Marantz CD400B output level

[63909]

Hi All,
second request, is there any way top increase the signal output of the 400B? for the moment I have it going into a SQD2020 via the Discrete inputs and the volume output of this union is pretty low. Its all there - very clear and all that - just a bit on the low side.
Many Thanks
Joe

 

[Quadwreck]

I don't have the answer you're looking for, but my Marantz 400B has output that matches line-level output on other devices. You may have something failing inside.

 

[63909]

Thanks for your reply, I'll check that out.

 

[Doug G.]

Yes, what's needed is to check the CD400B to see if it's output meets its specifications. Does that Sony have variable input level on it's inputs? The SQD 2050 does.

Doug

 

[par4ken]

The SQD 2020 has an input level control on the back but that is only for the stereo input. Nothing for the discrete quad input.

The rear output has two sets of jacks one low level the other high level.

I assume that both the front and back sound low. The comment that "Its all there - very clear and all that - just a bit on the low side" makes me wonder if there is an actual problem at all. It might be just that the decoder's stereo input is set too high? By turning it down you should be able to make the two levels better match.

 

[barfle]

I’m recapping mine and replacing the jacks on the back. I have a service manual, nd there are a dozen or so potentiometers on the circuit board that could get dirty. I’ll know more as I try to make it all work.

 

[63909]

Hi all,
Yes there’s plenty on that main board, quite a few through hole vias too, don’t forget them. I’ve had a go at making the test circuit, but as yet not got round to actually trying it. So as this unit is quite an age maybe that should be on my list. It’s been such a long time since I had it up and running it’s hard to remember what it was like volume wise - but a ray of hope on the Cb400 front, I connected up the Teac a3440 and it was the same output so that’s a relief. If there’s a problem I think it must be in the SQD somewhere, it could be a mismatch with the power amps - I’m effectively using it as a preamp - not sure if that’s correct as back in the day they still show integrated amps at the outputs…..
I’ll be interested how you get on with the recap.
Thanks again for your help.
Joe

 

[par4ken]

Hi all,
Yes there’s plenty on that main board, quite a few through hole vias too, don’t forget them. I’ve had a go at making the test circuit, but as yet not got round to actually trying it. So as this unit is quite an age maybe that should be on my list. It’s been such a long time since I had it up and running it’s hard to remember what it was like volume wise - but a ray of hope on the Cb400 front, I connected up the Teac a3440 and it was the same output so that’s a relief. If there’s a problem I think it must be in the SQD somewhere, it could be a mismatch with the power amps - I’m effectively using it as a preamp - not sure if that’s correct as back in the day they still show integrated amps at the outputs…..
I’ll be interested how you get on with the recap.
Thanks again for your help.
Joe

It should be fine as a preamp. The only caveat is there are bass and treble controls for the rear channels only. It was meant to connect to a stereo integrated amp or receiver using that for the front channels. The rear channel amp as an add on could be either just a basic amplifier or an integrated amp.

 

[63909]

Many thanks,
So looks like I’ll have to dust off the service manual if I can find it

 

[63909]

By way of an update - the service manual has one level check that looks like it can be done without the SQ checker or test circuit - its detailed on page 22 section 3/10 and refers to two voltages that need checking against a test point voltage - no signal applied. I did this and it definitely improved things. Now I've just got to work out how the rest of its done without a VTVM.....

 

[~dave~~wave~]

Now I've just got to work out how the rest of its done without a VTVM.....

Vacuum tube volt meter?

We had those in tech school 50 years ago for higher load impedance than moving coil meters, but haven't they been replaced in this century by DVMs - digital volt meters?
Small, cheap, accurate, reliable.

Have fun with it.

 

[63909]

Hi,
I’m hoping it can all be done with my resident Fluke…. The service manual asks for final Db figures when setting up ( input a given frequency at -10db, check there’s *db at the output), I believe I can use a DVM and just look for the correct corresponding voltage?
Regards
Joe

 

[DuncanS]

Hi,
I’m hoping it can all be done with my resident Fluke…. The service manual asks for final Db figures when setting up ( input a given frequency at -10db, check there’s *db at the output), I believe I can use a DVM and just look for the correct corresponding voltage?
Regards
Joe

dB is a relative measurement with respect to a reference, so yes you could use a DVM, the voltage you should expect to see would be

Vout = Vin*10^([dBout+10]/20)

Where dBout+10 is the expected gain, and is due to your (-10dB input) x Circuit Gain giving a signal level of dBout.

e.g. -10dB input level & expecting a 10dB output = 20dB Gain, so Vout = Vin*10^([20]/20) = Vin*10^1= Vin*10

Do they state what they regard as 0dB in the service manual? As you could calculate it that way

 

[63909]

Hi,
Thanks again, here’s some info from the SM:

So for instance:

I think this is the correct starting point?
I have a HP3335, so I was hoping to use that as both the frequency supply and attenuator.

In this case the lower line of equipment.
Kind Regards
Joe

 

[DuncanS]

Hi,
Thanks again, here’s some info from the SM:
So for instance:

I think this is the correct starting point? Looks correct
I have a HP3335, so I was hoping to use that as both the frequency supply and attenuator. That is OK as you should be able to key in a -10dB i.e. 245mV 2kHz signal

In this case the lower line of equipment.
Kind Regards
Joe

But, in the lower diagram they have a dual o/p sig gen, and it goes into a "signal mode selector", which I suspect selects and adds in the required phase shifts to give the output on Lf, Lb, Rb & Rf when selected.
Hope you get it all working