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Eico HF-85...YUCK...

cooljjay

cooljjay

Super Member
Banned
Ok I really don't like my hf-85 preamp, it has a great phono input and good sound. But the volume pot is driving me insane, every time I turn on my system the balance is messed up. If I am in phono mood and turn it down I lose a channel...I am sick of spending more time adjusting the controls then using the preamp. Now I feel everyones frustration on these preamps, at first I was well I don't believe what they say etc...now I want to throw it out the window. I like it because it matches my eico hf-85's but I think I am going to replace it with a lafeyette KT-600 when ever I can find the assemble manual so I can restore it. Just wanted to let the fellow eico hf-85 owners know I feel your pain...:tears: Maybe one day a suitable replacement can be found.
 
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No pain here. I have grown accustomed to the infamous gain pot. Yes, it's crazy hot. It's also hard to keep both channels balanced. I would suggest an SPL meter and once you've found that perfect balance, strictly use the larger dial.

My tube tech recently rescued and refurb'd a Dynaco pas3. He does excellent work and is infact a mod at the Yahoo EICO group. After filling it with NOS Tele's, he still couldn't believe the sonic inferiority as compared to the HF85.

I have had mine fully refurb'd including TOTL caps, sockets, RCA's, etc. I also have a hot rodded RIAA circuit which is deadly accurate. Combined with any high end tube, the result is deadly. Clean and quiet, detailed, and technically astute. Sonically, it adds dimensionality to the players and surrounding spaces that is unrivaled.

I can't imagine a better way to voice my system. I was on a fence for sometime. It was between my Bozak 919 (horrid state) and the HF85. The Bozak is just so clean sounding, with a wonderfully accurate low gain. Since making the last couple of upgrades to the EICO, including a full set of Psvane tubes, it's soared past the Bozak and without a doubt, is the better pre.

Hang in there man, it's worth it. Like I said, it's possible to dial in the pot. Unfortunately, those pots are barely in existance. My tech has refurb'd countless HF85's and the gain pot is it's Achilles' Heel.
 
Frankly guys, I don't know the specific info. My tech looks after me in this regard. I'm sure some of the guys here will comment. If not I can email him and find out.
 
hmmm, I dont see why you cant just replace it with a similarly spec'ed ALPS pot or something similar
especially if its causing issues like you have noted here...
 
mackinthebox said:
hmmm, I dont see why you cant just replace it with a similarly spec'ed ALPS pot or something similar
especially if its causing issues like you have noted here...
Click to expand...

What I have heard is that the pots shaft is the problem, the pot can be replaced but finding one with the same shaft is the difficult part. Here is a photo of the bass/volume/treble pots that I pulled from a parts unit that I sold, gives you an ides of the length. Don't give me beef about parting one out, it was modified to death, to the point you couldn't figure out what was done to it, plus it was missing the bottom/cage :D

2s60sg3.jpg
 
are those just stacked pots that turn at the same time or do you pull on the knob to change which one youre adjusting?
my local electronics parts store has some that look very similar...
 
mackinthebox said:
are those just stacked pots that turn at the same time or do you pull on the knob to change which one youre adjusting?
my local electronics parts store has some that look very similar...
Click to expand...

They're stacked, and adjust independently. Once set, they can move together by turning the larger, outside dial.
 
You can replace them with a standard dual gang pot. You won't be able to adjust each channel separately but the new control will track better anyway. I'm replacing these on my HF81. It really doesn't seem necessary to have separate control over the tone in each channel, at least for me.

I will be sourcing some shaft couplings to extend normal length shafts.
 
so im assuming this means being able to adjust tone (bass/treble) for each channel by pulling the nob out to adjust one channel and using the large nob to adjust both?
youre right, it doesnt seem necessary
anytime I adjust tone, which happens less frequently now, it gets adjusted evenly for both channels
 
mackinthebox said:
so im assuming this means being able to adjust tone (bass/treble) for each channel by pulling the nob out to adjust one channel and using the large nob to adjust both?
youre right, it doesnt seem necessary
anytime I adjust tone, which happens less frequently now, it gets adjusted evenly for both channels
Click to expand...

Here's a pic. I will direct my tech to this thread and get his wisdom on it.



attachment.php
 
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mackinthebox said:
are those just stacked pots that turn at the same time or do you pull on the knob to change which one youre adjusting?
my local electronics parts store has some that look very similar...
Click to expand...

mackinthebox said:
so im assuming this means being able to adjust tone (bass/treble) for each channel by pulling the nob out to adjust one channel and using the large nob to adjust both?
youre right, it doesnt seem necessary
anytime I adjust tone, which happens less frequently now, it gets adjusted evenly for both channels
Click to expand...

No, they're dual concentrics with a very odd shaft length. The lower knob adjusts one channel and the upper adjusts the other. Unless you hold one in place while turning the other, friction will cause both shafts to move together.

My HF-85 is missing the volume pot, I still haven't figured out exactly how I'm going to fix it. I'll probably have to end up dismantling several different pots I have to build one that's close to the right length and value.

Don't be too sad about Jason parting out an HF-85. The faceplate is going on mine. :D

poppachubby said:
I have had mine fully refurb'd including TOTL caps, sockets, RCA's, etc. I also have a hot rodded RIAA circuit which is deadly accurate. Combined with any high end tube, the result is deadly. Clean and quiet, detailed, and technically astute. Sonically, it adds dimensionality to the players and surrounding spaces that is unrivaled.
Click to expand...

Do you have any details on the RIAA circuit mods?
 
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I remember that style of pots being used on virtually all car stereos back in the day. I would love to find something similar (and the necessary knobs) for new builds as I much prefer the dual concentric volume control to the volume control and separate balance control. Kind of odd for tone controls but not an entirely silly idea either as most graphic EQs also allow different curve for each channel which could be useful if you had different room interactions for each channel (likely).

mike
 
The volume control on the HF81 is just a dual pot with one knob, not a dual concentric, so I will be fine with that one. On the tone controls I will probably glue the two knobs together so they resemble the selector knobs.


Actually, since I removed the focus control, I may just use dual mono volume controls to get some balance adjustment. Not really an option on the 85 I think.
 
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The "loudness fix" will improve the range of the lower half of the volume control - below the loudness tap. I forget the details, but it's simple enough...
 
Sam Cogley said:
Do you have any details on the RIAA circuit mods?
Click to expand...

Sam it was inspired by the Lipschitz curve. We couldn't do Lipschitz EXACTLY perfect on the HF85 because the voltage values were too low.

Overview- The signal goes (backward) from the output (plate) of the second RIAA tube to the cathode of the first RIAA tube, both of them are 12AX7s. Here's the formula and instructions, step by step:
1. A 1.21m ohm resistor and a 2,640 pf cap, which are in parallel, are soldered to the second RIAA tube plate. This output signal is, in turn, soldered, in series, with;
2. A 100k ohm resistor and 750pf cap, which are also in parallel;
3. The output of this is finally soldered to the cathode of the first RIAA tube.

So, in effect, you have two separate resistor/capacitor "couples", with the signal going first through one of them, then the other (in series), finally ending at the cathode of the first tube, and becoming the RIAA equalization feedback.
 
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