REDDI DI

[ruffrecords]

The Carnhill VTB2291 should do very well. It is a gapped type so it is able to pass some dc. How much is anyone's guess but it is probably more than the few mA needed for the DI design.

Cheers

Ian

 

[CJ]

specs on the transformers i wound were
3.67:1  turns ratio = 8K:600

pri ind: 175 H @ 20 Hz at an input voltage of 22 volts.

core was 100 EI butt stacked (gapped) but with no paper in the gap, just metal to metal

you might ask Carnhill for their pri ind specs for 2290 (gapped) vs 2291 (un-gapped)

 

[ruffrecords]

I have measured the VTB2291 primary inductance at 100Hz and found it was 106H so I would expect it to be somewhat higher at 20Hz. Don't know about the gapped version.

Cheers

Ian

 

[Bernardo]

hello good evening, i'm building this version of reddi but i have two problems.
I would be very grateful if someone could help me.
The first is that I have no idea how to wire the carnhill 2290 output transformer, I don't know which pin the 170v is connected to nor do I know how to configure it for 9k / 600
My second problem is that the 39k resistor that is in the 170v power supply gets very hot.
I have a 5w ceramic on.
Thank you so much.

 

[rock soderstrom]

The 39k resistor is probably getting hot because you are running your power supply unloaded and/or your power transformer has a too high secondary voltage.

Under normal operating conditions the 5W are sufficient. The resistor has the function to discharge the capacitors when the device is switched off or the PSU is operated without load. It is called a bleeder resistor.

I would move the position of the bleeder to the output of your 170V DC power supply. This will lower the DC voltage applied through the series resistors of the filtering and thus the power dissipation of the 33k resistor as well. You could also increase this resistor a little bit, here you have to find the balance between power dissipation and discharge time.

I'm not sure if this Carnhill Transformer is the right one, as its specs are a bit off. (turns ratio?) it will work.

According to the data sheet, see attachment, you have to connect the windings in series.

 

[rock soderstrom]

Finger painting on my mobil phone...

 

[Bernardo]

Thank you very much Roca, this is the information that I needed to wire the carnhill 2290.
Regarding the resistance of 39k I think you are right, the toroidal is large, 211v.
I think I am going to take turns of the wire from the toroidal until the source of about 180v.
thank you very much again.

 

[rock soderstrom]

The Carnhill VTB2291 should do very well. It is a gapped type so it is able to pass some dc. How much is anyone's guess but it is probably more than the few mA needed for the DI design.

Cheers

Ian

I'm sure that's only a typo I just noticed.

The VTB2291 is ungapped and therefore not suitable for REDDI projects. The VTB2290 is the gapped version.

 

[Bernardo]

Good evening, I just finished finishing assembling the project of this instrument preamplifier but I have a serious hum problem, I also have a problem with the ground, since when I disconnect the input jack it is atrocious.
I suspect the problem comes from the 170v power supply.
I have to say that I have not been able to complete the circuit connecting the 480k resistor that comes from the ground to the 1,25k resistor that comes from the input because the noise gets even worse.
attached image with red circumference.
the lm317T regulator of the heaters cannot connect it either because although it gave me 6.3v the heaters did not turn on.
any help and guidance will be appreciated.
Thank you so much

 

[rock soderstrom]

It is hard to tell what the problems are from a distance.

Is your heater ground connected to the 170V HT ground? If not, this will lead to massive hum.

Are the input and output voltages of the power supplies correct?

Please take pictures of the power supplies and the amplifier and post them here. Give us more info so we can help you better.

 

[Bernardo]

Hello, thank you very much for answering, as soon as I can upload photos.
just say that I have followed the scheme as it is, my measurements of the output of the power supplies are 170v and 6.5v.
The only modification that I have been forced to make is not to connect the 480k resistor with all the masses to the 1.25k pin 2 resistor.
Thank you so much

 

[rock soderstrom]

Ok!

Just to be sure, plz. answer this.

Is your heater ground connected to the 170V HT ground? If not, this will lead to massive hum.

 

[abbey road d enfer]

The only modification that I have been forced to make is not to connect the 480k resistor

Should be 470k...

with all the masses to the 1.25k pin 2 resistor.

This resistor cannot be left unconnected in the absence of a source connected to the input.

 

[Bernardo]

Thanks for the answers.
After connecting the 470k resistor, the ground noise effectively went away when there was nothing connected, and the other fault I had was a connection error in the rectifier bridge made with 4 diodes, an amateur novice fault, which is actually what that I am.
Could you say advise me what potentiometer I could install to attenuate the input level?

What if I also wanted to install an analog vumeter to measure the input level?
Would you have to connect the positive pin to pin 2 of the 6np1 and the negative to ground?

thank you very much to all.

 

[My3gger]

Most sources driving DI already have means for output level control. Why not install carbon pot at the output as on schematic? Alpha are big enough; i had small and expensive dual conductive plastic fail in power amplifier driving monitors, such pots don't take heat as well as carbon pots.
Vu meter isn't needed for a DI or preamp because you can hear what levels are needed. They are more helpful for compressors, mixers and similar.

 

[Bernardo]

in the output I have installed a two-pole switch with 10 steps, subdividing 1k into 11 resistors and in the trs connector 2 300R resistors as shown in the diagram.
but I would like it to also have an entry level, like some preamps, a kind of attenuator per potentiometer for when I connect instruments with more gain than others, something simple, which I don't know what the value of that potentiometer would be.
Regarding the vumeter, it is more a detail than usefulness, I already bought it and I would like to install it.
I know I have to remove the diode tip to adapt it to the circuit.
Thank you so much

 

[Bernardo]

help please connel vumeter,
I can't get it to move.
It is a 500ua coil vumeter, with a 210-ohm resistance header, it has no diode bridge or resistors, only the negative that I connect it to ground, and the positive that I have tried to remove from the katodos and from pin 1-6 with resistance, but I can't get the bush to move.
any suggestions?
Thank you

 

[patricks]

Hi, has anyone tried alternative transformers, apart from CJs? Shipping on the Carnhill to Australia is as much as the transformer itself.
Would something like the Cinemag CM-2180 work?

 

[My3gger]

CM-2810 won't work without gaping the core, even then low frequency response might not be that good. Check CJ's remarks about cores being pretty big for this type of DIs.
I recall Edcor having good sounding model, Cinemag should be even better if you provide them with details about the core, tube, circuit, use and so on. Lots of people wound their own saying they perform well.

 

[patricks]

Great, thank you!
Also, is CJ building any more transformers? It's been a while since I saw the last post about a build run