 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
24.197.131.115
I'm using a Jolida JD-9 phono preamp that is about 10 years old. I replaced the stock Chinese 12AX7 pair with new production EH tubes when I bought it new. I would like to make this phono stage sound as good as it possibly can.
I need the highest gain I can get. Would 5751 12AX7's lower the gain? Any suggestions would be greatly appreciated. I have a matched pair of RCA Command 12AX7s that I haven't tried yet.
Follow Ups:
the power tranny was marked 110vac and his local power company frequently showed 120 and greater, up to 127vac in the wee hours. The tranny was ok but it took out a power supply cap for the tubes and destroyed it - you could easily see the bulge growing out of the seal.
Besides that it didn't sound very good either. Further examination showed a crapload of switches for gain and impedance and too many opamps. I repaired it for him and then listened to it and it did NOT sound what I would call hi-fi or hi end. I hope you don't take this as insulting, you can do much better.
Replace the Jolida with something more deserving and higher quality so go to the Vinyl Asylum and get a few suggestions on what to replace it with at the same or lesser price.
Best sounding 12AX7 are new JJ E83CC. Available at Amazon for $29.
i can not confirm, sorry. i bought/tried them twice and sold them twice again.
they only sound the first time you listen. after listening to them for a long time they sounded annoying.
I had this preamp for over 10 years. There are plenty of switchable gain settings on the back panel, check out the chart at the link below. One of the best mods I found was replacing the existing op-amps with OPA627's. Easy to do as they just pop out and pop in.
Edits: 07/13/23
Vacuum tubes are not light bulbs. You can't just replace one tube with another like changing a 60W bulb for a 100W bulb. Vacuum tubes have amplification factor, transconductance, and plate resistance. These three parameters are all significant to the design engineer when selecting an operating point for a tube. When you change a circuit engineered for a 12AX7 by installing a 5751, you are corrupting the the carefully engineered circuit in unpredictable ways. This is because the components that support the tube, e.g. resistors, capacitors and the plate supply voltage are all part of the meticulously designed circuit. If the engineer had intended the 5751 tube to be used, he would have selected components that supported the 5751 in the circuit.
Carefully engineered... meticulously designed...
This is Chinese consumer grade, so I think that's really a stretch. I agree though about the need to accommodate various tube types with appropriate circuit values.
If you look at a schematic of that unit, all the amplification is done by ICs. The tubes are used solely as cathode followers, which add no gain, and are there so that it can be sold as a tube unit.
Certainly all the gain surrounding the phone EQ is from ICs but the last stage of each channel is a so call Totem Pole (or SRPP) made from both halves of a 12ax7 and it does have gain. It is considered one stage but the first triode of the Totem Pole is the gain part and the second triode is a cathode follower output.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"The tubes are used solely as cathode followers, which add no gain, and are there so that it can be sold as a tube unit."
More and more fraudulent junk like that has appeared on the market over the last few years. Reminds me of the "10 Transistor" radios in the '60 that had four transistors hanging in the wind.
5751 is NOT the way you want to go IF max gain is the goal.
If best sound is important, and you don't want to potentially waste a BUNCH of money on noisy, microphonic old stock, then look no further than the JJ frame-grid E83CC.
I have less than no affiliation with Tube Depot other than as a satisfied, multi-year customer.
I second the new JJ Frame Grid tube. I bought several and they are very, very good.
OP: "I would like to make this phono stage sound as good as it possibly can.
I need the highest gain I can get."
I am not sure that these two statements are complimentary or necessary-
Highest gain - for LOMC Cartridges? why do you need a high gain?
Most power amps put out full power at 2Vrms - I am sure that a pair of 12AX7s can exceed that...
As to the sound - what makes you think it does not currently sound as good as it can get?
Yes, 5751s will lower the gain - that is a function of the tube...
Most 12AX7s fall in spec - so, if you want more gain, different circuit ...
Happy Listening
5751's have 70% of the output of a 12AX7, so yes, it will lower the gain.
Sovtek 12AX7LPS - I've used the Sovteks in my JD9 for a long time with no complaints or urge to tube swap. I 've also tried new production Mullards which were fine (the Mullards eventually landed in my old Jolida cdp.)
From my research and a little experimentation, IMO, 5751s will lower gain/output. For me, gain has never been a problem with the JD9. It had plenty for the 3.3mv Ortofon MC-3 Turbo (a high output mc) and the 0.3mv AT33EV (low output MC). Check your "Low Output" and "High Output" terminals on the back to make sure you're using the right one for your cart. IIRC, the labeling was somewhat counter-intuitive to me when first purchased.
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]