Meridian 101 pre amp needs new power amp

[RCruz]

Now Ricardo we DID ask you to cut your siglines down to three line maximum, as that is the policy here.

Hi Mark

I did not get scared with Andrewá comments.... I am always willing to learn more... It makes sence that replacing psu caps can not alter freq response....

Now I do not want to break any rules here so could you explain what you mean by posting only three lines ?

Regards

Ricardo

 

[Thomo]

I think he means your signature lines underneath your posts.

ps: I'm still working on that board layout, adding shunt reg.

Cheers, Lee.

 

[RCruz]

Thank you Lee

I will amend that right away.

Can you help me with the volume knob on the 101 ?

I see a small screw like hole in each knob (volume/balance) but can not find any wrench to suit... maybe it is not a screw ?

Ricardo

 

[AndrewT]

I see a small screw like hole in each knob (volume/balance) but can not find any wrench to suit... maybe it is not a screw ?

it could be a slotted grub screw, or a cross head grub screw, or a hex headed (allen key) grub screw.

 

[RCruz]

it could be a slotted grub screw, or a cross head grub screw, or a hex headed (allen key) grub screw.

I imagine that is possible but the size is so small (less than 1.5 mm), that I can not find any suitable wrench.

 

[AndrewT]

both 1.5mm and 1.6mm hex keys are available.
I have seen and used smaller but at these small sizes the keys must be good quality else you risk rounding the key and damaging the grub screw.
UNBRAKO are good.

 

[RCruz]

both 1.5mm and 1.6mm hex keys are available.
I have seen and used smaller but at these small sizes the keys must be good quality else you risk rounding the key and damaging the grub screw.
UNBRAKO are good.

I believe these must be 1.4mm

Thank you so much for the tip.

My system is sound awefull now.

 

[Thomo]

Hi Ricardo.

It is a tiny Allen key grub screw.

Are you positive you need to remove it? I don't remember doing so before. I won't get chance to have a proper look til tomorrow night though.

Lee.

 

[RCruz]

Your pre-amp...

1) raises 120mV to 775mV and hence has a gain of x 6.5 . (Note that 775mV is a standard reference level in the professional audio industry, and hence this is why the Meridian is specified reference this level).

2) has a maximum output of +20dBm which is (if I recall accurately) 7.75 V across 600 Ohms.

The Rotel RB 06 and Audiolab 8000P require about 1 V for full output, so you should have no problem with driving them from your pre-amp.

Both of these amps seem to work well at their price points.

Hi Gordy

Following the general ideas from this thread I decided to upgrade the Meridian instead of replacing the power amp.

I already recaped the 103 psu, made a dedicated direct Mains cord and started to mod the 101b pre.

In this case I replaced the regulators and rectifier by a 317/337 / hexfred setup and recaped the psu.

In the output module, I have replaced the stock opamp by a LM4562.

Now I would like to replace this opamp by a buffer stage. (Pedja...)

As I am a bit confused about the idea (a buffer should be used to couple between different impedances)
My big question is:

Do I need a gain of x 6.5 on this buffer ?

Regards

Ricardo

 

[AndrewT]

you should be able to decipher the resistors on the input & output pins to determine the gain currently set up through the opamp.
Then arrange for either a 0dB buffer or +xdB discrete gain stage to fit the opamp pins.

 

[RCruz]

you should be able to decipher the resistors on the input & output pins to determine the gain currently set up through the opamp.
Then arrange for either a 0dB buffer or +xdB discrete gain stage to fit the opamp pins.

Hi Andrew

So you mean I can replace the LM4562 by a pedja buffer (o gain) once I figure the pin layout ?

 

[RCruz]

Then arrange for either a 0dB buffer or +xdB discrete gain stage to fit the opamp pins.

Well I know this opamp is arranged to have x6.5 gain.

I could replace it by a better opamp (like the new metal can available) but I know that a discrete design is much better, particularly if it is built with jfets and no feedback.

So I decided to build a pedja but I am afraid this kind of buffer is a pure voltage follower (0 gain).

Can the pedja be modified to have some gain ?

Regards

Ricardo

 

[Thomo]

Hi Ricardo. Are you sure you need any gain in the pre?

I built a Pedja buffer and I still have more than enough for loud volumes.

Cheers, Lee.

 

[RCruz]

Hi Lee

With my present RIAA, I need this gain, otherwise the sound would be too low.

With the CDP, I really have too much gain so maybe I could do with the buffer.

How does the output from Salas RIAA compare to the CDP on your setup ?

Ricardo

 

[Thomo]

The Salas RIAA has around the same output as my cdp. I haven't measured it, but it's plenty loud enough.

Lee.

 

[RCruz]

Your pre-amp...

1) raises 120mV to 775mV and hence has a gain of x 6.5 . (Note that 775mV is a standard reference level in the professional audio industry, and hence this is why the Meridian is specified reference this level).

2) has a maximum output of +20dBm which is (if I recall accurately) 7.75 V across 600 Ohms.

Hi Gordy

It may seem strange to get back here, but I understand you have acces to Meridian info.

I replaced the 101 pre by a buffer (DCB1) with great results.

Now I would like to know how to determine the Meridian 103 power amp gain based on it´s specs:
Output: 35W/ch in 8ohm
input: odBm (775mV) over 10k for 35W (Does it mean the input impedance is 10k?)

 

[RCruz]

super bump

 

[RCruz]

Now I want to replace the Meridian 103 PSU but I do not know what are the specifications of the toroid... anyone ?

 

[RCruz]

After a long search for suitable transformers I found the FEAS 26V 250VA.

Due to sme T$me constraints I could only buy two and as these have single 26v secondaries, I could not implement a true double mono setup, so I used them in series to feed dual rectifiers as in the schematic.

 

[RCruz]

So far so good.... sound is much more open and detailed with the new setup.... but I am having trouble at power on. My house has an old electrical instalation that can not withstand too much inrush current.

Every time I power the new psu and have other appliances running, the mainsboard fuses trigger.

How can I limit inrush current during power on ?