EZ Tube Mixer Support Thread

[wave]

Awesome work!!

 

[ruffrecords]

Absolutely brilliant. Well done. Looks like Holger has some competition now!!

Cheers

Ian

 

[Timjag]

This is just awesome! I'm going to do it when I get some ££ for the trannies

 

[Rocinante]

Wow. Awesome

 

[wave]

Hi everyone,
I'm considering using the Hi-Z relay driven input for the single channel I'm building right now.
Has anyone else added the Hi-Z input? I have a suitable 12V rail I can use (I'm driving other relays that I have added) and I would like to keep it simple by just having a switched jack. I'm thinking it has to be a "make" type jack as I need to energize the relay to use the Hi-Z in. I have a version 3 PCB so should I add external diode and filter cap for this relay?
Or is it just easier to use a dedicated push button or toggle to drive the relay?

I appreciate all opinions!

Thanks,
Dave

 

[ruffrecords]

The relay was added because a lot of people said they would like an option for a DI input but I do not know if anyone has ever actually used it. The reason a relay was used is to ensure the signal path for the mic signal is kept as short as possible. As it is a high impedance circuit it can be prone to interference. The 'normal' way to do a DI is to run a screened cable from the mic transformer secondary to a switched jack socket on the front panel and then a screened lead from there to the first tube input. You don't need a relay for this but the long screened cable can pick up interference and its capacitance may alter the high frequency response. Despite this, a lot of DI are done this way and I have done them this way myself on the Classic Solo board with no ill effects.

If you use the relay it will need a diode to catch the back emf and I would recommend you feed the supply via a small value resistor and connect an  electrolytic capacitor from the end of the resistor to the relay supply 0V.

Chees

Ian

 

[Dnukas]

Hi friends,

It was long ago since my last post.
I had some health issue and also was so busy, but in these days I have time to finish my console.
I finally finish chassis work and put all together.
I finished and tested all buffers and filters modules.
Everything works fine at this moment.
Only issue is that buffer have plenty of gain...I turn down the input signal and input trim is approx at 1/3 .
What you think about idea add NFB like in attachment?

I upload some fresh pics :
https://www.flickr.com/gp/151151270@N04/5M7527

Lukas

 

[ruffrecords]

You will also need to add a resistor in series with the 100nF input capacitor. The gain will be set by the value of the feedback resistor divided by the the series resistor; very much like an inverting op amp. This resistor will also set the input impedance of the buffer. At the moment it is about 330K (determined by the 470K pot in parallel with the 1Meg grid resistor). Does it need to be this high?

Cheers

Ian

 

[Dnukas]

Hi Ian,

thanks for fast reply.

You are right, input impedance is unnecessarily too high.
Is good idea to keep grid resistor reasonable high value aprox 470k and decrease the value of input trim to 47k?
Or is better option decrease the both value to aprox 100k?

When I will try NFB, input resistor should be placed between 100nF cap and tube grid, Am I right?
Place it between Input trim and 100nF CAP is pointless because there is  no DC coupling?

sorry for basic question .

Lukas

 

[ruffrecords]

Place it between C5 and R9.

On balance it is probably better to go for 47K pot and make the input impedance (= input series resistor). For example, 300K input resistor and 1Meg feedback will give a gain of around 10dB.

You probably do not need R9 because the 100K to ground at the output and the feedback resistor already provide a dc path to ground for the grid.

Cheers

Ian

 

[Dnukas]

Hi Ian,

thanks .
I tested it and gain look fine now.

There is some noise from AC heaters but nothing critical.
I try it with external DC PWR supply and results are much better, but i think it's  definitely usable with AC heaters too.

Problem is that I have strange interference issue...It's the same with or without NFB.

It's very low freq...Spectral analyzer for my digital converter have lowest FREQ 25Hz.
I look at it in DAW too and it looks like interference is bellow 6Hz( very roughly).

Interference are there even power supply is disconnected...(until heaters go cold and HT+ CAP are still charged)
Its not constant level , just random peaks?

I try to bypass in and out at converter and its OK without any noise or interference.
I recorded it and add pic to attachment.

Any clue what I missed?

thanks for reply

Lukas

 

[guavatone]

I totally missed this impactfully cool project.  Awesome work Holger, Ian and other’s I’m sure i’m Leaving out.  Did you aver are any A/B comparison files from SSL?  Stunning work guys.

