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In Reply to: RE: Ordered this by mistake posted by jedrider on June 07, 2018 at 12:47:47
it now looks like this.
Oops. Now the hard part which is getting it into a chassis.
Anyone have suggestions on how to punch holes in lightweight aluminum for the RCA's in the rear, let me know. I can drill out the front for the volume and selector controls.
Is it worth it, I don't know, but it cost less than $7500.
It passes a square wave rather well. It drives a JBL portable loudspeaker well, too. I haven't soldered the final connections in, so it is hard to tell how it really compares with better gear.
Follow Ups:
A 7500$ preamp based on Analog Devices op-amps?
I did hook it up for a real audition. Even included input switching.Well, sounded a little direct when first powered up (the amplifier, too, needed warm-up) so, maybe, this is the solid state I want to avoid ran through my head.
Compared to the pre-amplifier section in the Classe CAP-100, it blows away the CAP on detail and bass extension. The Classe design is based upon the OP-27 op amp and is pleasant but a little veiled. An Emotiva theater processor that I have is not even as pleasant and is somewhat electronic sounding (no doubt based upon op-amps, too).
This miniscule pre-amplifier with undersized transformer just out jumped it's competition handily in multiple areas. It deserves a chassis, so I"m working on that now.
Edits: 06/17/18
It's interesting for me to see a very high end preamplifier - in my eyes the most difficult to design / to select in a system, and wich has a huge impact on the sound- to be based on opamps.
while I've seen many mid-fi / entry-level high end preamps based on the technology, I always assumed the ultra high end to be the sole realm of discrete and / or tubes.
Now I understand it's the implementation that matters, but still.
i do love the MBL brand for their baroque aesthetics and wouldn't mind owning something from their catalog one day :)
I had a look over the eBay variants of 6010D clone designs and almost wish I had ordered already assembled (and I think it is a wise choice actually). I usually will tweak the power supply eventually and using a larger case than is usually supplied is advantagious for tweaking. I use to build Heathkits in my youth, and a little soldering comes naturally to me.So, getting back on topic, there are some variants available that are balanced with input buffering (why does it need input buffering I don't know, but having buffering for the tape outs seemed like a good idea to me, so, does anyone know about this??)
The IC count is already 12 for some of these and I would not be surprised if the original MBL had at least 20 circuits. Maybe they had dual power supplies. The control circuitry must have been very sophisticated. The casework is out of this world and, maybe, over the top ;-)
So, price-wise, not too surprising.
Many older designs were discrete and I can hazard a guess that they didn't have available such modern opamp designs that can actually be quite good, I suspect. Burson audio sells opamp replacements that have some discrete components added to an opamp, I would guess, that help in input and output drive, etc, and they sell for $40-$80 a piece.
So, I think we should get over the discrete design aspect and the better designs may be using an opamp at the heart of the circuit.
I owned a Parasound Preamplifier, the P2000, that was just chock full of components! John Curl said his design can be easily compromised by poor choice of individual components, but for the life of me, I cannot imagine so many components sounding so bad. I think the initial compromise was having some balanced circuitry, which if you don't need it, completely compromises the design choices.
To me, balanced equals an unnecessary expense. When I can afford $7500.00 components, then that would be the way to go!
Edits: 06/20/18 06/20/18
For RCAs I use "stepped" drill bits. I've achieved clean holes up to 3/4" in steel and aluminum with these. Common sizes are: 1/8" to 1/2" in 1/32" steps and 1/4" to 3/4" in 1/16" steps. Use of lubricant (cutting oil) is recommended for steel.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
n/t
My guess is for voltage or current? If you don't get a answer here, check at DIY Audio. My guess is there are members there who have built the kit and know the details.
10mm hole punch.
"Without followers, evil cannot spread." Spock
and be easier to use, I think. May require a lot of hand strenght though.
This kit came with ZERO instructions. I don't have a schematic. If I knew what I am suppose to adjust for, maybe, that will help ;-)
Measure the voltage with the output grounded with a 100K resistor and set the pot so the output reads close to zero as you can. If the pot does not affect DC offset, it could be an output trim or a bias setting. Doubtful on the bias as 8 Pin Dual Op Amps rarely require this.
I'll put a 100K on the output, but there are two stages for each channel and I assume that I measure from the output pin on each op-amp. OK, now, let's see how steady my hands are.
Thanks.
Hi jedrider, what type of power supply are you using for the DIY project?
You can see the PS caps and two regulators on the board. It's all there.
I have a tiny toroidal, +-9 VAC
and a bigger toroidal, +-13 VAC
I'm not sure if the 9 VAC is sufficient though to put the PS into regulation mode or not. Maybe somebody could chime in on this?
Even the 13 VAC toroidal is insufficent for most +-15 VAC projects, but they sell for much less on eBay. My experience with them, it that they work out just great.
I'm using the little one until I can put the unit in a box. If I mistakenly short something, I want the 0.5 ampere transformer in place and not the 1 amp transformer.
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