Mismatched pre/power amps


Hi I'm new to the forum so hope this is the right place.

I still have my cherished lecson AC1 preamp which I used with my AC3 power amp before it died. I also have an Audiolab 8000S - with pre/integrated/pre power/pre power.av - connected to an 8000P power amp which are bi-wired to my Epos ES12 speakers. CD is an Audiolab 8000CD.

Out of curiosity - and really nothing more than nostalgia - I wanted to see what the Lecson preamp would sound like with the Audiolabs, but I think there must be a voltage mismatch - with the volume on the Lecson turned to maximum the sound output is very low and totally unusable. I have a lead made up by Lecson many years ago to allow the AC1 to be used with other power amps and one of the phono pickups altered to allow for a CD player. Unfortunately, I no longer have the output and sensitivity values.

I have tried all combinations of settings and the only one which gave me the output was to connect the AC1 main output to the Power IN socket on the 8000S and use the Pre Power AV switch to allow the AC1 to drive the power amp in the 8000S. I also had this scenario with an old Yamaha cassette player. I tried connecting directly to the 8000P power amp but no results. Having said this, I suppose if the output is so low, other connections may be working but just inaudible.

I'm getting to the limit of my working knowledge, but is it possible to boost the output from the Lecson in some way or perhaps go about this differently? Or am I just dreaming of a bygone era.......?

Any thoughts/suggestions would be gratefully appreciated. Many thanks.


willi49
I think here is your problem not enough gain from the Lecson.

By the looks of it the Lecson pre out can only do .5v output,
https://www.hifiengine.com/manual_library/lecson/ac1.shtml

And the Audiolab 8000p has an input sensitivity of 1v
https://www.hifiengine.com/manual_library/audiolab/8000p.shtml

You still should get up to a normal listening level though.

Cheers George
Thanks for your prompt reply George.

If you think I should still get normal listening levels I shall start again in case I did something stupid - not unknown! So many cables I need photos of all the connections - thanks to old age I guess.

Let you know if I have success.

Best Alan


Hi George

Well, I disconnected everything and started from scratch with only the CD connected to the AC1 and 8000P and all I got was background hum. I guess that means something is happening. Is this hum noise heard because the AC1 cannot produce enough voltage to drive the 8000P and get audio from it?

I have heard of line drivers to increase the output from preamps. Is this a viable option to consider do you think?

Sorry to be somewhat lacking in knowhow with this.

https://www.google.com/search?q=lecson+AC1+preamp&source=lnms&tbm=isch&sa=X&ved=0ahU...

George,

Click on your link, and then look at this one. I get different preamps.
On a preamp that is this old, the hum could be coming from capacitors that are degraded and dried out.  This is a common root cause of hum on equipment.  The degraded capacitors will not filter voltage properly coming in from the A/C mains and you'll get 60hz hum.  This can also cause the preamp circuit to not have enough power to provide the gain you need.
https://www.google.com/search?q=lecson+AC1+preamp&source=lnms&tbm=isch&sa=X&ved=0ahU...

George,

Click on your link, and then look at this one. I get different preamps.
That’s an Armstrong pre that opens, not a Lecson AC1 as the OP owns.

Cheers George
On a preamp that is this old, the hum could be coming from capacitors that are degraded and dried out. This is a common root cause of hum on equipment. The degraded capacitors will not filter voltage properly coming in from the A/C mains and you'll get 60hz hum.  This can also cause the preamp circuit to not have enough power to provide the gain you need.

Hi auxinput

I had not thought about that possibility. I had something similar with the AP3 power amp where the circuitry continued to degrade until I had no choice but to retire it. I've read about line drivers which I believe boost the preamp signal. Is this a possibility to see if the circuitry is degrading and preventing the preamp from giving the gain necessary without costing a great deal?  Thanks
I see it now. The pic I posted is tagged Lescon AC1, but if I look close at the pic, I see the label.
You would probably have to have it looked at by an electronic repair person.  Replacing electrolytic caps is not usually expensive (maybe up to a couple hundred) unless the device uses specialty caps that cost a lot.  You just need to listen to the type of hum.  If it's a 60 ha buzz type of him, then it could definitely be caps failing.
Thanks very much for the input - I can see the way I probably need to go now.

And to all who took the time to help - many thanks, it is appreciated.