ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #360 on: August 15, 2019, 04:42:32 AM »
I always assumed your design was 100% spot on Ian and you'd accounted for everything.  Hope it didn't sound like I thought otherwise.
No, you didn't sound like that. Back in the day, inductor dcr might well have been an issue because they did not have or use the high AL materials available today so basically you are right. Even today, dcr is important for the bass inductor (7 Henries) and you need to compensate for it in the design. Mid section you can more or less ignore it.
Quote
I figured it was an issue with a wrong resistor value, and short or wiring issue on the boost inductor etc. 

Good luck EWalter 👍
I agree, that is the most likely reason.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #361 on: August 15, 2019, 01:51:32 PM »
...dcr is important for the bass inductor (7 Henries) and you need to compensate for it in the design. Mid section you can more or less ignore it.
OK got it.  I plan on using your scheme in a squalid-state pre I'm working on for my son, full credit will be given to the designer of course 🌝
I may incorporate active mids from Neve 1081 type, not sure yet, but I always thought that the high end lift on the Helios, Sound Techniques etc.  was sweeter sounding than a Baxendall high shelf.  Some of my fav.  sounding records recorded on Sound Techniques at Trident etc.

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #362 on: August 15, 2019, 04:22:30 PM »
OK got it.  I plan on using your scheme in a squalid-state pre I'm working on for my son, full credit will be given to the designer of course 🌝
I may incorporate active mids from Neve 1081 type, not sure yet, but I always thought that the high end lift on the Helios, Sound Techniques etc.  was sweeter sounding than a Baxendall high shelf.  Some of my fav.  sounding records recorded on Sound Techniques at Trident etc.

Of all the EQs I have designed I like the REDD the best. To my ears it is certainly the most musical. Despite the very broad mid boost it is remarkable how it can bring out individual instruments in a mix. Second place of course goes to the Helios.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #363 on: August 15, 2019, 05:13:17 PM »
Of all the EQs I have designed I like the REDD the best. To my ears it is certainly the most musical. Despite the very broad mid boost it is remarkable how it can bring out individual instruments in a mix. Second place of course goes to the Helios.

Cheers

Ian

Oh without doubt, that mid boost is great!  My comments were more about the high end shelf of Helios or EMI 'Classic' as incorporated in yours being a really sweet sounding one compared to a typical Baxendall of a decade later which would be imparted with the sonic attributes of the amps the tone control enclosed which, sometimes, weren't the best at being linear upat the top end to be honest.
But having the mid of the 'Pop' too is fantastic.  To look at the curves of the original EMI which were plotted for each implementation of boost and cut and the responses available as they reacted with each in boost and/or cut, you realise that a lot was possible with just two bands available on the desk.
I don't think the 'Classic' cassettes were ever employed in the Studio 2 REDD.51 desk and, possibly, neither were they in the Studio 3 one.
Classical was a Studio one thing with its REDD.37, and also the REDD.37 in Kingsway Hall which was used by both EMI and Decca.

Anyway, 👍
« Last Edit: August 15, 2019, 05:17:28 PM by Winston O'Boogie »

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #364 on: August 15, 2019, 05:28:05 PM »
P.S.  To follow up on my thoughts re.  Dick Swettenham and the EMI EQ connection postulate, it seems he left Abbey Road just before they took delivery of the REDD.37 desks which incorporated the Pop and Classic EQ.  If there were any REDD desks there before he left, it would have been the REDD.17 with a similar, but not identical classic type tone control.
I think he took the Pultec basic scheme and scaled it up in impedance, adding bits of his own based on what he'd found out were useful while being a maintenance engineer.   We will never know for sure though so... 
Cheers.

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #365 on: August 16, 2019, 03:50:35 AM »
P.S.  To follow up on my thoughts re.  Dick Swettenham and the EMI EQ connection postulate, it seems he left Abbey Road just before they took delivery of the REDD.37 desks which incorporated the Pop and Classic EQ.  If there were any REDD desks there before he left, it would have been the REDD.17 with a similar, but not identical classic type tone control.
I think he took the Pultec basic scheme and scaled it up in impedance, adding bits of his own based on what he'd found out were useful while being a maintenance engineer.   We will never know for sure though so... 
Cheers.

Ah,  hoisted by the timeline petard. If he left before the 37s arrived he would have known much less. I am not sure about Pultec with scaled up impedance. I did that with my poor man's EQP1A project. The topology is somewhat different to the Helios but an interesting thought nonetheless. After all, they all consist of a pot divider with frequency selective components on each arm.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

EWalter

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #366 on: August 16, 2019, 11:58:48 AM »
I don't have his latest/last revision schematic on hand but, looking at the boost plots you made @2K7, is it possible there's a short on the last winding of your inductor? 
I'm not exactly sure why the cut would be off in Q, it's using a different inductor than boost and is located as a shunt reactance.   But it could be widened by inserting some resistance in series with that particular tap of the inductor.  Maybe wait for Ian before changing anything there though. 
Check the boost inductor tap for problems there in the meantime.
Persevere, you're almost there! 
Whereabouts can I find Ian's up to date schematic?

Here is all the info on the build: https://drive.google.com/drive/folders/0B_n67A1hN3qtfjNQX0Z3Y1V3UTFYelRJZWp6UXQ5dmhWcXVXOFZ3Z0VtOWotemNjbHo3dnM

I checked all of the inductors in the cut path and they all check out just fine. L9 is the only one that is unique to the 2k7 circuit and it measured at 10.44mH. The rest of the inductors checked out, and are all used on other bands that don't have this same problem.


I figured it was an issue with a wrong resistor value, and short or wiring issue on the boost inductor etc. 



I agree, that is the most likely reason.


I checked all resistors and there were a couple that were slightly off do to my having different values. R12 is 390 and I had put in a 419 & R17 is 5k6 and I had put in 6k2. I've since replaced these with the correct values but I'm it didn't solve anything. I believe these are being used in the cut circuit of all frequencies, so I'm not sure this was the issue seeing as though all other bands are working well.

I also double-checked the caps on the 2k7 band cut and they're all correct values. I even pulled them out and tested them to be sure and they checked out.

I also beeped through the entire signal path on the 2k7 switch and didn't find any issues.

I'm hitting some walls here, but I want to say that this EQ sounds amazing! I'd be more than happy with it as-is at this point, I just want to see if I can get this last bit sorted out. I'm really happy with the way this little channel strip project has turned out so far and will post some pics once I get it wrapped.

Cheers,
Erik

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #367 on: August 16, 2019, 12:13:56 PM »
HI Erik, just to be clear, the only part you now have a problem with is the 2K7 Hz cut - is that right? And you are using my PCBs?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

EWalter

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #368 on: August 16, 2019, 12:19:19 PM »
Hey Ian,

That's correct! And yes, I'm using your PCB.

Thanks,
Erik

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #369 on: August 16, 2019, 06:15:26 PM »
Hey Ian,

That's correct! And yes, I'm using your PCB.

Thanks,
Erik

OK, does the 2K7 cut work at all?

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


EWalter

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #370 on: August 17, 2019, 08:33:05 AM »
OK, does the 2K7 cut work at all?

Cheers

Ian

Hey Ian,

It does work, it’s just extremely narrow while the boost is extremely wide.

Thanks,
Erik

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #371 on: August 17, 2019, 05:28:50 PM »
Hey Ian,

It does work, it’s just extremely narrow while the boost is extremely wide.

Thanks,
Erik

Is this true of all cut frequencies or just the 2K7?

Cheers

ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'


 

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