Simple EQ for Neve 1290

[Spencerleehorton]

T7 on BA284 needs replacing as not getting any voltages, correct voltages are E = 2.4v, B = 3.06v, C = 2.7v, i was getting nothing!!
will change and see what happens

 

[Spencerleehorton]

well not quite sure what the correct voltages are for T4,T5,T6 but the voltages match with T7,T8,T9 and there is 0.6v between The Emitter and Base.
Had to change 2 BC184s in the end.
I think now i can actually get on with building the other channel then fine tuning this unit.

One channel is working now, there are a couple of issues which im sure that i can iron out.

 

[ruffrecords]

Good news.

Cheers

Ian

 

[Spencerleehorton]

thanks for all you help so far Ian, couldn't have got here without you, let alone everyone else.

Slight issue i have on the MF, on the first click so that would be 360hz, when i put a 1khz sinewave in it goes into a funny shape (see picture attached) it cuts everything off if fully CW?

 

[Spencerleehorton]

here's a pic with EQ in but everything off, so waveform isnt quite right? and level is down from 8.2vpp to 6.2vpp

 

[Spencerleehorton]

this is the sinewave with the HPF CCW, the level drops to 4.7vpp and the waveform gets smaller

 

[Spencerleehorton]

Just a side note for everyone, my transistors all measure 450+ hfe.

 

[Spencerleehorton]

Just turned it on today and the K and M inverter amp is down again!! changed T7 and monitored the signal when powered up and for about 2 seconds i get perfect signal with EQ on, waveform looks great, then T7 goes down again and signal drops out!!

How many problems am i having with these inverter amps!!!!

T8 and T9 checkout as ok, don't understand why T7 keeps blowing? any ideas?

also it seems when i attach the first inverter amp to b205 it flattens out the bottom of the waveform?

need to get these tip top it seems!!!

 

[Spencerleehorton]

finally fixed all inverter amps and i'm satisfied that im getting similar readings on all.

Just a weird thing that happens, within the first 10 seconds of powering up i get a nice clean sinewave and then after about 5-10 seconds it turns into more of a mountain peak shape (triangle wave form?)

any ideas?

 

[Spencerleehorton]

I’ll try isolating the problem by just using either the b205 or b211 Pcb and see if waveform and level changes.
Hopefully can work out why?

On the inverter amp problem i noticed I was getting 200R between T7 and ground rather than 3.3k, I had to remove everything around that transistor then resolder then it was ok? Strange problem but seems good now!!

I’m connecting other channel now to see if I can get this one to work any better!!

I wonder whether it’s a capacitor issue?
The fact that the waveform slowly changes makes me think a capacitor charging?
Perhaps it’s something on the b205 Pcb?

 

[Spencerleehorton]

Also I think there maybe another mistake in the schematic?
On the main schematic it doesn’t show a connection from K on the b205 to S3a of the switched pot?
On the switch diagram S3a shows a connection to K?

Is this correct?

 

[Spencerleehorton]

ive just put in the b205 and the waveform at the bottom slowly goes up!!
also what i notice is that when switched to 35hz and 60hz the 50k pot works CW for boost, on the next two settings it works in reverse!! so i think my wiring is off here, but will check tomorrow?

 

[Spencerleehorton]

right, i finally have some good (working) results to report back on!!!

Well it seems my inductors are fine, at least on the B205 pcb, i have checked and doubled checked wiring, and i have abandoned using the inverter amps on channel B and decided to use the ones on channel A instead.

I now have a lovely waveform and the eq selection works perfectly and the boost and cut worked exactly as you would expect.
Levels wise it all looks great.

So time to record what voltages are on the channel A inverter amps and then get the other inverter amps as close as possible to the working ones.
There must be something affecting the bottom end as the bottom of the waveform gets cut off?

will try and introduce the other pcbs now and see if i can get one channel fully working.

at least i know now its the inverter amps which need looking at and my pcbs are good, along with my inductors i've wound.

 

[Spencerleehorton]

I now have one fully working channel!! merry xmas to me!!!

now to get the other one working!!!

 

[ruffrecords]

I now have one fully working channel!! merry xmas to me!!!

now to get the other one working!!!

At lear  you now know the design and build will work.

Cheers

Ian

 

[Spencerleehorton]

Yes exactly Ian, just got to get to the root of this inverter amp problem.

on first view it looked liked it was working, before i tested the other channels amps.
The not working amps have T4 = E = 2.4v, B = 3v, C 2.7v
compared to the working channels T4 = E = 1.65v, B = 2.2v, C = 8.69v

so that points me to look at R15 (27k) on the T4 collector or C14 (22uf), R18 (180k) or R17 (120k)

must be something going on with one of them?

C15 (64uf) which i notive on my working amp ive got 100uf rather than 68uf? might be worth changing?

all other caps seem to check out at a quick glance, will pull them all out and check though, could just be cold solder?

 

[Spencerleehorton]

think I've found my mistake R30 was 1.5k rather than 3.6k, will change and see if better!!!

yep that was the problem, all inverter amps working fine, finish the build now!!

thank you all for your help, couldn't have done this without you, and Merry Xmas Everybody!!! X

 

[ruffrecords]

That is a rather nice Xmas present you have given yourself. Enjoy!.

Cheers

ian

 

[Spencerleehorton]

Thought I was done with this!! Getting wildly different input voltages, gonna have to check these input txf, and see why one channel I’m getting 10.3vpp and other I’m getting 3.2vpp!!

I am using a chameleon labs mix and line txf but thought I had the line txf round the other way!!

Will wind a couple of my own and check the other txf over, hopefully that’s all it is!!

 

[Spencerleehorton]

Just measured the input txf and getting wildly different output levels so that would explain why my outputs where so different.
Gonna wind a few 10468 as need to for the 2254 build in doing!! Have 8 to wind as two for this, two for another two Neve 1081s and 4 for the 2254 as will use 2 in reverse for the line in txf.
While I’m at it I might as well wind some more 1166 output txf as well!!