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Is it possible to connect a Pioneer SPEC-1 preamp to a pair of L-05Ms?

A

ampman

AK Subscriber
Subscriber
Hi,
I am asking a question about matching a pair of Kenwood L-05M mono blocks to a Pioneer SPEC-1 preamp.

I have been lucky to find a pair of L-05Ms and a SPEC-1 that are not modified or damaged, still in good to excellent shape. My hope is to use them together

I read a post (here in AK, I think) that stated the L-0xM line needed a preamp that connected to a 10-ohm input (at the L-05M) load. One needed a matching network to ensure proper operation. As I'm not a design engineer this confused me as to this need. I don't want to assume this combination will connect directly without issue, that will end up damaging either unit.

The SPEC-1 has an output (Level/Impedance) of 2V/600 ohm.
The L-05M has stated Input Sensitivity/Impedance of 1v/50k ohms.

To my thinking this is an okay match.

Please explain if this is a good match and the need for a matching network if it is needed.

Thanks
 
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For comparison, the L07C II has an output impedance of 10 ohm: however is was so low because they were connected with long signal cables (12 meters long the ones that came in the box), to keep the power cables short.
How long your cables are (signal and power)?
 
claneg said:
For comparison, the L07C II has an output impedance of 10 ohm: however is was so low because they were connected with long signal cables (12 meters long the ones that came in the box), to keep the power cables short.
How long your cables are (signal and power)?
Click to expand...
Hi,
Thanks for the reply.
The signal cables will be 2 meters or less shielded cable with RCA connectors.
The power cables will be 1 meter in length made of 14ga stranded copper wire tinned at the amp and soldered/ended at the speaker with ring connectors.
 
I'm using a McIntosh preamp with my 07m. Seems fine to me.

I've used other preamps too (Yamaha c4, Kenwood kc209, hafler 101, ...).

I do have a 07c but haven't tried it. Maybe it will be better.

I just enjoy the music.
 
ampman said:
Hi,
Thanks for the reply.
The signal cables will be 2 meters or less shielded cable with RCA connectors.
The power cables will be 1 meter in length made of 14ga stranded copper wire tinned at the amp and soldered/ended at the speaker with ring connectors.
Click to expand...

I think you'll be just fine.
 
Just hook them up and try it. Trust your ears. If it sounds good you are fine.
 
Well I went down the preamp to power amp matching rabbit hole.

my understanding you want a low preamp output impedance and high power amp input impedance (to minimize loading down the power amp).

here are my preamps I used with my 07m mono blocks (assuming I read the manuals correctly and didn't forget any):
Hafler DH-101 47,000 ohms (not really sure)
Kenwood C2 100 ohms
Kenwood KC-209 330 ohms
Kenwood L-07c 10 ohms
McIntosh c26 200 ohms
Yamaha C4 600 ohms

The Hafler is the only odd ball. The 07c was used as a reference.

you can also measure it by using this formula (found here):
Z = (A1*RL/A2) - RL

Where:
Z = Output impedance
A1 = Open circuit voltage amplitude
A2 = Loaded voltage amplitude
RL = Load resistance

you will need a scope and a signal generator.

BTW, google said your SPEC-1 is 600 ohms.
 
Last edited:
opnly bafld said:
Hafler DH-101 spec above is for phono preamp input, not output impedance.
Output impedance will be well below 1000 as the others listed.
Click to expand...
this makes more sense. it does sound fine.
I did re-read the 'Kit Report' review from Audio Amateur from 3/78 and the output impedance wasn't listed (or I missed it). Even the 'Modifying the Hafler DH-101: Circuitry' article in Audio Amateur 4/1980 didn't list the output impedance. Both focused on the phono section (and the RIAA curve).

I'll update my post above.

BTW, attached is the 101 specs from the assembly manual.
 

Attachments

The typical rule of thumb is minimum of 10:1 ratio for input to output impedance.

50,000 input and 600 output is 83:1. There is no reason to expect anomalous behavior in regard to "matching".

Far as cable length, at only 2m on 600 ohm output impedance, the cables would need to have pretty high capacitance to cause any concerns in HF rolloff as well.

Prognosis? The patient and plan are A-OK without any sort of additional matching gadget(s).
 
Last edited:
whoaru99 said:
The typical rule of thumb is minimum of 10:1 ratio for input to output impedance.

50,000 input and 600 output is 83:1. There is no reason to expect anomalous behavior in regard to "matching".

Far as cable length, at only 2m on 600 ohm output impedance, the cables would need to have pretty high capacitance to cause any concerns in HF rolloff as well.

Prognosis? The patient and plan are A-OK without any sort of additional matching gadget(s).
Click to expand...
Thanks all. Have a better understanding of the L-05M now.

One question: where does the 10:1 ratio come from?

So appreciate the help!!
 
ampman said:
One question: where does the 10:1 ratio come from?
Click to expand...

It is usually the recommended minimum, higher is fine/good.

kappclark

Thread 'Output impedance vs input impedance'

connecting Preamp to power amp question - Have read about importance of keeping output impedance low on preamp, and input impedance high on power amp ..

is there a simple explanation for why this is ?? I recall with antennas the impedance needs to match as closely as possible .. is that because there needs to be high % of power transferred (antenna) but not with preamp - power amp ? What wld be the typical result if the impedances were the same with the pre and power amps ??
 
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