Needless to say, I am also interested although I have doubts about the possibility of eliminating magnetic induced hum pickup on the tonearm cable without the aid of a transformer. A differential input stage with these kind of super-duper high gm valves at the kind of currents required to extract this high gm might be initially balanced but it is my experience that these valves drift fairly quickly when run hard.
I'm about to start using MC again after many years because I decided to bite the bullet and get a decent arm for the first time ever (312S), which has a detachable headshell, so I need to make a headamp; I'm not ruling anything out for the moment although a phone call to Sowter would be the easy way!
I'm about to start using MC again after many years because I decided to bite the bullet and get a decent arm for the first time ever (312S), which has a detachable headshell, so I need to make a headamp; I'm not ruling anything out for the moment although a phone call to Sowter would be the easy way!
I've been following along with the development of the various Mini Muscovites. I learned stuff (thanks!). I was surprised that you wound up with a cascoded ECC88/6DJ8/6N23P in the first stage. It makes sense. Lots of gain. Very low input capacitance too, the lack of which would be a good thing if adding a SUT...
Hi,
Glad to see there's actually is some interest.
Trust me, it can be done as I've done it before as shown in the hyperlink posted higher up.
It's cheap to build (all things being relative) and performs well enough for me and I'm a rather demanding kind of guy.
That said, everything can be improved and I feel that by integrating the MC capability (and abandoning MM needs) we can improve it further).
The headamp is definitely dated and needs an alternative for the CCS J-Fet. BF245As can still be found but aren't exactly cheap.
Key is the Idss of the Fet. A full technical description can be had so anyone wanting to build one knows what's what.
When built properly it outperformed any SUT I've ever heard so there you go.
And....It can be improved upon. Great news, no?
But, before I go any further, yes, Kevin, let's start a proper thread. I've jacked yours long enough.....
Shall I or will you?
First issue on the list might be a proper design brief, IOW, we need to decide what exactly we want to achieve, then decide how to go about it etc...
That is, if you don't mind.
Cheers to all,
Glad to see there's actually is some interest.
Trust me, it can be done as I've done it before as shown in the hyperlink posted higher up.
It's cheap to build (all things being relative) and performs well enough for me and I'm a rather demanding kind of guy.
That said, everything can be improved and I feel that by integrating the MC capability (and abandoning MM needs) we can improve it further).
The headamp is definitely dated and needs an alternative for the CCS J-Fet. BF245As can still be found but aren't exactly cheap.
Key is the Idss of the Fet. A full technical description can be had so anyone wanting to build one knows what's what.
When built properly it outperformed any SUT I've ever heard so there you go.
And....It can be improved upon. Great news, no?
But, before I go any further, yes, Kevin, let's start a proper thread. I've jacked yours long enough.....
Shall I or will you?First issue on the list might be a proper design brief, IOW, we need to decide what exactly we want to achieve, then decide how to go about it etc...
That is, if you don't mind.
Cheers to all,
Can it be assumed that higher coil resistance is the result of finer wire rather than more turns? If the latter, then inductance rises and the resonance with the input capacitance moves towards the audio band. Perhaps this could be a scaled preamp with the number of parallel input valves dependent on the cartridge used.
Hi,
Ok....
After that we're left with noise.
How do we reduce that?
The only way I know of is by //ing the sources of it . End of story really.
It's relatively easy to design once you understand what you want to achieve.
Anyway, I think I'll take the secret to my grave........LOL.
OTOH, it's all there already, published it here years ago and they still don't get a clue.................
Cheers,
Ok....
After that we're left with noise.
How do we reduce that?
The only way I know of is by //ing the sources of it . End of story really.
It's relatively easy to design once you understand what you want to achieve.
Anyway, I think I'll take the secret to my grave........LOL.
OTOH, it's all there already, published it here years ago and they still don't get a clue.................
Cheers,
So busy with work I have not been able to pay much attention to what is going on here unfortunately. I'll start a new thread and move these relevant posts to the new thread..
Note that my current step ups include two sets of LL1941 and a multi-tan chip based head amp (26dB) - none are configured for balanced operation or galvanic isolation and yet the levels of hum in my system are inconsequential.. The low source impedance of the SPUs I used undoubtedly helps, but even my DL-103 which was in the range of 40 ohms or so hum was not a significant issue.
