During my recent rebuild I changed the trip pots for 20 turn units and that has made adjustment much more sensible.
Fixed resistors are a great idea but they require a mu tube with matching sections and its likely the fixed resistors only match one specific mu tube which makes swapping tubes more interesting!
If you have noise on one channel it could be a noisey resistor
Fixed resistors are a great idea but they require a mu tube with matching sections and its likely the fixed resistors only match one specific mu tube which makes swapping tubes more interesting!
If you have noise on one channel it could be a noisey resistor
Yes, that's also why I did not recommend to do what I did
Certainly a 20 turn, or a small resistor and a smaller value trimmer in series is the more flexible solution. That being said, I have swapped mu tubes, and the anode voltage did not change more than a volt or two so no adjustments needed (might be different with other Mu tubes than the ones I have).Cool to see, that you got the Rod Coleman DHT regs installed... It is indeed a seriously good upgrade for the sound of the Tram II, and I agree on your sonic impression: Much more natural, dynamic and lifelike. People who say ''they have no real noise issues so don't install them'' are totally missing the point. As said many, many times: These regs are the biggest sonic upgrade for this preamp, the much improved noise performance is just the bonus.
For the slight mechanical sound you still hear, then try different input caps. The teflon caps these preamps come with are really good, but IMHO all teflon caps are slightly mechanical sounding. Duelund (or Dueland as everyone from English speaking countries for some reason call the brand named after Steen Duelund) are not that expensive in these small values.
Last edited:
Nice. I wonder if you are using 45's or 2A3's and what resistor values were needed? Thanks.
How about using one 2K 25 turn trim pot in parallel with two 200ohm resistors to yield R=66-95 ohms =80 +/- 14 (using 200-2000ohm range on the potentiometer)? Will this reduce the impact of any trimmer drift with two fixed resistors dominating the load while still providing plenty of adjustment? This is my very first circuit design so be nice
Last edited:
Hello kazap
i use JJ2a3 tube,,,,and the value for the resistor is close to 80ohm...to get the 120v right i use a parallel resistor..2.7kohm.
it is not so difficult to do this...
i have not tried to use a trimpot to get the right resistor value...but i think it sounds like a good idea
the fixed resistor have give me less noise ..thats the best parts of it
i use JJ2a3 tube,,,,and the value for the resistor is close to 80ohm...to get the 120v right i use a parallel resistor..2.7kohm.
it is not so difficult to do this...
i have not tried to use a trimpot to get the right resistor value...but i think it sounds like a good idea
the fixed resistor have give me less noise ..thats the best parts of it
Thats great news about less noise.
It looks like 80ohms is about right for 2A3's.
So if using only2A3 tubes and wanting some very fine adjustment with minimal drift from the pot, these values might perhaps work.
All in parallel:
R1=150ohms
R2=180ohms
R3=Trim pot (25 turns) = 20k
Rtotal = 80 +/- 1.4 using the trim-pot from 2k-20k range
via ~20 turns gives +/- 0.14 V/turn
It looks like 80ohms is about right for 2A3's.
So if using only2A3 tubes and wanting some very fine adjustment with minimal drift from the pot, these values might perhaps work.
All in parallel:
R1=150ohms
R2=180ohms
R3=Trim pot (25 turns) = 20k
Rtotal = 80 +/- 1.4 using the trim-pot from 2k-20k range
via ~20 turns gives +/- 0.14 V/turn
Thanks for the tip about warm up before adjusting the trim-pot.
This 20k trim pot looks OK
but I wonder if there are better?
This 20k trim pot looks OK
An externally hosted image should be here but it was not working when we last tested it.
but I wonder if there are better?
Hi Rab28. I also live in Melbourne and would greatly like to know who is doing the modification work for you. When my tram broke down the first time I sent it back to DIYHiFi in Hong Kong but after it broke down the second time I sent it to a repairer in Canberra. It's been functioning beautifully since then. But only on 45's. I have not used 2A3's despite having a brand new pair of Full Music 2A3's. He told me that the Tram is not robust enough to handle 2A3's. When I asked him to fit the Rod Coleman DHT regulators he declined saying that the Tram was really a DIY enthusiasts project and he didn't really want to work on it anymore. I've sent you a private message and I would appreciate hearing further from you.
Reggie
Reggie
That is his opinion, and even though I don't agree, I understand what he is saying because the mains transformer do run hot. You can argue that if a mains transformer runs hot, then it's too small. On the other hand you can argue, that the mains transformer in the Tram II is running within specs, also with 2A3's so there is no problem. Must of us use 2A3's in our Tram II because we feel they sound better, and there is zero issues - so it works...
Last edited:
I can see the trafo is 195v 0.12amp,,,,this is not much ampere...thats the reason for the warm trafo..i do not know if it had anything to do with the sound..but if i some time will build the Tram in another cabinet...then i will use a bigger trafo,,,just for safe.
still a wery happy owner of the Tram
still a wery happy owner of the Tram
this Projekt X Chassis 70 x 300 x 320mm with 7mm anodized aluminum faceplate has the same footprint as the Tram2 so could be a base power unit stuffed with R-core trannies?
Last edited:
No, the main reason for the hot transformer is the heater windings. They are speced to 3A and with 2A3 there is a current draw of 2,5A. Since this is a constant current it builds up heat... But again: It's within specs.
Will a bigger transformer sound better: No, not likely. With constant currents the source impedance from the transformer windings are not ''seen'' by the circuit and when choosing bigger trannies this is often done to get lower impedance to the circuit. Will a better transformer sound better: Yes, maybe (some people think that for instance C core transformers sounds better than toroid transformers like the one used in the Tram II).
Making two chassis and what not to implement bigger transformers is -in my opinion- to create a solution that is looking for a problem (or however it is you're saying in English what I'm trying to say ;-))
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.