Resurrecting a 1980s analogue preamp project

[Monkeyboi]

Years ago back in 1981, ETI published their Series 5000 Control Preamplifier project.  At that stage I had been using a Yamaha CA700 integrated for quite a few years with some degree of satisfaction but felt the MC and MM phono stages left a bit to be desired in the signal to noise ratio stakes.  So when ETI published their new preamp design claiming a much better noise performance using the latest available ICs and matched balanced low noise transistors I thought it was time to get out the soldering iron and put their claims to the test.  Well that was some 37 years ago.  Yikes!!! 

 

So where does this post fit in some almost 4 decades later?  The original preamp was stolen when the house got broken into.  The idiots took the preamp but left the external power supply behind.  Insurance paid out and they replaced the preamp with a Sony TA-E77ESD which I found to be more than satisfying.  Needless to say I stupidly traded it for another preamp which was in retrospect a poor decision, but I'm quite sure we have all been there at some stage(s) in our quest for audio nirvana. 

 

Okay, if you are still reading you're probably wondering where does a circa early 1980s analogue kit preamp fit into today's audio world and why bother even building it?  Some may say 'nowhere" or even "why bother?"; whilst others (like myself) might have perhaps a bit too much spare time on their hands or perhaps a bit of a hanker for a trip down nostalgia lane.  For me it was the latter two.  Besides a few years back I was trolling Fleabay and someone was selling their unassembled kit.  The price was right so I clicked on the Buy Now button and a week or so later a cardboard box arrived with all the goodies inside.  I started assembly of the main board and my mind was cast back to 1981 when I built my first 5000 Series preamp.  Hmmm... lots of shielded cables coming from this board as well as other wiring and I was thinking "servicing or modification nightmare".  Solution: make the board easily removable by using connectors.  So a perusal of the various catalogues revealed a simple cost effective solution - Dinkle (TM) connectors. They aren't expensive, proved to be reliable in previous projects and low enough in profile to fit into the 1RU height case.  This idea flowed onto the same been used on the moving coil and moving magnet phono boards as well as the power leads to the LED level meters.   The rationale behind all of this is simple.  I will no doubt want to modify the original design, so the boards need to be able to be removed and reinstalled easily.  Also minimal modification to the original printed circuit boards were required.  At my stage in life, patience with fiddly things is no longer my forte. 

 

Now, a few years after buying the kit on Fleabay, the project has finally reached completion to the electrical and initial listening test stages.  So far so good.  Found the Master volume control tracking was not very good.  Well, hey, it's a cheap $4.00 logarithmic pot from a kit supplier - what did I expect? At full clockwise (maximum level) or counter clockwise rotation (minimum level) there was only 0.1dB difference between left and right channels.  However at other positions 25%, 50% and 75% rotation the level mismatch was 0.5dB.  I would have used different potentiometers but my preference for ALPS blue series won't fit into the space between the switch PCBs.  So a fix needed to be implemented.  Simply bridge the wiper to common (ground) connections on the louder channel with a bypass resistor.  In this case fitting a 470k reduced the tracking error to a mere 0.1dB over the entire range. Sweet, a 2c fix .

 

So what is different about my version of the original ETI 1981 design?

Main Board

• Upgraded power supply which included an externally housed 30VA toroidal transformer, change in power connectors on the chassis and shielded cabling between the external power transformer and the case of the preamp. This is a significant improvement over the original ETI design that used (would you believe?) 3 pin DIN audio connectors for the power.
• Upgraded power supply filtering on the main board which were increased to 3300uF per main d.c. supply rails before the regulator ICs.
• Installation of 0.1uF monolithic ceramic bypass caps across the regulator IC inputs as well as decoupling the +/- 15 volt rails at all the audio ICs.
• Installation of Dinkle (TM) connectors to facilitate easy removal and reinstallation of the PCB if required.
• Changed the original NE5534 ICs to the higher noise spec NE5534A versions.
• Installed sockets for all the ICs except the regulator IC of course. This will facilitate "rolling" or brown dogging with ease
• Replaced all the electrolytics. I figured that ones that had been sitting around unused for 30+ years would be of suspect specs.
• Replaced the open trim potentiometer with a sealed cermet type.
• Installation of testing points at strategic parts of the circuit for testing purposes.
• Installation of heatsinks on all the regulator ICs.  I found the one that feeds the LED level meters got quite warm in use.  
• Changed the output resistors in the monitor stage only to 22 ohms from the original 1k ohms.  Checked to ensure amplifier stability was not compromised by running it into a 600 ohm load paralleled  by 1000nF of capacitance.  With a 1kHz square wave there was zero instability or ringing evident even with the output driven to just below the onset of clipping.
• External 12v trigger output.

