[ACMP investiupgradifications] All things PREAMP

[rodabod]

This gets marginally interesting again:

http://homerecording.com/bbs/showthread.php?t=180964&page=196

That forum has a pretty bad s/n ratio though. In fact, it's awful. I think it's fairly obvious what's going on though (despite the number of people who seem to think otherwise).

 

[clintrubber]

[quote author="rodabod"]This gets marginally interesting again:

http://homerecording.com/bbs/showthread.php?t=180964&page=196

That forum has a pretty bad s/n ratio though. In fact, it's awful. I think it's fairly obvious what's going on though (despite the number of people who seem to think otherwise).[/quote]
Thanks for monitoring.
Looks like a few people over there decided to fill the time until the gear arrives with filling page after page over there with endless non-conversations...

I wouldn't mind if AH posted all he knew - let's be informed.

 

[Jim50hertz]

[quote author="rodabod"]This gets marginally interesting again:

http://homerecording.com/bbs/showthread.php?t=180964&page=196

That forum has a pretty bad s/n ratio though. [/quote]

Roddy, Aye.

[quote author="clintrubber"][I wouldn't mind if AH posted all he knew - let's be informed.[/quote]

Clintrubber, I'm with you on that, let's have it...

 

[tommypiper]

Well, it seems AH feels he designed the whole thing. And he's not saying it directly, but seems he's 1) slighty pissed off that 797 is selling it now and, 2) peeved that Chance was either misled by 797 or purposely misled buyers into believing it was his (Chance's tech's) design, or both.

We've seen the schem. If we get the same thing that's in the schem, then it's mostly going to be a matter of component quality, not design quality. AH has made noises in this direction several times by mentioning inductor resonance problems, that the iron is Chinese-made, and other general comments.

I expected this. When I saw the open hood photo, I could see it was more or less a N**ve, and probably closer rather than farther from the real thing. And I posted that several times in the Black Market thread. And I predicted there would be other questions like layout, details, components, etc could potentially be trouble. We'll see. If it's a good foundation with not too much to replace or change I'll be more than pleased.

 

[clintrubber]

[quote author="clintrubber"]I wouldn't mind if AH posted all he knew - let's be informed.[/quote]
BTW, let me add to that that with this I don't mean to join either 'side'- if there's a matter of choosing sides anyway, which I don't think so or at least don't want to get into, just appreciating the efforts of Chance et al. - whatever confusion has popped up or was made to exist.

[quote author="tommypiper"]Well, it seems AH feels he designed the whole thing.[/quote]The obvious 'how about RN then?' could be added here, but I could imagine he (AH) has at least spent considerable effort on preparing it for the present way of implementing etc.


Anyone perhaps spotted schematics yet of the two other types ? ('*1, '*4)


Cheers everyone,

Peter

 

[okgb]

i'm surprized that no one has mentioned the obvious , and not to flame
this cause bottom line no one expects that this is not a chinese preamp .
But if there was a prototype who wouldn't have taken pics? other than
what looks like a b&w pic of a brochere ?
Not sure if AH justs wants someone to say he is right or why he persists
or why the two haven't talked . neither seem 100% open but sticking to
the story , other than technical i won't post more of this cause that would
be helping someone else

If he cared , he could cough up the schematics , Al that would be nice
thank you .
He does offer one possibility that the inductors may need to be changed ,
hope they used a common value

 

[W DeMarco]

Wow, Thats some thread of BS. Glad that, for some reason, group DIY is so calm! Im so excited to get my 81 that I can hardly contain myself, let not to mention my ribbon. And unless Rupert designed it I really don't care who did or didnt. Good work on the GB Chance. I hope all the bullshit floatin around over at that other forum doesnt affect you permanently.

Onto the TRANX. Anyone found some good iron to swap yet?

 

[reg presley]

[quote author="rodabod"]This gets marginally interesting again:

http://homerecording.com/bbs/showthread.php?t=180964&page=196

That forum has a pretty bad s/n ratio though. In fact, it's awful. I think it's fairly obvious what's going on though (despite the number of people who seem to think otherwise).[/quote]

!!!!!ouch!!!!! makes for a painful read.

 

[tommypiper]

Yes, really unpleasant over there. I'm not following the politics or care much who is right or wrong. Just waiting to work with the box when it arrives.

