Moby

Soundcraft 1624 control room
« on: March 30, 2006, 08:36:32 PM »
Guys, here's the schemo of master section (source select & control room).
After recabling and some chip "upgrade" I found that this old bastard really suffer from "modern" overcompressed music. Actually, think that input unbuffered network (10k pot / (5k1/3k3) is maybe too low for single op amp to drive hot signals. Note that this is non balanced configuration... Maybe I'm wrong :?  If not, do you have some sugestion about rearanging this circuit? I'm talking about light green stage :wink:
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com


Moby

Soundcraft 1624 control room
« Reply #1 on: March 31, 2006, 10:42:54 AM »
:shock:  polite bump
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

dale116dot7

Soundcraft 1624 control room
« Reply #2 on: March 31, 2006, 02:33:00 PM »
I've got a 2400 which is very similar to the 1600, and yes, it's unbalanced, and yes, there's a lot of unbuffered stuff in there. Since most gear inputs are bridging (10k input impedance or thereabouts) these op-amps can drive it fine. That being said, I'm slowly working on changing the inputs to balanced but leaving the outputs as unbalanced for everything except the master section, which I will probably balance.

Most op-amps should drive a 2k load with absolutely no difficulty, and many will drive a 600 ohm load just fine, too. Watch the data sheets.

I've found decoupling is pretty important if you're upgrading the original TL072 op amps (at least that's what my 2400 is loaded with) and you gotta watch the power consumption of the board. I've been using LM833's for my upgrades and to my ears the bass sounds tighter though I haven't really listened that carefully. I have two power supplies so I can upgrade the power feed to my board easily, but I will have to give up the automation (which I need to work on anyways) until I get or build a new power supply for it.

I like the sound of the LM833 because it is fairly simple but performs well. It's also pretty inexpensive, which is why I have not been using OPA2134 or OPA2604 op-amps. I may look at the summing amplifiers once I get through all of the channel strips and monitor returns first.

Moby

Soundcraft 1624 control room
« Reply #3 on: March 31, 2006, 03:59:41 PM »
Thanks Dale, yes, from data sheets, that's possible to drive few Kohm, (NE5534 can drive 600ohm) but op-amp sounds like working in pure class B  :cry:  I'm complaining about sound here, not about possibilities.
BTW, I never saw non-buffered, nice sounding (just op-amp) volume control with pot under 10k :?  Am I wrong?
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

Moby

Soundcraft 1624 control room
« Reply #4 on: April 01, 2006, 06:26:08 AM »
Quote
Since most gear inputs are bridging (10k input impedance or thereabouts) these op-amps can drive it fine

I agree :grin:
But here in 1600 sch load is around 4.5K ( 10k pot / 5.1k+3.3k)
Is that too low for critical monitoring? I know that almost any op-amp will handle that, but don't know is there any sound diff if I maybe change the pot to 20K and resistors to let's say, 12k+8k2.

BTW, about 2400, I will suggest you to rid of CD4066/4016 as switch. I replaced all of them and that was my leading improvement inside 1624 :wink:
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

Moby

Soundcraft 1624 control room
« Reply #5 on: April 04, 2006, 10:32:51 AM »
I have to find some more opinion about this..... Really, are 4k too low for single op-amp driving high line level :roll:
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

Moby

Soundcraft 1624 control room
« Reply #6 on: April 12, 2006, 09:23:13 PM »
And I'm thinking again, talking to myself... :wink:  Do I really need R51/R36 pad , since I changed CMOS switch with relay board? Nice talking with you guys :wink:
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com

Moby

Soundcraft 1624 control room
« Reply #7 on: April 17, 2006, 05:02:42 PM »
I removed the pad R51/R36 and rearranged the IC6 for unity gain. Seems that now sounds more detailed  :roll:
For microphone transformers,  BV.8,  Bv.11,  Bv.12, etc.. contact me at mobyelectronics at gmail dot com


 

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