waxscum

mic 2200 line driver
« on: June 28, 2019, 08:38:53 AM »
I've been messing with a Boringer ultragain valve stage and now the whole unit  has too much gain. I'd like to loose it in the line driver so as not to effect the metering.
If i short R18, and increase R4 to 15K, the gain will reduce to unity, but ideally it'd be good to loose another 6dB. Is this possible, or should i shove a passive attenuator in front of this stage.
Ta for now.


squarewave

Re: mic 2200 line driver
« Reply #1 on: June 28, 2019, 09:24:58 AM »
I've been messing with a Boringer ultragain valve stage and now the whole unit  has too much gain.
Or perhaps the gear your trying to drive cannot handle pro-level signal?

Note that if you're sending to a computer audio interface, sometimes there's an input level control that switches input attenuation.

waxscum

Re: mic 2200 line driver
« Reply #2 on: June 28, 2019, 09:47:07 AM »
I could use it as is, in fact i am using it, but when the meter is at 0dB its shoving out 12Vp-p. Doesn't leave a lot of headroom and i'd like the metering to be accurate if poss.

squarewave

Re: mic 2200 line driver
« Reply #3 on: June 28, 2019, 10:17:08 AM »
I could use it as is, in fact i am using it, but when the meter is at 0dB its shoving out 12Vp-p. Doesn't leave a lot of headroom and i'd like the metering to be accurate if poss.
Right. But that's normal. At least for a pure tone it is. If you put white noise in, it would probably read 0dB when the average output level is more like in the 3 Vpp range. This is because the meter is a measure of power and not instantaneous peak voltage.

Try just setting up a mic and see what sort of real world levels you're getting.

Sometimes gear has a consumer level switch on the back (a lot of old Tascam gear does) that switches in a -14dB pad. But I don't think any modern pro-level gear would have a switch like that so you probably wouldn't want to hard wire it that way.

PRR

Re: mic 2200 line driver
« Reply #4 on: June 28, 2019, 09:29:15 PM »
> should i shove a passive attenuator in front

Probably the best path.

ruffrecords

Re: mic 2200 line driver
« Reply #5 on: June 29, 2019, 03:13:17 AM »
Sorry to state the obvious, but if it now has too much gain, why not undo whatever it was that you did to it to give it more gain?

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'

waxscum

Re: mic 2200 line driver
« Reply #6 on: June 29, 2019, 03:48:40 AM »
I changed the valve stage to give it more current and took the output from a 10k anode load. To my ears its now sounding less strangled, but its now got extra x4 gain. I could go back to a cathode follower but as i have another with that i thought it'd be good to compare them.

abbey road d enfer

Re: mic 2200 line driver
« Reply #7 on: June 29, 2019, 06:28:51 AM »
I changed the valve stage to give it more current and took the output from a 10k anode load. To my ears its now sounding less strangled, but its now got extra x4 gain. I could go back to a cathode follower but as i have another with that i thought it'd be good to compare them.
So replace the anode res with a 2.2k.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

moamps

Re: mic 2200 line driver
« Reply #8 on: June 29, 2019, 07:07:53 AM »
I changed the valve stage to give it more current and took the output from a 10k anode load. To my ears its now sounding less strangled, but its now got extra x4 gain. I could go back to a cathode follower but as i have another with that i thought it'd be good to compare them.

Just replace the resistor on + input of IC18 (R162) with trimmer of 150 or 220k and connect its wiper to + in of IC18. Adjust it to get the same level at output as on non-modified channel.


abbey road d enfer

Re: mic 2200 line driver
« Reply #9 on: June 29, 2019, 07:13:14 AM »
Is the transformer actually fitted to the board? If not, the balanced line driver may be upset if inserting an attenuator at its input. CMRR of EBOS is dependant on very low Z drive.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


waxscum

Re: mic 2200 line driver
« Reply #10 on: June 29, 2019, 10:07:22 AM »
Thanks for all replies.
Although the board is easy to work on once its out of the box, its SMD so there is no room to add trimmers. I might get a pair of fixed resistors in there.
Had to look up ebos and found;- https://groupdiy.com/index.php?topic=34561.0
I had a vague recollection this had been discussed before, but my search terms were inadequate.
Will read and digest.

ruffrecords

Re: mic 2200 line driver
« Reply #11 on: June 29, 2019, 12:10:43 PM »
If you get the sound you want with a 10K anode load then keep it but split into say 9K and 1K and take the output from the junction of the two.

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'


 

Related Topics

  Subject / Started by Replies Last post
5 Replies
2700 Views
Last post July 06, 2004, 07:17:33 PM
by SonsOfThunder
5 Replies
3266 Views
Last post September 02, 2004, 09:51:10 PM
by PRR
26 Replies
11452 Views
Last post June 03, 2005, 04:55:21 PM
by clintrubber
1 Replies
3136 Views
Last post December 02, 2011, 08:56:52 PM
by pucho812