Rarely Seen WAD, Andy Groves Designed, IC Phonostage

[JohnG]

I have stripped all the Caps of the Blutak casings they had from the time of having this Phonostage Built.
A olden tweak for novice tinkerers. Ws there a improvement in performance, I,m sure the jury has debated this one many times.
The images show the rarely seen internals of this model.
After running it side by side a Clones Audio PA1, in the Blutak applied state, it was shown as having a few shortcomings, but still a nice on the ears listen, when directly fed into the 845 Monoblock. A little more air between the performers and it would be a more desirable performance, the bass control has always got the party going.
I feel confident I can tweak this. I intend on placing it in a New Real Estate and using a much heavier material.
If any one sees a way to improve on this circuitry and extract a performance that is seen as improved, I,m all ears.
I can put a few more images on a new thread, if requested.


Image-1a.jpg

Image-2a.jpg

[Richard]

Very interesting thanks for posting John. Are the chips AD797 and Ad 743? If so it looks like the phono amp covered in 2 supplement articles in 1993 and 1994 and available on Matthew's Platinum CD sales@world-designs.co.uk . They give a complete write-up and include circuit and parts. A kit with pcb was available but I've never seen or heard one.

There were many chip phonos in use at that time and notes for manufacturers in data sheets such as 5532 etc. Having used a phono with the later low frequency roll off and found it sounding bass light, something I would look at is the stated -1dB 40Hz of this unit. (This would be a subjective thing, reverting to the earlier standard or making it switchable, as I'm sure Andy's design would be difficult to improve otherwise.)

[JohnG]

Hi Richard, I was just trying to work out how long I have had a friendship with my Valve Electronics Engineer who has built all my projects, it looks like we go back to 1993/4 and are still working together today on the 845 Monoblocks.
I am happy to put this in the post and let you have a listening experience, it has been away from home in the past, so another excursion will not harm.
I loaned it to another forums Phonostage Bakeoff at the 2017, Scalford Show, I went off doing the show thing. When I picked it up, I was told it done a good job and was very usable.
If you want a listen let me know.

[Richard]

Hi John, Thanks for the kind offer. How's your phono built, for MC or MM?

Reading the article there are adjustments you can make. It can be set for MC or MM by changing IC1, R1, R3, and the low frequency roll off can be adjusted by changing C1.

I have a high output MC which expects MM gain and a 47K load but think this phono was usually built for a MC.

[JohnG]

Hi Richard
I have just rooted through all my old Supplements, I,m a hoarder,
I found this model in the December 93 and April 94.
Yes it is a MC Design, and this is at present of interest to me, as I have recently purchased a Hana SL MC.
My set up is for MM, so a few component exchanges are required.
I have recently seen at a Phonostage Bake off, resistor connectors that were inserted into the female RCA sockets, that are used to change the cartridge loading, I was not to inquisitive at the time, is this something I could try when the set up is for MC, I feel the investigation is worth while as I have very good experiences with this model.
So hearing it as a MC Stage has got my attention.
I also like the idea of using it with my Phillips GP 390 Ceramic, so it may find a few different components being used periodically.

[Richard]

Hi John,

Yes the April 94 issue details the items to change for MC or MM. A quick check to confirm the setting of yours at the moment would be to see which op-amps are fitted. For the Hana you would want MC setting, for that particular Philips Ceramic it looks like it should work into MM setting.

The resistors you mention fitted into the RCAs at the bake off would be to fine tune loading for the particular cartridge used rather than MC/MM gain or low frequency roll off.

[JohnG]

I am using the Phonostage at present, doing a evaluation, with it in its new Blutak Free State.
I will compare it to the Clones Audio PA1 and see if it has got any more separation and air between the players, compared to the Blutak applied experience.
When this is done, I will have a little fun with the GP390, and a
Dynavector DV 20 H, after this, I will then I will set it up as a MC Stage.
I will compare it with the Clones on each occasion.
Could it be made switchable between MM/MC ?
I will put the 100 ohm R1 and then the RCA Loading plugs can be used to decrease the ohms and get a idea of the effects of different loading.
If all goes well I will be using it on a different Turntable/arm combination, so a further insight to the performance will be available.
When it is in the MC Setting, the offer to have a loan is still available thumbsup:

[Richard]

That sounds a plan and it will be interesting to hear how it goes.
Two things,
Making it switchable MC/MM; you could indeed make R1 switchable 100R/47k, R3 switchable 56k/5k6 (and C1 switchable 100uF/470uF for bass roll-off) but the noise would be worse unless you changed the op-amp to the optimum one for each setting as per the article. If yours are in sockets this would not be difficult though.
Secondly, it confused me a bit when you mentioned the bake-off RCA resistors, as changing the input loading is usually something done for a MC set up rather than MM, hence me asking which op-amps are in now

[John Caswell]

Got one of these, and very good it is too.
The way it was designed AG changed the ICs around MM to MC so it may not be easily possible to make it dual standard, but by all means have a look and see.

John

[bikerhifinut]

Just a mad barmy thought.
Would a pair of MC step up transformers be acceptable to you?
That would certainly allow you the option of switchable mm/mc inputs.

Andy.