"Out-Hacker" a Hacker GP42?

[saxmaniac]

Originally Posted by Edward Huggins

A good ceramic cartridge e.g. Acos GP96 or a Sonotone 9TA/HC tracking at the correct weight c.3.0 grams is not going to cause any more damage than a MM! There is a limit to how light that Garrard tone arm can track anyway.

Can you get a sonotone new that is any good? I bought one a few years ago but it was so bad as to be useless. Horrible distortion on high frequencies and dynamics, I presume due topoor cocompliance. I've got an AT91 with 2.5 grammes and a preamp which work great though as I say there's no discernable difference in audio quality

[ukvrshaun]

Originally Posted by cmjones01

Yes, start here. The loudspeaker and its cabinet will make by far the biggest difference to the sound of the record player. After that, improvements to the cartridge, arm, suspension and deck will be next. It's the places where electricity meets mechanics that have the largest impact.

Any changes to the amplifier will be relatively hard to hear, unless what's already there is grossly inadequate or is faulty. Push-pull ECL86s are already as hi-fi as you're likely to want, as long as the output transformer is big and well-designed enough.

Using boutique resistors and capacitors will make no measurable or audible difference, again unless the originals were faulty. The big wins are not in the electronics!

Thanks Chris for your clear advice. I'll consider it all carefully.

Originally Posted by Radio tirana

Not much wrong with the amplifier from a GP42 IMHO if anything it's the loudspeaker that lets it down slightly. I have added small tweeters to my own Hacker Cavalier and AL15 amplifier fixed between the speaker and the front grill to extend the frequency response. I have also been down the magnetic cartridge and solid state preamplifier route but was not happy with the result, the rumble from the motor and rim drive were reproduced too faithfully and the extra gain increased the mains hum to an unpleasant level. I experimented with different ceramic cartridges and on balance I think the BSR SC12M gives the best performance.
I much prefer the models fitted with a SP25 to the 2025/3000 series decks.

I put a SC12M on my Hacker too after doing some forum research. I'm pleased with the result. Interesting empirical evidence regarding an actual MM conversion. This was exactly my concern, although another poster did similar and hasn't had the same issue.

Shaun

[ukvrshaun]

Originally Posted by saxmaniac

Can you get a sonotone new that is any good?

I think we're talking about used/NOS only here. Same for the SC12M. I have my SC12M tracking at 4g, which I believe is the minimum recommended.

[Herald1360]

Originally Posted by ukvrshaun

I put a SC12M on my Hacker too after doing some forum research. I'm pleased with the result. Interesting empirical evidence regarding an actual MM conversion. This was exactly my concern, although another poster did similar and hasn't had the same issue.

Provided that the preamp itself is hum free and care is taken that its output level is similar to the original cartridge then the rumble problem could be addressed by suitable high pass filtering. Certainly an SP25 should be good enough for a budget MM cartridge to be happy.

[ukvrshaun]

I did recently skim read low and high pass filtering in pre-amp design for eliminating record scratch and rumble, but hadn't quite put 2 and 2 together. Now I understand the possibilities. Thanks for your help.

[Edward Huggins]

I would not have thought the effort to fit a rumble filter on this would be worthwhile. Whilst the unit does deliver a good, strong bass - it is essentially a "high bass" c. 70Hz and that's above the normal rumble frquency. After all, Hacker knew what they were doing when they designed this.

[ukvrshaun]

Here is my first design effort




I've concentrated mostly on the speaker and cabinet following some great advice that was given earlier. I'm going try a full-range speaker, Fostex FF125WK, in a Planet-10 Hi-Fi dFonken inspired front-ported enclosure (that is isolated from the player's amplification and turntable portions). I hope this will 'solve' the 'missing' GP42 higher frequencies, while still offering adequate (small room) bass. The speaker is 4.5" and is easy to drive and this should suit my choice of valve amplification. The speaker and cabinet interior will be damped with wool felt as required.

I'm going to build a Mullard 5-10 and Pre-amp (to Mullard spec, minus the additional inputs). This was always my plan. These will be housed at the back of the cabinet, with quite a lot of ventilation provision.

The turntable portion is sized for something like a Dual CS 701. (I used the CS 701 cut-out plan to accurately size the space. The grey volume is the requirement). I'm going to pair with a MM cartridge. I've got further options to improve isolation for the turntable, if required.

I 'borrowed' a few design cues from the GP42 - lid, tone control location, feet. I worked on this design without reference to any other record player, but I wonder if it resembles any player that was actually made?

Shaun

[ukvrshaun]

A couple more pictures showing the speaker cabinet detail and valve amplification placement.



