REDD.47 clone build assistance, please...

[ron_swanson]

Hello,

I've been slowly building a point-to-point REDD.47 mic preamplifier based on a design and suggestions found here in GroupDIY and elsewhere. Hoping that those who have experience with a real unit, a clone and / or building one might be able to assist with what front panel controls would be considered minimum to be useful? I understand this last sentence is a lot of implied user 'preference', but in my case, I'm looking to complete a basic usable working unit. Most of the schematics I have found don't include any or only few front panel controls and I've found nothing that is 100% inclusive. A couple of the schematics I have on hand do show fine gain controls and rumble filters, but still not sure what to include and what is less than useful or not just important. Without having any first hand experience with a REDD.47, I'm not sure what exactly would make the unit a useful device.

At the moment, I have an enclosure with a built and tested power section and the basic amplifier in prototype status. So far, so good.

With this in mind, what would a builder / user consider the basic, must have controls?

1. Input and / or output gain controls
2. Rumble / high pass filter
3. Polarity
4. Fine gain controls
5. Meter - I see units on the Interwebs with a meter. Can't imagine that is a 'must have'.
6. Phantom Power - I have built a working 48V phantom circuit, designed and tested as best as I can at this point in the build.
7. Anything other?

The above aside, I'd really like to have a DI input, but can't find anything anywhere explaining how to do this. Any suggestions or pointers would be appreciated.

At the end of the day, I'm looking for this build to basic, no-frills, useful unit - at least as a start.

Any help or thoughts will be greatly appreciated.

Thanks in advance!

 

[TimG]

Check out this group member's build. Beautiful case design but also the most elemental functions of a Redd47.
https://groupdiy.com/threads/laser-engraved-faceplate-redd-47-build.78835/Awesome simplicity! You want to put it to work.

I am building a Redd47 clone (Orange86) and the designer thinks VU meters are entirely unnecessary although I'm adding a couple!! Phantom 48, Polarity. Gain. Pad. And "Squish".

 

[mattrad]

It really depends on your style! One gain knob could be all you really need.

If you plan on driving the tubes real hard for effect, both input and output volume controls are nifty to have- pump up the input into saturation and and then attenuate with output vol for sane output levels. Not really sure if the REDDs do the distortion thing too well but id be curious. Fine gain setup could be nice but ultimately seems unnecessary to me, one input knob works just fine!

If you plan on using condenser mics, go for phantom power. If not, skip it.

HPF and Polarity are a luxury (in my world) but could save your ass in a pinch.

You can very easily do without the meter. They look cool though.

From what i understand for a DI you can use a Mono jack w/ the tip straight into the first tube grid, and a 1M resistor to ground (at least thats what i've done). Maybe it shouldn't be that simple- Someone can correct me on this.

Also, not a bad idea to make the preamp bare-bones style and use it for a while to see if your process is begging for any extra features. If yes, add them in then.

 

[solkatten]

I think a output pad + load resistor, post opt is great option to drive the line stage + OPT into distorsion. The values are ok with any 600ohm seconadary OPT.

You cant place any hpf inside the feedback loop, before the grid of ef86 tube would do the job I think

 

[ron_swanson]

Check out this group member's build. Beautiful case design but also the most elemental functions of a Redd47.
https://groupdiy.com/threads/laser-engraved-faceplate-redd-47-build.78835/Awesome simplicity! You want to put it to work.

I am building a Redd47 clone (Orange86) and the designer thinks VU meters are entirely unnecessary although I'm adding a couple!! Phantom 48, Polarity. Gain. Pad. And "Squish".

I did see the 'most elemental functions of a Redd47.' thread. Very nice! And, 'yes' that build is the essence of 'basic'.

I too have a Orange86 kit that after spending an inordinate amount of frustrating hours I had to reluctantly abandon the build as I could not get my head around the build. Probably above my pay grade atm as clearly others have been able to successfully complete. I've built many tube guitar amps, and over a dozen studio devices ( both from kits and scratch built ), but the Organe86 just didn't sit with me for whatever reasons.

It really depends on your style! One gain knob could be all you really need.

If you plan on driving the tubes real hard for effect, both input and output volume controls are nifty to have- pump up the input into saturation and and then attenuate with output vol for sane output levels. Not really sure if the REDDs do the distortion thing too well but id be curious. Fine gain setup could be nice but ultimately seems unnecessary to me, one input knob works just fine!

If you plan on using condenser mics, go for phantom power. If not, skip it.

HPF and Polarity are a luxury (in my world) but could save your ass in a pinch.

You can very easily do without the meter. They look cool though.

