lentek head amp upgrade

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jayman67
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#1 lentek head amp upgrade

Post by jayman67 »

I original ask if Nik would do this for me but being the type to have a go i thought id jump in.
Nik has modified these head amps before in the past, see here , http://theartofsound.net/forum/showthre ... k-Head-Amp
So here we go,
First off the pcb is potted in silicone so after breaking off the plastic case you are left with a block of silicone covering the pcb,after an hour of picking it off you are left with this,
case top removed,
Image

here all the silicone has been removed,
Image

and here's a pick for people with more knowledge than me of the pcb and tracks going to the components.
Image

one thing of note is there appears to be 3 versions of the circuit,it would seem from comparing the mk2 pcb (mine) that my transistors are different,the ones in the mk3 (see below pic) are BD380 transistors where as mine are in metal cans,i have 2 marked BF X85 and 2 marked BC461 87742.
what the difference is and if ones better than another is over my head.
Image

Anyway i intend to replace the electrolytics ,looking for recommendations please, Sanyo OsCon?? and can any one suggest a good quality replacement for the ceramics? there are 3 used,2 marked N22 and 1 marked 10n.

wish me luck :D
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IslandPink
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#2 Re: lentek head amp upgrade

Post by IslandPink »

Good project.
For electrolytics up to 1000uF, these seem to be very good, I have done some limited comparisons, they worked nicely on the input of a chip amp.
https://www.hificollective.co.uk/compon ... on_es.html
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jayman67
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#3 Re: lentek head amp upgrade

Post by jayman67 »

thanks,they seem ideal,i might have grief finding suitable values for the ceramics.
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Nick
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#4 Re: lentek head amp upgrade

Post by Nick »

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DSJR
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#5 Re: lentek head amp upgrade

Post by DSJR »

I did mine many years ago now with assistance from an AOS member - I forget who and apologies if they remember, as they sent me some Oscons to fit in replacement for the tants originally fitted. My board wasn't potted so easier to modify.

Any better for it? Nah, it's still hissy and brightly lit to balance the sugary Entre in original form... battery life is woeful as it falls off its best after a very few hours' use, stabilising in mediocrity for a few more hours before dying. I tried to make a 9V external supply but it hummed and as I know nothing about supply design as regards output impedance and so on I reverted to battery before putting it into storage. I had some pics but they're not online now...
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Mike H
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#6 Re: lentek head amp upgrade

Post by Mike H »

I looked at that and thought eeek! Tantalums! :shock: But have forgotten why tantalums are 'bad'. Might be non-linear ESR vs freq., kind of thing.
jayman67 wrote: Sun Jan 28, 2018 12:00 pm one thing of note is there appears to be 3 versions of the circuit,it would seem from comparing the mk2 pcb (mine) that my transistors are different,the ones in the mk3 (see below pic) are BD380 transistors where as mine are in metal cans,i have 2 marked BF X85 and 2 marked BC461 87742.
what the difference is and if ones better than another is over my head.
The BD380 is a power transistor. Quite unsuitable for this kind of job I would have thought. Looks as tho someone put it in because they didn't have anything else. The others are old style TO5 case, more than likely obsolete.
 
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Mike H
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#7 Re: lentek head amp upgrade

Post by Mike H »

jayman67 wrote: Sun Jan 28, 2018 12:00 pm Anyway i intend to replace the electrolytics ,looking for recommendations please, Sanyo OsCon?? and can any one suggest a good quality replacement for the ceramics? there are 3 used,2 marked N22 and 1 marked 10n.
Ah yes the ceramics are 'bad' because they have variable 'k' with frequency, IIRC. ('k' = relative permittivity of the dielectric material between the plates. Very good in RF circuits tho as they hold they value quite well vs variations of temperature.)

Personally I would try to use polystyrene.
 
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jayman67
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#8 Re: lentek head amp upgrade

Post by jayman67 »

DSJR wrote: Sun Jan 28, 2018 5:56 pm I did mine many years ago now with assistance from an AOS member - I forget who and apologies if they remember, as they sent me some Oscons to fit in replacement for the tants originally fitted. My board wasn't potted so easier to modify.

