The No.1 Website for Pro Audio
Re-amp box - Splitter
Old 1 week ago
  #1
Here for the gear
 

Re-amp box - Splitter

Hello to all,

I would like to build a re-amp box with splitter to record 3 guitar amps simultaneously.
I search in the net to find a schematic about it without any success, i found only for passive reamp and with one output.
As I know the circuit must have a buffer in front and 3 transformers to make the impedance matching.

Does anyone have a schematic for a build like this?
Thank you in advance!
Old 1 week ago
  #2
Lives for gear
No need for impedance matching transformers. You do want the guitar to see an impedance of about 1 Mohm, so just use that as biasing resistor for your unity gain opamp buffer, which in turn will happily drive the three guitar amp inputs in parallel, unless you want separate gain adjustments or something.

If you use a FET opamp and a symmetric (e.g. +/- 15 V) supply, you can have your input DC coupled and use a 1M biasing resistor, but if you use a bipolar opamp and/or a single supply circuit, use a DC-blocking cap. Usually what I do is use a 2M2 biasing resistor for the opamp and another one on the input side of the cap (so the input impedance is 1M1), to make sure the input is at 0 V and you don't get clicks / pops when plugging in. A 100 n film cap will do.
Old 1 week ago
  #3
Lives for gear
 
nosebleedaudio's Avatar
 

The main issue is isolating the amps chassis's, you could try using one reamp box with a Y cable driving both amps and see if you have Hum/buzz compared to only ONE amp..
3 Reamp's would/should result in NO issues..
Old 1 week ago
  #4
Here for the gear
 

Hello Cabirio,

thank you for your help.
I forgot to mention that I'm interesting to build an Active Re-amp box for studio use.
Yes, I would like 3 separate outputs.
I found on web the Radial JD7 and on their block diagram they show the signal chain.
Basically what I am looking for is the Balanced In section and the output 2,3,4.
The transformer after balanced in I think is the part that it makes the conversion from balanced to unbalanced, please correct me if I am wrong.

So after the conversion I must use 3 buffers for 3 output channels and 3 transformers for phase split?
All of them based on the Radial block.

Thank you
Attached Thumbnails
Re-amp box - Splitter-radial-jd7.jpg  
Old 6 days ago
  #5
Lives for gear
Apologies, I misread, I was talking about guitar -> three amps, not a re-amp box. Michael above has a point about chassis isolation, so output transformers is a good idea. You don't really need one at the input, a normal balanced receiver (ic or opamp-based) will do, or do you want one for colour?

Edit: also, do you want a single overall gain adjustment, or separate ones for each output?
Old 6 days ago
  #6
Here for the gear
 

Quote:
Originally Posted by nosebleedaudio View Post
The main issue is isolating the amps chassis's, you could try using one reamp box with a Y cable driving both amps and see if you have Hum/buzz compared to only ONE amp..
3 Reamp's would/should result in NO issues..
Michael thank you for your answer.
I didn't try to use one reamp with Y cable and to be honest I would like to have three separate reamp boxes to be safe and to don't have any issues with hum/buzz, quality loss.
Old 6 days ago
  #7
Here for the gear
 

Quote:
Originally Posted by Cabirio View Post
Apologies, I misread, I was talking about guitar -> three amps, not a re-amp box. Michael above has a point about chassis isolation, so output transformers is a good idea. You don't really need one at the input, a normal balanced receiver (ic or opamp-based) will do, or do you want one for colour?

Edit: also, do you want a single overall gain adjustment, or separate ones for each output?
Cabirio thank you. I didn't explain it very well also.

I want to be 3 separate reamp boxes with gain adjustments.
As for the transformer, I think that it's better to use a transformer for the conversion and if it's a good one will not add to much colour to the sound.

Based on this idea I must use a transformer for the conversion, 3 buffer circuits one for each channel and a transformer on for each channel for galvanic isolation.
Am I right?
Old 6 days ago
  #8
Lives for gear
See attached. Comments:

- I have used Jensen JT-11P-1HPC input and JT-11-FLPCH output transformers because I happen to have simulation models that I built for them. Some of the circuitry is specific to them, in particular the 11P doesn't require the usual RC damping network if the load is 10k as shown and the Pin1 connection to ground is also what's shown in its datasheet, others may be different.

- As shown, with P1, P2, P3 being 20k linear pots, the gain adjustment range would be roughly from -30 to +10 dB (wiper fully right / left, respectively), which sounds reasonable to me. This is assuming the 11P input transformer, which has a 3 dB insertion loss, others may be different. It would be easy to increase / decrease the overall gain by increasing / decreasing R3.

- For clarity I don't show ground lift switches, they would simply connect each of Pin1, Out1-, Out2-, Out3- to ground. Also no phase reversal switches, if required you can copy the wiring from the block diagram you posted. Btw the circuit will keep absolute phase as both the input stage and the buffers are inverting.

- The LM4562 is a pretty good opamp, cheap, widely available and the input one will drive the worst case ~600 ohm load (with all pots on max. gain) with ease. It's dual so conveniently you can use two of them. There are better, more modern SMD opamps that you could use with browndogs but I don't think you would get an audible improvement.

- I show the usual +/- 15 V supply but you can increase it to +/- 17 V Γ  la Douglas Self for more headroom or use the LME49860 (same thing with a higher supply range) with a psu of up to +/- 21 V for even more headroom. Even if you go with standard values (+/- 15, +/- 18) avoid fixed 78XX / 79XX regulators, the LM317 / LM337 have much better ripple rejection and noise performance.

- Not shown are the usual supply bypassing caps, 100n ceramics (X7R) from each opamp supply pin to ground placed as close as possible to the opamps. Edit: also 100u bypassing electrolytics (e.g. Panasonic FM/FR) from + and - to ground where the supply enters the PCB, if you have it on a separate board. For C2-C5 use film (e.g. Wima FKP) or NP0/C0G ceramics.
Attached Thumbnails
Re-amp box - Splitter-reamp.png  
Old 6 days ago
  #9
Here for the gear
 

Cabirio, thank you so much!

Your design is very helpful and very clean!
Thank you!
In case that I can't find Jensen transformer I will try to find something similar to them.

You are great, thank you!
πŸ“ Reply
Topic:
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
πŸ–¨οΈ Show Printable Version
βœ‰οΈ Email this Page
πŸ” Search thread
♾️ Similar Threads
πŸŽ™οΈ View mentioned gear