 

Moving Magnet and Moving Coil Stages

• Installation of Dinkle (TM) connectors for both signal and power.
• Changed all of the electrolytic capacitors for the same reason as on the main board.
• Installed sockets for the 8 pin DIL ICs to allow rolling and brown dogging at a later date.

 

MM phono input loading board

• This was never part of the original ETI design.  After owning the original version I now have two turntables and a number of different cartridges.  One of the problems was changing cartridge loading.  For example, my beloved Shure V15 Type III works better in to 47k ohms shunted by a whopping 450pF of capacitance whilst my other cartridges seem to work better into other load combinations.  Most MM phono preamps don't offer this much loading compensation.  Yes, you could do this externally but IMHO it's messy.  So to overcome this problem I designed and etched a small PCB that allows each MM input to be loaded independently with up to 3 resistive and 5 capacitive loads with simple adjustment via DIP switches. By switching in or out the resistors and capacitors, a very large range of loading options are possible.  You can see this board on the left side of the chassis in the open case picture attached.
• The other rationale behind the loading board was that the capacitance of turntable leads vary considerably from model to model and some users may use custom leads. By being able to change the shunting capacitance within the preamp allows the user to vary the loading from no additional loading other than the few pF from the internal shielded cabling inside the preamp to within +/ 25pF of the desired loading for reach input MM1 and MM2 as well as each channel independently.

 

Chassis / Case

• Nothing exciting here -
• Fitted new 5 pin power connectors in lieu of the original 3 pin DIN audio connectors.
• 12 trigger output.
• Earthed grounded binding / banana post for the turntable grounding leads.
• Tapped M3 threads instead of the self-tapping offering of the original case design.  This will make removing and replacing the top cover more expedient.  I found self tappers in this role unsuitable as they tend to strip out the chassis base with repeated securing over time.  So the M3 screws are now those nice black ones which will hopefully go unnoticed.
• Tapped M3 metal posts in lieu of the plastic ones supplied in the kit.  All internal boards secured with M3 screws, nuts and shake proof washers.
• Fitted 50mm diameter "hi-fi" style feet in lieu of the square stick on rubber feet supplied with the kit.

 

60dB range peak and average LED Level meters

       The original design is pretty well much untouched except for the following -

• Drilled holes in through the PCBs where the offset and level adjustment trim potentiometers are located.  This is so the calibration adjustments can be made with the boards in situ as they are mounted component side down in the original design.  Adjustment of the right channel meter needs to be done before the left channel meter PCB is installed.
• Changed the LED colours.  -48 to 12dB are now in green; -9 to -3dB in yellow; 0dB in orange and +3 to +9dB in red. 
• Power leads fitted off with a Dinkle (TM) connector.
• The red LEDs will need to be replaced as the ones supplied in the kit don't match the brightness of the others.  A task to be completed when I next perform a mod to the preamp.

 

Electrical Testing

Minimal done so far except to measure gain, channel balance, stability and calibration of the LED level meters.  I am going to do some extensive subjective listening tests before checking out how this preamp measures on the bench. 

 

Subjective Testing so far

So far the line inputs are inky quiet. There is absolutely no sibilance or hint of harshness using a wide variety of program material when the preamp is driven from the analogue unbalanced outputs of my Sony SCD-XA5400ES SACD/CD player.

