Passive Pre-Amp advice please

[AJSki2fly]

I have recently got back into Vinyl as a friend sold me his Project 2 Xperience with Ortofon Rondo blue and Cambridge Azur Phono Stage, which sounds pretty good going into my Meridian 562/556 and 557 amp driving Dali Ikons.

However I want to loose the Meridian digital pre-amp stage, so I am thinking of introducing a passive pre-amp between the Phono-stage and the Meridian 557 (200w per channel). I have used a NVA P50 passive pre-amp some years ago and found it pretty good, so this is a possibility, but I have also come across the Tisbury Mini Pre-Amplifier (http://www.tisburyaudio.co.uk/mini-passive-preamplifier) and wondered if anyone here had used it or any opinions on it. I know there are lots of more expensive ones out there but for now the budget is limited, and if I want to save money to upgrade the phono stage next.

[struth]

Lots of folk here used a tis. they have a new one out now and I'm told its a bit better than the old one. Its a great bit of kit for very little money. they sell ok on 2nd hand market too. The TVR pres are pretty good too, and mine was my favourite. Not tried an nva so cant comment

[Macca]

I've had the Tisbury and the NVA (P90 and P90SA). The NVA is significantly better in every respect but is a lot more money. Not tried the P50 though, but I'd bet it is better than the Tis. The Tis is a bit light sounding in comparison to the NVA, lacks balls. You could also consider Rothwell, now of this parish I believe.

[hifinutt]

I've had the Tisbury and the NVA (P90 and P90SA). The NVA is significantly better in every respect but is a lot more money. Not tried the P50 though, but I'd bet it is better than the Tis. The Tis is a bit light sounding in comparison to the NVA, lacks balls. You could also consider Rothwell, now of this parish I believe.

yes agree with this . I had the stepped version recently which was much better than alp pot

there is a reprint of hifi critic article on passives including some very good priced ones like glasshouse on the mfa audio news site
Julian musgrave is reviewer

https://mfaudio.co.uk/latest-news/

my absolute favourite passive for vfm is the mfa copper mark 2

[Macca]

I'd deffo recommend going for a stepped attenuator whatever you go for. Worth the extra. Not saying the transformer passives are not also good but they are such a big cost step up and IMO you are not getting anything more, at least not to a significant degree. The best of those I've heard was Ali's which I think he knocked it up himself.

[walpurgis]

I'd deffo recommend going for a stepped attenuator whatever you go for. Worth the extra. Not saying the transformer passives are not also good but they are such a big cost step up and IMO you are not getting anything more, at least not to a significant degree. The best of those I've heard was Ali's which I think he knocked it up himself.

You've not heard my TVC matey. It's way better than any stepped attenuator or pot passive I've tried. And that's quite a few. It's also better than any active pre-amp I've used.

[Macca]

No, I've not heard it. But I've heard my NVA against the Music First and there wasn't a fag paper between them. And the Music First is 4 times the price. Although the power amp in that test was a Conrad Johnson valve job and a tiny bit coloured so that didn't help in spotting differences.

[high.spirits]

I use the Tisbury and for the money you cannot beat it.
There are improvement to be made as per other posts but at a cost.
Depends on whether you can hear the difference.

Try it they do a money back deal.

[DSJR]

I've had the Tisbury and the NVA (P90 and P90SA). The NVA is significantly better in every respect but is a lot more money. Not tried the P50 though, but I'd bet it is better than the Tis. The Tis is a bit light sounding in comparison to the NVA, lacks balls. You could also consider Rothwell, now of this parish I believe.

The P20 is basically a cut down P90 - one pot wired for stereo, two inputs plus direct and sells for £100...

http://www.ebay.co.uk/itm/NVA-P20-Passive-Pre-amplifier-/272074844462?hash=item3f58eca92e:g:rt0AAOSwzgRW1fI 7

I have the 'Tisbury' attenuators here and used them for a while. I soon returned to the little film pots and thought the sound slightly clearer and more 'musical.'

[RothwellAudio]

You could also consider Rothwell, now of this parish I believe.

Yes, indeed I am now "of this parish" but but passive pre-amps are no longer a production item for me. Many years ago - more than I care to remember - I started making passive pre-amps because so many of the active pre-amps I had heard simply weren't as good. I wanted to do something beyond simply a "pot in a box" so I developed my own stepped attenuator with fine and coarse controls giving smaller step sizes and a bigger range of control than anything else available at the time.
However, that was quite a while ago now and things change. These days stepped attenuators are much easier to obtain than they used to be and mine was quite expensive to produce. Besides, the interest in passive pre-amps seems to have dwindled over the years and what interest there is seems to be more focused on the transformer type of passive. So the upshot is that I thought it was no longer viable to keep my passive pre-amp in the catalogue.
But to answer the OP's question the Tisbury appears to be remarkable value for money, though I have to admit I have no direct experience of it. I think it would certainly be worth a punt.

