Spencerleehorton
Well-known member
As I’ve said before they all test good with the output not connected, as soon as I connect output the signal goes down by at least half!!?
Simple EQ for Neve 1290
- Thread starter Spencerleehorton
- Start date
Help Support GroupDIY Audio Forum:
Try 'mapping' the 'gain structure' from the input assembly .. shorted to the 'output assembly'.
Measure the gain structure with REW
Understand each of the 'transitions' .. like 'relative' to each other .. make a little 'functional block' .. with 'gain' on a diagram.
Again, and without wishing to be 'difficult' .. that's the 'baseline' point I'm making.
Measure the gain structure with REW
Understand each of the 'transitions' .. like 'relative' to each other .. make a little 'functional block' .. with 'gain' on a diagram.
Again, and without wishing to be 'difficult' .. that's the 'baseline' point I'm making.
And furthermore, '6dB' is about 'half' which can happen 'at the drop of a hat' ... meaning for any reason under the sun.
You need to do a 'gain structure' kind of diagram .. input -> transformer -> gain stage -> gain stage -> eq stage s -> fader -> output stage -> line amp [current] -> output transformer -> balanced outputs.
Like that. Then look at the eq .. which has a couple of 'unity gain flat' kind of stages in series.
Without a doubt it's not 'easy' and nor is winding 'one's own' .. but there it is. The result is well worth it and you are probably further along than it seems.
You need to do a 'gain structure' kind of diagram .. input -> transformer -> gain stage -> gain stage -> eq stage s -> fader -> output stage -> line amp [current] -> output transformer -> balanced outputs.
Like that. Then look at the eq .. which has a couple of 'unity gain flat' kind of stages in series.
Without a doubt it's not 'easy' and nor is winding 'one's own' .. but there it is. The result is well worth it and you are probably further along than it seems.
Spencerleehorton
Well-known member
Well there is no problem without any of the eq pcbs, good signal with loads of gain
Could you explain exactly how to connect the LM358 as this seems to be the only reliable opamp I have!!
Could you explain exactly how to connect the LM358 as this seems to be the only reliable opamp I have!!
ruffrecords
Well-known member
Spencerleehorton said:
Forgive me, I am a bit thick and still confused. What tests good? The EQ or the inverting amps? What output is not connected - amp or EQ?
As I have already mentioned, this EQ requires an inverting amp to work. You cannot really test it without one and say it is good.
Cheers
Ian
My take, is the input assembly and output assembly are working ... wide response with good 'level' control. Which is good.
The issue is the filters ... 'caught between two ..' worlds .. one being the right and proper nve way, and the other an 'out of nve' 'learning ex perience' ... re lm 35 whatever it's meant to be a 'learning thing' rather than [dare I say it] .. g
The missing parts are either 'proper wiring' or something mid way between 'reality and test-bed'.
But it can't be too far off, right?
That's why I posted some simple eqivalent circuits with generic op-amp - to help with the 'test bed' approach
But it doesn't 'map' to the E, F , G H thing etc without plenty of proper 'connecting the lines' unless one stays literally 'true' to that 'schema'.
Going from 'nay' to 'yay' is a either a 'literal' wiring thing or a 'correlation- translation-actualisation' 'thing' and paved with a truck load of ..testing .. and preferably in a convenient unit, like dB , dBu etc .
Volts etc isn't too useful outside of context. And 'half' or 6dB is very commonplace ... could be most anything.
At least, that's the way I see it. Some 'guy' down here, in Oz, said it best .. 'life ain't meant to be easy'. True.
Again, it's easier to do than to describe. Another way to put it .. sorry for all the inconvenience.
The issue is the filters ... 'caught between two ..' worlds .. one being the right and proper nve way, and the other an 'out of nve' 'learning ex perience' ... re lm 35 whatever it's meant to be a 'learning thing' rather than [dare I say it] .. g
The missing parts are either 'proper wiring' or something mid way between 'reality and test-bed'.
But it can't be too far off, right?
That's why I posted some simple eqivalent circuits with generic op-amp - to help with the 'test bed' approach
But it doesn't 'map' to the E, F , G H thing etc without plenty of proper 'connecting the lines' unless one stays literally 'true' to that 'schema'.
Going from 'nay' to 'yay' is a either a 'literal' wiring thing or a 'correlation- translation-actualisation' 'thing' and paved with a truck load of ..testing .. and preferably in a convenient unit, like dB , dBu etc .
Volts etc isn't too useful outside of context. And 'half' or 6dB is very commonplace ... could be most anything.
At least, that's the way I see it. Some 'guy' down here, in Oz, said it best .. 'life ain't meant to be easy'. True.
Again, it's easier to do than to describe. Another way to put it .. sorry for all the inconvenience.
Spencerleehorton
Well-known member
right, ive just popped home to let the dog out for lunch and had a very quick tinker, i actually have some results now!!!
B211 pcb E output goes to Inverter input pin 2 on LM358
Pin 1 output from LM358 to C on B205
Pin 3 to input B on B205
the EQ works and looks completely different, rather than this subtle difference it WORKS!!!
output level is now a little more, so will put bak in the 1.2k resistor which is ment to be in there.
but im on my way now, so yes it was the inverter amps that were not working!!
B211 pcb E output goes to Inverter input pin 2 on LM358
Pin 1 output from LM358 to C on B205
Pin 3 to input B on B205
the EQ works and looks completely different, rather than this subtle difference it WORKS!!!
output level is now a little more, so will put bak in the 1.2k resistor which is ment to be in there.
but im on my way now, so yes it was the inverter amps that were not working!!
I like that 'woof'.