I will need to drag out at least one of my turntables to listen to how the MM phono inputs perform.  I don't have a MC cartridge at the moment so this might have to wait for either someone to lend me one or I'll take the preamp to them and use it in their system.

The preamp has more than enough drive output from the monitor line out sockets to drive my ME-850 Hi-cap power amplifier to full power.

 

There are probably going to be dozens of addition mods to this simple little preamp over time.  Most likely the electrolytics in the signal paths will be upgraded, given time, budget and inspiration.   Maybe after that I'll trial some brown dog alternatives.

 

Apologies for the quality of the pics.  Taken with my mobile phone camera.

 

Cheers,

Alan R.

 

 

 

 

 

 

[A9X]

I built one of these back when, as part of a project when I was being taught to Mil-spec solder; I was not long post Uni and had had the kit on the shelf for some time. I honestly don't recall what happened to it, but I used to have a lot of gear flowing through the house. It was in my active Linn system replacing the Naim pre.

 

My suggestions would be; modern electros from a known reliable source, eg Farnell or RS. Leave the opamps alone for the time being as the PCBs are older designs and modern wide bandwidth opamps may oscillate if substituted*. Otherwise, leave it the hell alone. David was a very clever guy and I'd suggest most "audiophile" mods would add nothing or detract from it's performance.

 

I've just found a schematic, and when I have some time, I'll look it over again and see if I can add something else**.

 

Nice workmanship and write up. Bit of a blast from the past.

 

* First brief read confirms they are 5534's. Very good opamps, and I'd be loathe to replace them. Others may tell you there are newer and better, but Douglas Self would make a good case for them being fine.

 

** Re-read more closely (in between stuff at work so not as close attention as I should). Can't see much more to add to the list of mods you did.

Edited July 1, 2018 by A9X

[betocool]

Great project! Looks like you had lots of fun!

 

Any chance to find schematics somewhere?

 

I've used the 5534 and 5532 in different things, and I don't see me changing or upgrading, it's a very neutral and transparent chip. Of course, YMMV.

 

Cheers,

 

Alberto

[Monkeyboi]

3 hours ago, betocool said:

Great project! Looks like you had lots of fun!

 

Any chance to find schematics somewhere?

 

I've used the 5534 and 5532 in different things, and I don't see me changing or upgrading, it's a very neutral and transparent chip. Of course, YMMV.

 

Cheers,

 

Alberto

I have the original construction articles and can pass them on if you like.  Alternatively, if you have access to hi-fi engine, the complete project including the original LED level meters are available for download here - https://www.hifiengine.com/manual_library/eti/series-5000-pre.shtml

 

Cheers,

Alan R.

[betocool]

Thanks Alan,

 

I'll have a look at the website, seems interesting.

 

Cheers,

 

Alberto

[Addicted to music]

The 5534 5532 are found in just about any brand for that era.  Rotel had them 8n there CD players etc.

 

i use to be attracted by the UV meters on that Preamp when I come across it in my teens when I go inside a Dick Smith shop.   

 

I went ahead and built the AEM6010 and the Silicon Chip Ultrafedlity Preamp that involved the OPA 2134 when that opamp was 1st released early 2000.  

 

The AEM6010 tought me potentiometers, like you said,  supplied $5 carbon type.  I built a 2nd 6010 and the SQ destroyed the 1st.   Replaced the volume pot and it bought the 1st one up to speed...  Those volume pots were typical carbon types that nearly every manufacturer used regardless of esoteric or DIY.  Yes Naim used them as well until the mid 80s.   

 

I ordered wima 10uf MKP and they made a massive improvement replacing those bipolar.electro caps.

 

With the ultrafedility Preamp with the OPA 2134,  I got Silicon Chip to published a digital volume control base chip that when publish was superseded.  Of memory it was WM Chip that was expensive and the top of the line Marrantz used at the time.

