Harp voltage

[Badwolf]

Hi everybody,

i went through lot's of threads but couldn't find the the exact answer,
could somebody help me with this detail, i am looking to get the direct output voltage from the harp on MARK I from 1975 Suitcase ?

I have made with a good friend of mine great work on this piano, new composants in the preamp (5pins Peterson), everything is very clean now for this one, the amp is working well too, but ....  when the harp is connected to the the preamp and the preamp to the amp, we have a big distorsion in the sound ? it looks like if the harp send a too hight voltage and that the preamp distorded the sound.

Any ideas maybe ?

Thn'x a lot.

[retro-mike]

Peterson preamps are 4 pins, Janus preamps are 5 pins, just to clarify!

Start with verifying that you have installed the transistors and caps correctly.
Check the collector, base and emitter pinout of each transistor.
if you install a transistor in the pre-amp backward it will create distortion/clipping sounds.

There is a mixture of capacitor types inside. Some capacitors are standard "plus & minus" setup but- there are also non-polar capacitors.
if you install a standard in place of non-polar and vice versa, that can also create issues.

There could also be a biasing issue.

pics might help - its difficult to troubleshoot electronics without bench gear (scopes etc)..
if you get in a bind we can rebuild your preamp, amps etc- very common thing to do

Good luck!

[Badwolf]

Hi,

Thn'x a lot Retro-mike, i gave these informations to my friend he is the electronician and we'll be able to talk with you.
here is my preamp https://www.youtube.com/watch?v=u3GSJc8YbEM  but we have modify and use a 5 pins without using the fith one.

have a nice day !

Badwolf

[pianotuner steveo]

The actual harp itself is passive- no voltage. The preamp has voltage, but not the harp.

[Jenzz]

Hi .-)

I think he wants to know the Audio voltage comming from the harp. If you hit a 10-fingered chord hard, you can  get up to 800 mV pp...

Jenzz

[pianotuner steveo]

Well yes, there are millivolts, but it sounded like he was asking about the pin voltage for the preamp, which I believe is 25v.

[Badwolf]

Hi guys,

very busy those days  !

thn'x a lot yes this is what we would like to know the passive output of the harp in mV, so well for sure the more fingers the more mV !
i'll be back to give you news soon, i transmit this to my friend !

Badwolf

[pnoboy]

Plug an electric guitar into your preamp--if that sounds bad, then you'll know that there's something wrong with the preamp.  Does your preamp sound OK if you only press 1 key softly?  I think the Rhodes will put out a few 10s of millivolts--it, of course, varies greatly depending on how many notes are sounding and how hard the keys are struck.  You can easily find schematics for Rhodes preamps on the web.  Your friend can determine how much gain they have--that should tell you all you need to know.

[Max Brink]

I think we're going down a rabbit hole here... I don't think searching for mV measurements are going to be the easiest way to resolve this situation...

The very first question that I have reading the top post is: What components did your friend replace in the preamplifier and why did he decide replace them? (What issues was he encountering initially with the preamplifier that led him to decide to use new components, since many of the vintage components should still be healthy in many cases?)


I'm going to suggest going back to Mike's post above, which is the best advice so far. It's a broad check list but these are the things to look for in most electronics repairs. It's likely just a bad cap or transistor and it's a matter of finding the culprit(s). If you're not sure about what you're looking for off Mike's list I'd take it to an expert and have it done right. Respectfully, your friend may or may not be the best for the repair if he's not already working on the ideas that are listed in Mike's post.


As long as you or your friend are comfortable with Mike's list, here's one more thing that I would add to narrow things down a little more:

Is the Distortion coming from both channels of the power amplifiers or is it in one side? If it's in just one side then you can narrow it down to that power amplifier channel. If it's in both then you can likely start narrowing your search to the preamplifier. (But it may also be the power supply leading to the preamplifier...) The quick way to check this by ear is by turning the intensity of the vibrato all the way up and the speed all the way down and then listening to the two channels as the vibrato flips back and forth between them.

[Chris Carroll]

Hey Maybe this will help you or anyone else to determine where to begin finding the issue. This is a basic procedure many overlook.

https://youtu.be/d_lduHVFsys

You could also send your pre amp to Vintage Vibe for quick repair, restoration or replacement.

www.vintagevibe.com

973-979-2178