(note my speakers are 100dB+ efficient and get down to very very low 30s on the bottom end.)
I don't think input (ne miller capacitance) is going to be too big a deal with cartridges having source impedances of 100 ohms or less. Consider that a 1:16 step up reflects 26nF of capacitance back to the cartridge for a still rather good 100pF input capacitance. This incidentally is why I ended up with cascode front ends and think that 16X is really close to the practical upper usable limit for most step up transformers. (I have had up to 1:32 and found them quite problematic in terms of sound quality above a few kHz.) Sorry for the long babble.
Note that my current step ups include two sets of LL1941 and a multi-tan chip based head amp (26dB) - none are configured for balanced operation or galvanic isolation and yet the levels of hum in my system are inconsequential.. The low source impedance of the SPUs I used undoubtedly helps, but even my DL-103 which was in the range of 40 ohms or so hum was not a significant issue.
(note my speakers are 100dB+ efficient and get down to very very low 30s on the bottom end.)
I don't think input (ne miller capacitance) is going to be too big a deal with cartridges having source impedances of 100 ohms or less. Consider that a 1:16 step up reflects 26nF of capacitance back to the cartridge for a still rather good 100pF input capacitance. This incidentally is why I ended up with cascode front ends and think that 16X is really close to the practical upper usable limit for most step up transformers. (I have had up to 1:32 and found them quite problematic in terms of sound quality above a few kHz.) Sorry for the long babble.
A small parcel containing a quartet of 6S45P-E is sitting at my post office waiting for me to pick them up tomorrow morning.
Should we also consider 6J51P and 6J52P as well? Perhaps one of these would be suitable for 0 bias operation as Frank proposed. Transconductance is pretty high for both..
Any ideas for first stage; I have some, but they might employ devices Frank does not approve of..
My thoughts would be to try and get as much gain out of the first stage as possible, keeping things to two stages if possible with a high current output circuit.
A dissimilar cascode with a really high current and not necessarily high transconductance triode or triode wired pentode on tube might be worth looking at. Several paralleled triodes on the bottom for noise and gain.
Other ideas?
Should we also consider 6J51P and 6J52P as well? Perhaps one of these would be suitable for 0 bias operation as Frank proposed. Transconductance is pretty high for both..
Any ideas for first stage; I have some, but they might employ devices Frank does not approve of..
My thoughts would be to try and get as much gain out of the first stage as possible, keeping things to two stages if possible with a high current output circuit.
A dissimilar cascode with a really high current and not necessarily high transconductance triode or triode wired pentode on tube might be worth looking at. Several paralleled triodes on the bottom for noise and gain.
Other ideas?
A dissimilar cascode with the high current shunted through the lower valve only perhaps; the upper valve could be a much higher impedance but linear valve to give a better load for the lower one. How would something like 6FS5 be on top? 6J51P seems better made than 6J52P but there's no denying the latter's very obvious advantage. How much DC current can a typical MC catridge tolerate without affecting performance?
edit; I mean 6SF5, I think; can't remember where I put my stash!
edit; I mean 6SF5, I think; can't remember where I put my stash!
Last edited:
Oddly the manufacturers generally don't give a specific value, but as close to none as possible. I guess a few uA is probably OK, this is the concern I have with zero bias operation as significant grid current is likely.
My highest output MC has an output of 250uV @ 5cm/sec lateral recorded velocity, and lowest 200uV.. Impedances range from 2 to 6 ohms. For me a front end with really low noise is going to be important I'd really like to target cartridge noise performance in the range of 1 - 3 ohms which given limited transconductance, gaussian noise and 1/f noise which I bet will prove to be the real issue here all concern me. (And the RIAA curve will exacerbate 1/f noise whereas it tends to mitigate broadband noise in the nuisance spectrum of human hearing.)
My highest output MC has an output of 250uV @ 5cm/sec lateral recorded velocity, and lowest 200uV.. Impedances range from 2 to 6 ohms. For me a front end with really low noise is going to be important I'd really like to target cartridge noise performance in the range of 1 - 3 ohms which given limited transconductance, gaussian noise and 1/f noise which I bet will prove to be the real issue here all concern me. (And the RIAA curve will exacerbate 1/f noise whereas it tends to mitigate broadband noise in the nuisance spectrum of human hearing.)
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.