I'm pretty sure my computer art skills will surpass my 'out-hackering' ability, but I'll give it a try anyway...

Shaun

[saxmaniac]

Where will you source transfomers for the amplifier? I take it that these will be critical to the sound quality

[Herald1360]

Sowter will do you a new one for a price. For not a lot less there's online auctions for secondhand period ones. Possibly cheapest would be something from an unloved monster radio like my Siemens M57 which only cost me £10 and includes the power supply TX and output valves too. No, it's not going to suffer that fate, at any rate from me.....

[ukvrshaun]

VVT have a suitable UL 20-43 tapped output transformer at reasonable cost. I was going to order one of those first. I'm not sure why Sowter are asking 3x the price for similar?

I'm less worried about the mains transformer, there are a few more available sources.

[whyperion]

I've got a walloping surface mount Vortexion transformer (I think) sitting in the gas cupboard at the moment, looking for a good home...!
What my father did (using chipboard) was to recycle the Radiogram Amp into my guitar amp, and built twin side bass chambers rather than just the one I think I see in your box.
Would controls be better mounted at the front - just so they can be seen ?
Are you including the rather useful Hacker external input/output jacks and connections for (A) additional stereo amp - I know you said it is essentially a mono project, (B) Radio/Tape/Mic input/s and Tape Output ?

[ukvrshaun]

Thanks for the kind offer whyperion, but I've now ordered my transformers. In fact I've got most of the build components sorted and on their way to me.

An update on my design. I've turned the speaker cabinet on its axis, making better use of a larger dFonken cabinet design in 18mm ply, and a larger full-range driver. This has also allowed a more 'classic' 60s record player shape in about the same volume as before. It has just a little more volume than a GP42. I've now shamelessly borrowed most of the styling cues from the Hacker too! I'm probably not going to bother adding additional inputs and outputs I won't use.

I think I've done my research (definitely learnt a lot), gathered together some fine ingredients and I'm looking forward to 'baking a cake'. This is an ambitious project for me and I go into the build phase having some trepidation about the possible result!

Shaun

[Edward Huggins]

From your dimensions, it looks as if the full range driver you plan to use will be 6.5" in diameter?

[ukvrshaun]

Hi Edward

I've actually chosen a 5.5" driver (Mark Audio Alpair 10P), although the same cabinet volume would house the 6.5" driver (Alpair 12 earlier generation), with slightly different porting.

This is the 'mini-Onken' speaker cabinet I'm incorporating into the record player chassis:
http://p10hifi.net/FAL/downloads/CGR...lan-040414.pdf

I thought this was my one-off best chance at getting some reasonable bass (to match the Hacker) in a smallish cabinet with a full range driver (which should better the Goodmans 10x6). Using a 'tuned' driver/cabinet pairing has clearly more chance of working than me randomly matching a 'nice' driver and an arbitrary cabinet volume.

Along with my Mullard design amp & pre and a donor Dual CS 704 with a Shure V15-III, I think all my components are 'up to snuff', but of course the combined component synergy will define the result. I will only find that out by putting it all in the (robust) plywood box...


Shaun

[mhennessy]

I've just looked up the details of that driver.

Having just gotten over the price(!), I then stumbled across a frequency response chart. Wow

You could do so much better with a conventional woofer and tweeter for half that price. What you have there is a "boutique" drive unit aimed at the full-range hi-fi fraternity - and the price reflects that.

As a random alternative, take a look at this one: http://uk.rs-online.com/web/p/speaker-drivers/3643307/

Though personally, I'd go larger (and add a tweeter). Plenty of room in that enclosure. The loudspeaker+enclosure will dominate the sound quality, next comes the cartridge. The turntable and amplifier (assuming competent design) makes much less difference than people like to think - unless you plan to run the amplifier into clipping.

So my design efforts would be focused on the speaker system first and foremost, and would include a crude MDF mockup of that part of the enclosure to test with a range of drive units and porting arrangements. During that phase of development, a standard hi-fi amplifier and CD player would be used. Only once I'd go the best possible sound from that phase would I begin to think about the rest of it.

The advantage of that approach is that you've "partitioned" the tasks and can work in isolation on each. And if you run out of steam early on, you might still be left with a decent speaker design that could later be turned into something else. Or, you haven't wasted a fortune (and a whole load of time) trying to build the entire cabinet.

Say you get further than that - perhaps with the cabinet built and the deck mounted - you could chuck in a cheap solid-state "chip-amp" kit to get it up and running, and maybe build a valve amplifier at a later date when funds and enthusiasm allow.

