EMI RS124

[weiss]

Hey guys,

I'm finally continuing some builds since I didn’t have time in the past.

I did some changes to the layout to make it work with 240V mains instead of 120V. The secondaries of my power Tx are 200V which shouldn't make much difference i guess?

I am unsure about the balance potentiometers in the layout. The chandler version has only one balance potentiometer with balance push button (I'm assuming cathode balance??) on the left side front panel and not cathode + plate balance + meter trim potentiometers like in the schematic. i also don't find them back in the original 436 schematic..
where would you put the meter + plate balance trim? on the back?

Is it possible to include the superfuse mode in this layout?

thanks!

 

[letterbeacon]

Which schematic are you using? I used Winston's that the posted a few years ago. That one only had the 'balance' trim on the cathodes of V1.

In addition to that, I used a trim in place of R25 and a trim in place of R8. I used a small trim pot intended for a PCB for these two as they're only in there temporarily. I'm planning on measuring the value they're at and replacing with a fixed resistor when I next open it up. So I will basically only end up with one trimmer, the same as the Chandler.

In terms of where I placed them - I have a tag strip next to the meter on the front panel that I placed them on.

I hope that helps.

 

[snod_donkey]

Hi and hope you are getting on well with the comp builds! 

I started to build a unit a few years ago but did not get too far so i thought it was time to sort that out!

The circuits i have for this are the DRIP circuits from a good few years back and i see the EMI drawing here too.  Being as i had started the drip circuit build i might go ahead and use that but was not sure if anyone else had done that and got a good working unit?  This is going to be a point to built build

It appears to have a couple of extra POTS, has a 25k pot on V3 for Threshold Adj.


Any thought on this circuit build?

Thanks 

 

[Rob Flinn]

Hi and hope you are getting on well with the comp builds! 

I started to build a unit a few years ago but did not get too far so i thought it was time to sort that out!

The circuits i have for this are the DRIP circuits from a good few years back and i see the EMI drawing here too.  Being as i had started the drip circuit build i might go ahead and use that but was not sure if anyone else had done that and got a good working unit?  This is going to be a point to built build

It appears to have a couple of extra POTS, has a 25k pot on V3 for Threshold Adj.


Any thought on this circuit build?

Thanks 

Might be useful if you posted a circuit diagram.

 

[scott2000]

Might be useful if you posted a circuit diagram.

I think this it it

 

[Rob Flinn]

Interesting, he's just subbed in parts of the UA 176 circuit.

 

[snod_donkey]

I think this it it

It's not hat one. It is actually the RS124 clone apparently.  I will dig the circuits out

I am thinking to start i might built the standard 436c and get that working as per the original circuits and then start adding in the mods.    I am looking for transformers at the moment that will do the job.  The sowter would be nice but might be a bit pricey for this project.

I have lots of old 10K to 10K types kicking about so could give them a try.  Not so sure on the output TX though

 

[letterbeacon]

If your aim is an RS124, why not just build the schematic Winston O Boogie posted? There are quite a few verified builds on this thread of it.

Unless I guess if you want to compare the two circuits.

 

[snod_donkey]

If your aim is an RS124, why not just build the schematic Winston O Boogie posted? There are quite a few verified builds on this thread of it.

Unless I guess if you want to compare the two circuits.

I am thinking to maybe compare the 2.  It will be very easy to add the mods in after i have the basic unit working. There is not actually much difference looking at them.

Doing it this way will probably make it easy to fault find should i have any issues.  Just got to work out what transformers will work best too

 

[Rob Flinn]

I wouldn't bother with the basic 436, every one I have built sounded unusable to me.  Winston's circuit is the one to use, it sounds very good.  Drips circuit is probably ...... Drips circuit.

The edcor 600:10k & 10k:600 work well for in & out on this project.

 

[snod_donkey]

I wouldn't bother with the basic 436, every one I have built sounded unusable to me.  Winston's circuit is the one to use, it sounds very good.  Drips circuit is probably ...... Drips circuit.

The edcor 600:10k & 10k:600 work well for in & out on this project.

Hi Rob and thanks for the input!

I am actually building 2 units side by side, one with the standard original circuit and one with the mods.  Got spare time on my hands so just an interesting project to play with.

As for the TX i did look at the Edcor as a "low cost" option. 

Was unsure why a 600 ohm to 10k though as i thought the input might want to be a higher impedance and less step-up to the signal?

As for the output is 10k primary high enough.  Asking as i actually have some 10k to 600 ohm output TX which are un-gaped. They may well work.  As a push pull circuit i think un-gaped "should" work

 

[Rob Flinn]

Hi Rob and thanks for the input!

I am actually building 2 units side by side, one with the standard original circuit and one with the mods.  Got spare time on my hands so just an interesting project to play with.

As for the TX i did look at the Edcor as a "low cost" option. 

Was unsure why a 600 ohm to 10k though as i thought the input might want to be a higher impedance and less step-up to the signal?