 

Those rotary selector switch were a PITA.  I’ve had to replaced a few as they got noisy and the contacts would go funny.  The Ultrafedity used relays to resolved this issue.

 

Also mega fun rolling in opamps.  The OPA 827/1612/2134  And some LME are all part of there sound plus range and are heavily compensated,  are unity gain and are equivalent to the 5534/5532.  Some of the LME devices with unity gains are also compatible. Can’t see these oscillating but make sure you use a CRO.

[LogicprObe]

 

Those carbon pots were pretty much all we could afford back then anyway.

You gave them a spray if they started being noisy and if it continued, you just changed them!

[Monkeyboi]

Okay, the electrolytics for the signal paths have arrived with the replacement potentiometers.

Will be replacing all the electrolytics in the signal paths on all the board boards except (obviously) the LED Level Meters with Elna Silmic II types.

Replacing the Master and Monitor level controls with ALPS Blue potentiometers. I suspect these will be a tight squeeze.  Hopefully I won't have to remove and shave down the adjacent switch PCBs to accommodate the bigger ALPS pots.

 

Cheers,

Alan R.

 

[MarcAL]

I have one of these also but never considered upgrading it as the screened cables and layout was not very up-grader friendly. However I might now after seeing your approach.

There was also the Series 5000 mosfet power amp of the same era. This I have upgraded several times, mainly the power supply and is still going strong. My favorite mosfet amp.

Excellent job throughout, keep up the good work.

[audiofeline]

On 01/07/2018 at 3:48 PM, Monkeyboi said:

...

• Installed sockets for all the ICs.... This will facilitate "rolling" or brown dogging with ease   Maybe after that I'll trial some brown dog alternatives.....

Nice work Alan, looks good.

I know what IC "rolling" is.  I'm not familiar with "brown dogging" - could someone please translate? 

Thanks

[Monkeyboi]

On ‎19‎/‎09‎/‎2018 at 7:04 PM, audiofeline said:

Nice work Alan, looks good.

I know what IC "rolling" is.  I'm not familiar with "brown dogging" - could someone please translate? 

Thanks

Brown dogging is essentially using either a brown dog or a brown dog adapter to replace or substitute a conventional integrated circuit (IC) in a circuit.  The explanation for each follows -

 

Brown dogs are small discrete component equivalents or versions of IC OP amps built on to small compact printed circuit boards and have pinouts the same as their IC originals.  They are designed to plug in or be directly soldered to the main board just like the IC originals. The manufacturers generally claim superior performance over the original IC component.  See attached picture of a typical brown dog using discrete SMD components with pins that allow it to "replace" a standard 8 pin DIL IC package.

 

 

There are also Brown dog adapters which allow you to solder on newer SOIC IC versions of now discontinued DIL packaged IC to a small printed circuit board that has the DIL equivalent pins.  See the picture below.

 

I hope this helps explain my post.

 

Cheers,

Alan R.

 

Edited September 21, 2018 by Monkeyboi
Added text

[audiofeline]

1 hour ago, Monkeyboi said:

Brown dogging is essentially using either a brown dog or a brown dog adapter to replace or substitute a conventional integrated circuit (IC) in a circuit.  The explanation for each follows -

 

Brown dogs are small discrete component equivalents or versions of IC OP amps built on to small compact printed circuit boards and have pinouts the same as their IC originals.  They are designed to plug in or be directly soldered to the main board just like the IC originals. The manufacturers generally claim superior performance over the original IC component.  See attached picture of a typical brown dog using discrete SMD components with pins that allow it to "replace" a standard 8 pin DIL IC package.

  

There are also Brown dog adapters which allow you to solder on newer SOIC IC versions of now discontinued DIL packaged IC to a small printed circuit board that has the DIL equivalent pins.  See the picture below.

 

I hope this helps explain my post.

 

Cheers,

Alan R.

 

   

Thanks for the detailed explanation.  Brown dogs appear to be an interesting concept, I'm surprised I haven't heard of it before (but I think I've seen one before!). 

