use?  Its all they have at digikey and I am trying to somewhat consolidate my purchases (and yes I know capi carries them).

Non-shorting Lorlins for the variable resistors should be OK. There is not possibility of switching capacitor charged with dc voltages at that point in the circuit so shorting is not required. If you are really concerned you can put a 4M7 resistors from the wiper to each end of the Lorlin to ensure there is always a dc connection path. For the Grayhills, non-shorting are OK for the Hi amd Mid controls. The Lo control really should use a shorting type for the low cut part of the circuit as the capacitors in the part of the circyuit have no independent dc path to discharge them. Again, if you are really concerned about this you can wire 4M7 resistors between all successive pairs of contacts on the lo cut section.

I was also hoping on using edcor 10k/10k in and the 600/600 ohm output xfmrs and would like to hear some opinions on how they are since they seem to get mixed reviews.  Maybe sowter in and edcor out or vice versa?

The output transformer is the more critical one. The input transformer can probably be any 10K:10K type provided it is driven by a low impedance source. The main limitation of the poor man's tube gain make up stage is its relatively high output impedance. This means it need a good quality 600:600 output transformer with a high primary inductance in order to give good performance.  Edcors tend to have lower primary inductance that Sowter. If you want to save money use an Edcor at the input and a Sowter at the output.

And finally concerning inductors are there single inductor alternatives to the Carnhill vtb 9042 and 9043?
If the carhill inductors are a necessary component for the helios 'sound' id rather not diminish anything and will just suck it up but if I could save a buck or two that would be pretty helpful.

I am in contact with one of the original designers of the Helios 69. The Helios 'sound' is in part due to the properties of the surplus inductors they used in the early builds; inductors that they bought over the counter in the Tottenham Court Road. Needless to say these inductors are no longer available. Carnill make inductors for many classic designs including Neve (in fact one of the original factories used for making Neve transformers and inductors has been part of the Carnhill group for many years) so their quality is very good. Whether the sound they produce in my design is the same as the 'Helios' sound is not for me to say. You need to judge that for yourself. groupdiy member Chrion did make alternative lower cost inductors for a time but I have not seem him around for some time.


Cheers

Ian

 

[Rocinante]

Thanks for chiming in Ian. I have used Carnhills in a few builds (1290, 1084, etc..) and can certainly attest to them being the Rolls Royce of xfmrs so imagine they probably have a significant enough impact so will stop screwing around and just use them. 
Edcor in and Sowter out sounds good to me.
Thanks again
Dylan

 

[Rocinante]

One last inquiry (for awhile anyway);
Do you (or anyone) see any problems using Carnhills vtb 2281?
The specs seem right.
Might as well
btw happy xmas everyone.

 

[Rocinante]

Uhhmmg
So Antek is currently out of the 05t240.  Bummer. They do have:

http://www.antekinc.com/as-1t250//[...ore than likely gonna try. Thanks in advance

 

[ruffrecords]

One last inquiry (for awhile anyway);
Do you (or anyone) see any problems using Carnhills vtb 2281?
The specs seem right.
Might as well
btw happy xmas everyone.

VTB2281 will do fine and nice and cheap too.

Happy New Year

Ian

 

[Rocinante]

Happy New Year!!!

Okay so I am beginning to wire up the Helios and am following Dave's
really great wiring diagram made for the Poor Man's Pultec
and have a question regarding the eq bypass.  I am using the PMTGMU which
in Dave's diagram has the boards connected to the eq via the DPDT in/out
switch.  But...  the Helios has a provision on the board for an eq bypass
as well.  Now a clever man might add both to one DPDT switch but I read
somewhere (which I can't find now and it's driving me crazy ) where it was
suggested to use just the Helios bypass in/out.  I imagine then that I would
just go directly to the PMTGMU from the Helios in and outs.  Am I on the
right track?

Thanks
Dylan

 

[ruffrecords]

Yes. The Helios  is unique for one of my EQs in that the bypass switch is built in - I literally copied it from the original - so you do not need the DPDT bypass used in the poor man's EQP1A. You can just go straight into In and IG (ground) from the Helios EQ out. You do not need to fit VR2 either or the 470 and 10K resistors next to it.

Cheers

Ian

 

[Rocinante]

Yes. The Helios  is unique for one of my EQs in that the bypass switch is built in - I literally copied it from the original - so you do not need the DPDT bypass used in the poor man's EQP1A. You can just go straight into In and IG (ground) from the Helios EQ out. You do not need to fit VR2 either or the 470 and 10K resistors next to it.

Cheers

Ian

Thanks Ian.
Good to know.