Lentek Head Amp - Naked!

As part of a prep to create a 9V external supply for this head amp, I thought I'd take a deeper look and see if the circuit could be exposed.

Success.....

http://i132.photobucket.com/albums/q...s/DSCF1456.jpg

The little pot is just a cover and was glued to the sides of the inner tray. The board was also attached via a sticky pad to the base of the tray and the adhesive had worn out -

http://i132.photobucket.com/albums/q...s/DSCF1460.jpg

Here's a closer look at the board -

http://i132.photobucket.com/albums/q...s/DSCF1453.jpg

For copyright (?) reasons, any printing has been removed from the transistors, but hopefully the pics can tell someone the values of the very close tolerance (for the period) transistors used.

As for the caps, the outer tantalums are 6.3V 47 (uF?), the inner ones are 16V 10 (uF?), the two purple topped flat caps are n22's and the three little flat red ones have black and orange dots on (black at top, orange bottom right).

Am I right in thinking that the tants might be the cause od the slight "solid state brightness" this unit exhibits (and has always done from memory?). I don't know enough to know..

I've fitted a PP3 socket to the existing plug, which I've repaired, and taken the leads out through one of the screw holes (screw wrapped and placed in battery tray for posterity). This should make things possible to put back to original easily.

By the way, I've measured the voltage of the extra long life Alkaline PP3 I fitted and on my digital volt-meter it measures 9.14V. This makes me think that the regulator output shouldn't be set to more than 9.5V I think, unless anyone recommends differently :)

http://i132.photobucket.com/albums/q...s/DSCF1460.jpg

Mmmm, a few things there could be moddified ;)

First up set your regulator to 9 or 10V, it won't be a problem...

If i was you & i owned this head amp i'd change all the resistors for decent ones. The n22 capacitors i'd change to 220pf (which is what they are) polystyrene caps. Pity i can't see the circuit drawn out so we could establish exactly what the tantalum caps are doing precisely :scratch:

The transistors look like TO5 jobbies, i'm guessing that they'll likely be medium power & rated at about 1Amp. These kind as well as TO126 trannies are often used in MC pre amps simply because they have a lower noise floor.

Perhaps if you could get a decent shot of the PCB track side square on i might be able to draw the circuit out & then you can modify to your hearts content :)

I've put it all back together now and couldn't tilt the board any more without removing some wires :(

I thought the resistors were 1% ones, both metal film and a few carbon ones. I can certainly open it again sometime and try to get better shots (I don't have an enthusiasts camera I'm afraid). Poly caps are fine to change to, but what are the ones with dots on in value?

Am I being picky regarding the tants, or are they really good (I have "memories" of Naim gear stacked to the gunwhales with 10uF tantalums :eek:)

There are much better caps out there that'd fit in place of the tantalums. Sanyo Os-cons spring to mind & they'd be a similar size with those voltages & capacitances you quoted :)

E2A:- Those 1% resistors you are refering to happen to be 20% tolerance (red band at the end) & they are most likely carbon ;) Sorry i have no idea of the value of the dotted caps...

Red band at the end is +/- 1% - i.e. 2% I thought - I checked on some charts again to make sure...

I'm not going to go totally mad here, but caps will definitely be looked at at some point. Thanks for advice regarding supply voltage too.

Hi Dave,

Most interesting, and well done for opening up the old girl! I sense some future 'tweakage' shenanigans :eyebrows:

I'll be following this thread with interest...... :)

Marco.

Btw, here's an interesting thead about the Lentek on Lenco Heaven:

http://www.lencoheaven.net/forum/index.php?topic=2317.0

And one here: http://www.thecrossovernetwork.co.uk...ep-up-for-sale.

Marco.

Welcome back Marco. It wasn't the same without you, it was like being in class with the Teacher out...:eyebrows:

Hi Dave,

Gosh, it's nice to be missed :o

And yes, it's good to be back! :cool:

Marco.

Been anywhere nice?

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Originally Posted by DSJR

Red band at the end is +/- 1% - i.e. 2% I thought - I checked on some charts again to make sure...

I'm not going to go totally mad here, but caps will definitely be looked at at some point. Thanks for advice regarding supply voltage too.

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Yes, you are quite right, they should in theory be 2% tolerance as brown is 1% :doh:

Hi Ali,

Quote:

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Been anywhere nice?

