EWalter

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #380 on: August 26, 2019, 04:01:26 PM »
Hey, glad you got it sorted Erik, nice one.
Easy mistake to make.  I haven't turned on a piece of gear I made yet that failed to amaze me when audio comes out the other end.
Down some wires. 
Cool 👍

It really does sound so much better when you make it yourself!  ;)


Sorr

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #381 on: September 20, 2019, 11:02:05 PM »
Ian,
You wrote in post 285, "Hooking up the Helios EQ PCB is quite simple. Your input goes (via a 10K:10K transformer) to the pad labelled IN "
I thought it required a low I/P driving Z, such as 600 ohms?

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #382 on: September 21, 2019, 03:16:57 AM »
Ian,
You wrote in post 285, "Hooking up the Helios EQ PCB is quite simple. Your input goes (via a 10K:10K transformer) to the pad labelled IN "
I thought it required a low I/P driving Z, such as 600 ohms?

Transformers do what it says on the tin - they transform. The input impedance of the EQ is about 10K so I recommend a 10K:10K transformer to successfully reflect this input impedance to its primary. It looks like a regular line input to the outside world. The EQ is designed to work from a source impedance of no more than 2500 ohms. This is so it can be used directly after a 10K fader in a mixer. If you drive it from a low impedance source you can add a series resistor (there's a place on the PCB for this) to raise the soirce impedance to 2500 ohms. You don't have to do this though - if you drive from a low impedance source without the extra resistor, all that happens is the maximum boost and cut is increased by about a dB.

Bottom line is for a bakanced input you need a 10K:10K transformer but you can drive it from a low impedance source.

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'

letterbeacon

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #383 on: June 03, 2020, 04:27:13 AM »
I'm looking forward to  building a couple of your Helios EQs - thanks again for making them open source.

I think you've answered this above, but just to confirm - I have some 600:600 input transformers lying about. I know the circuit is designed with a 10k:10k in mind, but if I read your above post correctly, I can use a 600:600 but the maximum boost and cut is increased by a dB. Is that correct?

My other question is that I would like to use the 2128 amp circuit for make-up gain that was used in the original desks for the same purpose. Would the 2128 amp work with your circuit?

Here's a link to a doc with the 2128 in: https://groupdiy.com/index.php?topic=58393.msg948059#msg948059

ruffrecords

Re: REDD EQ, Helios 69 and Dick Swettenham
« Reply #384 on: June 03, 2020, 06:12:00 AM »
I'm looking forward to  building a couple of your Helios EQs - thanks again for making them open source.

I think you've answered this above, but just to confirm - I have some 600:600 input transformers lying about. I know the circuit is designed with a 10k:10k in mind, but if I read your above post correctly, I can use a 600:600 but the maximum boost and cut is increased by a dB. Is that correct?

My other question is that I would like to use the 2128 amp circuit for make-up gain that was used in the original desks for the same purpose. Would the 2128 amp work with your circuit?

Here's a link to a doc with the 2128 in: https://groupdiy.com/index.php?topic=58393.msg948059#msg948059

Yes, a 600:600 input transformer will be fine. Its lower source impedance may give you an extra dB of boost. Cut should be relatively unaffected.

The 2128 amp is perfect for gain make up.

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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