 

[ruffrecords]

Hi Ian,

thanks .
I tested it and gain look fine now.

There is some noise from AC heaters but nothing critical.
I try it with external DC PWR supply and results are much better, but i think it's  definitely usable with AC heaters too.

Problem is that I have strange interference issue...It's the same with or without NFB.

Lukas

Difficult to see what this is from the spectrum plot because a lot of it is off screen. Can you adjust the scale so we can see the whole plot? It is quite usual for noise to rise at low frequencies. This is known as 1/f or flicker noise. All audio systems have it to some degree.

Cheers

Ian

 

[Dnukas]

Are this plots better?

thanks

Lukas

 

[ruffrecords]

Yes, that is better. This spectrum has two unusual features. First the rising response towards the high end. Unless there is some EQ in circuit t would be more usual for the spectrum to be fairly flat at the top end. And the second thing is the big bump at 25Hz. What were the conditions under which these measurements were made? Is it the whole mixer or just the output section (level control turned right down)?

Cheers

Ian

 

[Dnukas]

Its just one buffer amp, EQ section is bypassed.
I try it on others buffer modules and it`s the same.
I also try different tubes- the same.

Signal path:
converter OUT->input transformer->E88CC buffer->output transformer->converter IN.
No input signal.

Response towards highend-it`s noise floor of converters .
When buffer is is power off , it`s the same but levels are below -110 dB

On plot are noise of converter+noise of buffer with no input signal to buffer(but buffer was connected to converters)

That strange impulses-big thumb are visually between -80dB to -65dB.
It`s actually below 8Hz , but on this  spectrum analyzer lowest  display value is 25Hz.
I look at it in my DAW and it looks below 8Hz.
I use external power supply. When I disconnect  PWR supply (unplug it from console), It's the same till heaters are enough hot and HT+ caps are charged.


thanks

Lukas

 

[Dnukas]

I think that I got it...

I check the converters inputs without any sources....just alone.

I change the sample rate to 44kHz 48kHz 96 kHz and 192Khz
And there is that energy  in 25Hz bar with all tested sample rate ->level is very low beyond -120dB.
Also the signal to noise ratio for freq beyond human hearing is worse and worse...
But with buffer this low freq energy had undesirable levels

So i think that buffer is innocent.

Maybe It's  antialiasing problem of converters or so....

I'm sorry for offtopic problem.

I add screenshot of  converters input without source signal.

Lukas

 

[ruffrecords]

I have heard that some of the drivers are a bit suspect at the higher sample rates I have seen something similar with my Scartlett interface. Nice to know it is not the tubes.


Cheers

Ian

 

[matriachamplification]

Hello groupDIY EZ Tube Mixer Support Thread.

In hopes of keeping Mr. Thompson-Bell and I's CTC Design conversations to this thread I am ignoring the 120 day auto-prompt urging a new thread be started.

Given our discussions have led to designs developed by Holger Classen homage to passive tube mastery, the 12 channel Krassemascine. (well done mate!)

That said, my endeavour into the world of Analog Audio Design is educationally motivated and medically prescribed to replace costly therapy for Amnesia, DID and C-PTSD, instead re-focusing my thought patterns to PASSIVE TUBE AUDIO THERAPY through the fantastic art of PCB Population!
Long and Short term memory loss is the largest factor. Already the repetition of researching Mr. Thompson-Bell's designs has helped me to recall some simple electronic basics from my past.

DISCLAIMER: This type of therapy is not recommended as actual Medical Therapy. Mr. Thompson-Bell has been guiding me to this point for well over a year with many therapy sessions making note of the progress. This decision was made to re-educate myself and in turn my 12 year old son and 2 year old daughter in the art of Soldering.

In case anyone makes it this far, I should state that the largest contribution I hope to  make to the Custom Tube Console line of Audio Designs is to build out and thoroughly document the process, with both documentary style filmed footage and coloured step by step "The Custom Tube Console Playbook" coffee table read on every and all CTC designs i/we can work on togethers.

Outside of some main outlandish design ideas (the HexaQuad 64 - a Dolby Atmos Custom Tube Master Monitor Controller) I can share the current design layouts, once I have shared them and gotten feedback from Mr. Thompson-Bell.

Wall

 

[ruffrecords]

Welcome to the group Wall. There is a wealth of expertise here all willing to offer advice.

Cheers

ian