[walpurgis]

The Tisbury is popular and I have heard it sounding good. You can't grumble for the money.

There again. Stepped attenuators are not too expensive from China and putting together a passive using one is easy enough. If you are feeling adventurous, extra input sockets with selector switching can be included.

[Sovereign]

I have an Stereo Coffee LDR passive I could sell you if that helps.
I use a Stereo Coffee LDR in my main set up and I'm totally satisfied with it.

[JohnJo]

I'm not coming from a massive knowledge point here but a key with passive preamps seems to be getting the right resistance of potentiometer or stepped attenuator to suit the rest of your system.

This seems to be a largely trial and error affair as there doesn't seem to be any easy way to determine source current capability in particular and also power amp input impedance.

The Tisbury I had sounded very refined with nice stage depth but seemed to blunt rhythms and leading edges ever, ever so slightly in the context of my system, but obviously fine in others. It was a 10K so that may have been the issue. My usual passive pot is 50K and seems to suit my system better from a loading point of view.

One thing to note, the lower the pot resistance the further you have to turn it to get normal listening levels.

Hope that helps.

[walpurgis]

Maybe experiment with cheap pots to see what suits, then get a stepped attenuator of the best value.

[DSJR]

With modern sources and amps, values don't mean much to be honest in my experience. I've used 10k and 47k film caps and apart from slight position differences for the same perceived 'volume,' I'm darned if I can hear a difference otherwise.

The following is personal opinion from bit's I bought for myself, but I purchased a pair of the attenuators Tisbury use. Tracking at the very bottom of the control range was superior to the little film pot I know so well, but I swear something was 'missing.' After a few months I returned to the inexpensive 10k film pots (I bought my own, by the way!) and honestly feel the sound was better.

I also have a 50k approx. (can't remember if it's 47 or 50k) ladder-type stepped attenuator using Dale and similar resistors and a rather clunky switching mechanism, which I bought from eBay. This offers nothing over the film type in terms of sonics, but again, the channel matcking on the first couple of 'clicks' is excellent. The law is too cautious even for me, as little happens in the first two thirds rotation, but all hell breaks lookse in the last three or four 'clicks.'

Lastly, I have made one so far myself, a shunt type 47k stepped attenuator using plain Vishay metal film resistors - one resistor always in series apart from the top step which is straight through, the volume drop done by varying resistor values 'across' the load, hence the term 'shunt.' (I think I have this right - please correct me if it's wrong). I was suspicious of this as matching impedances are all over the shop from minimum to maximum setting, but I must confess, I thought the sound excellent and need to make another for myself - pain to do, but I used 1/2W resistors, where a 1W might be better for soldering and overall rigidity.

Sorry to possibly cloud this issue, but I have done some comparisons and believe me, film pots may be cheap, but they're not bad in any shape or form.

[Arkless Electronics]

I'm not coming from a massive knowledge point here but a key with passive preamps seems to be getting the right resistance of potentiometer or stepped attenuator to suit the rest of your system.

This seems to be a largely trial and error affair as there doesn't seem to be any easy way to determine source current capability in particular and also power amp input impedance.

The Tisbury I had sounded very refined with nice stage depth but seemed to blunt rhythms and leading edges ever, ever so slightly in the context of my system, but obviously fine in others. It was a 10K so that may have been the issue. My usual passive pot is 50K and seems to suit my system better from a loading point of view.

One thing to note, the lower the pot resistance the further you have to turn it to get normal listening levels.

Hope that helps.

'Fraid that's wrong.... Could be you have different makes of pot with different log law to them or possibly a high impedance source which is loaded down by 10K pot.

[Firebottle]

With modern sources and amps, values don't mean much to be honest in my experience. I've used 10k and 47k film caps and apart from slight position differences for the same perceived 'volume,' I'm darned if I can hear a difference otherwise.

The following is personal opinion from bit's I bought for myself, but I purchased a pair of the attenuators Tisbury use. Tracking at the very bottom of the control range was superior to the little film pot I know so well, but I swear something was 'missing.' After a few months I returned to the inexpensive 10k film pots (I bought my own, by the way!) and honestly feel the sound was better.

I also have a 50k approx. (can't remember if it's 47 or 50k) ladder-type stepped attenuator using Dale and similar resistors and a rather clunky switching mechanism, which I bought from eBay. This offers nothing over the film type in terms of sonics, but again, the channel matcking on the first couple of 'clicks' is excellent. The law is too cautious even for me, as little happens in the first two thirds rotation, but all hell breaks lookse in the last three or four 'clicks.'

