EMI RS124
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craptical
Well-known member
Greetings from Abbey Road Studio 2! 
craptical
Well-known member
Sorry, they didn't let me take them apart! ;D
Im re attempting to build RS124 on my bench couldnt get it to work 1st time round......My question is will a Sowter 4383 input transformer work ok with the 50k input pot......the sowter 4383 is 1:4 600/10k with centre tap......It used for a LA2A input...
http://www.sowter.co.uk/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2esowter%2eco%2euk%2facatalog%2fsearch%2ehtml&WD=4383&PN=SOWTER_TRANSFORMERS_MIC__LINE_INPUT_3%2ehtml%23a20#a20
I have made the amp part & working better than before but It does distort easily .....have some hum but I just think it needs sheilding, its just layed across my bench....
thanks
http://www.sowter.co.uk/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2esowter%2eco%2euk%2facatalog%2fsearch%2ehtml&WD=4383&PN=SOWTER_TRANSFORMERS_MIC__LINE_INPUT_3%2ehtml%23a20#a20
I have made the amp part & working better than before but It does distort easily .....have some hum but I just think it needs sheilding, its just layed across my bench....
thanks
MagnetoSound
Well-known member
Aside from any other conditions that might be causing the distortion, the Peerless 4651A in the Altec is 1:2, so your 1:4 might be cranking the gain quite a bit.
Thanks yeah C tap on secondary, my tran is Sowter 8540 ( I got mixed up) but still 1:4 600/10K.... I was sold it by Brian Sowter for my DIY BA6A got it long time back before he listed irons for the BA6A
I wonder if I can use a OEP tran for the input....
I tried a 25K input pot as in BA6A the distortion is gone & also the hum I had to my surprise,
Can anyone explain why different vari mu circuits have different values of input pots /daul ladders....
It seems to be compressing with no side chain circuit......I have a mic & mic pre hooked up to it & ouptput to daw..... when I speak loud 7 sharp I get the familiar in balances pops/thumps the levels squashes & rises back up about 1 second release time I guess, the meter works and show this too.......If I speak carefully (less attack) I can loose the pops.......but why is this doing this....? Is it as Magnetos says my IP tran is higher 1:4 ratio......still shouldnt do this right .....PS using 6BC8 as in original 436 sadly I dont have a 6ES8 at the moment....
Im going to re build it onto a chassis today as its a bit of a mess at the moment and I do need to sort out the correct B+, Im running it a bit high
Thanks for reading
I wonder if I can use a OEP tran for the input....
I tried a 25K input pot as in BA6A the distortion is gone & also the hum I had to my surprise,
Can anyone explain why different vari mu circuits have different values of input pots /daul ladders....
It seems to be compressing with no side chain circuit......I have a mic & mic pre hooked up to it & ouptput to daw..... when I speak loud 7 sharp I get the familiar in balances pops/thumps the levels squashes & rises back up about 1 second release time I guess, the meter works and show this too.......If I speak carefully (less attack) I can loose the pops.......but why is this doing this....? Is it as Magnetos says my IP tran is higher 1:4 ratio......still shouldnt do this right .....PS using 6BC8 as in original 436 sadly I dont have a 6ES8 at the moment....
Im going to re build it onto a chassis today as its a bit of a mess at the moment and I do need to sort out the correct B+, Im running it a bit high
Thanks for reading
Gary, I have build this compressor using a Lundahl LL1540 as input transformer (with windings in serie)
I know that the original one is a step up transformer (10k: 60k Ohm) but with the Lundahl it works very well (may be you have less compression if the input signal is low)
I suggest you to remove the 50k input pot and put the pot (dual 2k2 Ohm as attenuator) in the input before the transformer (like the uad with pops, cracks, noises, but after I removed the pot everything is disappeared.
I don't know the reason beacuse I am not a tech, but with this mod the compressor is working perfectly
I hope this can help you!
