EZ Tube Mixer Support Thread

[letterbeacon]

Apologies if this isn't the correct thread for this, but I couldn't find a thread for the twin line amp.

I was to build a 2U EQ box with 2 seperate Ruffrecords EQ. I haven't decided on builing the Pultec 3 band EQ or the Helios one.

I will, however, be using the twin line amp as the make up gain. I would like to use vintage transformers in this build and I'm struggling to find 10k:10k ones for it. Am I able to use and 1:1 transformers or do they have to be 10k:10k?

Thanks a lot.

 

[ruffrecords]

I will, however, be using the twin line amp as the make up gain. I would like to use vintage transformers in this build and I'm struggling to find 10k:10k ones for it. Am I able to use and 1:1 transformers or do they have to be 10k:10k?

Thanks a lot.

You can use a 1:1 input transformer. You just need to be sure that whatever you drive it from is capable of driving it and also that the transformer is able to cope with the expected input levels without excessive distortion.

For example, the original Pultec EQP1A uses a 600:600 transformer at the input. Whatever drives it needs to be able to drive a 600 ohm load. If you use something other than a 10K:10K type you will need to load the secondary with the required impedance.

Do you have any particular transformers in mind?


Cheers

Ian

 

[letterbeacon]

Thanks Ian.

So I could use any 600:600 vintage transformers in the circuit as long as my interface (Fireface 400) or anything outboard I plug into it can drive it?

I may be buying some vintage transformers but I don't know the exact impedance yet, although apparently they are 1:1. The seller is going to measure the impedance for me and get back to me. Just to confirm - your pultec eq has an input impedance of 100k, right?

 

[ruffrecords]

My Pultec EQ is designed to roughly 'look like' a 10K load to the transformer. Via a 10:10K input transformer, whatever is driving the EQ 'sees' a load of 10K. If you use a 600:600 transformer then you will need to load its secondary with 600 ohms - the EQ is happy with that. Via the 600:600 transformer, that 600 ohm secondary load 'looks ;like' 600 ohms at the input.

It is important to remember that transformer s do not have an impedance as such even though they are nearly always specified in terms of input and output impedance. All a transformer does is transform an impedance from its primary to secondary and vice versa. However, it will only do this over the whole frequency band for a limited range of impedances which is why they tend to be specified by impedance.

Bottom line is your friend really needs to measure the primary inductance of the transformer to tell what impedances it will work best at. Read the attached article and hopefully all will become clearer:

Cheers

Ian

 

[joaquins]

My Pultec EQ is designed to roughly 'look like' a 10K load to the transformer. Via a 10:10K input transformer, whatever is driving the EQ 'sees' a load of 10K. If you use a 600:600 transformer then you will need to load its secondary with 600 ohms - the EQ is happy with that. Via the 600:600 transformer, that 600 ohm secondary load 'looks ;like' 600 ohms at the input.

It is important to remember that transformer s do not have an impedance as such even though they are nearly always specified in terms of input and output impedance. All a transformer does is transform an impedance from its primary to secondary and vice versa. However, it will only do this over the whole frequency band for a limited range of impedances which is why they tend to be specified by impedance.

Bottom line is your friend really needs to measure the primary inductance of the transformer to tell what impedances it will work best at. Read this article and hopefully all will become clearer:

http://www.ianbell.ukfsn.org/EzTubeMixer/docs/EzTubeMixer/Iron/TransformerInductance.pdf

Cheers

Ian

Acording to Ricardo, inductance is not as important as THD at LF (at a determined freq, amplitude and source impedance)
http://groupdiy.com/index.php?topic=57249.msg729762#msg729762

JS

 

[ruffrecords]

According to Ricardo, inductance is not as important as THD at LF (at a determined freq, amplitude and source impedance)
http://groupdiy.com/index.php?topic=57249.msg729762#msg729762

JS

They are both important.  The inductance determines the frequency response at LF and other factors determine the distortion. I was particularly interested in inductance because:

• It is easy to see how it affects price
• It is not too hard to measure
• Manufacturers rarely specify it.

Notice Ricardo also says that the achieved THD also depends on the source and terminating impedances as does the frequency response. I suspect some manufacturers test the frequency response with a low source impedance in order to improve their figures (frequency response and distortion).

Cheers

Ian

 

[anjing]

I just ordered a few XSM 2.4K/600 from edcor....will report back and maybe post audio samples if anyone is interested.

Regards!

Pierre

 

[ruffrecords]

I just ordered a few XSM 2.4K/600 from edcor....will report back and maybe post audio samples if anyone is interested.

Regards!

Pierre

I think you will be pleasantly surprised. P.S.  I will post your 2MODMOTHER PCBs today.

Cheers

Ian

 

[anjing]

Good day Eztube enthusiasts,

  Thanks Ian for the motherboards. I finally installed them. With the decoupling cap trick i am now back to a 84 hp mixer. I am also finally able to use a longer cable with connectors for my power supply.
Edcors were just mailed, can't wait to try those.
Mixer sounds awesome as usual...

Regards,

Pierre

 

[anjing]

Ian, i was looking for some data in your eztubemixer folder on line and i saw the drawing of a 1k pot across the output of a car hill trafo....is it to reduce the gain? I know the direct out on my console are very hot....

Regards,

Pierre

 

[ruffrecords]

@Pierre

Really pleased you got the mixer up an running again and that you still think it sounds good.

The 1K output pot was for use with a passive summer project. The idea was to allow the gain make up amp (twin line amp) to be run hotter to get a little more 'tube sound' and then reduce the output level to compensate. It uses what I call the 'Neve trick' to make simple attenuator on a balanced output with a single pot. We used this 'trick' at Neve in the 70s on monitor outputs.  It allows you to make a stereo balanced monitor level control with just a twin ganged pot ( you need a 4 gang pot to do a proper stereo balanced attenuator). If you want to use it to tweak the output level down to a level more compatible with you other equipment then it should be fine.  If you want to do it 'properly' then you should use a dual 1K log pot. I can draw you a schematic for that if you wish.

Cheers

Ian

 

[anjing]

I would really appreciate it if you don't mind, I'm sure it will probably benefit others in the future.

So this morning i'm moving some modules to the other side, in the new expended left side. So let's crimp some xlr's for the inputs, move the modules, install the knobs and reconnect to the bus feed. Visual inspection.....check! Power on!.....smooooooke! Ok this is what happens when you foresee a small detail like a power connecter one pin off...I think i only damaged the last big reservoir capacitor ht power supply...

Regards,

Pierre

 

[anjing]

problems solved a few caps swapped out and all is back to normal.....

 

[ruffrecords]

problems solved a few caps swapped out and all is back to normal.....

Whew!!!

Schematic of balanced attenuator using dual pot is attached.

Cheers

Ian

 

[anjing]

Big Thanks Ian!

 

[Holger]

 

[wave]

Incredible Holger!

 

[rmaier]

Wow!!! Beautiful!

 

[ruffrecords]

Stunning, Holger!!

Cheers

Ian

 

[anjing]

Beyond words!

Félicitations!

Pierre