Bass pre-amp DI output - diyAudio
Go Back   Home > Forums > Live Sound > Instruments and Amps

Instruments and Amps Everything that makes music, Especially including instrument amps.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 13th May 2013, 11:17 AM   #1
diybass is offline diybass  New Zealand
diyAudio Member
 
Join Date: Jun 2012
Default Bass pre-amp DI output

I am looking to add a balanced DI output to my DIY bass preamp. It consists of a copy of the Carl Martin Compressor and a single channel copy of an Alembic F2B preamp, connected in an enclosure. The Alembic F2B output is line level. I would like to be able to switch between pre comp and post comp+preamp, but failing that I could easily live with just post output.
After the preamp, I have added a master volume control, so I don't know how that would work with a transformer? I guess I would have to add an active DI out circuit? I want a DI output that isn't affected by the master volume control. A volume control for the DI would be cool, but not essential.

Any suggestions? I'm still really new to electronics, so any help is really appreciated! Cheers.
  Reply With Quote
Old 13th May 2013, 11:32 AM   #2
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
Quote:
Originally Posted by diybass View Post
After the preamp, I have added a master volume control......

I want a DI output that isn't affected by the master volume control....

A volume control for the DI would be cool, but not essential.
I guess you could 'just' connect DI out SE/balanced line trafo before your volume control

but like you say, failures from wrong impedance matching scares me too
  Reply With Quote
Old 13th May 2013, 11:35 AM   #3
diybass is offline diybass  New Zealand
diyAudio Member
 
Join Date: Jun 2012
Thanks for the quick reply. Would it not be affected by the master volume control?
  Reply With Quote
Old 13th May 2013, 11:40 AM   #4
tinitus is offline tinitus  Europe
diyAudio Moderator R.I.P.
 
Join Date: Nov 2005
not if you can take the signal somewhere before the volume control, and connect directly to back panel XLR, via balanced trafo

but a schematic of your actual preamp is needed to be certain how to
  Reply With Quote
Old 13th May 2013, 11:53 AM   #5
diybass is offline diybass  New Zealand
diyAudio Member
 
Join Date: Jun 2012
Here's the schematic, I think it's pretty accurate.
Attached Images
File Type: gif AlembicF2B_SCH.gif (13.8 KB, 130 views)
  Reply With Quote
Old 13th May 2013, 06:03 PM   #6
diyAudio Member
 
chrispenycate's Avatar
 
Join Date: Aug 2006
Location: Geneva, Switzerland
250k pot; a touch high for most DI transformers. Is the volume pot linear or log? If it's lin you could just about get away with loading it with a decent passive DI transformer, which will probably load it with about 100kΩ. But do you really want the DI After the master volume, or will you want DI level to remain constant while you adjust your local listening level?

Anyway, with an impedance transformer like that, output will be mic level; if you want a balanced line level out, you really would like a buffer; a cathode follower would be a good solution (oh, sure we can do a solid state buffer; but that's your recording output, wouldn't it be nice to tube all the way? And the power supply's there (I assume there's some reserve power?), whereas, with transistors… I suppose we could run something off 300V, but it's a challenge.

With a buffer, no problem about putting it pre/post compressor (if you plan it to be switched, obviously. If you take the grid reference from the previous stage rather than doing a complete internal bias, sure switching is complex, so don't. It's only a few extra components).

Trouble is, it's another tube socket, more heater wiring, quite a lot more mechanics.

With a 10k output drive, for a bass, you need a big output capacitor, and your output transformer's going to be massive so as not to saturate the core with the low frequencies, and don't forget the ground lift switch.

Is that preamp really only giving line level off a bass? I''ve had a volt and a half off a fender on snap; not that that circuit would have any difficulty handling it, I just wouldn't be surprised at much higher peaks.

Where do you insert the compressor? Before the master?
  Reply With Quote
Old 13th May 2013, 11:39 PM   #7
diyAudio Member
 
Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
JENSEN TRANSFORMERS, INC. - LINE OUTPUT TRANSFORMERS
http://www.jensen-transformers.com/datashts/10k611m.pdf

check out the sample tube driver circuit for the DI...

We always favored the BM series for just 600:600 because they were SO hefty you didn't have to adjust the levels so often, they just sounded good if you got in the ballpark http://www.jensen-transformers.com/datashts/11bmcf.pdf but that's not direct from a tube. Main output from a mixing console...

The Trace Elliot V8 I'm starting to build a clone of uses only op amps for the DI, no transformer; it is considered the worst part of the amp.

Last edited by cyclecamper; 13th May 2013 at 11:48 PM.
  Reply With Quote
Old 14th May 2013, 01:18 AM   #8
diybass is offline diybass  New Zealand
diyAudio Member
 
Join Date: Jun 2012
The compressor is instrument level in and out, so it is before the preamp and has effects loop sockets on the back of the enclosure. Yeah, the preamp output is line level, but it is quite a hot output, that is one of the reasons I added the master volume.

I want the DI output to be mic level with a ground switch, mainly for gigging. I want the the DI level to be constant, so the master volume only controls my power amp and speaker cab.

I would like to keep it as few components as possible, Failing that I could go tube, I just don't have alot of money. That jensen sample tube driver circuit looks good, I don't know where I could get a 12BH7 from in NZ though, could be pricey. I don't mind spending a bit on a good transformer though. I do want to keep away from op-amps, the compressor is the only thing with op-amps in this unit.
  Reply With Quote
Old 14th May 2013, 01:44 AM   #9
diyAudio Member
 
Join Date: May 2010
Location: was Chicago IL, now Long Beach CA
Yes, using the Jensen transformer will be expensive too, but worth every penny, and TRUE floating unreferenced hum-cancelling balanced that won't be affected by a trucker with a CB linear or your local ham radio operator or localAM station or the neon sign behind your amp at the local bar. AND good bass!
  Reply With Quote
Old 14th May 2013, 02:17 AM   #10
diybass is offline diybass  New Zealand
diyAudio Member
 
Join Date: Jun 2012
So, could I use just a transformer? How would I wire it? Or is the master volume control creating problems? The master pot is 250K audio taper. I don't mind changing the output pot value to make it work.

It would work with two transformers wouldn't it? One for DI out, one for line out with volume control after tranny? But that is out of the question because of the price!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Expensive transformer for bass DI? kkurosawa Instruments and Amps 12 28th November 2012 07:22 PM
Acoustic Guitar Pre/Comp/EQ/Blender/DI Josh Duke Analog Line Level 9 26th May 2012 11:49 AM
Impedance matching for DI to Mic Pre Fezzle Instruments and Amps 67 27th February 2012 10:32 PM
Impedance matching for DI to Mic Pre Fezzle Solid State 1 10th February 2012 07:13 PM
Help needed with direct output (DI) for bass amp funk1980 Instruments and Amps 11 3rd February 2012 10:53 PM


New To Site? Need Help?

All times are GMT. The time now is 02:04 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2