 

[CHANCE]

I was just checking out "Tamura" xfrmrs ( http://www.eifl.co.jp/index/export/tamurat/tamura.htm ) that Scott Dorsey has used in the C-3000 mic. While I was there I was also checking out their 6072 tubes. 5000 for one! I hope that is yen. When I was there in the 70's it was 360 Y = $1.00. Anyone know todays echg rate?

 

[rodabod]

Chance, the class-a output will require a "gapped" output transformer. Not sure if any of those Tamuras are.

Either way, there's nothing to say that the stock transformers won't be any good.

 

[CHANCE]

for all interested heres the owners manual. We left in the part from China for laughs (Close your eyes etc)

http://www.compasspointstudios.com/TNC%20ACMP%20Manual.pdf

 

[clintrubber]

Let's proceed here in this thread:

[quote author="aortizjr"]Here are some ACMP-81 gut shots:

http://homerecording.com/bbs/showpost.php?p=3023296&postcount=5808[/quote]

Note that below I've copied a few tech-posts from the Black Market to keep the tech-discussion complete (since the inner-'81-pics above).

Bye,

Peter

 

[clintrubber]

[quote author="ChuckD"]Maybe some others can put there 2 cents in after me on these photos. Especially those ,like me, would built the 1081 circuit already.

I can say that yes this is a 1081! At least a cheaper version of a very very simular circuit. Here are the main differences just after glancing at the photos

1. using discrete ... well newer 5532 type opamps in the EQ section
2. input and output transfomers are China made.
3. different inductors like the transformers above.
4. big change to the output as it looks like the Class A output of the 1073. Much like Vintech does in there clone.

If you changed "all" of the above to actual 1081 specs especially the output to a class A/B B340 opamp. Then you would have something really close I think! <= my opinion...

The input transformers would have to be relocated but everything else could essentially "drop in"

Damn I should have gotten one. Oh well I have some nice mics coming instead to take apart.


-Chuck[/quote]

 

[clintrubber]

[quote author="wmtunate"][quote author="ChuckD"]
1. using discrete ... well newer 5532 type opamps in the EQ section [/quote]

Based on the schematic that was posted here a few months back of the 73 (I think it was), the ICs are only used to drive the LEDs, and aren't part of the audio path. That's probably the case in the 81 as well.[/quote]

 

[clintrubber]

[quote author="wmtunate"][quote author="ChuckD"]
1. using discrete ... well newer 5532 type opamps in the EQ section [/quote]

Based on the schematic that was posted here a few months back of the 73 (I think it was), the ICs are only used to drive the LEDs, and aren't part of the audio path. That's probably the case in the 81 as well.[/quote]

 

[clintrubber]

[quote author="ChuckD"]I see now the opamps of the EQ section are fixed on the board like the 1073 opamp stages are done. Then no unless you can bypass these and replace with the correct B338's for each then it will never be quite the same.


-Chuck[/quote]

 

[clintrubber]

[quote author="clintrubber"]Still a lot of discrete transistors on those pics though, at least 4 on each 'coil-PCB'... don't have the info here, how many of these should a real '81 have ?

But nice I'd say, a sweaty class-A gapped-TX outputstage for the China'81, we like that, right ? :thumb:[/quote]

 

[clintrubber]

[quote author="clintrubber"][quote author="aortizjr"]Here are some ACMP-81 gut shots:

http://homerecording.com/bbs/showpost.php?p=3023296&postcount=5808[/quote]

Thanks for spotting that they're there :thumb:
And if you're reading this, thanks drBill ! :thumb: :thumb:



But now this: see the four letter word there on the left ROHS.....

http://img.photobucket.com/albums/v248/drBills/Group Buy Gear/148-4829_IMG.jpg

Do we need to take that into account for eventual mods ?
Simply ignore ?

Bye,

Peter[/quote]

 

[clintrubber]

[quote author="ChuckD"]The 1081 uses a simple RLC "tank" circuit scheme for it's EQ. Switching between the caps and the resitors of the tank. The B338 at the top of the vertical strip making the tank give you the boost for that selected filter.

A good comparison to start would be simply to count the caps for each tank. The opamps are different then the B338. How that effects tone well ... opamps are strange that way.

-Chuck[/quote]