T-Rex - SQUEEZER

apollomusicservice · Post by **apollomusicservice** » 17 Aug 2013, 17:32

For bass players here is schematic and guts of tube-driven compressor which is also suitable for guitar.

electrosonic · Post by **electrosonic** » 17 Aug 2013, 17:51

200 volt preamp supply, very cool.

Interesting that they only used 1/2 of the 12ax7. It would have been simple to use the other 1/2 as a cathode follower to drive the output. As it is this looks to have a fairly high output impedance.

Andrew.

astrobass · Post by **astrobass** » 17 Aug 2013, 21:27

High output impedance is generally why tube amps sound "warm", right? So it makes sense that they'd go that route here - otherwise people would complain that it didn't sound very "tube-like".

apollomusicservice · Post by **apollomusicservice** » 18 Aug 2013, 06:30

I'm quite sure that it could be find a good "job" for second half of 12AX7.

bajaman · Post by **bajaman** » 18 Aug 2013, 08:01

yeah - they could have used it for an input buffer instead of the fet. Come to think of it - why did they even bother to use a tube at all ? another fet or op amp gain stage at the end would have worked just as well.

Oh right

yet another sales marketing ploy - put a tube in it and everyone will think it is a tube compressor

which it clearly is not

interesting switching high voltage supply though - any further details on the small encapsulated transformer turns ratio etc.

ppluis0 · Post by **ppluis0** » 18 Aug 2013, 22:57

bajaman wrote: Oh right yet another sales marketing ploy - put a tube in it and everyone will think it is a tube compressor
which it clearly is not

I'm a big fanatic to build tube based units and is very unpleasant see that the 12AX7 is used merely as marketing argument.

bajaman wrote:interesting switching high voltage supply though - any further details on the small encapsulated transformer turns ratio etc.

Steve, after a simple calculation the 555 is oscillating at 2.3 kHz, so I think that the transformer can have an ordinary iron core.

Perhaps you can test with the small one you can afford with 120 to 12 volts windings. At this frequency the resultant ouput voltage will be higher than the calculated at 60 Hz.

Also the duty cycle of the astable can alter the output of this tranny, I think.

Apollo, thank you for your work done to trace this unit, but take another look to find if you're missed one resistor placed between pin 1 of the tube socket and the power point labeled +UB

My instinct tells me that at this point there will be an 100 K resistor to complete this diagram.

Cheers,
Jose

bajaman · Post by **bajaman** » 19 Aug 2013, 00:37

that is what I thought too Jose

BUT take a look at the power supply - three 15k resistors in series provides the tube with a 45k plate load

Thanks for the 555 timer info

cheers
Steve

ppluis0 · Post by **ppluis0** » 19 Aug 2013, 04:38

Ooops !!!

You're right (as always

), bajaman...!!!!!!! I completely miss that part of the supply section.

I really wish to see more tube units dissected here at the forum, to learn the small tricks (as this PSU arrangement for example) that each manufacturer employs.

Cheers,
Jose

apollomusicservice · Post by **apollomusicservice** » 19 Aug 2013, 08:39

I found by measuring that the frequency of the oscillator 555 is 21.3 kHz and after re-checking the values of the capacitors C5=1nF.
Resistance of TR1 primary and secondary are 230 Ohm and 12 Ohm. Here is the applied standard application IC THAT4320
http://www.thatcorp.com/datashts/THAT_4 ... asheet.pdf
I like that is a part of the DC-DC converter mounted on a separate PCB but main PCB with all the other elements is quite unhandy routed, some lines cross a long way in parallel with the energy supply lines while the better arrangement of the elements of their lines were much shorter. In particular, the unhandy placed THAT4320 and THAT340 (operatin temperature range 0-70 ° C), take place under the 12AX7, which gives great heat after some time of use,
the distance is about 1-2 millimeters. I did not find any good reason why these ICs were placed so close to the tube.

bajaman · Post by **bajaman** » 19 Aug 2013, 09:26

I did not find any good reason why these ICs were placed so close to the tube.

probably to get THAT "warm" tube sound (pun intended)

ppluis0 · Post by **ppluis0** » 19 Aug 2013, 14:34

apollomusicservice wrote:I found by measuring that the frequency of the oscillator 555 is 21.3 kHz and after re-checking the values of the capacitors C5=1nF.
Resistance of TR1 primary and secondary are 230 Ohm and 12 Ohm.

