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Old 6th April 2004, 03:48 AM   #1
DC Dave is offline DC Dave  United States
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Default Preamp Opinions Wanted

I just purchased an old Hafler DH-101 preamp on Ebay with the intent on upgrading it. I know there have been many upgrades documented on the this preamp over the years.

My Question is weither to upgrade the existing 1978 components or to stripping them out and building a preamp in the existing chassis based on one like Rod Elliott's project 88.

Project 88 Preamplifier

What I am after is sound quality with best-bang-for-the-buck. Chances are I will not use a turntable as a source. But I want to put in a N.O. DAC and/or USB DAC in the chassis removing the existing power supply to a separate chassis.

For sources I will have a tuner, two CD players, PC, MP3 player.

What do you guys think is my best option? Upgrade a 25 year old design with better components or redesign with new technology (BB OPA2134 opamps)?

Also if anybody has a copy of the DH-101 articles that have appeared in the 1978 and 1980 years of Audio Amateur I would love to see a copy. Email Me.

I also need to know if there is somewhere to purchase RCA jumpers that go between the PreAmp's EQ In and Out RCAs. Or if that is something that can be made with a piece of wire, what size wire should I use?

Thanks for everyones input,
Dave
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Old 6th April 2004, 06:32 AM   #2
Werner is offline Werner  Europe
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Project 88 doesn't seem to be very inspiring to me.

If the Hafler has a bipolar power supply, i.e. + and - 18V or so,
then I'd suggest the classic Jung AD744/LM6181 combo
as linestage, and perhaps Thorsten Loesch's El Cheapo
2SK170 + OPA627 as phonostage. Both are well-documented on the net, I think. I am working on a similar phonostage with 2SK369 folded-cascode input, and may (or may not) publish the circuit in the coming months, pending success.

Spend some effort on power supply design. The cheapest acceptable solution seems to be LM317/337 preregulation, and TL431 shunt regs for opamp circuits, or simple followers for transistor circuits.
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Old 6th April 2004, 07:22 AM   #3
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I'd vote for modifying the existing circuit. Discrete transistors allows for many more optimization/modification possibilities than using a pre-packaged circuit in an IC. Kind of like making a cake from scratch instead of pre-mixed from a Betty Crocker box. More fun and better sounding.
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Old 6th April 2004, 10:41 AM   #4
AKSA is offline AKSA  Australia
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An IC amp will give you magnificent measured performance, particularly some of the later ones.

However, it's very difficult to incorporate capacitors into ICs, and often there are areas within an amp circuit where capacitors, judiciously used, will improve the perceived, audible performance. Examples are lag compensation and phase lead, low pass filters, and heavy decoupling of various stages.

Therefore a discrete design has a lot going for it if you are trying for the best possible sound.

Aside from that, Rod's design looks good, and appears well sorted. Difficult to know chapter and verse, however, until you build it.

Cheers,

Hugh
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