PL 700 II Clair Bros Rising from the Ashes
- Thread starter Peter S
- Start date
Thanks for the info regarding rev B and C back planes. I have the rev B's. When doing my noise measurements, I noticed about 1 mV of cross-talk, with the opposite channel being driven to maybe 5 or 6 volts. ( 1 kHz ) I wired the ground from right to left as instructed by the rev B documentation.
I am pleased with the current performance but would running the Right chan ground separately to the Power supply ground bus be a significant improvement?
Bit of a PITA pulling all output devices on the right chan to remove the back plane for soldering. Or would you take extra care and change those wires with the back plane in place?
I am pleased with the current performance but would running the Right chan ground separately to the Power supply ground bus be a significant improvement?
Bit of a PITA pulling all output devices on the right chan to remove the back plane for soldering. Or would you take extra care and change those wires with the back plane in place?
Significant is hard to quantify from a SQ perspective when it comes to crosstalk. I wish I could hear a millivolt crosstalk difference Peter.
That change is for design purity purposes since the control board went to 2 independent channels, the backplane wiring should logically follow. The ground currents are miniscule on the backplanes as they are only the return currents through the decoupling caps that run through these ground wires. Nothing on the backplanes except that decoupling current and the Zoebel return are ground referenced. You can see that in the schematic.
That change is for design purity purposes since the control board went to 2 independent channels, the backplane wiring should logically follow. The ground currents are miniscule on the backplanes as they are only the return currents through the decoupling caps that run through these ground wires. Nothing on the backplanes except that decoupling current and the Zoebel return are ground referenced. You can see that in the schematic.
I am starting a rebuild of the second PL700 II and will verify the necessity of the shield.
On to a side issue; it has been pointed out that my dummy load (pictured below, ex electric furnace ) may have some inductive properties. The elements were reconfigured to be 8 ohms.
This may be basic electronics, but could I test this by connecting it in series with an 8 or 10 ohm carbon resistor, then measure the voltage at the centre point with my scope? If the voltage does not shift with frequency, would this confirm the suitability of the dummy load?
As soon as my wife is not looking, I will escape to my shop and try this!
On to a side issue; it has been pointed out that my dummy load (pictured below, ex electric furnace ) may have some inductive properties. The elements were reconfigured to be 8 ohms.
This may be basic electronics, but could I test this by connecting it in series with an 8 or 10 ohm carbon resistor, then measure the voltage at the centre point with my scope? If the voltage does not shift with frequency, would this confirm the suitability of the dummy load?
As soon as my wife is not looking, I will escape to my shop and try this!
Attachments
Testing the first WOPL PL700 II for power output resulted in an impressive 450 Watts+ per channel, one channel driven, into my 8 ohm dummy load.
As the dummy load is actually from a retired electric furnace, the coiled elements could have inductive properties leading to false readings.
The following test arrangement was used, hoping to test the suitability of my 'cheap and dirty' dummy load.
A 10 ohm resistor was used and the dummy load was tested from 20 Hz to 40 kHz. The scope traces did not shift in phase or amplitude through this frequency range. To 'test the test' the dummy load was replaced with a coil from a crossover network and run through the same tone sweep.
As the dummy load is actually from a retired electric furnace, the coiled elements could have inductive properties leading to false readings.
The following test arrangement was used, hoping to test the suitability of my 'cheap and dirty' dummy load.
A 10 ohm resistor was used and the dummy load was tested from 20 Hz to 40 kHz. The scope traces did not shift in phase or amplitude through this frequency range. To 'test the test' the dummy load was replaced with a coil from a crossover network and run through the same tone sweep.
Attachments
Just starting on the second Clair Bros amp. Perry was right about a new WO chassis saving some hassle. This Clair chassis required a minor elongation of the holes for the bias transistor, to line up with the holes in the back plane pcb's.
Anyway, so far so good! Just thought I would continue my tradition of being a ship-disturber and post this excerpt from Henry Ott's book. (Thanks again, Glen). This may support my personal bias against relay contacts in the audio path;
Anyway, so far so good! Just thought I would continue my tradition of being a ship-disturber and post this excerpt from Henry Ott's book. (Thanks again, Glen). This may support my personal bias against relay contacts in the audio path;
Attachments
Hi Folks;
Hope you are all keeping well during these hectic times. I am making good progress on "The Second Phase". This PL700 II started out as a full complimentary. The second pic shows my AC wire routing; absolute shorted possible run from the IEC jack to the transformer. The wires to the power switch are shown in the upper left of the pic, routed further away from the left channel input IC.
.......and yes I accidentally bent over a couple of the caps on the back planes but I'm not going to straighten them up until the patient is ready to be closed up for good (hopefully).
Hope you are all keeping well during these hectic times. I am making good progress on "The Second Phase". This PL700 II started out as a full complimentary. The second pic shows my AC wire routing; absolute shorted possible run from the IEC jack to the transformer. The wires to the power switch are shown in the upper left of the pic, routed further away from the left channel input IC.
.......and yes I accidentally bent over a couple of the caps on the back planes but I'm not going to straighten them up until the patient is ready to be closed up for good (hopefully).
Attachments
PL14_20 rev G and the driver row of outputs installed. Hoping to install the rest of the outputs and do some testing today.
So, my 'harem' will consist of 2 Clair Bros WOPL's, a WOPL quasi PL700B, and an original PL700 still using all pl909's. Question; If I could Vbe match the pl909 outputs, would they be OK to use in a Peavey CS800 that I'm trying to restore 'on the cheap' and use as a backyard system?
So, my 'harem' will consist of 2 Clair Bros WOPL's, a WOPL quasi PL700B, and an original PL700 still using all pl909's. Question; If I could Vbe match the pl909 outputs, would they be OK to use in a Peavey CS800 that I'm trying to restore 'on the cheap' and use as a backyard system?
Attachments
- Joined
- Nov 1, 2014
- Messages
- 3,493
- Location
- Gaston, SC
- Tagline
- Victim of the record bug since age five