Author Topic: Comparing late Mk1 ('79 silver) and Mk2 ('80 black) haigler (slider) preamps.  (Read 1771 times)

Offline goldphinga

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So just been servicing a late (1979) mk1 and I have a 1980 mk2. Both have the haigler preamps in. Intriguingly, on the same piano when swapping the rails, the sound is very different. The late mk1 pre has considerably more gain, warmer/fuller midrange and general depth, whilst the mk2 has less overall gain and sounds much more scooped in the mids.

Now- i did have my mk2 preamp modded but just the switch and the vibrato intensity pot were changed to stop the trem bleeding into the audio path, i don't see how this would have such a radical bearing on the sonics if at all?

You can see that the mk2 pre has some different components ( the mk2 is the one with the orange caps in and the mk1 has blue)

Thoughts?

https://photos.google.com/album/AF1QipNl4FQgJudQKjy8K1-UdDvbaLAUdCRsGgBQLAQb

Offline vanceinatlance

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Your picture link says no access granted when I click it. Without seeing them it's hard to say.
It's a very interesting point you brought up though. I never thought of comparing the two preamps because I assumed they were internally identical.
I would suspect that the op-amps may possibly be different chips or the caps in the audio path may need to be reviewed on the weaker unit.
I don't have the two varieties at this moment or I would try the same comparison. I only have a 1980 MKII preamp to look at right now. I have changed the op-amps on it though.
I am going to look back at my pics of MK I units I worked on in the past to see if anything stands out.

Offline goldphinga

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New link: http://imgur.com/a/Mdo8f

The mark 1 is def a rev a preamp and the mk2 is marked rev d. So Rhodes def changed the components as you can see on closer inspection when zooming in. Question is which components are responsible for the lower overall output and general weaker mids/tone on the mk2 (rev D) pre...Maybe this change is one of the reasons why Mk2' suitcases are often said to have a more sparkly less ballsy tone. This mk2 rev D one here is all sparkly tops and round lows with massively scooped mids. 
« Last Edit: July 19, 2015, 07:41:53 AM by goldphinga »

Offline vanceinatlance

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Those pics show up great!
I don't see anything different between the two visually except for the different types of capacitors used in each circuit (ex. C2 C19 C7 etc.).
It may be that the older capacitor types they used on the MK I  gave more desirable results for frequency response? They are definitely marked as different revisions on the circuit board, but I can only find one version of the schematic for this pre-amp?
Hopefully someone else can chime in and enlighten us more on the differences.

Offline Tim W

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It appears the MK2 preamp was modded in addition to the vibrato switch. 
Those caps in the front end and the resistor underneath are not from the factory.  They did not use components that looked like that.  You can also see that the soldering on those components is not factory (i.e. wave soldered).
I would expect that those mods on the front end are what is creating the differences in gain and frequency response. 
The apparent board rev has nothing to do with it.

If you put your Mk2 back the way the factory intended you will get the same sound as the Mk1 rail.

Best regards,
Tim
retrolinear.com



Offline goldphinga

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It appears the MK2 preamp was modded in addition to the vibrato switch. 
Those caps in the front end and the resistor underneath are not from the factory.  They did not use components that looked like that.  You can also see that the soldering on those components is not factory (i.e. wave soldered).
I would expect that those mods on the front end are what is creating the differences in gain and frequency response. 
The apparent board rev has nothing to do with it.

If you put your Mk2 back the way the factory intended you will get the same sound as the Mk1 rail.

Best regards,
Tim
retrolinear.com



Hey Tim, so remove the resistor underneath, replace C19 and which others? Many thanks for your help!

Offline vanceinatlance

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Wow, great observations! That's why pros are worth their weight in gold, and then some!
I somehow mixed up the two boards in my mind and was trying to figure out why the replaced cap version would sound better.
I can't make out the op amp
R2 is supposed to be 220k(red red yellow) and c2 is supposed to be 120pf. It looks like they placed the resistor, wich should not be there , underneath in parallel with r2 aboveC19 should be .001. Those to me are the obvious changes that Tim may be pointing out.
Hopefully he will have time to verify.