ARC pre amp-modded with Kimber caps-anybody used these caps before?

[fdegrove]

Croft,

One day a guy bought one of glens amps back to him for upgrade,this was flung into a bin over the otherside of the room and glen said that his desighns did not need any alteration??

Quite a character indeed.
But let me tell you:I know a thing or two about valves but Glenn just knows everything you can imagine.

Anyway I need to go,see you.

 

[croft]

Wow,thats great Frank.I will deffinately e-mail you if you dont mind with regard to the mega micro,it does look like we have the same unit(amazing).
What i was thinking was to try and get a better top box for the unit as the colour and shape is a bit like London on a rainy day(drab)
I will never forget the first time i hooked this unit up,the sound was REAL in every sense of the word,many jaws dropped that day,my unit does get hot but at this time of year its a great way to keep warm.The case i want to get is an audio reserach one,which are very good but the manufacturers dont like selling these items,everythin else but not the case
I have many ideas for the mods,does the tape input and tuner use the valve cuicuitry Frank?
Phono is sublime on my oracle delphi/souther linear tracking arm,wack the volume up and it just gets bettersolid state can only dream off
Like mike at the hi fi shop said to me "if it dont glow-it dont go"

 

[croft]

Cheers frank

Thanks for all the imfo frank,
Will try and talk to you again,
Mega

 

[fdegrove]

QQ

Croft,

I have many ideas for the mods,does the tape input and tuner use the valve cuicuitry Frank?

Well mine is phono only but I'm pretty sure Glenn routes the inputs to a selector switch, than to the volume control,than to the grid of the 12BH7A White cathode follower.

Cheers,

 

[Fred Dieckmann]

Electrolytics as coupling caps?

Never heard any Black Gates I take it........

I can hardly wait till I know everything and can fling amps about in fits of rage. I'm so dumb that I am still trying to learn things after 20 years of building audio circuits. But then, I am just a demigod.

pri·ma donna Pronunciation Key (prm, prm)
n.
1.The leading woman soloist in an opera company.
2.A temperamental, conceited person.

I guess the updates aren't over till the fat lady REALLY sings on my equipment!

Encore...... Encore,
Fred

 

[croft]

Thanks Frank.

Thanks for the greta imfo frank,i will have a look inside the mega micro that i have, Maybe a cd player could be put into the phono socket input with a tweaked interconnect.

Just had some great review books from the states,(stereophile)and in one theire is a review of the audio reserach sp9,the guy absolutely hated the unit and coulndnt live with the sound,interesting reply from the arc factory aswell.The conrad jhonson was freferd.Will probably get rid of my sp9 and look for---CONVERT AUDIO TECH SL-1,ARC SP11,NAGRA PLP.

Still want to get the croft unit modded,hard wiring is so far in front of pcb in terms of air around the instruments,pcb,s,suck.

Thanks Frank.

 

[fdegrove]

CROFT

Croft,


Err,please don't hook up any cd to your phono stage.
Phono uses the RIAA equalisation curve to work and you will overload that stage to boot.
In short it will sound badly distorted.

If you need gain on top of the output of the cd-player a dedicated preamp is in order.
I wouldn't spend a penny on these fancy names you mention.
I'ld rather talk to Glenn (or Amar),see if he can solve your problem.

Still want to get the croft unit modded,hard wiring is so far in front of pcb in terms of air around the instruments,pcb,s,suck.

I can only agree. But I would only change some components on the megamicro for higher grade ones.
Thing is Glenn is right,it is pointless to alter his designs.

Cheers,

 

[Peter Daniel]

And don't mod it too much if you want to get rid of it, waste of time and possible difficulties when potential buyer opens the cover.

 

[croft]

Thank you Frank

Cheers frank for the imfo,i will deffinately keep the player out of the phono.I usualyy use the tape inputs for cd,hope this is ok?

Have been thinking of which parts to upgrade on the mega micro, The caps look like there from RS components,the volume pots are big and clumsy and i was told that they were from a quad pre-amp.Have saw some very nice alps pots at £400+,also danish stepped ct-1.Also am not to shure if the caps in the power supply box would benefit from an upgrade.

Have noticed Crofts new pre-amp,electrostatic membrane desighn.Thsi looks awsome and in nice case aswell

Would love to know what Glen thinks of the other manufacturers products(arc,mark levinson,counterpoint).

