My apologies Frank. I didn't know that a circuit topology had already been decided on. Maybe one day I'll build that 6AS7G single stage buffer just for kicks. I'm following this conversation with great interest. Have you decided on a tube regulated supply?
or IC regulated? DC on the heaters? Just curious.
G
or IC regulated? DC on the heaters? Just curious.
G
PREAMP.
Hi,
The heaters will be DC and IC regulated, the B+ is silicon rectified and series regulated using tubes.
You could rectify with tubes too, just change the specs for the powerxformer accordingly + it may require a self to achieve decent filtering.
Anything prior to the reg will be a decent electrolytic cap, after the reg I recommend a film cap.
I hope to have everything ready before the end of the week, my only concern is now that the input impedance (1Meg.) may be too high for a CDP.
If anyone has concerns about this, please let me know.
It is nothing crucial but the attenuator series values and the shunt will need to be changed accordingly then.
The gridleak on the 12BH7A is 1Meg and I like to keep that value constant for the attenuator not to be compromised, its' value could lowered though.
Cheers,
Hi,
The heaters will be DC and IC regulated, the B+ is silicon rectified and series regulated using tubes.
You could rectify with tubes too, just change the specs for the powerxformer accordingly + it may require a self to achieve decent filtering.
Anything prior to the reg will be a decent electrolytic cap, after the reg I recommend a film cap.
I hope to have everything ready before the end of the week, my only concern is now that the input impedance (1Meg.) may be too high for a CDP.
If anyone has concerns about this, please let me know.
It is nothing crucial but the attenuator series values and the shunt will need to be changed accordingly then.
The gridleak on the 12BH7A is 1Meg and I like to keep that value constant for the attenuator not to be compromised, its' value could lowered though.
Cheers,
Attenuator impedance
What does a 1 Meg Input impedance means in terms of using a 50K attenuator?
Would a 50K att be to low? Why?
fdegrove said:
I hope to have everything ready before the end of the week, my only concern is now that the input impedance (1Meg.) may be too high for a CDP.
Cheers,
What does a 1 Meg Input impedance means in terms of using a 50K attenuator?
Would a 50K att be to low? Why?
PREAMP.
Hi guys,
The reason I asked about the high input impedance was that with some highly capacitive cables it may cause a HF roll-off.
I am not sure I follow you on this one.
The idea is to use a 1Meg attenuator where the gridleakresistor would be 1Meg too.
So we would have only a series R that would be switched over 23 usable positions, the gridleak would be held constant.
A ladder attenuator built like this is ideal since it does not affect the load on the tube in any way.
Cheers,
Hi guys,
The reason I asked about the high input impedance was that with some highly capacitive cables it may cause a HF roll-off.
I am not sure I follow you on this one.
The idea is to use a 1Meg attenuator where the gridleakresistor would be 1Meg too.
So we would have only a series R that would be switched over 23 usable positions, the gridleak would be held constant.
A ladder attenuator built like this is ideal since it does not affect the load on the tube in any way.
Cheers,
Re: PREAMP.
So this will mean that we would have to use high value series resistances? say >1 Meg?
fdegrove said:Hi guys,
The idea is to use a 1Meg attenuator where the gridleakresistor would be 1Meg too.
So we would have only a series R that would be switched over 23 usable positions, the gridleak would be held constant.
A ladder attenuator built like this is ideal since it does not affect the load on the tube in any way.
Cheers,
So this will mean that we would have to use high value series resistances? say >1 Meg?
1 Meg Attenuator.
Frank,
Still don't have a clear picture of how the att and grid leak are connected.
I do understad how a grid Leak resistor is connected which of course is always a fix value, as far as I have seen.
Then the shunt resistance of the ladder is usualy in // to the grid resistor. The shunt is usaly a small value reistor and the series is a high value, near the impedance of the attenuator.
From what I have understand from your post's we would have the shunt reistor of the attenuator set fix at 1 Meg which will be // to the grid leak forming a combined grid load (grid leak) of 1/2 Meg.
How would the series resistors be working to form an adecuate voltage divider if we use <1Meg values?
What I'm missing?
Frank,
Still don't have a clear picture of how the att and grid leak are connected.
I do understad how a grid Leak resistor is connected which of course is always a fix value, as far as I have seen.
Then the shunt resistance of the ladder is usualy in // to the grid resistor. The shunt is usaly a small value reistor and the series is a high value, near the impedance of the attenuator.
From what I have understand from your post's we would have the shunt reistor of the attenuator set fix at 1 Meg which will be // to the grid leak forming a combined grid load (grid leak) of 1/2 Meg.
How would the series resistors be working to form an adecuate voltage divider if we use <1Meg values?
What I'm missing?
Preamp.
Hi,
Quite simple, really.
The attenuator switches a calculated value in series with the signal path, nothing more to it than that.
