I have been building my audio system over the last year. Allhough quite happy with it ( in the end it's only for the hobby room ) I have to put the last details together. As a part of this, I want to look into the possibillity to upgrade the Velleman kits.
has anyone experience in this or can give me some general hints.
has anyone experience in this or can give me some general hints.
I don't have one of these units - just had a look at the schematic, so the following suggestions are things I would try based entirely on theory and past experience.
1/ Tube rolling - try JJ Electronics ECC99 in place of the 12AU7 tubes. I would also be tempted to cut the tracks immediately next to pin 2 of these tubes sockets and bridge the gap with say 330 Ohm or 470 Ohm (grid stopper) resistors. Some say that the "Old" carbon film resistors work very well for this job. Only need to be 1/4 or 1/2 Watt rated.
2/
Check the following Capacitors
C16 and C17 2.2uF these are to block any DC on any of your signal sources. There should not be any DC on signal sources so I would simply replace them with a piece of wire. If you are at all concerned about DC isolation of your signal sources then check these caps and make sure that they are at least good quality Polypropylene caps. 63V rated would be fine. An alternative would be some Blackgate NX caps (value not critical as long as they are at least 2.2 uF) - even though they are rated at only 6.3V.
C18 and C19 68nF/630V these should be good quality polyproylene as well - check what is there currently and replace if they are ordinary polyester - watch the voltage rating, they need to be at least 400V rated, 630V rated are readily available and would be better.
C21 and C22 4.7uF 160V thes should also be good quality polypropylene - you may want to try Auricaps for here. Auricaps have a good reputation for high quality sound. From my own experience with Auricaps I would add "so long as they have at least 50V DC across them" which they do in this circuit. Auricaps tend to sound a bit dead when there is no DC bias on them. Auricaps have a faint orange band on one end. Put this end of the cap to the tube pin 8 side.
Not and expert opinion BUT ideas for you to try.
Cheers,
Ian
1/ Tube rolling - try JJ Electronics ECC99 in place of the 12AU7 tubes. I would also be tempted to cut the tracks immediately next to pin 2 of these tubes sockets and bridge the gap with say 330 Ohm or 470 Ohm (grid stopper) resistors. Some say that the "Old" carbon film resistors work very well for this job. Only need to be 1/4 or 1/2 Watt rated.
2/
Check the following Capacitors
C16 and C17 2.2uF these are to block any DC on any of your signal sources. There should not be any DC on signal sources so I would simply replace them with a piece of wire. If you are at all concerned about DC isolation of your signal sources then check these caps and make sure that they are at least good quality Polypropylene caps. 63V rated would be fine. An alternative would be some Blackgate NX caps (value not critical as long as they are at least 2.2 uF) - even though they are rated at only 6.3V.
C18 and C19 68nF/630V these should be good quality polyproylene as well - check what is there currently and replace if they are ordinary polyester - watch the voltage rating, they need to be at least 400V rated, 630V rated are readily available and would be better.
C21 and C22 4.7uF 160V thes should also be good quality polypropylene - you may want to try Auricaps for here. Auricaps have a good reputation for high quality sound. From my own experience with Auricaps I would add "so long as they have at least 50V DC across them" which they do in this circuit. Auricaps tend to sound a bit dead when there is no DC bias on them. Auricaps have a faint orange band on one end. Put this end of the cap to the tube pin 8 side.
Not and expert opinion BUT ideas for you to try.
Cheers,
Ian
Thank you for the advice.
I think that te caps are all Wima MKT or MKP I will check this.
Concerning removing the 2,2 Caps. What can go wrong if I get DC on the input ?
The current source is an older type of Technics tuner and CD player.
Will replace the CD player probably within the next year.
I think that te caps are all Wima MKT or MKP I will check this.
Concerning removing the 2,2 Caps. What can go wrong if I get DC on the input ?
The current source is an older type of Technics tuner and CD player.
Will replace the CD player probably within the next year.
DC on a selected input will disturb the bias of the tube making it conducr extra current or less current (depending upon if its +ve or -ve voltage). The DC level would be divided according to the Volume control setting.
The 2.2uF blocking caps are there for protection if one of your sources goes faulty. While everything is OK they don't do anything (except degrade the sound a bit).
Cheers,
Ian
The 2.2uF blocking caps are there for protection if one of your sources goes faulty. While everything is OK they don't do anything (except degrade the sound a bit).
Cheers,
Ian
- Status
- Not open for further replies.