[Leinster Lad]

Wow, blast from the past

Back in the day I built both the pre and power versions of these kits. ( plus the playmaster 200 with a custom made stupidly massive power supply bolted underneath.)

 

Seem to remember that the phono boards were housed in metal boxes for shielding ?

And yes, and all of those shielded cables !!!

 

One thing that I remember from the pre-amp VU meters was that I could never get them to read identically.

Also, the display was "blurry" due to the light from the lit LED bleeding into the adjacent LED's.

Painting the edges of the LED's black should cure this.

 

Currently resurrecting the ETI 5000 power amp and would really welcome any of your "upgrade" tips   @MarcAL 

 

You have inspired me to resurrect the pre-amp and your upgrade notes will come in handy. Thanks for the trip down memory lane !

 

 

Edited October 19, 2018 by Leinster Lad

[Leinster Lad]

On 26/07/2018 at 2:40 PM, Monkeyboi said:

Okay, the electrolytics for the signal paths have arrived with the replacement potentiometers.

Cheers,

Alan R.

 

 

Hi Alan, where did you source your caps and pots from ?

regards

Dave

[Monkeyboi]

9 hours ago, Leinster Lad said:

Hi Alan, where did you source your caps and pots from ?

regards

Dave

Hi Dave,

 

Sourced the components from Mouser.  Couldn't find a source of the Elna Silmic II electrolytics in Australia, so was forced to import them.

After a lot of testing measurements, the Monitor Output stage appears to have a bit of bass roll off into a lower impedance load (600 ohms) due to the series 47uF capacitors.  Works perfectly into higher impedances, but my ME-850 Hi-Cap power amp has a lowish input impedance compared to may other amplifiers.  So I am modifying the circuitry around the Monitor Output stage to utilise the d.c. offset capability of the NE5534AN op amps so the 47uF output coupling capacitors can be bypassed.

 

Actually there is a bit more to it.  Installed some header pins to give me the option of a.c. coupling via 470uF capacitors (up from the original 47uF), or d.c. coupling.  Also dropped the value of the output series resistors to 12 ohms.  To accommodate the modifications, some components are mounted on the underside of the main pcb.

 

I will post some pics and more details of the modifications plus the test results when I have finally finished.  The preamp is currently in bits on the workbench at the moment.  Implementing a 15 second delay to the external 12v trigger output using a simple 555 timer IC.

 

Cheers,

Alan R.

[Monkeyboi]

10 hours ago, Leinster Lad said:

Wow, blast from the past

Back in the day I built both the pre and power versions of these kits. ( plus the playmaster 200 with a custom made stupidly massive power supply bolted underneath.)

 

Seem to remember that the phono boards were housed in metal boxes for shielding ?

And yes, and all of those shielded cables !!!

 

One thing that I remember from the pre-amp VU meters was that I could never get them to read identically.

Also, the display was "blurry" due to the light from the lit LED bleeding into the adjacent LED's.

Painting the edges of the LED's black should cure this.

 

Currently resurrecting the ETI 5000 power amp and would really welcome any of your "upgrade" tips   @MarcAL 

 

You have inspired me to resurrect the pre-amp and your upgrade notes will come in handy. Thanks for the trip down memory lane !

 

 

Hi Dave,

 

Actually you are correct about the light bleed from adjacent LEDs.  I didn't think about painting the side edges black.  Seems like a good idea worth trying. 

 

The LEDs that came in this kit didn't have equal brightness.  The red ones were a lot lower in intensity compared to the rest which were pretty even.  Solved the problem by replacing the red ones with newer ones, but alas they were the opposite.  Way too bright, however that was an easy fix by adding series resistors using SMDs to the track side of the boards.

 

Yes, getting the meters to accurately track is an issue.  Each board requires a sequence of adjustments to VR2 and VR3, then a final sensitivity adjustment with VR1.  And of course due to the case design, the boards are upside down and stacked just to make it difficult. 