Regards
Fab
I know that the original one is a step up transformer (10k: 60k Ohm) but with the Lundahl it works very well (may be you have less compression if the input signal is low)
I suggest you to remove the 50k input pot and put the pot (dual 2k2 Ohm as attenuator) in the input before the transformer (like the uad with pops, cracks, noises, but after I removed the pot everything is disappeared.
I don't know the reason beacuse I am not a tech, but with this mod the compressor is working perfectly
I hope this can help you!
Regards
Fab
Interesting to read fab thanks will be experimenting with IP tran and different value pots, In a past project a federal AmU864 I found that a input pot of a way lower value worked great in that circuit & the stock value was useless, I dont understand what goes on between input tran & pot but would like to learn if anyone can help (be gentle)
I see Winstons schematic C5/C6 are .02 uf & in the revisions various values but ending up .022uf.....were they ever .02uf, I gues wont make much didderence so Im solering .022uf in place now, might fit a switch for a choice of value later if the thing sounds good
My DIY RS124 is coming along so will be testing experimenting very soon....
thanks for yr thoughts
I see Winstons schematic C5/C6 are .02 uf & in the revisions various values but ending up .022uf.....were they ever .02uf, I gues wont make much didderence so Im solering .022uf in place now, might fit a switch for a choice of value later if the thing sounds good
My DIY RS124 is coming along so will be testing experimenting very soon....
thanks for yr thoughts
spase
Well-known member
Anyone could make a pcb ?
?The circuit has a threshold for both compression and overload (distortion) that will hold true regardless of what value of step up on the input transformer or what value dual pot is used. They will both affect how quickly that threshold is achieved but do not change the circuit constants.
Even with a 1:2 or 1:3 input you may still find situations where you need a small pad - before - the input transformer when feeding a hot signal. I have a 1:15 on mine and almost always require a 20db pad on the front.
I'd base your input transformer choice on what works best for your situation. Same with pot, though a dual 50K should give you plenty of rotational flexibility even with higher ratio input transformers.
It sounds like you may just be feeding the circuit too high an input level.
Even with a 1:2 or 1:3 input you may still find situations where you need a small pad - before - the input transformer when feeding a hot signal. I have a 1:15 on mine and almost always require a 20db pad on the front.
I'd base your input transformer choice on what works best for your situation. Same with pot, though a dual 50K should give you plenty of rotational flexibility even with higher ratio input transformers.
It sounds like you may just be feeding the circuit too high an input level.
spase said:Anyone could make a pcb
http://www.dripelectronics.com/index.php?option=com_kunena&func=view&catid=12&id=2957&Itemid=41
Read this whole thread. I've got two, waiting for transformers and new front panel:
http://www.diy-racked.com/DIY/RS124B.jpg
Ok I have my point to point RS124 working on my bunch as a straight amp it sounds good no humming now its on a metal chassis the meter now stays in the middle gotta do some more testing but its seems to me leveling without the side chain connected...........Im not sure how .......
When I connect to side chain I have constant control voltage popping......& more faster pops as input signal gets bigger ... so its working now I have to balance out the pops, the cathode pot doesnt tune the pops away.....
When I connect to side chain I have constant control voltage popping......& more faster pops as input signal gets bigger ... so its working now I have to balance out the pops, the cathode pot doesnt tune the pops away.....
I have soldered the thing together on a matal chassis the amp is now stable no hums or pops the strange behavior has all gone sounds lovely .... I then added the side chain & that too works perfectly, I have a 3 position release switch as EMI switch positions 1 2 & 3 I may add a release pot too....
For now across the output I have a 1K pot as reostat & 2, 220R resistors in line ...It brings the level down to where I need it for my RME sound card
I made the neon relaxation oscillator circuit to inject the clicky sound, I tried it not totally sure how to use, I must re read this & other threads but, I tried to tune out the clicks with the cathode pot, it tunes them out but at one end of the pot, I was thinking it should middle ish of the pot, I dont know but I CANT hear and control voltage pops at all at any setting of the cathode pot.....so I guess thats good.