Any better for it? Nah, it's still hissy and brightly lit to balance the sugary Entre in original form... battery life is woeful as it falls off its best after a very few hours' use, stabilising in mediocrity for a few more hours before dying. I tried to make a 9V external supply but it hummed and as I know nothing about supply design as regards output impedance and so on I reverted to battery before putting it into storage. I had some pics but they're not online now...
thats strange dave because on the thread im following http://theartofsound.net/forum/showthre ... -Amp/page8
you said this after doing yours,post 78

Well, I've been running this thing rebuilt all evening into the "office" lo-fi setup and frankly, I'm stunned. The system up here doesn't "do" fine details, so only the obvious bits are reproduced. The Shadows first album (1980 stereo version) has air and space that isn't quite as clear using the AVI on its MC setting. Less bass though, but that doesn't bother me, as the "quality" of the bass seems superior.
jayman67
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#9 Re: lentek head amp upgrade

Post by jayman67 »

Mike H wrote: Sun Jan 28, 2018 7:10 pm
jayman67 wrote: Sun Jan 28, 2018 12:00 pm Anyway i intend to replace the electrolytics ,looking for recommendations please, Sanyo OsCon?? and can any one suggest a good quality replacement for the ceramics? there are 3 used,2 marked N22 and 1 marked 10n.
Ah yes the ceramics are 'bad' because they have variable 'k' with frequency, IIRC. ('k' = relative permittivity of the dielectric material between the plates. Very good in RF circuits tho as they hold they value quite well vs variations of temperature.)

Personally I would try to use polystyrene.
thanks for the info mike,im going with nicks recommendations.
jayman67
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#10 Re: lentek head amp upgrade

Post by jayman67 »

im getting a bit confused with regards to replacing these capacitors,nf,pf or uf??
i need 2 of these,
Image

and 3 of these,
Image
nick if you see this,please check with the ones you linked too
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Nick
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#11 Re: lentek head amp upgrade

Post by Nick »

10nf is as I linked, n22 = 0.22nf = 220pf as I linked.

Image

Mike, medium power transistors can make good low noise devices, the large die size means a low current density.
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jayman67
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#12 Re: lentek head amp upgrade

Post by jayman67 »

thanks for confirming,ive been reading up on cap markings and got there in the end,already ordered :)
looking at suitable enclosures now to put it in.
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DSJR
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#13 Re: lentek head amp upgrade

Post by DSJR »

jayman67 wrote: Sun Jan 28, 2018 7:10 pm
DSJR wrote: Sun Jan 28, 2018 5:56 pm I did mine many years ago now with assistance from an AOS member - I forget who and apologies if they remember, as they sent me some Oscons to fit in replacement for the tants originally fitted. My board wasn't potted so easier to modify.

Any better for it? Nah, it's still hissy and brightly lit to balance the sugary Entre in original form... battery life is woeful as it falls off its best after a very few hours' use, stabilising in mediocrity for a few more hours before dying. I tried to make a 9V external supply but it hummed and as I know nothing about supply design as regards output impedance and so on I reverted to battery before putting it into storage. I had some pics but they're not online now...
thats strange dave because on the thread im following http://theartofsound.net/forum/showthre ... -Amp/page8
you said this after doing yours,post 78

Well, I've been running this thing rebuilt all evening into the "office" lo-fi setup and frankly, I'm stunned. The system up here doesn't "do" fine details, so only the obvious bits are reproduced. The Shadows first album (1980 stereo version) has air and space that isn't quite as clear using the AVI on its MC setting. Less bass though, but that doesn't bother me, as the "quality" of the bass seems superior.
I'm sorry, I subsequently tried to learn not to spout off after just a few minutes of listening! The battery went off after a very short time ( four or five hours and later confirmed by Marco I seem to remember) and after replacing it, the extra 'deetail' became a little wearing once the initial appeal wore off. Believe me, my Phono 2/PSU is in a different league given half a chance and it really shows how basically gutless the Lentek could be with anything other than the cartridge it was designed to be used with, namely an original Lentek-Imported Entre 1 (The EC1 model wasn't at all the same although it looked similar I remember). I seem to remember the updates cleaned things up a little, but I'd love to hear it with a properly regulated quality power supply.

I also needed to remember that the AVI S2000MP+P phono stage needs 45 minutes minimum to open up fully (many samples I used in the shop and not just my two) and it can sound too thick all too easily with the wrong cartridge. The geriatric IC-150 phono stage is very good indeed on MM although there's something in the NVA that adds a little body without it appearing to be a colouration as the AVI could appear to do.

This is the issue with old forum posts in my opinion. What they say is how the poster feels 'at that time' in the course of a conversation. Without verifiable evidence, it's purely an opinion of that moment and subject to change with mood and greater experience in the poster. That's why I don't accept the 'Trust your ears' subjective argument as we're so easily fooled.

