damn, now I see. I was looking at the phono circuit. I will calculate gain again and post a new set of values. Wait a bit.
OK, the gain of the right part of the circuit is 27dB. So now I am a bit confused because the attenuator has 60 db for the least gain and 50 db for the next step up.
You said the second step was too loud, 27dB gain from pre-amp minus 50 db from attenuator still provides 23 dB of loss. This should work fine. Is your power amp unusually sensitive?
On my passive pre (i.e. gain equals 1) normal listening is about -12 dB, your second step is 10 dB more attenuation than that. In my system you would still need two-three more clicks up with a your pre to achieve the same volume.
Any way, if you cut the 82.5K resistor to about 20K gain will be reduced by 12 dB. For this design a new 62.5K resistor bypassed by a 1uF (film 200V) cap should be added to the first stage plate circuit (i.e. in series with the 20K, between it and the plate DC supply) this will keep the DC current about the same since the second buffer grid is DC coupled to the first plate.
My apologies for misreading the schematic.
You said the second step was too loud, 27dB gain from pre-amp minus 50 db from attenuator still provides 23 dB of loss. This should work fine. Is your power amp unusually sensitive?
On my passive pre (i.e. gain equals 1) normal listening is about -12 dB, your second step is 10 dB more attenuation than that. In my system you would still need two-three more clicks up with a your pre to achieve the same volume.
Any way, if you cut the 82.5K resistor to about 20K gain will be reduced by 12 dB. For this design a new 62.5K resistor bypassed by a 1uF (film 200V) cap should be added to the first stage plate circuit (i.e. in series with the 20K, between it and the plate DC supply) this will keep the DC current about the same since the second buffer grid is DC coupled to the first plate.
My apologies for misreading the schematic.
Hi Chris,
Eric
PV12 is an open loop (feedback-free) power supply and line stage. 😉anatech said:
Eric
In re-reading my last post I may not be clear on the changes, attached is a schematic segment I hope will be clear. Note I have not calculated dissipations so this needs to be done to verify wattage ratings.
Some small capacitors are not shown, they should be left in the circuit.
Some small capacitors are not shown, they should be left in the circuit.
Attachments
Thank you very much Hermanv, I understand now with the schematic! I will try this, maybe with cheap resistor to see if the gain is better, after that, I will buy good quality resistor...
Also, do you think this modification gonna have an effect on the sound ????
I don't think my amplifier is a lot sentisive,is has a 26db gain, here is the spec:
http://passlabs.com/downloads/old product/a30manr0.pdf
But, when I hook a cheap 50$ DVD player to the system, I have a good control on the volume... With the Arcam, it is very loud... the Arcam spec are 2.3V output, 150 ohm impedance.
A final question about the modification, I keep the 47.5 Ohm output resistor??
Thank you very much for your help !!!
Also, do you think this modification gonna have an effect on the sound ????
I don't think my amplifier is a lot sentisive,is has a 26db gain, here is the spec:
http://passlabs.com/downloads/old product/a30manr0.pdf
But, when I hook a cheap 50$ DVD player to the system, I have a good control on the volume... With the Arcam, it is very loud... the Arcam spec are 2.3V output, 150 ohm impedance.
A final question about the modification, I keep the 47.5 Ohm output resistor??
Thank you very much for your help !!!
IMHO any effect the mod will have on the sound will be due to the shunt C, I'd recommend a good one, I know they are not cheap. The mod might cause a turn on thump, if this is a problem I see a way to add a zener that will stop the effect but drop out of the way once power is up.
Yes keep the 47.5 resistor, it doesn't really affect gain and probably helps stability and to a minor extent protects the pre-amp from voltage surges coming back in the output jacks
Yes keep the 47.5 resistor, it doesn't really affect gain and probably helps stability and to a minor extent protects the pre-amp from voltage surges coming back in the output jacks
After only a couple days with my new PV-12 preamplifier, I burn my 2 FE103E Fostex speakers. I have this speaker until 1 years without any problem. At the beginning, I was thinking that the preamplifier draw some DC voltage at the output, but I have only about 12mV on one channel and 7mV on the other at the output of my power amp...
Maybe because I didn't make the timer circuit... I remember one time or two, I turn on the power ampb efore the preamp...it make a bog noise...
So now, I will moke the timer circuit, and I will reduce the gain with the hermanv suggestion.
What do you think about my burning speakers???
Maybe because I didn't make the timer circuit... I remember one time or two, I turn on the power ampb efore the preamp...it make a bog noise...
So now, I will moke the timer circuit, and I will reduce the gain with the hermanv suggestion.
