Feeler: EZ Tube Lunch Box

[dipfrik]

Hey Ian,

that was too easy

I'am a little bit confused right now, after jumping back a few post on this thread. In a past post i asked about the trimming of the 2nd gain stage. Because the EQ works by changing the gain of of the 2nd amp by altering the negative feedback, in my scribble the gain trimmer is still there? Your answered at my question:

In the diagram the signal first goes to the channel fader via a 4K7 trimmer pot. It is this trimmer that is used to trim the overall gain. It usually drops the input level by about 2dB. Then the fader has 10dB in hand so at its 0dB position it attenuates a further 10dB making a total loss of 12dB. The amplifier then adds 18dB of gain so its output level is +6dBu.. The VTB2291 then drops the level by 6dB because it is a 2:1 transformer and the output ends up at 0dBu .

So my question is: Is it really only lifting the 100uF/250V from ground with the actual amp card, add the whole EQ parts as shown in my scribble and i'am good to go? The gain trimmer for the 2nd amp stage is still there?

Thanks, Sven

 

[ruffrecords]

So my question is: Is it really only lifting the 100uF/250V from ground with the actual amp card, add the whole EQ parts as shown in my scribble and i'am good to go? The gain trimmer for the 2nd amp stage is still there?

Thanks, Sven

Apologies, I should also have said that you do not fit the trim pot and you need to short it out with a wire link. The EQ is effectively a frequency variable resistor that replaces the trim pot.

I am still waiting for my 1H inductors from Banzai before I build a prototype.

Cheers

Ian

 

[dipfrik]

I am still waiting for my 1H inductors from Banzai before I build a prototype.

I see, since today the supply date jumped to 1-2 weeks

Cheers, Sven

 

[ruffrecords]

I am still waiting for my 1H inductors from Banzai before I build a prototype.

I see, since today the supply date jumped to 1-2 weeks

Cheers, Sven

yes, I had an on line chat with a guy from Banzai. he checked with the warehouse who said they expected them in mid next week.

Cheers

Ian

 

[ruffrecords]

The 20AWG wire arrived today so I had a go at wiring up the 9 pin power connector. The result is in the attached pic. On the right is the connector that mounts on the rear panel of the 28HP PSU module. I have used socket contacts so it it harder to stick your fingers in there. On the left is the free plug that would be wired to the motherboard. It uses male contacts. It seems to mate ffirmly and has a rotating locking action so it should not come loose.

I am still confused about these connectors. The distributor and manufacturer data appear to be internally inconsistent. The two connectors are:

Flange mounting standard pin casing size 13 by TE connectivity (AMP):

Rapid part No: 50-0135

Manufacturer Part No: 182922-1

Also available from Farnell Part No: 2060320

According to the Rapid web page this housing takes male pins - it even has a picture showing that. I have used female sockets in it (more on that later). Farnell just calls it a receptacle.

The other connector is Free Plug standard socket housing CPC (AMP):

Rapid part No: 50-0131
Manufacturer's Part no: 182645-1

Also available from Farnell Part No: 5899597

The Farnell web site says its gender is plug and its contact gender is socket. I have used male pins in it.

There is no data sheet on the Rapid web site but there is one at Farnell:

http://www.farnell.com/datasheets/103627.pdf

The top of this data sheet says the flanged housing is a receptacle takes a pin contact. It says the free plug takes a socket contact. I have them the other way round.

However, the second page of the data sheet says the plug with sealing ring accepts male Type  III+ contacts and the receptacle accepts female Type III+ contacts so I think what I am doing is legitimate.

The Rapid web site is incredibly confusing about the range of contacts available so I got them from  Farnell. The pins were part number 592950:

http://uk.farnell.com/te-connectivity-amp/66103-4/contact-pin-24-20-awg-crimp/dp/592950?mckv=s6nNfS3DB|pcrid|39078245888|kword|66103-4|match|p|plid|&CMP=KNC-GUK-***-GEN-SKU-MDC

which are Type III+ contacts. The sockets were part number 592973:

http://uk.farnell.com/te-connectivity-amp/66105-4/contact-socket-24-20-awg-crimp/dp/592973?ost=592973

which are also Type iii+ contacts.