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Yes thanks, we were in France/Belgium for a week, and also Luxembourg at one of our favourite haunts in a beautiful medieval village in the north of the country:

http://www.hotel-de-la-sure.lu/index...mid=13&lang=en

The food is absolutely stunning there!


Here are some pics of the picturesque medieval village of Esch-sur-Sûre (where the Hôtel de la Sûre, above, is located):


http://img267.imageshack.us/img267/6...rsurepanao.jpg



http://img22.imageshack.us/img22/202...tsideofesc.jpg


And of Vianden, another of our favourite places in Luxembourg:


http://img837.imageshack.us/img837/7505/vianden1.jpg


http://img718.imageshack.us/img718/4960/vianden2.jpg


I'm not sure if you've been to Luxembourg before, but it's an absolutely fabulous place, very unspolied, immaculate throughout, and with beautiful scenery (a bit like a mini Switzerland in some respects) and with the best of French and German cuisine (and beers) rolled into one - awesome! :cool:

Marco.

Looks very nice Marco.

Indeed it was, but it lacked the 'vivacious' ambience and overall joie de vivre of Dunfermline! ;)

Marco.

Ha!

There's worse places though...

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Originally Posted by hifi_dave

Welcome back Marco. It wasn't the same without you, it was like being in class with the Teacher out...:eyebrows:

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+1! Hope you've had a great time, sounds like you have! Look forward to your proper return!

...and on a similar but slightly different subject, can I just add that whilst most of Mark's (Reid Malenfant) posts go "wooosh" right over my head ('cos he's dead clever) it's great that he is contributing so much to AoS and already feels like he is part of the furniture - thanks Mark, good to see you getting stuck in. :eyebrows:

Quote:

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There's worse places though...

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Damn right, dude! I like Dunfermline - the people are very friendly and there are some nice places to go. Fife, in general, is a lovely area of Scotland.......... :)

When Del and I lived in Glasgow we used to celebrate our wedding anniversary at Balbirnie House in Glenrothes:

http://www.balbirnie.co.uk/

Marco.

P.S Dave, apologies for the thread drift!

Hi Alex,

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+1! Hope you've had a great time, sounds like you have! Look forward to your proper return!

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Cheers, dude - hope you're still listening to proper music software via your Naga! :eyebrows: ;)

Marco.

P.S Agreed on Mark :)

Quote:

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Originally Posted by Alex_UK

...and on a similar but slightly different subject, can I just add that whilst most of Mark's (Reid Malenfant) posts go "wooosh" right over my head ('cos he's dead clever) it's great that he is contributing so much to AoS and already feels like he is part of the furniture - thanks Mark, good to see you getting stuck in. :eyebrows:

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:lolsign: I might know a thing or two about analogue electronics but i know next to nothing about digital :rolleyes: I have learn't what i needed to know to do my job/s & it basically boils down to wanting to learn so i could make some of my own equipment :)

I have no formal qualification in electronics, however, that didn't stop me being invited into a research & development lab to help design stuff in one job. It also didn't prevent me from fixing rather a lot of switch mode power supplies that my supervisor (with an HND in electronics) was incapable of doing in another :mental:

Thanks very much Alex, nice to feel at home :smoking:

Join the Open University and see if an Open degree can be constructed (it's modular and covers multi-subjects) to suit as I'm hoping to do.

I want to try the Lentek as-is with an external supply to start with. I have found a Maplin mutli-voltage regulated power supply with LM317T regulator inside (they're going for £9.95 at the mo) - http://www.maplin.co.uk/Module.aspx?ModuleNo=32754 - I'm getting a male DC socket and shall fit this to the Lentek trailing wires when it's delivered..

Dave, i have 6 spare Os-con capacitors here which you are welcome to if you want them ;) They are 22uf 20V, yes they may be different values to those tantalums but in reality it'll make virtually no difference to the way the circuit performs (except the sound :lol:). The worst case scenario is that the LF rolloff might be a tad higher though i should imagine it'll already be very low anyway simply because the warp filtering will be taken care of in the phono pre-amp proper ;)

Totally agree with Alex
Mark its great to have you on board

Mark,have you got any further with trying the balanced trannies yet?

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Originally Posted by Ali Tait

Mark,have you got any further with trying the balanced trannies yet?

