EMI RS124

[emrr]

I gave them an "unofficial" EMI 1961 serial number since I wasn't aware of any originals from that year.

Looking around, I see some other replicas with 1965 serial #s.  What's the logic to the A/B/C at the end of the serial #? 

What color would you call that paint?

 

[emrr]

Motherload, thanks!

 

[letterbeacon]

I've nothing to add except to say thank you, Winston, for all the knowledge you're sharing in this thread and all the others on this forum.

Have a great weekend!

 

[rock soderstrom]

I've nothing to add except to say thank you, Winston, for all the knowledge you're sharing in this thread and all the others on this forum.

+++1

 

[Kid Squid]

Fantastic stuff. Thanks John !

 

[emrr]

There doesn’t seem to be any one official knob set, does there? There’s Altec knobs on some, chicken heads on some, GR’s on some, etc.

 

[andre tchmil]

and why did they choose to name it RS124 ?

 

[anvl]

Hello from Spain.

I've just finished my first RS124 PTP clone. You can see a handwritten prototype faceplate.

· Hammond power transformer
· Sowter iron IN & OUT (1231 + 1232)
· PSU modified (without diodes) using GZ34 rectifier + 2x0A2 regulators
· Stepped attack, stepped recovery
· Variable threshold
· Stepped output attenuator.

Works lovely !!!!! I will try to make some video and sound clips to clarify those who want to know how it sounds.

I also tried 6ES8 tubes instead of 6BC8. Both work nice.

In NO COMP position (sidechain to ground) it becomes a 16dB Gain line preamp, full of colour, full of flavour (tubes+transformers working).

I hope you like it

 

[Rob Flinn]

Hope this is the right thread to post this - please let me know if not and and I will delete and create a new topic.

London (UK) based and need a little help with the calibration of a vari mu I am finishing off - hopefully it will just be the final calibration steps as I don't have a distortion meter or scope and have promised not to buy any more kit I will only use occasionally (and this time I really mean it )

Can anyone recommend a good shop or DIYer who would be able and willing? Of course I am happy to pay in one or more of the following: cash, beer or spirits for someone's time.

Pretty much the only calibration is press the osccilator button on the front of the box with no signal applied. Listen to the box and adjust the balance pot so the ticking noise is at it minimum.

 

[Rob Flinn]

Thanks for the Reply Rob

Below is what I have in my notes for the calibration - is none of this really needed?? Would be awesome if that is the case !

Test Equipment required:​

• Low distortion Audio signal generator.
• Distortion Analyzer or Meter Trimming tool.

For each channel :

1) Take out the tube in the sidechain smallest (6AL5) tube.

2) Let the other tubes heat up for a few minutes.

3) Split a 1kHz signal and feed it into your input tube (connect the same signal in phase to pins 2 and 7 of the ECC85) reference to ground.

4) Set the trimmer between the ECC85 and ECC81 (DC Balance) for the lowest output signal possible.

5) Disconnect the Signal.

6) Connect a 50Hz signal to the "Link" point on the PCB

7) Set the trimmer next to the ECC85 for lowest output signal possible

8) Repeat everything from step 3 until no more reduction on output can be achieved.

9) Reset the GR meter trimmer with no signal applied to 0dB.

___________________________________________________________

5.2 Meter Alignment​

Under no circumstances use the meter mechanical adjustments on the meter front to correct readings.

The electronically ‘zero biased’ meter settings will require periodic re-adjustment. The metering circuit is necessarily very sensitive, change from the ‘zero’ position is quite normal and is not a cause for concern. The causes are normally slight
changes in valve performance due to ageing or variations in
the mains supply voltage.

5.3 Meter Adjustment​

Procedure:

1. Turn power on, wait for five minutes for the unit to warm up.
2. While waiting, make tea or other refreshing beverage.
3. With no signals present at the input, ensure Input Level
controls are turned right down.
4. Set Threshold to ‘zero’, Attack to ‘Fast’, Release to ‘Slow’.
5. Ensure Stereo Link switch is in ‘up’ position (no linking).
6. Use a trimming tool or small instrument screwdriver turn the
appropriate multiturn preset located on the front panel below
the Power and Stereo Link switches until the meter needle
is at the ‘0’ position on the scale.
7. Repeat procedure to other channel.
8. Drink tea or other beverage.

5.4 Distortion Trim​

Always get this done if a signal valve has been changed.
This procedure should be carried out by qualified personnel only.

Test Equipment required:
Low distortion Audio signal generator.
Distortion Analyzer or Meter Trimming tool.

Procedure:

• Connect generator to input of compressor.
• Connect Analyzer or distortion meter to output.
• Ensure the compressor has warmed up for at least five minutes.
• Set generator for 1 Khz and +4dBm output.
• Set Threshold to 5.
• Set Attack to ‘Fast’, Release to ‘Slow’.
• Adjust Input Level control to obtain 2 dB of gain reduction.
• Ensure Stereo Link switch is in the ‘up’ position ( no linking).
• Adjust the presets with a trimming tool or instrument screwdriver
• shaft which are inside the hole in the black plastic nuts (one for
• each channel) located on the valve deck, for minimum distortion.

Note: If using an analyzer which displays harmonic analysis adjust for minimum odd order distortion.

Not sure you're posting this in the right thread. I made my RS124's point to point exactly to the EMI circuit diagram with no pcb. The original circuit doesn't have all these extra presets. I think your project is the "Nu Varimu 436" which has it's own support thread [BUILD] NU VARIMU 436 build & help thread

 

[Rob Flinn]

ahhhh, that would make sense! Should I delete all my posts on this thread to clean it up?

That's up to you. I'm not a moderator here.

 

[anvl]

Working on vocals (mobile sound). I'll upload audio files (bypass vs comp ON) to listen carefully.

 

[thomasdf]

It appears to be working great ! but the vocals clearly are louder when the comp is engaged, you should tame the output.
Can't wait to see your finished unit ! Bravo
edit : nice metal work also !

 

[anvl]

I agree. Output attenuator is set to -10dB, maybe we could try -15dB to compare correctly. I will upload audio files (bypass vs comp ON) to listen carefully. I wanted to show how warm the vocal track is compressed using this RS124, more presence in the mix, even recording with mobile sound.

 

[thomasdf]

it certainly sounded denser and warmer ... beautiful !

 

[anvl]

Available if you want to send me other tracks to play with and make more testing on different scenarios.

 

[anvl]

RS124 vocal - bypass
https://1drv.ms/u/s!AsFe9VV3iBv0gT45x55llQfnI-uD
RS124 vocal - comp ON
https://1drv.ms/u/s!AsFe9VV3iBv0gT8jwcnYOPRTAO9t

 

[anvl]

RS124 bass - bypass
https://1drv.ms/u/s!AsFe9VV3iBv0gUBVwJ94niWMys_P
RS124 bass - comp
https://1drv.ms/u/s!AsFe9VV3iBv0gUG2gOXxdnSJOvAu

 

[anvl]

RS124 acoustic guitar - bypass
https://1drv.ms/u/s!AsFe9VV3iBv0gULl9Ms70i3Myu3D
RS124 acoustic guitar - Comp
https://1drv.ms/u/s!AsFe9VV3iBv0gUNy0-boycaM2ddA

 

[anvl]

Opinions? It would be great to hear people who listened to original units.
Thanks !!!