REDDI DI

[dmp]

Transformer coupled can swing to higher voltages than resistance coupled. That's why tube amps typically have a transformer coupled push-pull output.
Either design could be used though with the proper thought to levels. Different flavors.

 

[ruffrecords]

I'm interested to know what are the advantages of this DC-coupled transformer design over much more economical capacitor-coupled one such as the attached?

They both have their pros and cons.

For a transformer in series with the anode, it has to carry dc current. This means it needs a gap in order for it not to saturate which lowers its inductance which means it needs to be pretty big in order to have a decent bass response. The advantage of this topology is that the plate voltage can swing up to twice the supply rail making this class A capable, in theory of achieving 50% efficiency,

The capacitor coupled topology has the advantage that the transformer does not have to carry dc so it needs no gap. This means it can be smaller and cheaper for a given primary inductance and bass response. Its disadvantage is the maximum plate swing only equals the supply rail so its maximum efficiency is just 25%.

In both cases, the achieved efficiency is a lot lower than the theoretical.

Cheers

Ian

 

[CJ]

you could also use a parafeed with a plate choke, but this does not save much money, or space,

the direct coupled approach is not that much more expensive one you figure in the 7 bucks for a good hi voltage lytic,  plus, how much is the smaller transformer going to cost you? Triad HS 50's are not cheap, i guess you could find something from Edcor for 25 bucks, shipping will bring that up a bit,

 

[emi2345]

So it’s a hefty gapped transformer of a nice 1+uF capacitor and a smaller transformer such as this http://www.sowter.co.uk/specs/4383.php

Are there any typical differences in sound between the two or is it all in the choice of parts and implementation?

CJ are you still making and selling your transformers?

 

[CJ]

yes, 

 

[alexc]

I'm just working out my version of the redddi  'powered by CJ'  8)  during  this winter's downtime  ..

Quite excited to get this one going as a near time priority ...  still working on some power supplies and what not.

Hopefully it will be doing some nice things next 'diy season'  in a few months hence.

Mine is an external psu  and I'm hanging a second tube in there 'just in case'   

......

I just hope I don't get too distracted by more tube amps ....

 

[beatnik]

I have a quick question about a new DI build.

I have a power transformer laying around that is rated 230V AC on the HT secondary.

Would like to use this transformer for the REDDI circuit however it seems that the required B+ of 170V DC is much lower.

I am wondering if I should just try bringing down the B+ with dropping resistors, or maybe a zener diode ?

Or maybe best option would be re- biasing the 6N1P changing the cathode resistor ? Is the output transformer going to take the extra voltage without issues ?

 

[ruffrecords]

I have a quick question about a new DI build.

I have a power transformer laying around that is rated 230V AC on the HT secondary.

Would like to use this transformer for the REDDI circuit however it seems that the required B+ of 170V DC is much lower.

I am wondering if I should just try bringing down the B+ with dropping resistors, or maybe a zener diode ?

Or maybe best option would be re- biasing the 6N1P changing the cathode resistor ? Is the output transformer going to take the extra voltage without issues ?

It is common to drop HT using a resistor or resistors. Use them to add additional HT smoothing caps along the way for a quieter HT line.

Cheers

Ian

 

[s2udio]

Just started on a REDDI build ,hopefully using CJ's transformer,
Thinking of going for a P to P build, but out of interest anyone doing a PCB of this at the moment ?
Thanks

 

[s2udio]

bump

 

[ruffrecords]

Some people used my tube gain make up board for the but I don't make them any more.

Cheers

Ian

 

[Rob Flinn]

I have a quick question about a new DI build.

I have a power transformer laying around that is rated 230V AC on the HT secondary.

Would like to use this transformer for the REDDI circuit however it seems that the required B+ of 170V DC is much lower.

I am wondering if I should just try bringing down the B+ with dropping resistors, or maybe a zener diode ?

Or maybe best option would be re- biasing the 6N1P changing the cathode resistor ? Is the output transformer going to take the extra voltage without issues ?

I had a similar scenario.  I just used 1 or 2 dropper resistors with some extra caps to get to 170v.

 

[Rob Flinn]

Just started on a REDDI build ,hopefully using CJ's transformer,
Thinking of going for a P to P build, but out of interest anyone doing a PCB of this at the moment ?
Thanks

It's such a simple circuit it's really easy doing it p2p.  Even if a pcb was available, personally, I wouldn't have bought it.

 

[s2udio]

Thanks was thinking  that's the way to go........let it be !   

 

[CJ]

you don't even need a tube socket, scrape the tube pins with a razor blade and solder the parts and  wires directly to the tube, 

or not, 

 

[Rob Flinn]

you don't even need a tube socket, scrape the tube pins with a razor blade and solder the parts and  wires directly to the tube, 

or not, 

Good idea CJ, but even I'm not that thrifty ....

 

[Rob Flinn]

I'm looking at all the diagrams that are floating around for this project.    The output attenuator to me seems wrong to me.    It looks to me like the 1k pot should be on the XLR side of the 300R resistors and not the transformer side.      If the pot is in the XLR side then when it is fully turned down the transformer is still driving 600R, whereas if it on the transformer side it it then the transformer is drives into a short . 

Looking at the one pic I have of the interior of the real REDDI, there is not enough detail to see how the pot is wired. 

 

[CJ]

easy to try it both ways, probably will not make much difference,

notice sec resistance is fairly high compared to most 600 winds, (around 150 ohms DCR)

current drag thru sec creates voltage drop which lowers turns ratio which compensates for lower reflected impedance on the pri side,

putting the pot on the xlr side will do the same thing but to a lesser extent,

will the tube act different when being loaded different?  try and see.

note that if the pot is on the xlr side it will short out whatever you are driving,  where as if the pot is on the sec side, you have a max load of 600 ohms to the input of the mixing board or whatever you are going into.

measure noise also. is there less noise with the pot on the sec side? never listened for that

 

[Rob Flinn]

I was wondering whether putting the pot on the transformer side loads the circuit to give a funky mojo.  As you say, have to try it out.

 

[ARITOSOUL]

Hi! any chance to use the 555 nixie smps to supply this proyect? it will draw enough current?

Thanks!