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Hi Ali, sorry for going :offtopic: No :scratch: you see i'm not going to get a listen until i build some kind of case, which in reality means a good one - the final one if you like. Now i have way more than enough MDF to make a suitable box & everything i need to make all the protection circuits :)

What i don't have is access to my table saw in the garage as there is rather too much stuff just chucked all over the place & i'll need room to move even a 4 x 2ft offcut of wood about, it's that bad :rolleyes: This also explains the lack of input recently on the sub build thread :doh:

I'll get there in the end though, my apologies as it's not even as soon as i'd like myself. The mind is willing but the body is fu**ed so i have to take things miles easier & slower than that damn tortoise (that raced the rabbit) :doh:

When i do get some room both projects will progress in a very short time :) Hopefully pretty soon to as it's damn depressing tbh & not only for you! :lolsign:

No worries,I just wondered! No pressure.. :)

Thanks for the offer mark. I'll be in touch shortly :)

I got the cheap Maplin supply hooked up and once I realised that the connections are inverted (two battery terminals have to be inverted to work together) I tried it.. There's a hum through the speakers from the supply which I think is lack of smoothing (I'll have to make my kit of parts up pronto).

As an aside, the Lentek works on 3V, the test light only just beginning to dim out compared to 6V+

The Carbon resistors look like Allen Bradleys, if used in critical positions in the signal path they tend to add quite a heavy signature . Be warned if your planning on changing these to say 1% metal film types ,it will probably change the sound a fair bit . You may or may not like it.
Tants can sound thin and bright, hard to say if their decoupling or coupling, also if theres any ceramic caps used in the filter etc these can be bright/harsh

Its hard to work out the circuit from the pic, it may have poor PSRR, some circuits are very picky regarding PSU quality

BTW if this thing was made for batteries I'd be careful going linear, it may make things sound worse unless the quality of regulation is better than average

I was thinking that myself, but at least it's easy to put back to original.

This head amp was designed primarily for the Entre 1 cartridge, which Lentek originally imported. This latter had a velvet, almost smothered quality (by today's standards) and was great for smoothing out those nasty early dome tweeters. It wouldn't surprise me at all if Phil Swift didn't deliberately add a little "life" to the sonics to partially balance the Entre. A year or so later, the Entre itself changed and became more "spiky" in sound, althoigh it's irrelevant now ;:

Hi Dave,

Any more updates on your Lentek experiments? :)

Marco.

I made up the power supply and there was too much hum. I don't know what to do to "improve" things, so a week or two ago I stripped the extra wiring out and returned the Lentek to normal. I'm so happy with the Decca right now (even though it's not being used to anything like its full potential) I haven't given it much more thought. The massive ear infection then got in the way and even now, things aint quite right (whatever "right" is for me).

Ah, I see... This ear infection of yours, mate, seems to be somewhat of a regular occurrence.

I presume you're receiving medication for it, and if so, I'm curious to know why that hasn't cleared it up and continues to give you problems :scratch:

It needs sorting - and permanently. Or is there something I'm missing?

Marco.

It all started when he ate the worm in his Tequila...:drunk:

Quote:

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Originally Posted by Marco

Ah, I see... This ear infection of yours, mate, seems to be somewhat of a regular occurrence.

I presume you're receiving medication for it, and if so, I'm curious to know why that hasn't cleared it up and continues to give you problems :scratch:

It needs sorting - and permanently. Or is there something I'm missing?

Marco.

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I'll get to David Wren in a moment :punch: :laugh:

Seriously, I've had catarrh all my life and apparently I have a touch of an adult version of "Glue Ear," but since my mid twenties I've often suffered inner-ear infections. In 1999 we moved to East Northants and something in the cloying air in this region (I wasn't alone) caused me to have severe ear infections (I went deaf in both ears twice for up to a week each time) and I'm convinced this started the Tinnitus up again. Since moving to the coast, I've been very lucky, getting bunged up but little else until a couple of weeks ago and the pain was dreadful for a few days. I've been dosed up and have had blood tests (I have to have another one) 'cos my blood-sugar is up a bit (I'm crossing fingers on this one..).

Not much I can do except keep my ear canal dry when showering and to make sure that colds and "flumonia" don't get out of hand...

Dave i've got summert to keep you ears dry in the shower.

PM received with thanks ;)