As for the output is 10k primary high enough.  Asking as i actually have some 10k to 600 ohm output TX which are un-gaped. They may well work.  As a push pull circuit i think un-gaped "should" work

You asked for " transformers at the moment that will do the job." & also said "The sowter would be nice but might be a bit pricey for this project".  I never said the Edcor were optimum, but I do know the circuit will work with them.

If you have time to experiment then you can try what you have & report back.

 

[snod_donkey]

You asked for " transformers at the moment that will do the job." & also said "The sowter would be nice but might be a bit pricey for this project".  I never said the Edcor were optimum, but I do know the circuit will work with them.

If you have time to experiment then you can try what you have & report back.

I know you didn't say that! I simply agreed with you as a low cost option

Thanks 

 

[snod_donkey]

The RS.124 really shouldn't sound as good as it does given how mostly unusable the original 436 is.  I've seen/read many folks dismiss the 124  based purely on the schematic but, anyone wanting to build a unit like this owes it to themselves to just forget building a stock 436 and just build a 124 as per the schematic!     

Transformers: 
In units I built from scratch (rather than modded Altecs) I used a honking nice Cinemag on the output.  It was the same I used on REDD.47 amps and, although expensive, was the best I auditioned in the spot.
On the input, I used a Sowter, but *not* the one they list online as being for the 436.  I guess it's moot now as I hear they don't build it anymore.  I guess the stock Sowter would work nicely and I see a couple from Lundahl that I would like to play with.
This is assuming a more 'cost no object' build and, without doubt, I would guess that the ones used by the folks on here are just fine too.
Take care fellas

Thanks for all the info

I have been playing with various transformers and found pretty much anything will "work" and sound ok.  Just a case of fine tuning to get what sounds best.  At the moment i am testing with a 600 ohm to 10k on the input and a 10k to 600 ohm on the output.

Does anyone have any sort of test specs for the compression though?  As in if i stuff 0db at 1k hz in what sort of compression i could expect to see say at 2:1 ratio settings ? 

I am struggling to get more than about 10 to 12 db reduction.   

Thanks

 

[Rob Flinn]

Thanks for all the info

I have been playing with various transformers and found pretty much anything will "work" and sound ok.  Just a case of fine tuning to get what sounds best.  At the moment i am testing with a 600 ohm to 10k on the input and a 10k to 600 ohm on the output.

Does anyone have any sort of test specs for the compression though?  As in if i stuff 0db at 1k hz in what sort of compression i could expect to see say at 2:1 ratio settings ? 

I am struggling to get more than about 10 to 12 db reduction.   

Thanks

I think I was getting maybe 18-20dB.  I don't think you can get  more than that  before the vari mu valves start to flake out.

 

[snod_donkey]

I think I was getting maybe 18-20dB.  I don't think you can get  more than that  before the vari mu valves start to flake out.

Thanks rob

I did wonder if that was the case. It struggles past a certain point but i imagine that is a huge amount of gain and it hits its limits.

Well it all appears to be working ok i think.  I can set the cathode balance fine and i also have an anode balanced control which when not compressing is well balanced.  As you increase the compression the anode voltage do get a bit off though and not sure how normal that is.  Tried a couple of valves with the same results.

It's sounding pretty good. Very different to the opto valve compressors i have done so just getting my head around what it is doing

On a side note i have just tried an ECC82 on the output stage and that has been running fine and again looks to be pretty good.
Just thought i would try that to see the difference

All good fun!

 

[Rob Flinn]

The anode volts will change dramatically under compression.  Think about it, you are shutting the valve down quite a lot.

 

[snod_donkey]

Shameless name drop:
Attached is a pic of Beatles engineer Ken Scott and I with one of my RS.124 comps.

When talking to Ken about the RS.124 in use at Abbey Road, he mentioned there were a couple of times when he was using them in the cutting/transfer room when the needles never strayed from max compression (he said 20dB) all the way through the track. 
Wish I could remember which particular Beatles tracks he was referring to but I'm not 100% sure now.

All very interesting stuff. I am learning quite a bit having this running on the bench too.  I actually have ordered some of those valves to try so will report back with anything i can find spec wise.

Might change the input transformer next too as 600 ohm primary might be a bit on the low side for some of the gear i want to run it with. I have a few Vortexion mixers which really want to see 10k or more to work best

 

[snod_donkey]

What you have'll work but, if it's a 600:10K in there,  you don't need that much of a step up on the front end. A 10K primary with dual 10K secondaries is more in line with what was there originally.

Thanks again for that.  Was thinking it may well have too much gain like that from the TX.  Will have a dig through some parts as i may have some old EMI transformers around that spec somewhere.

I do have a valve tester here so will see if i can get a few valves that are a bit more matched up too

Almost happy with it now anyway   

 

[Rob Flinn]

I do have a valve tester here so will see if i can get a few valves that are a bit more matched up too

What you need really is a valve curve tracer.  The point is to get valves where their curves match so they are matched when the compression level changes.  If you have them matched when there is no compression then there is a good chance they won't be matched when you have 10dB of compression happening & the bias is completely different on them.  Something like a Utracer is a good test tool for this.