Bottom line is it seems to work. Connectivity exists from the wires on one side of the conector to the other and the resistance meausres zero on my DVM.

Cheers


Ian

 

[dipfrik]

Hey Ian,

awesome research!

Where did you ordered the 20AWG wire?

Cheers, Sven

 

[ruffrecords]

Hey Ian,

awesome research!

Where did you ordered the 20AWG wire?

Cheers, Sven

The distributors all want to sell you 30m or 100m reels of wire which is rather expensive!. I got a 28m selection of 11 colours on eBay:

http://www.ebay.co.uk/itm/330760712353?_trksid=p2060778.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Cheers

Ian

 

[ruffrecords]

I just finished building the 28HP power supply and it is on test right now. Here is a pic of the two halves before final assembly:

On the upper part you can see the LD1084 bolted to the case instead of having a separate heatsink. If this tests out OK then the board layout gets simpler and there should be room for a separate utility supply regulator.

And here it is plugged in and wired up to the lunch box and powering four PCBs. I am going to leave it running for a couple of hours just to make sure the heater supply heat sinking works OK:

Cheers

Ian

 

[ruffrecords]

I ran the power supply loaded with four boards for over 3 hours last night. The hottest point on the case was 40 degrees C which was the bolt holding the 12V regulator. Overall the box felt warm to the touch but at all hot so I think it is basically OK. I will next need to do some tests to make ture it does not introduce hum into the nearest channe.

I have also created a front panel designer layout for a four channel rear panel. The idea is this hold the mic. line and direct out XLRs and also is used to mount the output transformer. The VTB2291 wits in OK as it has its terminal panel at the top. Although the Edcor 2.4K/600 is a smaller transformer, its connection tags are at the side and it looks like they will foul the XLRs. I do not have a solution to this yet. The attached pic shows the panel. The three holes in a vertical line on the left are for transformer mounting for channel four. The bottom hole is common, the top one is for the VTB2291 and the middle one is for the Edcor.

Cheers

Ian

 

[ruffrecords]

I have just completed an initial hum assessment of the 28HP supply in the lunch box. I fitted a couple of boards to load up the heater supply and then fitted the new  'classic' board as close to the power supply as I could get it. THe 'classic' board was fitted with a Cinemag 1:10 input transformer and configured as a single mic pre consisting of two cascaded stages. I fitted a 2K4:600 transformer to out 2.

Initial hum reading were very poor even with the gain turned right down (_36.7dBu). It got a few dBs better if I took the PSU out of the rack but it was still very high (around -42.6dBu).  Even with the PSU turned off the noise was only -63dBu and a small amount of hum was audible. Fortunately I realised I had forgotten to connect the HT 0V to the chassis/mains earth inside the PSU!!

So I corrected this an tested again. This time the noise with the PSU in the lunch box was down at -67dBu. However, I could not get a signal through the 'classic'. I got a low level output at -30dBu and the position of the level control made only 6dB difference. I tracked this down to two faults. First I had used 680 cathode bias resistors (as orinted on the PCB) when for the mu follower they should have been 220 ohms. I also found a wire had become un-soldered from the pot.. After fising these faults the output noise with the pot turned right down was -77dBu. I also checked the 'classic' 1KHz distortion unloaded via the transformer. At +10dBu it was 0.12% and at +15dBu it was 0.2%.

I then tried checking the gain of the 'classic'. I could easily obtain 70dB of gain even with the 6dB loss in the output transformer. However, as I tried to test for maximum gain, as the level control approached fully open, the amp began to oscillate. I have not yet found the cause of this. Alos the noise performance of the clssic is not good. At 60dB gain the noise was -36dBu which gives an EIN of only - 96dBu which is very poor. Clearly there is something wrong with the design.

Bottom line, it looks like the power supply is OK but this needs to be confirmed with a known good mic pre card.

Cheers

Ian

 

[dipfrik]

Hey Ian,

However, as I tried to test for maximum gain, as the level control approached fully open, the amp began to oscillate.

