Arkless Electronics
Trade: Amp design and repairs.
Input impedance only 10K on the passive eh? As I suspected. Some in-line attenuators at the input to the passive would be worth trying.
The vast majority of solid state sources should have no problem with 10K but there will be exceptions and it could be that your phono stage is one....
The vast majority of solid state sources should have no problem with 10K but there will be exceptions and it could be that your phono stage is one....
Tony L
Administrator
Looks easy, but it's beyond me, i.e. undoing the bolts doesn't mean it comes to bits! I'm not bothered as i don't need the tape outs, so I've not gone any further.
Interesting, I've always fancied a Decca...
Anyone got any feedback regarding the Croft Micro's built-in phono stage? I know I like the Micro 25 as a line stage as two of my friends have them (one a Micro 25, one a Basic, both line only). I'm curious as to how good the phono is, e.g. is it good enough to compete with a decent stand-alone stage like my P100, EAR 834P etc?
To be honest the Croft has not got a lot of competition that I'm aware of as pretty much everything else would need doctoring / tweaking - I've certainly read comments from folk saying things like Conrad Johnson, Audio Research etc are just too loud and I could do without the hassle of finding a nice second hand one and then having to get it modded before it's usable. The Croft can be spec'd for a Leak.
As far as I'm concerned this Leak is a keeper. I'm looking at it as my last 'main system' amp, so it's worth going to some hassle and expense to get it working exactly right. It's happy with the Tannoys, I'm sure it will love the Klipsch (must drag them through for a go), and is known good with LS3/5As, 149s etc, so I've plenty of speaker options over the years. I wonder what it's like into ESLs...
Robert
Tapehead
Ok, 125mv sensitivity on the Leak (Jesus!) coupled with 1meg Ohm input impedance. Likely less than 100pf capacitance too so literally anything will drive that as a load - and I mean anything. The cable LCR will also be immaterial unless L or C get get to utterly insane levels.
The problem has to be with the PAS02 and the 10k pot, as Jez points out.
Now, given the loading conditions on the Leak you can comfortably run with a 50k Ohm passive pot with no adverse effects. So if you want to keep the DV stage I'd suggest trying a different pot in the 50-100k range. Make sure to use short, low capacitance cable (the Klotz is perfect for this) between DV and passive.
As an experiment and just to check that the PAS02 isn't some special low impedance version, connect a DVM set to read resistance across one of the inputs and check the readings as you advance the attenuator to the position at which you'd normally listen. There are various ways to do a passive attenuator, including the shunt method whereby signal is progressively shunted to ground with decreasing listening level. That can really upset some circuits.
I'd put money on the combo working extremely well. Perfect for the ESL certainly, and the ESL63 if 10w goes loud enough which it should in a small room and nearfield listening position.
The problem has to be with the PAS02 and the 10k pot, as Jez points out.
Now, given the loading conditions on the Leak you can comfortably run with a 50k Ohm passive pot with no adverse effects. So if you want to keep the DV stage I'd suggest trying a different pot in the 50-100k range. Make sure to use short, low capacitance cable (the Klotz is perfect for this) between DV and passive.
As an experiment and just to check that the PAS02 isn't some special low impedance version, connect a DVM set to read resistance across one of the inputs and check the readings as you advance the attenuator to the position at which you'd normally listen. There are various ways to do a passive attenuator, including the shunt method whereby signal is progressively shunted to ground with decreasing listening level. That can really upset some circuits.
I'd put money on the combo working extremely well. Perfect for the ESL certainly, and the ESL63 if 10w goes loud enough which it should in a small room and nearfield listening position.
Looks easy, but it's beyond me, i.e. undoing the bolts doesn't mean it comes to bits! I'm not bothered as i don't need the tape outs, so I've not gone any further.
Interesting, I've always fancied a Decca...
Anyone got any feedback regarding the Croft Micro's built-in phono stage? I know I like the Micro 25 as a line stage as two of my friends have them (one a Micro 25, one a Basic, both line only). I'm curious as to how good the phono is, e.g. is it good enough to compete with a decent stand-alone stage like my P100, EAR 834P etc?
To be honest the Croft has not got a lot of competition that I'm aware of as pretty much everything else would need doctoring / tweaking - I've certainly read comments from folk saying things like Conrad Johnson, Audio Research etc are just too loud and I could do without the hassle of finding a nice second hand one and then having to get it modded before it's usable. The Croft can be spec'd for a Leak.
As far as I'm concerned this Leak is a keeper. I'm looking at it as my last 'main system' amp, so it's worth going to some hassle and expense to get it working exactly right. It's happy with the Tannoys, I'm sure it will love the Klipsch (must drag them through for a go), and is known good with LS3/5As, 149s etc, so I've plenty of speaker options over the years. I wonder what it's like into ESLs...
Croft pre's are and have always been, an embarassment to some very expensive pre's.
Arkless Electronics
Trade: Amp design and repairs.
Yep. Or try an attenuator like I suggested... The phono stage will then see the impedance of the attenuator rather than the passive unit. It should also give a wider range of setting for the volume 
Arkless Electronics
Trade: Amp design and repairs.