You may have found some level discrepancy due to the poor tracking of the Master Level potentiometer.  When I finished this second kit I found the level tracking between the left and right channels not very good from the 25% to the 75% rotation positions.  At the extremes the level matching was reasonably good.  I overcame this problem initially by shunting the wiper of the louder channel to the ground or common with a high value resistor and this improved the tracking between the channels.  Since swapping out the pot for the ALPS it hasn't been a problem.

 

As for the metal boxes over the phono stages.  Mine doesn't use them.  Found they didn't make a difference to the noise level at all.  As you can see from the pics in my original post.  My modification also adds an extra pcb with switches to alter the cartridge loading for MM1 and MM2 inputs.  One of my cartridges prefers 150pF of shunt capacitance whilst the other works best with 450pF.

 

Yes, all those bloody coax cables.  It's a nightmare.  After making my first 5000 series pre-amp I decided with this one to use connectors to most of the boards.  It's turned out to be a good decision considering the modifications that have been done since this second kit was put together. 

 

Cheers,

Alan R.

 

[Leinster Lad]

Excellent response  @Monkeyboi with some very interesting detail !

I like your cart loading boards, a very neat idea!

 

Looks like this little project will become bigger than ben-hur once I get started

If parts need sourcing from OS, at least that will give me time to finish off the series 5000 pwr amp project !

I had a quick look at mouser for caps and was quickly overwhelmed

Even the Dinkle (TM) connectors are confusing

If there is any way that you could share (pm me? if you prefer) your "shopping list" (part numbers), I would be eternally grateful   and at least I would know that I would be getting the right components, as you clearly have much greater knowledge and experience than I do.

 

After reading your idea of removing the 47uF output coupling capacitors, a look at the circuit shows that there are many other electro coupling caps that could be replaced with MKP Wima caps ?

Do you think this would be practical, or would fresh electro's be good enough ?

 

" d.c. offset capability of the NE5534AN "  i'd like to know more about this please.

 

As for the VU meters, they are such a mesmerising feature that I feel that they are well worth persisting with to get perfect.

Adjusting and calibrating would be easier if the trim-pots were replaced with 10 or 25 turn cermets, and then set up on the bench.

Just getting all the LED's aligned perfectly is a challenge, but I have an idea for that

And sorting out the light bleed, i think, will make them look even better !

 

[Monkeyboi]

No problem @Leinster Lad  I will resurrect my Mouser order which has all the part numbers.  I only replaced the electrolytics in the signal coupling paths with the Elna Silmic II caps.  The power supply decoupling won't benefit from any "audiophile" grade capacitors, so I left them as standard electrolytics.  IMHO, don't waste your money on Wima MKTs.  The off the shelf MKTs from Altronics will be just as good in this design if you really wanted to ditch the greencaps.  I used the polyester "greencaps" supplied in the kit. 

 

The only other parts you might consider adding are some 100nF monolithic ceramic capacitors to decouple the power supply rails close to the ICs.  I chose these as the are low profile and where required due to space constrains can be mounted on the underside of the Main board as close to the IC's power supply pins as possible.  As you are aware the gap between the Main board and the base of the case is very small.  I suggest placing a layer of rigid plastic sheeting between the case base panel and the stand-offs.  Thus is what I did with version 2 of the 5000 preamp.

 

The other parts for the cartridge loading boards and decoupling monolithic ceramics can be locally sourced.  I used parts from Altronics which are an Australian based company with many retail outlets and a mail order facility.

 

The Dinkle (TM) connectors and sockets are standard components available from Altronics.

 

Cheers,

Alan R.

 

 

 

Edited October 20, 2018 by Monkeyboi
added info

[Monkeyboi]

14 hours ago, Leinster Lad said:

Excellent response  @Monkeyboi with some very interesting detail !

I like your cart loading boards, a very neat idea!

 

If there is any way that you could share (pm me? if you prefer) your "shopping list" (part numbers), I would be eternally grateful   and at least I would know that I would be getting the right components, as you clearly have much greater knowledge and experience than I do.

