Turtlerock Forum

Hey that's pretty sweet! So update us on how it sounds...
M

Excuse my ignorance, but what exactly is a line amp for? If a signal is at "line level", why does it need to be amplified? (apart from by a poweramp to drive speakers?)

Kurt wrote:Excuse my ignorance, but what exactly is a line amp for? If a signal is at "line level", why does it need to be amplified? (apart from by a poweramp to drive speakers?)

I've wondered the same thing.

Hey Angus, do you have a schematic for the circuit of the A55. I have had a bit of a search in google and cant find it.

Rob, if you are there, what do you use to screen print on the front panels?

like many "univeral amps" from the early broadcast era these were designed for a max of around 50dB of gain. Some of the similar RCAs ran at 70+dB. They could thus be used as line amps, makeup amps or mic preamps. The required gain was set by the use of pads. Whilst this is not the best way to achieve optimal signal to noise ratios, for AM radio broadcast it was fine. These Trimaxs had the adjustable pad network after the input transformer and before the fixed tube amp stage. Reincarnated in these units the gain control has been brought to the front panel ( originally it was set with screwdriver ajusts on the rear of the unit ) and an output attenuator added for fine gain trim and taking advantage of the max +32dBu output level that these units can give.

I have the schematic...can't recall where it came from! These units had all been modified .. badly and were restored to the original bar one change that made sense. The power supply requirements were demanding using a -24V and +130V supplies plus +48V for the phantom and DI module.
They also have an unusual tube set of 2 x 6AU6 and 2 x 6AM6

The artwork is laser engraved to the black anodised panel

Top job there, seems almost a total rebuild. Looks like it's totally busted in the before pics. Is there anything Rob casn't fix. :)

Ahhh just waiting for my pair of telefunken pre's Rob racked last week for me, I really like the laser etching too, real pro. Very keen to give them a test run.

anguswoodhead wrote:Looks cool Heathen.
My next project with Rob is a 4 Ch Neve Mic Pre using vintage BA183 Amp cards and new Carnhill trannies. :D

Nice!

Looks like Gian and I will never know the mystical purpose of the line-amp.
At least if we don't know what it's for we won't need to spend money on buying/building/fixing them!

Kurt wrote:Looks like Gian and I will never know the mystical purpose of the line-amp.

Like the continuum transfunctioner, they are very mysterious and powerful devices whose mystery is exceeded only by their power........

umm... I thought i explained the "line amp" concept pretty well

lets try again: like many "univeral amps" from the early broadcast era these were designed for a max of around 50dB of gain. Some of the similar RCAs ran at 70+dB. They could thus be used as line amps, makeup amps or mic preamps. The required gain was set by the use of pads. Whilst this is not the best way to achieve optimal signal to noise ratios, for AM radio broadcast it was fine

consider that we are dealing here with an example of one of these "universal amps" ( my term ) and can equate to the "line amp" concept ( your term )

Haha, sorry Rob, missed your post!

So it's basically a generic pre, without phantom power, which can be added by clever people like you.

thanks Angus...not sure about the packing items bit...I've had a couple of units damaged in transit

although i'm learing all the ways that couriers find to trash a carton and where the weak links are!

hey Rob,

What are the turns ratio on the input and output transformer in this unit? and/or what would work well?

thanks

dunno...lifes too short to puzzle this sort of stuff out...I just concentrated on making them work as designed.

As regards the transformers, I can't remember off hand but its written on the tx's so Angus could have a look or if its important I can look when I get the others I have...
Myles

mylesgm wrote:As regards the transformers, I can't remember off hand but its written on the tx's so Angus could have a look or if its important I can look when I get the others I have...
Myles

Hi Myles

The reason I asked, was that I was considering building one of these units. But since the tube complement is a bit different, I have since decided against it. But I do appreciate you offering to look.

Thanks

My Byer 66 has a Trimax tranny.. I just had a quick look.. ;-)

Trimax transformers are excellent and if anyone wants one or two I've got quite a few...

M

Rob, you do some really nice work! I'm a young tech that only dreams of getting to your level. Inspiring. Good stuff! It's like art!

How's my babies going Rob??

tunetown wrote:How's my babies going Rob??

Heh, I smell a barbie and gear test day coming on.

I would like to propose something but not sure of the general consensus.

I've been engineering for the past 20 odd years, however, one of the things that annoys me is my lack of electronics theory/pracitcal. Our craft used to involve a whole lot more than what it does these days (lab coats being one) including the ability to maintain/build/tweak our tools that we use in the studio. In days of old studios created their own sound by what the engineer's and tech's of the studio were building or in need of (like Abbey Road etc...). This individual approach to sonics and the necessity for a studio tool that does something that nothing else on the market can do intrigues me more and more as I learn and develop my craft.

