8 Channel, 3U NEVE 1073 completed

[Le Roux]

Adding a pic of my 4 channel!

 

[Whoops]

So if Iwanted a 1200  ohm input with the vtb9045, I would eliminate the jumper between pins 3 and 4, and then jumper pins 2 and  3, and 4 and 5?

No, it's the opposite

For a 1200  ohm input impedance you need the primaries connected in Series, so you connect Signal + to Pin2, Jumper 3 and 4, and connect Signal -  to Pin 5

 

[Chrome Heart]

No, it's the opposite

For a 1200  ohm input impedance you need the primaries connected in Series, so you connect Signal + to Pin2, Jumper 3 and 4, and connect Signal -  to Pin 5

That is the wiring according to Martin's build guide, which I believe is 300 ohm.
Correct me if Im wrong, but that was my assumption.

 

[Whoops]

That is the wiring according to Martin's build guide, which I believe is 300 ohm.
Correct me if Im wrong, but that was my assumption.

Yes Martin's build guide shows that wiring but thats a Series connection so more turns on your primaries which gives you a lower turns ratio (and higher impedance primary), 1k2 in this case

Putting them in parallel gives you half the turns on the primary side, so it doubles your turn ratio, and makes your primary impedance four times lower.

 

[Dimitree]

sorry for the stupid question, but, is it possible to use a potentiometer instead of a rotary switch on the input sensitivity control?

 

[Chrome Heart]

sorry for the stupid question, but, is it possible to use a potentiometer instead of a rotary switch on the input sensitivity control?

The pcb is designed to use the Grayhill, even if you could jackleg a pot in there it wouldn't be worth the hassle.

 

[Dimitree]

Thanks
I’m not referring to the PCB layout, I’m just wondering if circuit-wise a potentiometer could replace the rotary switch. Obviously in reality is not pratical with this PCB layout

 

[Chrome Heart]

Thanks
I’m not referring to the PCB layout, I’m just wondering if circuit-wise a potentiometer could replace the rotary switch. Obviously inwe reality is not pratical with this PCB

Thanks
I’m not referring to the PCB layout, I’m just wondering if circuit-wise a potentiometer could replace the rotary switch. Obviously in reality is not pratical with this PCB layout

Sorry. Since this thread primarily addresses Martin's pcb and build, I responded accordingly.

 

[NannerPuddin]

Well I am finally getting around to building my pres.  I have Version 2.4 boards that I bought I think in2012.  I am nearly done with them, and plan to put these in a 1u Rack, with 4 pres.  I know it will be tight, and I will be using an external PSU.  My question, is that the filter caps, the 2200u/25v electrolytics are too tal for the 1u case.  The earliest pics that Madriaanse posted had much smaller form caps.  Is there any reason I cannot use the same value but smaller form factor caps in my build?  There are plenty availabe on Mouser.

Thanks,

Doug 

 

[sr1200]

values matter, form factor is a matter of convenience...

 

[Whoops]

My question, is that the filter caps, the 2200u/25v electrolytics are too tal for the 1u case. 

Bend the legs, put the caps horizontaly

easy fix

 

[NannerPuddin]

Bend the legs, put the caps horizontaly

easy fix

Actually, that is specifically what I was trying to avoid.  Besides it being a bit "untidy" for my tastes, the filter cap in the corner would occlude the mounting screw if it was horizontal.  I would normally just assume that as long as the values were the same, there would be no issues, I was just curious if anybody had experience of this in practice.

Thanks,

Doug

 

[dmp]

if the values are the same the height / diameter doesn't matter. match the uf, meet or exceed the voltage rating.

 

[XAXAU]

Has anyone made the 300/1200ohm switch mod? I think I have it figured out with a DPDT but just wanted to check.

Also, what is the purpose of the .01uF cap and 1K5 resistor connected between Pin 8 and 5 on the VTB 9049?

 

[Whoops]

Has anyone made the 300/1200ohm switch mod? I think I have it figured out with a DPDT but just wanted to check.

I did that in my unit, I think I used a DPDT, it's easy to do

Also, what is the purpose of the .01uF cap and 1K5 resistor connected between Pin 8 and 5 on the VTB 9049?

I'm not sure now from memory, I think it's for frequency response with that transformer

 

[XAXAU]

I did that in my unit, I think I used a DPDT, it's easy to do

I'm not sure now from memory, I think it's for frequency response with that transformer

Cheers!

Off topic (maybe) but could it have something to do with negative feedback? Like what Rupert does in his Silk? Saturating the transformer more?

I mean a resistor and a cap in series is not a filter afaik

 

[USIEL]

Hi guys ,finaly i’m finishing my 4chan 1290  but  two channels have  crazy voltages on transistor 1&2

Chan3.  Transistor1 : Emitter 2.4v ,Base 3v, Collector 4.2v  ... Transistor 2 voltages ok
Chan4.  Transistor1 : Emitter 0.002v ,Base 0.006v, Collector 1.1v .....
                  Transistor2 : Emitter 0.4v ,Base 1.1v , Collector 0.4v 

I’m not sure whats best to do now so your help is very much appreciated

 

[Whoops]

Hello USIEL,
the way you mounted the output transformers it's not ideal, you will have a lot of crosstak between channels.
That has been talked before here in this forum, I have a thread about it.

Check this videos for the crosstalk example:

https://www.youtube.com/watch?v=6yXgkk52bUo

https://www.youtube.com/watch?v=R_dqkKAFTKE

when space is tight this is the best positioning:

Conclusions:

- for all the possible positions I tried, the present positioning with all the transformers next to each other is the worst possible one

- shielding greatly reduces the crosstalk when the transformers are next to each other , in Neve desks thereswas 2 sheets of steel between the Transformers (modules cases), I used toroidal trafo shield from don audio for the test, it works fine

- Rotating the transformers 90 degrees decreases the the crosstalk to "roughly" the same level as having them next to each other with shielding

- Best position I found is having one transformer elevated and positioned horizontally. It's easier to see in the video than the drawings.

 

[USIEL]

Hello  Whoops,
Thank you and i will check the transformer  issue
But.....first i’v to  solve the transistor  voltages ,i”ve checked and double checked everything

Chan3.  Transistor1 : Emitter 2.4v        ,Base 3v,          Collector 4.2v 
                    Transistor 2 voltages ok

Chan4.  Transistor1 : Emitter 0.002v ,  Base 0.006v, Collector 1.1v .....
                  Transistor2 : Emitter 0.4v        ,Base 1.1v ,      Collector 0.4v 

 

[Whoops]

But.....first i’v to  solve the transistor  voltages ,i”ve checked and double checked everything


Chan4.  Transistor1 : Emitter 0.002v ,  Base 0.006v, Collector 1.1v .....
                  Transistor2 : Emitter 0.4v        ,Base 1.1v ,      Collector 0.4v

Hello Usiel,
no one will be able to know whats exactely wrong with your channel 4 problem just looking at the voltages.

Well, they tell us that channel is not working properlly,
so now you have to trouble shoot:

- Check all resistor values, measure them on circuit, compare values with good channel
- check all cap values
- check all caps polarity positioning
- Check PCB solder side, for possible solder bridges, inspect all solder joints
- check if gain switch is wired properlly
- Use a signal proble (DIY one if you dont have it)
- Take pictures, show us

- Check all transistors, Do you have a transistor tester? if not buy one, cheap on ebay and very good tester MK-328