Lastly, I have made one so far myself, a shunt type 47k stepped attenuator using plain Vishay metal film resistors - one resistor always in series apart from the top step which is straight through, the volume drop done by varying resistor values 'across' the load, hence the term 'shunt.' (I think I have this right - please correct me if it's wrong). I was suspicious of this as matching impedances are all over the shop from minimum to maximum setting, but I must confess, I thought the sound excellent and need to make another for myself - pain to do, but I used 1/2W resistors, where a 1W might be better for soldering and overall rigidity.

Sorry to possibly cloud this issue, but I have done some comparisons and believe me, film pots may be cheap, but they're not bad in any shape or form.

Good post David, shunt is correct :thumbsup:

[JohnJo]

'Fraid that's wrong.... Could be you have different makes of pot with different log law to them or possibly a high impedance source which is loaded down by 10K pot.

That's very interesting Jez. So regardless of the nominal resistance of the pot the ratio of output voltage over input voltage is the same for all pots with the same taper for a given rotational position, providing the source is able to drive the load without sagging?

In that case, as you say, my source is likely struggling to drive the 10K and 20K pots I've tried. The 10K was the Tisbury which needed cranked for normal levels, the 20K was an Alps Black which needed halfway and the 50K was an Alps Blue which needed about a quarter turn.

My power amp input impedance is supposed to be 100K but I think I read somewhere it was actually more like 40K.

Thanks for the clarification :)

[RothwellAudio]

One thing to note, the lower the pot resistance the further you have to turn it to get normal listening levels.


Jez is correct, the impedance of the pot shouldn't make a difference, but that's assuming a low source impedance and high load impedance. To elaborate without getting bogged down with too much technical stuff, a typical CD player or other modern source will probably have a source impedance of 200 ohms or less and a valve power amp will probably have an input impedance of well over 100k, probably more like 1Meg. With those impedances any pot between 5k and 50k should give you about the same performance as regards pot rotation against volume. However, a lot of valve sources (such as valve phonostages) have a much higher source impedance of several kilohms, and many solid-state power amps have an input impedance of between 10k and 100k. That will complicate things because the pot will load down the source and the power amp will load down the pot and everything will depend on the rotational setting of the pot. In those circumstances the impedance of the pot will affect the volume for a given rotational setting. 10k for the pot is a good value to work with a lot of possible combinations of source impedance and power amp input impedances.
Stepped attenuators are far superior to pots in terms of their absolute impedance value and their channel matching, particularly at low volumes, but passive pre-amps tend to be used well away from the bottom of their travel so channel matching at low volumes is less of a problem than it would be in an active pre-amp with lots of gain.

[Arkless Electronics]

That's very interesting Jez. So regardless of the nominal resistance of the pot the ratio of output voltage over input voltage is the same for all pots with the same taper for a given rotational position, providing the source is able to drive the load without sagging?

In that case, as you say, my source is likely struggling to drive the 10K and 20K pots I've tried. The 10K was the Tisbury which needed cranked for normal levels, the 20K was an Alps Black which needed halfway and the 50K was an Alps Blue which needed about a quarter turn.

Thanks for the clarification :)

Spot on. Not many sources are so high an impedance as to make much difference by being loaded down though. Most likely would be differences in log taper between makes.
I usually recommend 10K as a good compromise. Some valve sources will be better off with 50K though.
There are many valve sources where, although a cathode follower may be in use, and the output impedance may be quoted as lets say 250 Ohm, they don't have the ability to linearly drive current into the load. An output impedance of 250R implies that it should be able to drive a 250R load, losing half it's output though in the process. In practise there would be such gross distortion that it would be unusable.... unless you want everything to sound like its been through a fuzz box! This is why it's often best to go no lower than 10K ish when using a valve source. Some are worse than others of course... I've known ECC83's being used as cathode followers and they would be really bad at driving anything much really...

[Reffc]

Spot on. Not many sources are so high an impedance as to make much difference by being loaded down though. Most likely would be differences in log taper between makes.
I usually recommend 10K as a good compromise. Some valve sources will be better off with 50K though.
There are many valve sources where, although a cathode follower may be in use, and the output impedance may be quoted as lets say 250 Ohm, they don't have the ability to linearly drive current into the load. An output impedance of 250R implies that it should be able to drive a 250R load, losing half it's output though in the process. In practise there would be such gross distortion that it would be unusable.... unless you want everything to sound like its been through a fuzz box! This is why it's often best to go no lower than 10K ish when using a valve source. Some are worse than others of course... I've known ECC83's being used as cathode followers and they would be really bad at driving anything much really...


All true.

Many valve phonostages may have output impedances of 500 to 600 Ohms. Using a 10K pot with those may kill dynamics. The other consideration is that if capacitor coupled, the cap value itself can also affect response. You might get away with 20 to 50K for the pot value for many valve sources...suck it and see. If using valve sources, and your power amp has an input impedance of at least 100KOhms or more, a 50K pot should work fine in many cases. 20K would be better IF the valve source will drive it.