Maybe Nick should take a look at a Lentek again, measure the thing, post here about his findings and then possibly suggest some mods using modern components or suggest an external power supply that will genuinely improve the performance over a Duracell PP9!!! So long ago now and a lot has happened in seven years...
Last edited by DSJR on Mon Jan 29, 2018 4:25 pm, edited 2 times in total.
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Nick
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#14 Re: lentek head amp upgrade

Post by Nick »

Maybe Nick should take a look at a Lentek again, measure the thing and then possibly suggest some mods using modern components or suggest an external power supply that will genuinely improve the performance over a Duracell PP9!!! So long ago now and a lot has happened in seven years...
I am currently working on a headamp to match the PH1 phono I just did, working through different ideas. Problems are noise and noise, both self noise and noise from the power supply. I spent some time over the weekend trying to track down some power supply noise that was a smear at 1.6kHz, that I could measure and was 80dB down from a 100uV input level, so thats at the 10nV range, got it to go below the measurable noise floor, but it was still just about audible. That circuit is in the bin. Batteries do make life simpler. Its simpler if I use on the of the linear supplies I make, its just self noise to worry about, but not much point in a £200 head amp that needs a £200 linear supply.
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jayman67
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#15 Re: lentek head amp upgrade

Post by jayman67 »

DSJR wrote: Mon Jan 29, 2018 2:48 pm
jayman67 wrote: Sun Jan 28, 2018 7:10 pm
DSJR wrote: Sun Jan 28, 2018 5:56 pm I did mine many years ago now with assistance from an AOS member - I forget who and apologies if they remember, as they sent me some Oscons to fit in replacement for the tants originally fitted. My board wasn't potted so easier to modify.

Any better for it? Nah, it's still hissy and brightly lit to balance the sugary Entre in original form... battery life is woeful as it falls off its best after a very few hours' use, stabilising in mediocrity for a few more hours before dying. I tried to make a 9V external supply but it hummed and as I know nothing about supply design as regards output impedance and so on I reverted to battery before putting it into storage. I had some pics but they're not online now...
thats strange dave because on the thread im following http://theartofsound.net/forum/showthre ... -Amp/page8
you said this after doing yours,post 78

Well, I've been running this thing rebuilt all evening into the "office" lo-fi setup and frankly, I'm stunned. The system up here doesn't "do" fine details, so only the obvious bits are reproduced. The Shadows first album (1980 stereo version) has air and space that isn't quite as clear using the AVI on its MC setting. Less bass though, but that doesn't bother me, as the "quality" of the bass seems superior.
I'm sorry, I subsequently tried to learn not to spout off after just a few minutes of listening! The battery went off after a very short time ( four or five hours and later confirmed by Marco I seem to remember) and after replacing it, the extra 'deetail' became a little wearing once the initial appeal wore off. Believe me, my Phono 2/PSU is in a different league given half a chance and it really shows how basically gutless the Lentek could be with anything other than the cartridge it was designed to be used with, namely an original Lentek-Imported Entre 1 (The EC1 model wasn't at all the same although it looked similar I remember). I seem to remember the updates cleaned things up a little, but I'd love to hear it with a properly regulated quality power supply.

I also needed to remember that the AVI S2000MP+P phono stage needs 45 minutes minimum to open up fully (many samples I used in the shop and not just my two) and it can sound too thick all too easily with the wrong cartridge. The geriatric IC-150 phono stage is very good indeed on MM although there's something in the NVA that adds a little body without it appearing to be a colouration as the AVI could appear to do.

This is the issue with old forum posts in my opinion. What they say is how the poster feels 'at that time' in the course of a conversation. Without verifiable evidence, it's purely an opinion of that moment and subject to change with mood and greater experience in the poster. That's why I don't accept the 'Trust your ears' subjective argument as we're so easily fooled.

Maybe Nick should take a look at a Lentek again, measure the thing, post here about his findings and then possibly suggest some mods using modern components or suggest an external power supply that will genuinely improve the performance over a Duracell PP9!!! So long ago now and a lot has happened in seven years...
ok dave point taken,i agree its very easy to get excited and post then a few weeks later your opinion changes,been there myself with the decca c4e lol
using the lentek i find its a more enjoyable listen,im using a denon dl-103sa which when heard through the mc stage in my nakamichi pre amp (up there with the phono 2) sounds a little harsh in the top end.
the little lentek just tones it down a little.
anyway its a nice little project for me untill i get a more suited SUT.
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