Spencerleehorton
Well-known member
Ideally I’d like to find out why my inverter amps are not working on the b284 Pcb, I had a quick poke with a MM and no voltage present?
Maybe I just haven’t connected the B+ feed?
Will report back.
In the meantime these LM358 should do the trick!
Maybe I just haven’t connected the B+ feed?
Will report back.
In the meantime these LM358 should do the trick!
Spencerleehorton
Well-known member
I will check later that I’m getting voltage on D and L on 284 Pcb.
I’ve got a funny feeling that I haven’t connected this!!
Doh!!!!
I’ve got a funny feeling that I haven’t connected this!!
Doh!!!!
Spencerleehorton
Well-known member
right, i've checked D and L on BA284 and yes they are connected together but not connected to R57/C10, so thats why they are not working!!
will connect and test.
So far I have hooked up b205, b211 and b182 and i'm getting signal through and its all sort of working, this is using the LM358.
As you can see from the picture i took of the scope i'm not out of the woods yet!!
in bypass i'm getting 4.70vpp and with EQ in i'm getting 7.89vpp and the waveform is a bit all over the place!!
all controls are set to the off position, so i would need to get it to similar level and better waveform.
will connect and test.
So far I have hooked up b205, b211 and b182 and i'm getting signal through and its all sort of working, this is using the LM358.
As you can see from the picture i took of the scope i'm not out of the woods yet!!
in bypass i'm getting 4.70vpp and with EQ in i'm getting 7.89vpp and the waveform is a bit all over the place!!
all controls are set to the off position, so i would need to get it to similar level and better waveform.
Attachments
ruffrecords
Well-known member
Just a general note, your levels are generally a bit on the high side. The nominal internal working levell of the 1073 is about -6dBu which is about 1V pp. Might be an idea to turn the gain down a bit.
Cheers
Ian
Cheers
Ian
Spencerleehorton
Well-known member
gain is set to off but i didn't adjust the 5k trim pot to lower the level for the 3055 needs to be about 22.66v i think i was at 23v.
Im going to rewire the power leads and make that better as it was a complete mess!!!!
I've just changed all the caps from polyester to polypropylene and polystyrene.
once everything is a bit tidier it will be easier to work on.
Im going to rewire the power leads and make that better as it was a complete mess!!!!
I've just changed all the caps from polyester to polypropylene and polystyrene.
once everything is a bit tidier it will be easier to work on.
Spencerleehorton
Well-known member
well some success and some problems still, I'm pretty confident now that the inverter amps on the BA284's are all working now as they have power going to them!!!
I've tidied up the wiring a bit, now my problem is when the eq is engaged the signal is too loud and the waveform is too distorted!!
complete flip side to what was before!!
I've tidied up the wiring a bit, now my problem is when the eq is engaged the signal is too loud and the waveform is too distorted!!
complete flip side to what was before!!
Spencerleehorton
Well-known member
Today I will map the gain structure to see where the problems are!
Spencerleehorton
Well-known member
ok so here are results of mapping my signal now:
BA283 P = 670mvpp
B205 F = 670mvpp
B205 H = 611mvpp
B211 B = 611mvpp
B211 C = 2.04vpp
HPF com1 = 1.60vpp
HPF com2 = 1.60vpp
BA283 L = 5.15vpp
so something weird is happening on the output of the BA211 pin C
BA283 P = 670mvpp
B205 F = 670mvpp
B205 H = 611mvpp
B211 B = 611mvpp
B211 C = 2.04vpp
HPF com1 = 1.60vpp
HPF com2 = 1.60vpp
BA283 L = 5.15vpp
so something weird is happening on the output of the BA211 pin C
Spencerleehorton
Well-known member
found a mistake and now not working!!
had M on 284 to E on B211 and K on 284 to C on b211, i get massive signal square wave this way.
have changed to match schematic so M on 284 to C on B211 and K on 284 to E on B211.
B205 is connected M on B205 to C on 284 and H on B205 to E on 284.
i get the following now:
BA283 P = 630vpp
B205 F = 630vpp
B205 H = 465mVpp
B211 B = 465mVpp
B211 C = 32.3mVpp
HPF com1 = 32mVpp
HPF com2 = 30mVpp
BA283 to L = 30mVpp
this is getting silly now!!
had M on 284 to E on B211 and K on 284 to C on b211, i get massive signal square wave this way.
have changed to match schematic so M on 284 to C on B211 and K on 284 to E on B211.
B205 is connected M on B205 to C on 284 and H on B205 to E on 284.
i get the following now:
BA283 P = 630vpp
B205 F = 630vpp
B205 H = 465mVpp
B211 B = 465mVpp
B211 C = 32.3mVpp
HPF com1 = 32mVpp
HPF com2 = 30mVpp
BA283 to L = 30mVpp
this is getting silly now!!
Spencerleehorton
Well-known member
right, i've taken out the inv amp K and M on 284 and just used C and E on the B211 and im getting same signal in as when in bypass on output and sinewave looks good. 2.71vpp in bypass and EQ in its 2.37vpp, so the closest yet.
I have in the HPF and the B211 and both work how they should.
So i just need to fault find this inverter amp K and M, what i might do is swap the 284 for the other channel one and see if they both work now, if they do i'm in business and just have to compare voltages to find where its at fault. i have one working inverter amp that i know of so i'll use this as benchmark.
I have in the HPF and the B211 and both work how they should.
So i just need to fault find this inverter amp K and M, what i might do is swap the 284 for the other channel one and see if they both work now, if they do i'm in business and just have to compare voltages to find where its at fault. i have one working inverter amp that i know of so i'll use this as benchmark.