I've tried one with ESL57's and got very good results. It's the best I've heard a Stereo 20 sound in fact!
IMHO Croft gear is great value but I've heard better.... Once had a Croft power amp in and the Stereo 20 blew it away! Only heard that particular power amp though so don't know about all models.
IMHO Croft gear is great value but I've heard better.... Once had a Croft power amp in and the Stereo 20 blew it away! Only heard that particular power amp though so don't know about all models.
sideshowbob
Champagne fascia aficionado
Very hard to beat IME. Before ST20s became relatively expensive, and when people were spending silly amounts of money on good condition Quad IIs, it was probably the best cheap way to run ESLs on the end of a valve amp. One of those combinations which just works. Given that I sold my Tannoys when I moved to Germany, and will probably be back in the UK by next winter, and have a ST20 in need of a service, maybe I need to think about looking for a nice pair of ESLs too...
martin clark
pinko bodger
Tony - have you got plug space for a wallwart?
I'm thinking you could try a simple discrete gain-of-1 class-a buffer after the phono to deal with (drive) the passive pot load. I'll try to knock something up before visit...
I'm thinking you could try a simple discrete gain-of-1 class-a buffer after the phono to deal with (drive) the passive pot load. I'll try to knock something up before visit...
Here is (I believe) a current and related thread on the World Designs discussion on Leak 20 input sensitivity for the geek gifted in case its helpful
Tony L
Administrator
Ok, had another fiddle... It occurred to me that I'd not had a proper listen to the little plastic DIY stepped attenuator that came with the Leak, I just plonked it with the 303 in system #2 assuming that the Audio Synthesis would be a lot better given it's price / pedigree. I've no idea how many impedances is in the little plastic box, but it does seem to hoover up a little less slam from the 301/P100. Better, but no cigar. I don't know the rating of the stepped attenuator in this little box, I've opened it up and it's not written on it anywhere. IIRC the owner prior to the guy I bought the amp from built it specifically for the Leak, so I assume he picked a sensible one, albeit cheaply.
I'm thinking an active is the way to go here, and I have to admit I'd really like a balance control too as old Tannoys tend to be a db or two out here and there IME. I've yet to hear a perfectly matched pair anyway, and it's somewhat easier to twiddle a knob than move a speaker the size of a wardrobe...
PS Thanks Martin, though I think it makes more sense just to combine the pre and phono stage in one unit. I have no attachment to the P100, good though it is, so I'm quite happy to move it on. It makes sense to reduce the box count and go tubes all the way really.
I'm thinking an active is the way to go here, and I have to admit I'd really like a balance control too as old Tannoys tend to be a db or two out here and there IME. I've yet to hear a perfectly matched pair anyway, and it's somewhat easier to twiddle a knob than move a speaker the size of a wardrobe...
PS Thanks Martin, though I think it makes more sense just to combine the pre and phono stage in one unit. I have no attachment to the P100, good though it is, so I'm quite happy to move it on. It makes sense to reduce the box count and go tubes all the way really.
Arkless Electronics
Trade: Amp design and repairs.
Agreed! but I can't see what else it could be... diagnoses over the internet is notoriously unreliable!
Jonathan Ribee
Unavailable at present
Pop in any time!
gortnipper
loose nut
"Paging Dr. Blog...Dr. Blog, please report to The Forum!"
Paul R
pfm Member
Tony,
If you go to Maplin and get some 90k or so resistors and solder them in series with the signal wire between the phono stage and the passive you will change the nominal sensitivity to something normalish and significantly raise the impedance seen by the P100, to roughly the same as a valve pre might present.
For 10p and a couple of minor burns it might be worth it to establish what is going on.
Paul
If you go to Maplin and get some 90k or so resistors and solder them in series with the signal wire between the phono stage and the passive you will change the nominal sensitivity to something normalish and significantly raise the impedance seen by the P100, to roughly the same as a valve pre might present.
For 10p and a couple of minor burns it might be worth it to establish what is going on.
Paul
Tony L
Administrator
I thought we'd established it? The P100 is working fine, it has heft and slam through the Prima Luna, it also sounds fine via a Quad 34 into the Leak, it does however sound kind of lifeless and dead in the water via either passive, though the plastic one seems a little better than the Audio Synthesis, so is probably higher impedance. The CD sounds fine via either passive, in fact it sounds bloody superb, so the Leak is fine. As such the decision path is decided; either the passive or the P100 has to go. I have no real issue with this. I just need to decide whether to buy a preamp with a built in phono stage (e.g. Croft) or simply buy a new phono stage (e.g. something like an EAR 834P). Whilst I agree it would be interesting to know for sure I don't think it's worth cutting up some nice leads to prove given that the system building logic is already decided (new phono stage / pre / both).
PS I'm sure the Cambridge 640 is happy with the passive preamp. It is just not as good a phono stage as the Dynavector, i.e. it feels like a downgrade from what I had previously, even though it's giving what I'd expect from it (it's actually a pretty decent phono stage, though the P100, when happy, is superb). Please view any earlier comments about the Cambridge in this light.