As I have a 1:4 input tran ( with 50K as seems to work great after all) & because I dont always wanna squash so much, I wanted a threshold so I kinda copied the threshold pot from a 436 circuit I added a 22K pot and 270K resistor, I did try lowering the 270K to 100K for more range but am afraid I will fry my pot, but the threshold works well...
I didnt build the PSU circuit in Winstons schematic I am using a PSU I made for another project, it puts out 279 VDC a little higher than 255VDC as per schematics Im a little worried its too much my voltage readings are as expected a little off.....
Even tho the B+ is higher I only get 129 V on OP tran centre tap instead of schematics 145V ? is that weired or due to my OP tran ? (my OP tran is a Sowter 8650 that I bought for a Mccurdy AU300 pre amp...)
Plates of V2 are down too at 126V vs schematics 142V ?
V1 plates are higher which I suppose I expected they are 120V vs schematics 75V ?
Dispite the voltages it works great & sounds fantastic.....
I want to try a 6ES8 but dont have one I have just read the a ECC88C is the same.......I suspect its not....anyone know for sure ....
Thanks for reading....
Gary O.
For now across the output I have a 1K pot as reostat & 2, 220R resistors in line ...It brings the level down to where I need it for my RME sound card
I made the neon relaxation oscillator circuit to inject the clicky sound, I tried it not totally sure how to use, I must re read this & other threads but, I tried to tune out the clicks with the cathode pot, it tunes them out but at one end of the pot, I was thinking it should middle ish of the pot, I dont know but I CANT hear and control voltage pops at all at any setting of the cathode pot.....so I guess thats good.
As I have a 1:4 input tran ( with 50K as seems to work great after all) & because I dont always wanna squash so much, I wanted a threshold so I kinda copied the threshold pot from a 436 circuit I added a 22K pot and 270K resistor, I did try lowering the 270K to 100K for more range but am afraid I will fry my pot, but the threshold works well...
I didnt build the PSU circuit in Winstons schematic I am using a PSU I made for another project, it puts out 279 VDC a little higher than 255VDC as per schematics Im a little worried its too much my voltage readings are as expected a little off.....
Even tho the B+ is higher I only get 129 V on OP tran centre tap instead of schematics 145V ? is that weired or due to my OP tran ? (my OP tran is a Sowter 8650 that I bought for a Mccurdy AU300 pre amp...)
Plates of V2 are down too at 126V vs schematics 142V ?
V1 plates are higher which I suppose I expected they are 120V vs schematics 75V ?
Dispite the voltages it works great & sounds fantastic.....
I want to try a 6ES8 but dont have one I have just read the a ECC88C is the same.......I suspect its not....anyone know for sure ....
Thanks for reading....
Gary O.
If the tube had nearly equal halves - through the entire range of gain reduction - it probably would work out to be at the middle of the pot. But this is seldom the case with twin triodes - regardless of brand or variant. Best strategy there is to just buy a number of 6BC8 or your preferred variant and try them out until you find one that has better balance, if it becomes an issue.
I would recommend checking the difference in plate voltages on V1 for the static/idle position and under moderately heavy gain reduction and compare those numbers and see how well they correlate with what the neon circuit is telling you. I've tended to find that dialing in a static balance near zero is seldom the best setting for the balance pot as this will become a difference of maybe 6 to 8 volts under gain reduction which is often near the range that creates thumping conditions. You may find that a more balance setting may give 2 to 3 volts static difference and 4 to 6 volts under gain reduction, but of course this will vary from tube to tube.
As you raise B+ all the tubes will draw more current = higher voltage drop. Do check that the 6.8K/7K PS resistor isn't being pushed beyond it's ratings.
It should be easy enough to add another dropping resistor in your PS.
The DCR of the OT is another small factor that will influence drop on V2 plates. Probably not nearly as big a factor as the differences between tubes themselves. The voltages on the EMI schematic get flushed as soon as the tech puts in another set of tubes.