What do you think about my burning speakers???
Hi hermanv,
Actually, the turn on thump may damage the woofer. Oscillation would damage the tweeter, but probably not the woofer.
All preamplifiers should have a power on mute. This makes things much safer for the users.
-Chris
Actually, the turn on thump may damage the woofer. Oscillation would damage the tweeter, but probably not the woofer.
All preamplifiers should have a power on mute. This makes things much safer for the users.
-Chris
Hi Chris;
I suppose it depends on the edge speed of the "Thump". I lost a Scan Speak D2905/9900 revelator tweeter once. A $100 lesson, luckily I had to only pay for the repair, new ones are $200.
Still, you are correct, a turn on mute that shorts the pre-out to ground will pre-charge any capacitors and allow a safe turn on.
Didn't the PV-12 come with a mute reed relay?
I suppose it depends on the edge speed of the "Thump". I lost a Scan Speak D2905/9900 revelator tweeter once. A $100 lesson, luckily I had to only pay for the repair, new ones are $200.
Still, you are correct, a turn on mute that shorts the pre-out to ground will pre-charge any capacitors and allow a safe turn on.
Didn't the PV-12 come with a mute reed relay?
The timer circuit is finish, but it doesn't work !!!
When I turn on the power, the relay is On without any delay!!!
I use the schematic timer from the PV-10 preamplifier, http://www.drtube.com/audioamp.htm#CJ, with an NE555P from digikey.
What can I look to fix the problem, can I change resistance value??? I use 100k for R9, insteed 910k...Can this cause some problem ???
When I turn on the power, the relay is On without any delay!!!
I use the schematic timer from the PV-10 preamplifier, http://www.drtube.com/audioamp.htm#CJ, with an NE555P from digikey.
What can I look to fix the problem, can I change resistance value??? I use 100k for R9, insteed 910k...Can this cause some problem ???
arold19 said:
first - you must check - is it current consumption of relay coil smaller than max current which 555 can generate on output pin ;
Looking at the schematic the relay is supposed to turn on without delay (ON = short output to ground) then after a timeout it should turn OFF. In the OFF state audio is present on the outputs. This allows you to use a form "A" contact instead of the harder to get form "C".arold19 said:
Replacing the 910K with a 100K will reduce the time by almost 10 to 1.
Is C10 (the timing C) 47uF as shown?
Some brands of 555 timers are slightly different in how they work, get data sheet from your manufacturer and double check, maybe a link to your manufacturer for this thread?
Hi hermanv,
You lost a tweeter due to turn on thump? Wow, I am sorry to hear that. Are you sure it wasn't a burst of oscillation at turn on?
Most CJ stuff does use a muting relay. As for 555 timers, there are two types.
Hi arold19,
CMOS (little totem output spike) and bipolar (large glitch created by totem pole output stage. Those part numbers are bipolar, so make sure there is a cap across the supply pins right at the chip.
-Chris
You lost a tweeter due to turn on thump? Wow, I am sorry to hear that. Are you sure it wasn't a burst of oscillation at turn on?
Most CJ stuff does use a muting relay. As for 555 timers, there are two types.
Hi arold19,
CMOS (little totem output spike) and bipolar (large glitch created by totem pole output stage. Those part numbers are bipolar, so make sure there is a cap across the supply pins right at the chip.
-Chris
It's kind of impossible to know, we were developing a crossover for our three way design. The problem happened when we loaded the MLSSA application, it sounded like a loud thump. Now we make sure MLSSA is up and running before we turn on the power amp. It is probably impossible to duplicate the exact conditions.anatech said:
The speaker system is 4 Ohms and the Bryston 4B-SST we're using can dump 500 watts into that load. Now that the design is finished and after many, many turn on cycles we've had no further problems. It pays to be concise and careful.
you're right Hermanv but I don't understand!!! I change the 100K to a 910K, and it work like you said. When I put the power on, the relay is on for about 12sec...
But, when I'm looking at the schematic, the contact relay use are the Normaly close, so, the relay have to be energise when I listen music...
If I use the normaly open contact, the output of the preamp gonna be open to ground when I turn on the power, so I don't have any protection !!!
What can I do with that?
Thank you !
But, when I'm looking at the schematic, the contact relay use are the Normaly close, so, the relay have to be energise when I listen music...
If I use the normaly open contact, the output of the preamp gonna be open to ground when I turn on the power, so I don't have any protection !!!
What can I do with that?
Thank you !
The schematic is not labeled - but conventional notation is that the normally closed contacts are those drawn so the armature (moving contact) is up. The presumption is that the energized coil pulls the armature down.