The attenuation is calculated by keeping the shunt R (in this case this is the gridleak) constant, you only vary the series R.
The same as any other voltage divider except that it is calculated for an audio taper (logarthmic), not linear.
Cheers,
Hi,
Quite simple, really.
The attenuator switches a calculated value in series with the signal path, nothing more to it than that.
The attenuation is calculated by keeping the shunt R (in this case this is the gridleak) constant, you only vary the series R.
The same as any other voltage divider except that it is calculated for an audio taper (logarthmic), not linear.
Cheers,
PREAMP.
Hi,
It works...no reason for it not to.
The idea behind it is to keep input impedance constant so that the operating parameters of the tube remain constant.
It will have an almost constant frequency response no matter what the attenuator position is, which is something that can't be said about other types of attenuators.
Yes, I am rather proud of it,
Hi,
It works...no reason for it not to.
The idea behind it is to keep input impedance constant so that the operating parameters of the tube remain constant.
It will have an almost constant frequency response no matter what the attenuator position is, which is something that can't be said about other types of attenuators.
Yes, I am rather proud of it,
PREAMP.
Hi,
Your shopping list:
Basic partslist for preamp per channel:
Powerxformers:
1 x 0-250V 300mA - EI core.
1 x 0-6.3V 1.2A - EI core.
1 x 0-15V 300mA - EI core.
Diodes:
9 x 1UF4007 or better (i.e. Shottky)
Electrolytic Caps: (best quality, low ERC, 105 degrees C)
3 x 330uF/385V
1 x 10uF/400V
Sockets all sockets chassis mount type)
1 x Pico 7 ,phenolic
3 x Noval sockets (ceramic type or teflon, no Chinese)
Tubes:
1 x EL86/6CW5
1 x ECC83/12AX7A
1 x OG3/85A2/5651
1 x 12BH7A
Filmcaps: (all polypropylene or better)
1 x .47uF/400V
1 x .100uF/400v
1 x 1uF/200V
1 x .47uF/200V (optional)
Resistors: (all metalfilm, non-magnetic, values for vol. attenuator not incl.)
1 Watt:
3 x 1M
2 x 100k
2 x 1K
2 x 680R
1 x 47K
1 x 33K
1 x 68K
1 x 39K
1/2 Watt:
1 x 220K
Switches:
1 x DPDT miniature switch 2A, silver or goldplated contacts.
ICs:
1 x 7812 1A or better.
Miscellaneous:
- heat conducting paste.
- .4mm teflon insulated silver wire for signal carrying.
- mounting screws and bolts.
- tinplated/pvc insulated copperwire for PSU wiring
- 4 good quality female RCA sockets for chassis mount.
Optional:
- source selector switch, silver plated contacts, self cleaning.
Some stuff may have been overlooked, please multiply all component quantities by a factor of 2 for stereo.
I built the unit in two separate chassis, one containg PSU, other the preamp proper.
So, at least you have something to go on now.
Cheers,
Hi,
Your shopping list:
Basic partslist for preamp per channel:
Powerxformers:
1 x 0-250V 300mA - EI core.
1 x 0-6.3V 1.2A - EI core.
1 x 0-15V 300mA - EI core.
Diodes:
9 x 1UF4007 or better (i.e. Shottky)
Electrolytic Caps: (best quality, low ERC, 105 degrees C)
3 x 330uF/385V
1 x 10uF/400V
Sockets
all sockets chassis mount type)1 x Pico 7 ,phenolic
3 x Noval sockets (ceramic type or teflon, no Chinese)
Tubes:
1 x EL86/6CW5
1 x ECC83/12AX7A
1 x OG3/85A2/5651
1 x 12BH7A
Filmcaps: (all polypropylene or better)
1 x .47uF/400V
1 x .100uF/400v
1 x 1uF/200V
1 x .47uF/200V (optional)
Resistors: (all metalfilm, non-magnetic, values for vol. attenuator not incl.)
1 Watt:
3 x 1M
2 x 100k
2 x 1K
2 x 680R
1 x 47K
1 x 33K
1 x 68K
1 x 39K
1/2 Watt:
1 x 220K
Switches:
1 x DPDT miniature switch 2A, silver or goldplated contacts.
ICs:
1 x 7812 1A or better.
Miscellaneous:
- heat conducting paste.
- .4mm teflon insulated silver wire for signal carrying.
- mounting screws and bolts.
- tinplated/pvc insulated copperwire for PSU wiring
- 4 good quality female RCA sockets for chassis mount.
Optional:
- source selector switch, silver plated contacts, self cleaning.
Some stuff may have been overlooked, please multiply all component quantities by a factor of 2 for stereo.
I built the unit in two separate chassis, one containg PSU, other the preamp proper.
So, at least you have something to go on now.
Cheers,