Based on my research with Holger last week i have (massive) problems here with my prototype board (ez mixer amp card).
Both gain stages seperately working ok, but as soon i connect an eq (redd) between the stages, i have problems in maximum gain settings or in combination with the pad switch, the eq or the fader. I can only describe it as "flooding" in extreme settings and the effect can be reached with the fader, high gain settings or various positions on the redd eq in combination.

So i'am not shure right now, how your "oscillate" sound like?

Thanks, Sven

 

[ruffrecords]

So i'am not sure right now, how your "oscillate" sound like?

Thanks, Sven

I think it is supersonic. I cannot hear anything put the meter I have on the output just hits the end stop. I need to look at it with an oscilloscope.

When adding EQ you need to be careful how you  wire it in. Obviously you need to use screened wire. You should leave the cable screen  un-connected at OUT1 and connect it at the EQ input. Use a screened lead from the EQ input to IN2 and connect the screen to ground at the EQ end AND at the IN2 end. Make sure these cables ar routed well away from the mic and line in screened cables.

Cheers

Ian

 

[dipfrik]

Yeah, thats exactly what i started with great help from Holger last week, which made one point abundantly clear: "I'am not ready for a small mixer!"

But i think there is something more not right.
I will check your wiring too, but "well away" from mic and line in screend cables is nothing here.

Cheers, Sven

 

[ruffrecords]

Yeah, thats exactly what i started with great help from Holger last week, which made one point abundantly clear: "I'am not ready for a small mixer!"

But i think there is something more not right.
I will check your wiring too, but "well away" from mic and line in screend cables is nothing here.

Cheers, Sven

What make of tubes are you using?

Cheers

Ian

 

[dipfrik]

The same that i use in my big 1st testrig. The funny thing is, this 1st testrig with your original amp card, a combination of all three eq's with y VERY poor wiring, absolutely didn't care about grounding, shielding whatsoever, works like a charme!

Cheers, Sven

 

[ruffrecords]

The same that i use in my big 1st testrig. The funny thing is, this 1st testrig with your original amp card, a combination of all three eq's with y VERY poor wiring, absolutely didn't care about grounding, shielding whatsoever, works like a charme!

Cheers, Sven

Is the power supply different this time?

Cheers

Ian

 

[dipfrik]

Beside the fact that the voltages are not perfect, i checked both (the old initial one and the new one) in different scenarios, and always my 1st amp card from you working fine. I triple checked the layout and found no errors, so it must be a combination of component placement and correct shielding i think.

Cheers, Sven

 

[ruffrecords]

Beside the fact that the voltages are not perfect, i checked both (the old initial one and the new one) in different scenarios, and always my 1st amp card from you working fine. I triple checked the layout and found no errors, so it must be a combination of component placement and correct shielding i think.

Cheers, Sven

Strange. The fact that the old board performed fine in a less than ideal environment seems to indicate the basic design is fairly robust. The new board acting strange in a relatively goo environment indicates something is wrong with it. The fact that the problem occurs with EQ connected and at high gains implies some kind of feedback is involved. Can you post a picture showing the new board and its EQ board together? Perhaps I can then offer some help.
Cheers

Ian

 

[MicDaddy]

The VTB2291 wits in OK as it has its terminal panel at the top. Although the Edcor 2.4K/600 is a smaller transformer, its connection tags are at the side and it looks like they will foul the XLRs. I do not have a solution to this yet.

Could these be ordered special with flying leads? 

Could the oscillation at high gain be related to the layout in its new environment?  Is there feedback going on in the design?  Perhaps some HF is getting into the loop?  Sorry for tangent questions, getting curious about this project.

 

[ruffrecords]

The VTB2291 wits in OK as it has its terminal panel at the top. Although the Edcor 2.4K/600 is a smaller transformer, its connection tags are at the side and it looks like they will foul the XLRs. I do not have a solution to this yet.

Could these be ordered special with flying leads? 

I don't know. It might be worth asking Edcor but I suspect they are geared up for a bunch of standard cores and termiantions.

Could the oscillation at high gain be related to the layout in its new environment?  Is there feedback going on in the design?  Perhaps some HF is getting into the loop?  Sorry for tangent questions, getting curious about this project.

That's why I asked for a picture showing the physical set up. It might provide a clue.

Cheers

Ian
[/quote]