[Scooby]

You could always build your own for peanuts. These pots are good:

http://www.omeg.co.uk/pce16brc.htm

[Ali Tait]

I'd deffo recommend going for a stepped attenuator whatever you go for. Worth the extra. Not saying the transformer passives are not also good but they are such a big cost step up and IMO you are not getting anything more, at least not to a significant degree. The best of those I've heard was Ali's which I think he knocked it up himself.

Yes, the Slagle autoformers can be had for 200 dollars, one of the best hi fi bargains out there IMHO.

[Arkless Electronics]

All true.

Many valve phonostages may have output impedances of 500 to 600 Ohms. Using a 10K pot with those may kill dynamics. The other consideration is that if capacitor coupled, the cap value itself can also affect response. You might get away with 20 to 50K for the pot value for many valve sources...suck it and see. If using valve sources, and your power amp has an input impedance of at least 100KOhms or more, a 50K pot should work fine in many cases. 20K would be better IF the valve source will drive it.

I wouldn't personally agree with the dynamics bit... Distortion is the issue long before this comes into play. Take it far enough and yes there is huge dynamic compression just as in a fuzz box, and usually asymmetric.
The main point I was making is that even if a valve source has an output impedance of 500R its actual ability to drive real loads may be more akin to a 10K output impedance (I guess this is all rather confusing to the layman though....).
The point you make about the output capacitor is a good one (there will be one in 99.999% valve gear!). It needs to be several uF really if loads of below 50K or so are to be driven without bass loss.

[Reffc]

I wouldn't personally agree with the dynamics bit... Distortion is the issue long before this comes into play. Take it far enough and yes there is huge dynamic compression just as in a fuzz box, and usually asymmetric.
The main point I was making is that even if a valve source has an output impedance of 500R its actual ability to drive real loads may be more akin to a 10K output impedance (I guess this is all rather confusing to the layman though....).
The point you make about the output capacitor is a good one (there will be one in 99.999% valve gear!). It needs to be several uF really if loads of below 50K or so are to be driven without bass loss.

I like to see (& use) at least 3u3 coupling caps for that very reason.

[Arkless Electronics]

I like to see (& use) at least 3u3 coupling caps for that very reason.

Same here.

[JohnJo]

So it shouldn't matter if you have say a 50k pot that measures 50k on the outside pins of one channel and 53k on the other channel, so long as the RATIO of wiper to ground resistance divided by total channel resistance is close between channels.

In this case the channel balance will be accurate although there will be a slightly higher current following in the channel that measures 50k but this shouldn't affect sound quality.

Is this correct?

[danilo]

If that worries (shouldn't) then try one or two (use two as a combo volume balance) of these.
http://www.ebay.ca/itm/DACT-Type-SMD-Stepped-Attenuator-21-step-Volume-control-pot-D-Shape-Shaft-/181534837651?hash=item2a4451cb93:g:M2QAAOxyXzxTILZ Z
Yes.. Cheap Chinee copies of Dacts. for seemingly V little coin.
BUT and it's a big But, these do work Really well. Surprising results for Chinese stuff.
You will need Supermans' Hearing and .. really damned good gear.. to hear any audible differences betwixt these and a Goldpoint.
Not even a big risk to try.

[DSJR]

If that worries (shouldn't) then try one or two (use two as a combo volume balance) of these.
http://www.ebay.ca/itm/DACT-Type-SMD-Stepped-Attenuator-21-step-Volume-control-pot-D-Shape-Shaft-/181534837651?hash=item2a4451cb93:g:M2QAAOxyXzxTILZ Z
Yes.. Cheap Chinee copies of Dacts. for seemingly V little coin.
BUT and it's a big But, these do work Really well. Surprising results for Chinese stuff.
You will need Supermans' Hearing and .. really damned good gear.. to hear any audible differences betwixt these and a Goldpoint.
Not even a big risk to try.


That little film pot linked to some posts above is better sounding - and even I could hear it - and I BOUGHT examples of both! The shunt stepped attenuator I made up is better again - and it was bass substance and overall 'tonality' I thought that did it - more like an amp upgrade and I don't know why.


The reason why 'we' are called audiophools is that we tend to 'sense' certain differences, the best of which are repeatable. That DACT style thingy as Tisbury use goes through the basic musical motions just fine, but the little green film pot just seems to let the musical essence through better, despite the construction and very low cost - I can't describe it any other way. Since I can no longer afford to hear with my eyes and buy what my eyes tell me sounds better, I just try to listen and if I see a bargain priced thing that does the job better, then brilliant. Anthony TD did mention a beautiful stepped attenuator made with decent resistors at Goldpoint prices that I did like the look of, but I can't afford it so put it to one side.. The little plastic film pot needs great care in soldering up though, as I discovered it can suffer thermal damage if overheated by a soldering iron.