@Leinster Lad 

Please see attached pdf with the details of the electrolytic capacitor upgrade to the Elna SILMIC II types.  Complete details on how to modify all three boards are included along with the Mouser part numbers.  Please verify the part descriptions before ordering.  I might have made a typo error or two when authoring the document.

 

I will publish the other modifications once I have fully tested them for performance enhancement and reliability.

 

Cheers,

Alan R.

 

ETI 5000 Series Control Preamplifier Modifications - Part 1.pdf

Edited October 20, 2018 by Monkeyboi
wrong version of pdf

[Leinster Lad]

Thanks heaps Alan. A lot of detail there that will make this restoration a lot easier !

Kudos to you Sir  You have certainly gone above and beyond.

 

I'll keep everyone in the loop as to how this project ( and the 5ooo power amp ) comes along.

 

[Leinster Lad]

Funny what one stumbles on while searching the inter-webs.

 

http://mirror.thelifeofkenneth.com/sites/www.americanradiohistory.com/Archive-Electronics-Today/Australia/80s/

 

Helpful indeed !

[MarcAL]

 

1 hour ago, Leinster Lad said:

Funny what one stumbles on while searching the inter-webs.

 

http://mirror.thelifeofkenneth.com/sites/www.americanradiohistory.com/Archive-Electronics-Today/Australia/80s/

 

Helpful indeed !

Wow, thanks for that link, it's an excellent find.

[dan_tech]

Note that Dr Tilbrook, who’s a member of the DIY Audio forum, mentioned there that he later realised he’d compromised the sound quality of the ETI-5000 preamp slightly by putting the muting transistors (Q5-Q12) across the outputs. He recommended snipping them all off, when he was responding to some discussion about a Doug Self preamp (a huge thread!), where someone mentioned the ETI-5000. He said the only reason he’d used the muting transistors was because he’d designed it with very flexible switching aimed at taping, it was possible to select the same tape deck as both input and output, which isn’t good, so he’d made that impossible through the muting.

 

Incidentally, on the HFE website linked to above, they did the phono stage signal to noise ratio specs a disservice, by not mentioning they were unweighted figures. Also, the signal to noise ratio of 71dB they quoted for the MC input was with an input voltage of 200µV, rather than the more normal 500µV. With a 500µV input, the phono preamps article showed the MC preamp improved to 79dB unweighted (83dB A-weighted), so it was exceptionally quiet, thanks to those LM394’s and 5534A’s. The weighted figure for the MM inputs was 92dB for 5mV input, which is also excellent, and compares favourably to the best current phono preamps (the MC stage beats many of those).

 

Its best features were the phono stages, input switching and LED level meters, which made it superb for taping (probably illegal in those days!), and the worst feature was that front panel, which is really hard to read clearly unless you look closely under good light, although I have seen pictures of ones which came from at least one kit supplier which used easier to read white on black lettering.

 

I must agree that all those shielded cables made it hard to build – I was young and had good soldering and wiring skills (I worked for a certain large telecom company…) when I built mine in the early-80’s, but it took me about a week to build, after I’d finished the ETI-5000 power amp in a Saturday afternoon! I was congratulating myself too soon after finishing the power amp. By contrast, the SC Studio Series preamp from 2005/6, which I built last decade, was a doddle to build, as they’d made it much easier to put together.

 

Regards,

Don

Edited November 3, 2018 by dan_tech
Spaced paragraphs

[Monkeyboi]

On ‎3‎/‎11‎/‎2018 at 2:53 PM, dan_tech said:

Note that Dr Tilbrook, who’s a member of the DIY Audio forum, mentioned there that he later realised he’d compromised the sound quality of the ETI-5000 preamp slightly by putting the muting transistors (Q5-Q12) across the outputs. He recommended snipping them all off, when he was responding to some discussion about a Doug Self preamp (a huge thread!), where someone mentioned the ETI-5000. He said the only reason he’d used the muting transistors was because he’d designed it with very flexible switching aimed at taping, it was possible to select the same tape deck as both input and output, which isn’t good, so he’d made that impossible through the muting.