In the C-J schematic he lower set of contacts is engaged, I read this as the normally open set. Like I said earlier this is also the only way a form A relay could be used. Most reed relays are form A. Everything appears to be normal. Use the normally open set.
I've been designing for more than 30 years, the answer seemed clear to me, but I can easily understand why it might not seem clear to others. If you draw schematics for others to use, it helps to be very clear for just this reason.
When you first listened to your project, you were not that impressed with the sound. Have you put a few hours on the unit, does it sound any different to you?
If you haven't, I would put a CD in the payer, set it to repeat, turn OFF the power amp and let it run day and night for about 3 days before any critical listening. The whole concept of "break in" is controversial, George Cardas has as good a possible explanation on his site as any I've seen. Whether you believe or not, is certainly seems harmless to allow the CD to spin for 72 hours.
In the C-J schematic he lower set of contacts is engaged, I read this as the normally open set. Like I said earlier this is also the only way a form A relay could be used. Most reed relays are form A. Everything appears to be normal. Use the normally open set.
I've been designing for more than 30 years, the answer seemed clear to me, but I can easily understand why it might not seem clear to others. If you draw schematics for others to use, it helps to be very clear for just this reason.
When you first listened to your project, you were not that impressed with the sound. Have you put a few hours on the unit, does it sound any different to you?
If you haven't, I would put a CD in the payer, set it to repeat, turn OFF the power amp and let it run day and night for about 3 days before any critical listening. The whole concept of "break in" is controversial, George Cardas has as good a possible explanation on his site as any I've seen. Whether you believe or not, is certainly seems harmless to allow the CD to spin for 72 hours.
Thank you very much Hermanv for your help.
I made your modification with a 1uf tin foil polypropylene cap from Solen, and now, the gain is perfect!
For the sound, it is very nice. Better than my Bride of Zen,but in the BOZ, I don't use exotic component.
In the PV12, I use polypropylene capacitor for the power supply, I use good resistor from Part Connexion, also, I use the AC filter 10VR1 like in the CJ PREMIER 10. I have 3 regulator for the high voltage. I also use the regulator from CJ Premier10 for the heaters.. Also, the expensive DACT CT2 attenuator. Kimber kable for the signal cable....
But, I like the sound, but I don't have the tube feeling....
I have an 30w integre amplifier with 12AU7 preamplifier tube and EL34 power tube, this integre sound very warm... I have a lot more details and precisions with the combinaison of the Pv12 and the Pass Labs Aleph30, but not the warm of the EL34...Maybe in a couple of week, it gonna sound more warm...
Thank everybody for your help.
My computer doesn't accep my camera for now... I will post pictures in a couple of week...
I made your modification with a 1uf tin foil polypropylene cap from Solen, and now, the gain is perfect!
For the sound, it is very nice. Better than my Bride of Zen,but in the BOZ, I don't use exotic component.
In the PV12, I use polypropylene capacitor for the power supply, I use good resistor from Part Connexion, also, I use the AC filter 10VR1 like in the CJ PREMIER 10. I have 3 regulator for the high voltage. I also use the regulator from CJ Premier10 for the heaters.. Also, the expensive DACT CT2 attenuator. Kimber kable for the signal cable....
But, I like the sound, but I don't have the tube feeling....
I have an 30w integre amplifier with 12AU7 preamplifier tube and EL34 power tube, this integre sound very warm... I have a lot more details and precisions with the combinaison of the Pv12 and the Pass Labs Aleph30, but not the warm of the EL34...Maybe in a couple of week, it gonna sound more warm...
Thank everybody for your help.
My computer doesn't accep my camera for now... I will post pictures in a couple of week...
I have big Pass Labs (X250), it is fast and I think accurate, but not really warm. I made some changes to my room (more damping) and interconnects to bring out more warmth. I took a little tunning, but in the end I am quite happy.
Do nothing until everything is settled, this includes you getting used to the new sound. If your speaker has a tweeter gain knob, you may have turned it up to add some punch to the previous tube gear, maybe turn it down a little.
You probably know that some tubes are warmer than others, after the unit settles in, try and borrow some from any audiophile tube buddies for comparison.
Good luck.
Do nothing until everything is settled, this includes you getting used to the new sound. If your speaker has a tweeter gain knob, you may have turned it up to add some punch to the previous tube gear, maybe turn it down a little.
You probably know that some tubes are warmer than others, after the unit settles in, try and borrow some from any audiophile tube buddies for comparison.
Good luck.
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