Remember - when it comes to audio, price is no indicator of quality

[ukvrshaun]

mhennessy,
Thanks for your comprehensive reply. This is why I'm posting. Although I'm doing 'extensive' research, I'm obviously coloured by what I 'stumble across' and read.

Originally Posted by mhennessy

You could do so much better with a conventional woofer and tweeter for half that price....

Could you explain the "so much better" above (in broad terms, but not considering cost)

The loudspeaker+enclosure will dominate the sound quality, next comes the cartridge. The turntable and amplifier (assuming competent design) makes much less difference than people like to think - unless you plan to run the amplifier into clipping.

Yes, I had that same advice earlier and it has become my mantra...

So my design efforts would be focused on the speaker system first and foremost, and would include a crude MDF mockup of that part of the enclosure to test with a range of drive units and porting arrangements.

Effectively, I've tried to 'sub-contract' that out to somebody who knows more than I do, to shorten the project delivery!

The advantage of that approach is that you've "partitioned" the tasks and can work in isolation on each. And if you run out of steam early on, you might still be left with a decent speaker design that could later be turned into something else. Or, you haven't wasted a fortune (and a whole load of time) trying to build the entire cabinet.

Yes, I believe that has been my philosophy since early on. The pre+amp are discrete (and I have a separate goal to build one anyway). The speaker cabinet design is discrete. The turntable is discrete. All should be separately 're-usable' if this doesn't pan out.

Thanks again for your reply!

Shaun

[mhennessy]

There are compromises with any approach, but in my experience, even the good full-range drivers are just not good enough for hi-fi. Some of the really expensive full-range systems are just bizarre - perhaps as a result of trading quality for efficiency for the benefit of the SET brigade. The cheap ones can be surprisingly good for the price. But not hi-fi. You might as well stick to the unit used by Hacker originally...

The only downside of a multiway system is having to design the crossover. This can be daunting, but it's not impossible. There's no shortage of advice out there - no point repeating it all here.

Another avenue might be to consider a co-axial system. The KEF Uni-Q system is good, and you might be able to buy the bare driver complete with a crossover (though I didn't locate a supplier in a 2 minute search - perhaps they're no longer available to the DIY market).

Alternatively, I'd be tempted to pick up a s/h KEF Q15 or similar for parts. You could measure the internal volume and make sure yours is the same. Transfer the driver and crossover into your cabinet. You'd probably have to make your own port and tune it to length - that could be an offcut of plastic waste pipe. Total cost? A few 10s of pounds if you buy wisely.

Of course, that approach would work with any s/h hi-fi speaker that you like the sound of. As I say, just match the box volume and copy the port tuning if applicable. If you can make the height of the front of the player equal to the width of the original baffle, then so much the better.

Perhaps that sounds like cheating, but unless learning how to design loudspeakers is the goal, that approach will get the project moving with a strong chance of success.

To get into the theory - even in broad terms - would take far too long, and I'd probably end up writing a whole bunch of stuff you already know. Instead, feel free to ask specific questions.

Good luck,

Mark

[Edward Huggins]

I can't quite work out if all this is about building a good sounding record player or a compact mono Hi Fi.
The big issue not yet addressed is cabinet resonance and internal waves.
As posted earlier, I would recommend a good quality 6.5" long throw driver unit coupled with a 3" dome tweeter - cost c. £25.00. This would take care of the prescribed 10 watt power handling requirement, give a well extended bass and a sweet, well dispersed, treble. Any 5.5" full range driver is unlikely to match that.

[ukvrshaun]

Thanks Mark

The KEF Uni-Q system does look interesting and seems to major on 'addressing' the cross-over mid-range area, similar to the full-range objective. Certainly an option I could consider.

I should perhaps admit that I have heard a couple of reasonable full-range speakers in smallish Onken type cabinets before and I liked the concept and results. My listening is mostly voice, classical (but not 1812 end), blues, jazz. My Hacker has also been used for playing some 60s rock/pop! I tend to play at reasonable volumes only. I've just played House of the Rising Sun 'loud' and measured it. It was 85 dB...

Good sound is a v. subjective term. I own acoustic gramophones including an HMV 163. Definitely not hi-fi (well it actually was back in 1928), but a really engaging and rewarding listen. The Hacker isn't hi-fi either, but it makes me keep putting records on it, more so than the 'good digital stuff' in another room...

A donor KEF Q bookshelf could be a good call, though, for this particular project and my particular listening tastes. Thanks!

It's certainly not cheating. I'm a hobbyist 'constructor' not an audio designer (or even a vintage hi-fi enthusiast, if it relies on electricity - EMG anyone?). I try hard to achieve my goals/aims and I inevitably learn a lot of things along the way.

Regards
Shaun