Long live the valve.

 

[fdegrove]

modding

Peter,

Quite right Peter.
Always a good idea to make mods reversible,just in case you want to sell the thing later on.

See you.

 

[fdegrove]

CROFT

Hi there,

Cheers frank for the imfo,i will deffinately keep the player out of the phono.I usualyy use the tape inputs for cd,hope this is ok?

Must be ok and the CF will nicely isolate the tuner,tape,cd from the ouside world and it can swing 120V PP in case you worry about that.
In laymans terms,it can drive even the most unreal stuff.

The caps look like there from RS components,the volume pots are big and clumsy and i was told that they were from a quad pre-amp

On mine the caps were Roedestein MKP1841,most resistors were Roederstein Resistas and the volumepot was from ALPS.

I wouldn't touch the PSU,it's pretty much beefed up as is.
About 100 x that of any other preamp you can find:regulated (valves) B+ for every single tube,left and right channel separately,
500mF storage perchannel and so on,four dedicated transformers,dual moni to extreme....
Why would anyone change that?

Would love to know what Glen thinks of the other manufacturers products(arc,mark levinson,counterpoint).

Don't tempt the man.

Cheers,

 

[croft]

Hi Frank,caps away

Thanks frank,Will deffinately start with the caps,sounds like your unit was modded before?Mine looks like its still in its original state the sound is very remarkable but having heard more expensive caps i think that the rs ones are letting it down I tried jeff waynes "the war of the worlds soundtrack"on remasterd sony cd and this was so incredibble i had to go in the garden and get some fresh air,when the alien lid fell off on the common i "felt"instead of "heard"the weight of the metal being moved.Sometimes i wonder if this is possibly one of the best pre-amps ever built.In todays money it must cost a fortune to construct

An unknown legend
Thanks for the imfo on the psu,like you say Frank everything is pretty well taken care of,good point

 

[fdegrove]

CROFT

Hi,

Maybe mine is not his run off the mill stuff but I got it directly from Glenn so no previous modding there.

Back in the early nineties I changed the coupling caps for MIT polysterene and foil,the pots for selfmade 1M rotaries,cathode resistors for Holco (I regretted that) and all series resistors with Vishay S102 bulk foils(at 20 UKL a pop),I used leadfree silver solder and replaced all wiring with silver wire.
I perfected the RIAA correction to get 0.08 dB tolerance,upped the cathode decoupling caps (WIMA polyester standard) with some extra MKPs to gve me 10Hz extra bandwith in the bass (you need a well isolated TT for that) and that is about it.

In all honnesty it was about a 10% improvement,just to give you some idea about how good it was standard.

We have a thread on volumecontrols:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=6847

The addictive part about this design is IMO dynamics,awesome!
CDs sound compressed in comparison.

Regards,

 

[croft]

Many Thanks Frank

Brilliant imfo Frank,100%usefull.Not to many have shed me any light on this pre-amp since i owned it 5 years ago.

Have printed off all of the mods that you mentioned and was thinking of taking the unit to croft who are now based in IRONBRIDGE.All of the main caps in the output look cheap and nasty so i think any upgrade should take it a step closer to its full potentiol

Was thinking of making the cable lenghts shorter within the top box and less bunched up and taking out the tape facility.
Have you any idea what the valve comliment is on this pre Frank,reason being the valves in my unit do not have very readible text on them and i am curios to which valves to order

The volume control sounds fassinating,will deffinately give this some reading,
I have just took some pics of the pre and will try and scan them inn
Many Thanks,

 

[fdegrove]

CROFT

Hi,

All of the main caps in the output look cheap and nasty so i think any upgrade should

Maybe I was lucky with the Roederstein caps which I still regard as a fine coupling cap.

Have you any idea what the valve comliment is on this pre Frank,reason being the valves in my unit do not have very readible text on them and i am curios to which valves to order

I do,in the regulator you will find per stage a EL86,85A2 and ECC807(the ECC807 is a typical Brimar valve,dual triode with no equivalents,if you can find any and want to spend the money buy them although they should not need replacement.Glenn claims they would last a lifetime,I concur.)
Phonostage 1 x ECC83 per channel (Telefunken's are his favourites,same goes for me,another make that sounds fine is the E83CC from TESLA)
Finally the 12BH7A,I don't think you will hear much difference there,it's a CF)

Hope this helps,