From what i understand for a DI you can use a Mono jack w/ the tip straight into the first tube grid, and a 1M resistor to ground (at least thats what i've done). Maybe it shouldn't be that simple- Someone can correct me on this.

Also, not a bad idea to make the preamp bare-bones style and use it for a while to see if your process is begging for any extra features. If yes, add them in then.

Yes, condenser mics are in the mix. I guess I could use a in-line phantom box, but prefer having it part of the build.

Your DI tip is likely a workable resolve and is what I was thinking would likely work, but is it as simple as just making a connection to the first grid? Do I need to somehow shunt the mic input using a switch(able) jack or ?

I agree, I'm trying to work out what is 'bare-bones' enough without going crazy. Anything found lacking after some use could be added is really necessary.

I think a output pad + load resistor, post opt is great option to drive the line stage + OPT into distorsion. The values are ok with any 600ohm seconadary OPT.

You cant place any hpf inside the feedback loop, before the grid of ef86 tube would do the job I think

Thanks for the pad tips. I found something simular elsewhere in this forum that was supposedly used in a REDD.47 build taht I'm considering, but I'll take a look at what you have added here. Thanks!

>> You cant place any hpf inside the feedback loop, before the grid of ef86 tube would do the job I think

You CAN'T or CAN? Your sentence above seems to contradict itself or maybe I'm mis-reading.

Thanks to all who submitted replies!

Cheers!

 

[solkatten]

I did see the 'most elemental functions of a Redd47.' thread. Very nice! And, 'yes' that build is the essence of 'basic'.

I too have a Orange86 kit that after spending an inordinate amount of frustrating hours I had to reluctantly abandon the build as I could not get my head around the build. Probably above my pay grade atm as clearly others have been able to successfully complete. I've built many tube guitar amps, and over a dozen studio devices ( both from kits and scratch built ), but the Organe86 just didn't sit with me for whatever reasons.



Yes, condenser mics are in the mix. I guess I could use a in-line phantom box, but prefer having it part of the build.

Your DI tip is likely a workable resolve and is what I was thinking would likely work, but is it as simple as just making a connection to the first grid? Do I need to somehow shunt the mic input using a switch(able) jack or ?

I agree, I'm trying to work out what is 'bare-bones' enough without going crazy. Anything found lacking after some use could be added is really necessary.




Thanks for the pad tips. I found something simular elsewhere in this forum that was supposedly used in a REDD.47 build taht I'm considering, but I'll take a look at what you have added here. Thanks!

>> You cant place any hpf inside the feedback loop, before the grid of ef86 tube would do the job I think

You CAN'T or CAN? Your sentence above seems to contradict itself or maybe I'm mis-reading.

Thanks to all who submitted replies!

Cheers!

Hi before the grid would be outside the feedback loop, so its a bad idea to place the hpf inside the loop. I hope that make sense

 

[janos.hardi]

This my main inspiration for the redd build: Delta 4-7 Plus dual preamp — Highland Dynamics. The input gain structure and attenuation is puzzling to me though. The switchable nfb is a great idea i think, you can turn the nfb off (completely?).

 

[solkatten]

The original redd 47 has 3 gain steps, they just added a forth that disconnects the feedback loop. Full gain and full THD
Removing feedback is never a problem, adding more could lead to stability issues….

 

[janos.hardi]

The original redd 47 has 3 gain steps, they just added a forth that disconnects the feedback loop. Full gain and full THD

exactly, maximum color, especially with the fully variable pre and post attenuator

 

[BigPauly]

I think a output pad + load resistor, post opt is great option to drive the line stage + OPT into distorsion. The values are ok with any 600ohm seconadary OPT.

You cant place any hpf inside the feedback loop, before the grid of ef86 tube would do the job I think

Ok, can you elaborate on this D.I. setup? When the D.I. plug(guitar, for example) is not plugged in how does the 1 M resistor to ground affect the tx input? Then, the schematics pics show the circuit going to something labeled as HP, with what looks like four terminals? What is that?

 

[rock soderstrom]

Ok, can you elaborate on this D.I. setup? When the D.I. plug(guitar, for example) is not plugged in how does the 1 M resistor to ground affect the tx input?

If there is no instrument in the DI input, the influence of the 1M resistor is small, as it is in parallel with the termination (Rx) of the IP transformer, which is much smaller. Rx essentially determines the input impedance of the circuit, i.e. also the impedance that the microphone "sees" on the primary side of the IPT. ( for a 1:7 stepup IPT it would be Rx||Rg divided by 7×7)

Then, the schematics pics show the circuit going to something labeled as HP, with what looks like four terminals? What is that?

HP=high pass aka rumble-filter in this application. Basically a switch with two capacitors here. The more capacitance the more low frequencies will enter the amplifier and vice versa.