Rob, have you ever considered running some audio electronics workshops or are you currently?

I'm not interested in TAFE courses or gaining any certificates etc.. it wouldn't be directly dealing with the field I'm most interested in (audio electronics) and ofcourse time is an issue as well. But a couple of weekend workshops would set me straight with some simple projects and give me an idea if I'm patient enough for it.

Mostly I want to DIY with confidence and pickup some of the principals of building and modding military grade audio units whether pre's, comps or something that makes an individually tailored sound I'm after (like a cranking distortion/comp box with heaps of attitude), you get the picture.

Anyway, what do people think?

Rob, any suggestions to these types of workshops?


cheers

Ben...interesting thought...maybe I could become the next Tom Misner...with a chain of audio electronics schools scattered across the globe!

the idea of disseminating technical information, is in part, the reason I write the On The Bench articles for Audio Technology mag. Indeed in the next issue, due out any day soon i'd expect I talk about DIY audio electronics.

The area of electronics is vast and even in the realm of pro audio electronics there are lot of pidgeon holes that people park themselves as suits their abilities and interests. I know of great design engineers who couldn't fault find a dolphin torch. I know repair techs who have an amazing knack of finding and fixing the most complex faults but have no interest in designing anything. There are guys who know everything to know about tube amps, but very little about logic circuits.

It is probably reasonable to say that i've found a bit of a niche with what I do and happily it gives me a chance to refurbish some wonderfully designed and constructed equipment, drill holes and cut big slots in chunks of metal, layout front panels, and design and build new devices. But to bottle this and teach it...whew. I do what I do as result of having started out when I was about 10 years old and having never stopped. For the last 40 years and continuing today i spend a good slab of my day learning new things. For me this is the key...each day, find out something I didn't know before the day started.

there are heaps of resources out there...magazines, books, forums, web sites...just make a start and don't stop

Fair call Rob. And nicely said.

I train Certificate II and III in Music technical production from my studio and some days it's the most rewarding thing I can do, but others I just want to kill them. Passing on technical info is not the easiest thing to do especially in a few weekend workshops or a magazine article.
Ultimately I want to spend the next phase learning more about what's in the box and how it's best put together than simply using the parameter controls on the outside. I love it when I fix something that wasn't working and I don't mind getting the soldering iron out so I guess those are a good guide that I will enjoy the process.

Looks like it's back to Prodigy Pro. :-)

Hey Angus,

I also got a couple of these racked by Rob. Tracked with them earlier in the week - similar experiences with needing to peg the gain up esp. with dynamic mics / softer sources.

So far have used them on a male hip hop vocal, acoustic guitar and bass (DI).

My impression is that these are a nice, clear pre - much less affected than other tube gear I've used. Not a 'character' piece (a good thing) but still 'nicens up' what I've put into it.

Despite flat measurements I have found myself reaching to pull out 2-3dB of 150-250Hz-ish on everything I've used them on so far - but this could well be a function of the room I was tracking in (treated by not ideal).

Noise is present but no worse than my Langevin AM16s or the other bits and pieces of older gear I have in my rack.

Bought a pair of these off Myles (thanks again) on the basis that it's always better to have a pair of something than a single channel and looking forward to trying these on drum overhead duties.

Rob's patience and commitment to getting these racked was really admirable as this wasn't an easy job - thanks again.

You could always run a pre-pre-amp. Didn't Rode release a mic booster jobbie a while ago?

and that mic booster was crap! Tested it out in store thinking that it would be excellent for ribbon mics and it was no good there. Then I thought lets try it out dynamics cause thats what it was designed for, failed again. Was always hissy, and though it boosted the gain the noise floor was terrible. The mixers mic inputs were better by far...

Glad to hear that the trimax's are out and about and working again. I love old aussie gear! For those interested I think I have a couple still left.

Myles

Well that sucks!

mylesgm wrote:and that mic booster was crap! Tested it out in store thinking that it would be excellent for ribbon mics and it was no good there. Then I thought lets try it out dynamics cause thats what it was designed for, failed again. Was always hissy, and though it boosted the gain the noise floor was terrible. The mixers mic inputs were better by far...

Glad to hear that the trimax's are out and about and working again. I love old aussie gear! For those interested I think I have a couple still left.

Myles

Got a chance to test out the Telefunken V676b's on a classical guitar today, they sound bloody excellent, quite clean but they have a very nice smooth vibe to them. Great in the bottom end and mids,almost too much bottom end which I like, with the filter set to 50hz it was perfect though.

Tracked it straight in with no eq (well except 50hz filter) or comp and was very impressed.

anguswoodhead wrote:Update - I have been using the Trimax and I love it.
Especially on Acc Gtr and Acc Piano.
Thumbs up Rob - you da man !!!

Is the 55 model similar to the 63?
40dB gain.. etc
Sound quality..