At this freq, the core of this transformer must be of some type of ferrite.

mozwell · Post by **mozwell** » 22 Aug 2013, 04:17

any standard type of "transformer" ferrite will do
Input volts = 15VDC approx when transistor is turned on, as this is not a flyback converter, we are doing a hard switching forward converter, so all we need to do is look at input & output volts to get the turns ratio.
15VDC in, output 250V approx + 2 diode drops & winding resistance, so lets use 255V, so turns ratio is 255 / 15 = 17
We need to know the core size to work out actual turns, but these small switch mode fixed frequency transformers are easy enough to design, the harder part is winding your own, getting the small core & even smaller magnet wire.....

mozwell · Post by **mozwell** » 22 Aug 2013, 04:25

also, as the output is connected to pcb 0V, a simpler design, just using an inductor would be the Bajaman blackstar HT power supply, or the 555 based supply, just be sure that "noisy" power supply 0V lines are connected at one point only with the clean signal 0V for the analague circuitry, ie star grounding , as you would with a valve amp

mr coffee · Post by **mr coffee** » 04 Dec 2013, 04:15

Hi apollo music service,

Thanks for tracing this out. Pretty sophisticated circuit. Looks like the tube HV might even sag to actually do something when pushed hard.

Would you check to be sure C21 is really 10 uf ? Noticed C20 was also 10 uf.

That seems like pretty heavy filtering of the RMS detector signal when there is further filtering in the attack and decay circuitry that follows.

And shouldn't there maybe be a capacitor on the non-inverting input of IC2A - looks like the transistors don't have a cap to charge and discharge for attack and decay.

Anybody else confused by this?

mr coffee

Maybe I just need to study the circuit more

apollomusicservice · Post by **apollomusicservice** » 04 Dec 2013, 10:30

Mr Coffee thank's

for notes about missing Cx 3u3/50V capacitor on schematic (pin3 of IC2 to positive and ground to negative pin of Cx).
C20 and C21 are really 10u which can be seen on my photo3
For the study here is one interesting http://www.thatcorp.com/datashts/THAT_4 ... asheet.pdf for THAT4320.
Cheers

tube_S_cream · Post by **tube_S_cream** » 09 Dec 2013, 11:42

Very interesting.. til today i thought, the T-REX Squeezer would be a tube compressor

O.k. taking an THAT 4320 is a very good choice for a compressor-circuit but in the end it is a tube gain stage, driven by a compressor.
If the schematic are right, there is one point, that is surprising. The tube circuit represents a second order highpass with a cutoff around 70Hz. This should result in a significant loss of bass frequencies especially for low B or even deeper tuned instruments. A real tube overdrive is only possible if makeup gain is cranked up very high.
It makes sense if you use this pedal in front of a solid state preamp. For use in front of tube preamp the pure 4320-Circuit would be enough...

AJPalma · Post by **AJPalma** » 24 Feb 2014, 12:47

Hi guys, I need the T rex squeezer schematic, anyone can help me please? thx...

mirosol · Post by **mirosol** » 24 Feb 2014, 21:05

AJPalma wrote:Hi guys, I need the T rex squeezer schematic, anyone can help me please? thx... :P :P

Something wrong with the one on this particular page?

xaxxop · Post by **xaxxop** » 23 Mar 2014, 11:09

Apollo thank you so much, good job!

Manfred · Post by **Manfred** » 23 Mar 2014, 12:22

bajaman wrote:that is what I thought too Jose
BUT take a look at the power supply - three 15k resistors in series provides the tube with a 45k plate load Thanks for the 555 timer info
cheers
Steve

Tricky drawing, indeed!

T-Rex - SQUEEZER [schematic]