Need help wiring DI output in tube preamp

[nbtone]

I wonder if anyone knows what it would take to wire a DI output from a 12ax7 preamp circuit? It would seem to me that all I would need is a 1/4" jack, some wire, and maybe a diode or two. Any input would be appreciated.

[andrew_k]

I wonder if anyone knows what it would take to wire a DI output from a 12ax7 preamp circuit? It would seem to me that all I would need is a 1/4" jack, some wire, and maybe a diode or two. Any input would be appreciated.

Do you mean DI or preamp out? A preamp out would be what you described. A DI output as I know the term describes a balanced output at ~600ohm for running into a mixing desk or similar. That would require an output/isolation transformer, probably something like 10k:600ohm

Very happy to be told I'm terribly wrong as I plan to eventually add the same feature to a bass pre.

[Enzo]

In this day and age of people using the wrong terms for things all the time, I think it perfectly proper to ask just what we might have in mind here. Especially when the asker proposes diodes.

My immediate reaction - and I am assuming a plain old line out preamp signal such as an effects send - is that you need to consider the voltages. Line level signals are about a volt. SIgnal levels on 12AX7s is usually considerably more than that. That in an of itself is not a problem, but you do have to deal with it.

Without seeing your circuit, it is impossible to advise much further. You want it pre- or post- some controls, like pre-EQ? You want a clean steady signal - like a tuner out?

[nbtone]

Hi,
Thanks for the reply. I need a balanced output for plugging into a mixing desk. I'm manufacturing bass guitar preamps, and I recently approached a recording studio to see if I could unload a few of them. They want a DI out before they"ll buy one. I guess they're afraid the loose screws in the windows and doors would get into the mix. What should I do? My preamp is for live situations. It goes between the bass guitar and the amp.

Do you mean DI or preamp out? A preamp out would be what you described. A DI output as I know the term describes a balanced output at ~600ohm for running into a mixing desk or similar. That would require an output/isolation transformer, probably something like 10k:600ohm

Very happy to be told I'm terribly wrong as I plan to eventually add the same feature to a bass pre.

[nbtone]

The circuit can be found here: Google Patents There are a few changes in the production model that I'm marketing, but this is the main idea. I need to output the final signal to a mixing desk. Not sure what you mean by a tuner out.

In this day and age of people using the wrong terms for things all the time, I think it perfectly proper to ask just what we might have in mind here. Especially when the asker proposes diodes.

My immediate reaction - and I am assuming a plain old line out preamp signal such as an effects send - is that you need to consider the voltages. Line level signals are about a volt. SIgnal levels on 12AX7s is usually considerably more than that. That in an of itself is not a problem, but you do have to deal with it.

Without seeing your circuit, it is impossible to advise much further. You want it pre- or post- some controls, like pre-EQ? You want a clean steady signal - like a tuner out?

[Enzo]

A tuner output is a feature on some amps. it is an output right after the input, so no processing of the signal. Just the sort of thing you'd want to send to a tuner.

Um... Google patents comes up a search window claiming 7 million patents. Perhaps the title or number of said patent?

ANyway, so you want the preamp output to also be available in a balanced form.

tear open a direct box and steal the circuit.

[stingray_65]

check out Webers

they have a transformer I have used with great sucsess that taps off of one of the speaker out.

https://taweber.powweb.com/store/balun.jpg

I replaced R1 with a locking pot like you would use for a tube bias (also can be found at Webers)

I suppose you could use any pot there, dial it in and measure it, replace with a resitor. the advantage of using the pot though is if you like to roll tubes like I do you can get too wide of a range of output levels.

I terminated mine with a 1/4" jack for personal convienience, but an XLR chassis socket may be more apropriate to most (also available at Webers)

this circuit can be applied to most any amp I would guess and cost less than $20.

Ray

[nbtone]

I'll try it again. Sorry! Electronic bass instrument tube ... - Google Patents

A tuner output is a feature on some amps. it is an output right after the input, so no processing of the signal. Just the sort of thing you'd want to send to a tuner.

Um... Google patents comes up a search window claiming 7 million patents. Perhaps the title or number of said patent?

ANyway, so you want the preamp output to also be available in a balanced form.

tear open a direct box and steal the circuit.

[Enzo]

Stingray, he's making preamps - no speaker.

[stingray_65]

Stingray, he's making preamps - no speaker.

I saw that after the fact


Ray

[nbtone]

I found a schematic that might work

Do you think this one might work?

http://www.jensentransformers.com/as/as007.pdf

I don't know if I will need the input "ac coupling option" for my purposes.

[tedmich]

Do you think this one might work?

http://www.jensentransformers.com/as/as007.pdf

I don't know if I will need the input "ac coupling option" for my purposes.

I think this is more of a DI box for Instrument->board, not preamp-> board, check the old Paia Stack in a box with an XLR balanced output from a single 12ax7 tube preamp:
http://www.paia.com/prodimages/siabsch.pdf

[nbtone]

I think the stack in a box has a xlr preamp out, but it doesn't have a DI out for pro recording purposes. There isn't a transformer to convert the signal. Check these DI boxes out:
Whirlwind Direct Boxes and Re-amp Devices Musical Instruments Products from Full Compass
The ones with the jenson transformers look real good.

I think this is more of a DI box for Instrument->board, not preamp-> board, check the old Paia Stack in a box with an XLR balanced output from a single 12ax7 tube preamp:
http://www.paia.com/prodimages/siabsch.pdf

[tedmich]

I think the stack in a box has a xlr preamp out, but it doesn't have a DI out for pro recording purposes. There isn't a transformer to convert the signal. Check these DI boxes out:
Whirlwind Direct Boxes and Re-amp Devices Musical Instruments Products from Full Compass
The ones with the jenson transformers look real good.

Ummm... a balanced XLR output IS a pro audio interface, and you needn't use a transformer to make it; Op amps work fine, some think better.

to quote the SIAB has "a balanced XLR output for interfacing with pro studio gear and both normal and inverted unbalanced outputs."

You could PM Mr Anderton at HC and ask his input, he's way knowledgeable and pretty approachable too.
Harmony Central Musician Community Forums - View Profile: Anderton

[nbtone]

I looked at the schematic for you SIAB, and the output is the same, whether you are using a 1/4" jack or an xlr jack. I can understand the manual. This isn't what professional studios want for plugging into the mixing console. See:Whirlwind / Unbal - Balanced Lines, where balanced xlr outputs are explained. Here is a direct box explanation: Whirlwind / Direct Box Tech Article

Ummm... a balanced XLR output IS a pro audio interface, and you needn't use a transformer to make it; Op amps work fine, some think better.

to quote the SIAB has "a balanced XLR output for interfacing with pro studio gear and both normal and inverted unbalanced outputs."

You could PM Mr Anderton at HC and ask his input, he's way knowledgeable and pretty approachable too.
Harmony Central Musician Community Forums - View Profile: Anderton