Hi!
I have build a DoZ (just one side for now), using the PCB from ESP, 2N3055 transistors, a 225 VA 30 - 0 - 30 toroid, and the suggested supply with four BYW29E soft recovery diodes and two 10000 uF BHC SlitFoil caps.
First part of testing (with 10 ohms resistor in series to V+, measuring the output voltage at the + pin of C3) went OK, I got about half the supply voltage (about 19.8 V)
But then the second part of testing does not work. Connecting a 1 ohm resistor in series to V+, measuring voltage across the resistor in order to get the quiescent current, showed no current at all. And the amp does not heat up at all. And all the time the DC voltage at the output at the - pin of C3 (where the speaker should be connected) stays at about half the supply voltage... adjusting VR1 and VR2 does not seem to have any great affect...
Is maybe one of my transistors (also the driver transistors) broken? Is there an easy way to measure this? I do not think I made a mistake stuffing and soldering the amp, since it was very easy to build, and I checked everything three times before powering up...
Any Ideas?
Thanks in advance,
Arndt
I have build a DoZ (just one side for now), using the PCB from ESP, 2N3055 transistors, a 225 VA 30 - 0 - 30 toroid, and the suggested supply with four BYW29E soft recovery diodes and two 10000 uF BHC SlitFoil caps.
First part of testing (with 10 ohms resistor in series to V+, measuring the output voltage at the + pin of C3) went OK, I got about half the supply voltage (about 19.8 V)
But then the second part of testing does not work. Connecting a 1 ohm resistor in series to V+, measuring voltage across the resistor in order to get the quiescent current, showed no current at all. And the amp does not heat up at all. And all the time the DC voltage at the output at the - pin of C3 (where the speaker should be connected) stays at about half the supply voltage... adjusting VR1 and VR2 does not seem to have any great affect...
Is maybe one of my transistors (also the driver transistors) broken? Is there an easy way to measure this? I do not think I made a mistake stuffing and soldering the amp, since it was very easy to build, and I checked everything three times before powering up...
Any Ideas?
Thanks in advance,
Arndt
An externally hosted image should be here but it was not working when we last tested it.
Figure 5 - The Complete DoZ Schematic (With Iq Stabilisation)
DOZ - ESP Project 36
--------------------------------------------------------------------
As you get the correct half voltage
there is no fault in the transistors and probably not
in any part.
You should check your wiring. Once again.
Especially around the pot/resistors that set
the Output Stage current.
Are the 3 connections to the pot, wired in the right way
to the circuit?
If you have connected the 1 ohm resistor correctly
you should have some small voltage drop over it,
at least 20-50 mV.
Because obviously the circuit get current, as the output is at 19.8V.
Check the wiring not only once or twice,
but 5 times.
Always a good advice!
Especially when you use circuits partly or totally without PCBs.
/halo
Hi again!
There is the smal possibility that I mounted VR1 the wrong way around. In the construction article, R. Elliot showed both pots with the adjustment screw facing "up", that is with the connections to the output transistors to the right.
But I think that VR1 should be mounted with the adjustment screw facing "down", since the pin under the screw is pin "A" or "1", and according to schematics pin A of VR1 should be connected to GND, which would lead to mounting it the way I did. R. Elliot did not answer my second email with this statement yet, but I think he probably will...
But am I mistaken when I think that after C3 almost no DC offset should be measurable?
And the voltage drop across the testing resistor, do you measure it by calculating the difference between the voltage before and after the resistor, or by simply attaching the measuring pins to both sides of the resistor? Boy, seems I should have paid more attention to my electrotechnical courses at university (one reason why I dropped out
)...
Anyway, thanks,
/Arndt - who just discovered that the testing heatsink for the DoZ would be absolutely ideal for a multi-channel GC using the OPA548T which arrived today, since they are so very small - TO220 -, and the sink already is pre-tabbed for that...
There is the smal possibility that I mounted VR1 the wrong way around. In the construction article, R. Elliot showed both pots with the adjustment screw facing "up", that is with the connections to the output transistors to the right.
But I think that VR1 should be mounted with the adjustment screw facing "down", since the pin under the screw is pin "A" or "1", and according to schematics pin A of VR1 should be connected to GND, which would lead to mounting it the way I did. R. Elliot did not answer my second email with this statement yet, but I think he probably will...
But am I mistaken when I think that after C3 almost no DC offset should be measurable?