The circuit could be modified to have the muting transistors drive miniature relays to perform the muting function.  Personally I would not recommend removing the mute function from the output that the user intends to connect a power amplifier to.  On power up the mute circuit clamps the output so that there is no switch on thump through the speakers which might cause damage to them in the long term.  This is especially important with d.c. coupled power amplifiers.  If anything the mute release delay IMHO should be extended a few more seconds than the original design called for.

On ‎3‎/‎11‎/‎2018 at 2:53 PM, dan_tech said:

 

Incidentally, on the HFE website linked to above, they did the phono stage signal to noise ratio specs a disservice, by not mentioning they were unweighted figures. Also, the signal to noise ratio of 71dB they quoted for the MC input was with an input voltage of 200µV, rather than the more normal 500µV. With a 500µV input, the phono preamps article showed the MC preamp improved to 79dB unweighted (83dB A-weighted), so it was exceptionally quiet, thanks to those LM394’s and 5534A’s. The weighted figure for the MM inputs was 92dB for 5mV input, which is also excellent, and compares favourably to the best current phono preamps (the MC stage beats many of those).

The original ETI article did state the performance parameters for both the MC and MM stages in isolation to the rest of the pre-amp.  See my attached extract from the original article which quotes both unweighted (flat) and A weighted noise measurements and under what conditions.  There are some minor typo inconsistencies between the voltage gains and those that appear on the block diagram for the pre-amp, but nothing significant.  For example the spec in the attached table indicates the gain (unspecified) for the MM stage at 1kHz is 74, whereas the block diagram for this stage in the whole pre-am implies it is 75 and the quoted gain of the MC stage of 24 calculates to be closer to 22 going by the figures on the block diagram.  

Agreed that these s/n ratio figures compare quite favourably with current commercial offering.

 

You may note in my second build some 30 odd years later I made a few modifications.  One is the absence of the metal shielding over the MC and MM electronics as well as the addition of user selectable cartridge loading for the two MM inputs.  I found the shielding boxes did not reduce the level of noise or hum when the boards are housed in steel case.

On ‎3‎/‎11‎/‎2018 at 2:53 PM, dan_tech said:

 

Its best features were the phono stages, input switching and LED level meters, which made it superb for taping (probably illegal in those days!), and the worst feature was that front panel, which is really hard to read clearly unless you look closely under good light, although I have seen pictures of ones which came from at least one kit supplier which used easier to read white on black lettering.

I agree 100%  I have seen both green and orange print versions of this pre-amp and yes it is difficult to read the panel lettering, especially under subdued lighting conditions.  As for the LED level meters, well IMHO they are more bling than necessity.  

On ‎3‎/‎11‎/‎2018 at 2:53 PM, dan_tech said:

 

I must agree that all those shielded cables made it hard to build – I was young and had good soldering and wiring skills (I worked for a certain large telecom company…) when I built mine in the early-80’s, but it took me about a week to build, after I’d finished the ETI-5000 power amp in a Saturday afternoon! I was congratulating myself too soon after finishing the power amp. By contrast, the SC Studio Series preamp from 2005/6, which I built last decade, was a doddle to build, as they’d made it much easier to put together.

 

Regards,

Don

You may have noticed that on my second build I made extensive use of connectors to interconnect the various boards and to the sockets on the rear panel.  I recall that assembling the first version all those yeas back was literally a PITA exercise.  I could only imagine it as a serving nightmare, hence my completely different approach to built V2.  Considering I've done numerous modifications to this second pre-amp the use of connectors on the main board has been a blessing.  I can now remove and reinstall the boards in a matter of minutes not hours. 

 

Cheers,

Alan R.

[Leinster Lad]

Alan, what are RV5 and RV6 ? ( and  ADLK1 and ADLK2 )

How are they connected ?