Ask a designer

[Simon Hickie]

IIRC Amstrad amps were promoted quite heavily by the HiFi press at the budget end of the market (I wonder why?). A Sansui AU-101 cost little more than an Amstrad IC 2000 amp but was much better in all respects. Unfortunately I had the latter...

[Dr Bunsen Honeydew]

Amstrad amps were nothing to do with Sinclair. In those days I had two fav amps - the Sansui AU101, and if you wanted more power especially with Goodmans Magnums then Rotel RA610.

[Simon Hickie]

I lusted after the Rotel RA610 when I was a student. I have no idea why I never bought one when I started work.

[Ithilstone]

ok another one:
Why AP20 plays louder (using cubettes and same source) than AP70 SA??
I know that the is expected loss with SA but shouldn't 50W still beat 25W ?

[Dr Bunsen Honeydew]

It doesn't !!!

You are confusing volume with position on volume control. The volume comes in earlier on the pot we use than the stepped attenuator. If you turn the amps up to the point they are clipping (into loudness) the AP70 will have more volume (SPL). Position on control is meaningless.

[_D_S_J_R_]

Best was the project 60 amp kits, got a lot of people learning to use soldering irons, main problem was the mess they made of them and then brought them back and dumped on the counter and expect you to sort it out for them.

I seem to remember the Z60 amp boards were based on the 1950's RCA PA amp design that Naim was also inspired by. The Sinclair had an output inductor though...

[Ithilstone]

Well I understand that position on control is meaningless, what I did is to set up a little experiment - my methods might be flawed thats why I seek answers or correction to my methods.
I have a DAC that has 2 outputs ( and no volume control) I connected one output to AP20 with one cubett ( on right channel ) and the other to AP70SA with another cubett on left channel
I played some music and matched the perceived volume - sitting around 1m away from speakers (as you said position on control is meaningless but just for reference ap20 was somewhere around 25% and ap70 around 40-45%)
then I simultaneously start to rise the volume on both - RC started to sound funny (clipping I believe - around 75%) but LC went all way to the end without any clipping and still didnt match volume of RC.

I didnt want to keep music at that levels for more than 5 sec ( I dont know what could go first, amps or speakers and I dont want to damage either )
I switched outputs on DAC (just in case that one is different to another) but with the same results .

Now I know it is not really scientific but I am puzzled why would that be the case.

and no I have no intention to listen to music anywhere near that volume levels I was just curious and it was easy to set up that test.

[Dr Bunsen Honeydew]

It is not the case. Quite simply it is impossible for the AP20 to be more powerful than an AP70 you are being confused somewhere. If you wish to return the amp for refund you can with pleasure, if you wish the SA to be converted back to pot you can with pleasure.

[Ithilstone]

No I don't wish to return it or have SA downgraded and I am not saying that something is wrong with any of the amps!!!

I am really happy with both and AP70 drives my HE-6s better ( for lack of other description - sound is fuller as well as bass is punchier - BTW full review / compression
will be posted but AP70 needs looong burning time if only for stepped attenuator)

AP 20 is relatively louder through HP socked but it has standard volume pot and you stressed it many times SA behave different
plus there probably is different resistor fitted but nor me nor you remember the value ;]]] It could probably benefit from
fitting one of a higher value so opposite to what you have done for me with AP70 (BTW HP on AP70 works perfect now as
comfortable listing volumes are now in region from 10 to 1 o'clock )

I set up a silly test with speakers just out of curiosity and with some unexpected outcome - now I am trying to understand what is happening here.

Something somewhere seems to be wrong - if it is with my way of testing or my understanding how it should all work.

As I said I am just puzzled - As I understand both amps should get into loudness (clipping) and AP20 is happy to do so
and AP70 is not, from the same source - and the only difference is interconnect one being some old Ecosse (AP20) the other
ones are some good looking but cheap ones don't remember the name (AP70) - could that be possible explanation - it would be hard to believe
that interconnects have such an impact? - but I have been wrong in the past

Unfortunately without rearranging both amps I cannot swap them the as Ecosse are too short.

[Lindsayt]

Ithilstone, if both amps go cleanly louder than you'd want for any listening session lasting more than 5 seconds, then both have planty power enough for your needs.
Keep whichever sounds best at your normal listening volumes. If you have no preference, the cheaper one wins. The max volume differences you've been getting? Who knows? Just one of those things. Not worth worrying about if both amps sound fine at your normal volumes.