And the voltage drop across the testing resistor, do you measure it by calculating the difference between the voltage before and after the resistor, or by simply attaching the measuring pins to both sides of the resistor? Boy, seems I should have paid more attention to my electrotechnical courses at university (one reason why I dropped out
)...Anyway, thanks,
/Arndt - who just discovered that the testing heatsink for the DoZ would be absolutely ideal for a multi-channel GC using the OPA548T which arrived today, since they are so very small - TO220 -, and the sink already is pre-tabbed for that...
- simply attaching the measuring pins to both sides of the resistor.
Yes, that is the way.
Start on 2 VDC range. If nothing go downto 200mV and 20 mV DC.
-------------------
- I think that after C3 almost no DC offset should be measurable.
C3 would be the output Cap.And there should be no DC-voltage
on the output side to ground. That is where the 2 leads to Loudsp will connect.
---------------------------
I can't help get thinking there is some connections
you have not done correctly.
And as no change in output voltage, 19.8V,
take place the pot VR1 does not work.
VR1 is used to adjust the Voltage to half supply voltage
And VR2 sets the Current in output stage,
and should make the voltage drop over an 1 ohm resistor change. (1 Volt = 1 Ampere)
If it worked alright.
--------------------------------------------
You will find the fault(s), in time.
Just keep checking.
/halo
Yes, that is the way.
Start on 2 VDC range. If nothing go downto 200mV and 20 mV DC.
-------------------
- I think that after C3 almost no DC offset should be measurable.
C3 would be the output Cap.And there should be no DC-voltage
on the output side to ground. That is where the 2 leads to Loudsp will connect.
---------------------------
I can't help get thinking there is some connections
you have not done correctly.
And as no change in output voltage, 19.8V,
take place the pot VR1 does not work.
VR1 is used to adjust the Voltage to half supply voltage
And VR2 sets the Current in output stage,
and should make the voltage drop over an 1 ohm resistor change. (1 Volt = 1 Ampere)
If it worked alright.
--------------------------------------------
You will find the fault(s), in time.
Just keep checking.
/halo
Hi,
I have build the Doz and my version didn't work because I had 100k ohm resistors for R5 and R8 instead of 100 ohm.
If you have placed the two BD 139 wrong it will give you half the supply voltage but it will not work (I am not going to admit that I had those wrong too ).
I also measured some dc at the - pin of C3 but after connecting a resistor (4 ohm) at the output the DC was gone...
good luck!
menno
I have build the Doz and my version didn't work because I had 100k ohm resistors for R5 and R8 instead of 100 ohm.
If you have placed the two BD 139 wrong it will give you half the supply voltage but it will not work (I am not going to admit that I had those wrong too
). I also measured some dc at the - pin of C3 but after connecting a resistor (4 ohm) at the output the DC was gone...
good luck!
menno
Doz circuit!
Hi Guys!
Funny circuit this one!
Q1 work with a current of +- 0.37 mA...the gain of Q4-Q5 is aproximately2000.so the output current in the load will be
0,37 mA X 2000=740mA
In a 8 Ohms load it wil put 2 W in the load...and less than 8 (+-6)volts...and all of this with a 40 volts power supply and 15 amps transistores...
That i call overkill...one more gain stage will have good efect!!
Cheers
Jorge Santos
Hi Guys!
Funny circuit this one!
Q1 work with a current of +- 0.37 mA...the gain of Q4-Q5 is aproximately2000.so the output current in the load will be
0,37 mA X 2000=740mA
In a 8 Ohms load it wil put 2 W in the load...and less than 8 (+-6)volts...and all of this with a 40 volts power supply and 15 amps transistores...
That i call overkill...one more gain stage will have good efect!!
Cheers
Jorge Santos
Hi!
Thanks for the input.
I will definitely try charging C3...
As for the driver transistors, I hope I did not put them in the wrong way around. I have put them in with the heatsink pointing towards the input...
Oops.. think that could be wrong... for example, I connected the base of the BD139 to R4... should be the emitter...
Maybe checking the datasheets would be an obvious thing to do prior to soldering... But I already used the BD139 on the DoZ pre, and there it works... maybe my mind is just twisted...
I heat up my soldering station and try it now...
Bye,
Arndt
Thanks for the input.
I will definitely try charging C3...
As for the driver transistors, I hope I did not put them in the wrong way around. I have put them in with the heatsink pointing towards the input...
Oops.. think that could be wrong... for example, I connected the base of the BD139 to R4... should be the emitter...
Maybe checking the datasheets would be an obvious thing to do prior to soldering... But I already used the BD139 on the DoZ pre, and there it works... maybe my mind is just twisted...
I heat up my soldering station and try it now...
Bye,
Arndt
I'm having trouble w/ dc offset as well. I was running the amp on a variac for testing, and the output was at almost 10v before the C3 and at the actualy speaker output after c3 there is 9v of DC. Is this oscillation? I'll ask Rod and see what he says, but it sounds like I'm not the only one w/ this problem. Anyone else?
-Matthew K. Olson
-Matthew K. Olson
Hi!
I've still not had enough time to re-try building the DoZ, since I had to finish the P3A first
I think it will be delayed until late summer or fall, since my next project is a Zebulon Ultra subwoofer (man, 120l, 58 kg...!!!)
But I think that I will rebuild it step - by - step, not trying to find out what I did wrong the first time. So I will use my unstuffed second board, and unsolder the first one...
But do post your experiences, if you find out what you did wrong! I will always keep track of this...!
Bye,
Arndt
I've still not had enough time to re-try building the DoZ, since I had to finish the P3A first
I think it will be delayed until late summer or fall, since my next project is a Zebulon Ultra subwoofer (man, 120l, 58 kg...!!!)
But I think that I will rebuild it step - by - step, not trying to find out what I did wrong the first time. So I will use my unstuffed second board, and unsolder the first one...
But do post your experiences, if you find out what you did wrong! I will always keep track of this...!
Bye,
Arndt
Ok, also, would anything close to 1k work? bigger than 1k would have a slower capacitor charging...but would it have less effect on the sound? Would 750 ohms work? I'm just thinking about paralleling some .5watt resistors and need to know what would be best...also have to consider what I have Later!
-Matthew K. Olson
Later!-Matthew K. Olson
Ok, I paralleled 2 2.2k 1watt resistors and got 1.08k...and put this across the speaker out terminals...basically from the c3 cap output (speaker +) to ground (speaker -). Now I have less than .06v DC offset instead of 9v. :-D AWESOME! Now my only problem is that my toroidal that I just got is too high of a voltage...so I need to install some higher voltage caps. I have 50v caps now (BIG 80kuf computer grades) and I'm now running close to +60v-0 supply. So time to install my 80vdc 61kuF caps I have an 800 va avel 40+40 toroid right now. should be plenty Bias will be around 2.5-3.0 amps. Any idea how much power I'll get into 8 ohms? 40 watts or so sound right? Thanks!
-Matthew K. Olson
I have an 800 va avel 40+40 toroid right now. should be plenty Bias will be around 2.5-3.0 amps. Any idea how much power I'll get into 8 ohms? 40 watts or so sound right? Thanks!-Matthew K. Olson
Well...the amp works. Thats the short of it. I'm actually running the rails quite high...66v!!!! I know thats really high, and bias at 3.3 amps. But i have 8 transistors and big heatsinks. Should hold it fine. Anyway, the amp works, I get some hum so far, though i haven't had time to mess with it. I'm also using Rod Elliots circuit for a balanced receiver, and had to take this out of the circuit for now because it was giving me LOTS of distortion. So I'm running it unbalanced and sloppily biased. I'll get it running better soon enough, and post pics too. Don't worry ya'll!
This is going to be a sweet amp!
-Matthew K. Olson
This is going to be a sweet amp!
-Matthew K. Olson
Ok, my house current has quieted down to give me a 53v rail. I have spent the past 2 hours trying to figure out a ground loop...the only thing that helps is lifting the ground. The chassis is grounded to the wall, but not to the main caps or the amp itself. I know that this is a no no...but its the only thing that seems to help. Anyway, initial impressions of the amp are that the highs are VERY nice...open soundstage...little light on the bass. Not sloppy at all...just...lacking? I have 2 2200uF panasonic FC caps on each output ...is this too little? I think this amp would be just great to biamp with...put this amp on the highs and do a gainclone or lm3886 (similar to gainclone) on the lows...it would be a great amp for sure! What a heater though...amazing how much heat this thing generates...especially with 3A+ bias. Pics soon.
-Matthew K. Olson
-Matthew K. Olson
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