Upgrading Marantz 7C capacitors

Dear alfcat, looking at the schematic of the amp. I like to tell you some things.

Not every change or mod give a better sound sometimes it is better to leave it.

Before you got modding set a goal of the things you like to improve.

In your case with the amp for example:

1 - change overall sound: just change C4 and C5 for other types like PIO or change tubes.

2 - If there is humm: replace R1 for a big inductor like 10 or 50 Henry

3 - Got more or less bass control: Change R13 for another value ( between 4K7 and 100K )or replace it for a variable resistor of 100K with in serie a 4k7 resistor. Now you can change feedback ( bass controll ).

Changing resistors with ones of the same value is only use full in low signal voltage amplifiers like phone stages or I/V conversion of DAC's. In power amps this is a waste of money.

Reading about mods is one but listening is the real thing.

Dear Viewer,

Where did you get the DALE resistors? I know that you can get 東京光音 from Mak's.

If you use RMG, it is going to cost you a lot of money I guess. How much it cost you this time?

CAT

Hi alfcat,
I used around $160 for this time.


I get 東京光音 from  寶樹. $5.00 each 1/2w $10.00 each 1w
I get DALE from 電子館 . $3 each 1/2w.
total costs $150.00. = one good film cap's amount.

can get it at 永盛 same price.

thanks.

On the power  amp mod, you do ask yourself a few questions that what you are not happy about ?

1. If you need more details , then change the resistor on the signal path,
2. If you need more smooth sound, change the electric caps and perhaps add a choke will improveit
3. If you need a different sound, change the C3,4 cap into some other type will improve it.

So it all depends on what you really need.

Dear Accphoto,

Actually there is little story about this modification I am looking for. After I got this ASL AV 25, another user "Viewer" forwarded me a link from another forum in the States. That owner of the AV-25 said the sound quality of the AV 25 can actually be improved by a few simple modifications. Unfortunately, when I send him a message, he said he already SOLD the AV 25 and can't recall about the modification.

I then sent another message to ASL, they replied saying that changing the Signal Path Resistor and the Capacitors will do the job.

1. If you need more details , then change the resistor on the signal path,
2. If you need more smooth sound, change the electric caps and perhaps add a choke will improveit
3. If you need a different sound, change the C3,4 cap into some other type will improve it.

And that is exactly what you are telling me here.

What I want to know more are:

1. Change the Resistor on the Signal path = change the VALUE of the resistors or change the BRAND to a better one?

2. For an idiot like me, which resistors are they referring to? R5? R6? R13?

For me, I would like to add more details / clarity to the system and hopefully just a little more bass.

And finally, if you have time ... can you explain a bit why changing the resistors will improve the details?

Many thanks.  

CAT

Basically, change the material will change the  sound quality. It is very difficult to explain but if the design is good enough, then change some better brand  resistor on the signal path normally will improve  the sound quality like details sound stage etc. Resistor in the signal path means any resistor that pass through by  signal from input to output. In your case, it should be R6 & R7 ( sorry, it is still very diffuclt to read). two resistors that after the signal caps. It is a common sense that Holco & RMG will yeild better details with sweet sound , dale are more neutral  and AB resistor are more musical. Normal carbon firm resistor will sound a little bit dull. Some wire-resistor ( white in color) will sound terrible.
Using different resistor like using salt and suger in cooking.
Normally change the caps and signal path resistors will change the sound quality as signal pass through these materials. If you want to improve the bass, then it will be another story
To get good bass, you really need to look at the power supply ,the frequency response of the transformer, and finally the design of the circuit. Since the transformers and the circuit are fixed, you can only modify the E-Caps on the power supply to provide a bigger supply of power  or change the feedback resistor to a different value. Changing the feedback will change the characteristic of the amp. For the E-caps, change to different brand of E-caps will yield different quality of bass. Someitmes, you can increase the value of the E-caps but it really need to be an experience mod. Premium brand like blackgate or Jensen should be able to do the job. Changing the  value feedback resistor requires some calculation. It can also be done by trial and error but just make sure that you do blow the speaker by the oscillation if the feedback is too large. As i say before " Good Bass is difficult to get" A lot  tube amps is lack of bass as it is limited by the output transformer and the design itself. I had built a 300B amp 10 years ago and try to improve the bass without success. Finally, I find out that there is some limitation on the design of driver stage so it does not provide enough power to drive the 300B.

Dear Accphoto,

I agree with you that using different materials will yield different sound effects. However, if the circuit is poorly designed, using better materials will just give opposite results --- magnifying the errors.

So far I have been running the 6L6 and the Matisse each and every day for 3 hours / day. The results of changing the capacitors are getting more obvious now. As I asked my wife and my girl how do they feel about certain piece of music, they like it more tho' they don't in the past.

In the past, I don't believe that a "good" power supply is that important. Now, I am a believer. I think a good power supply / source is even more significant for Tubes Amps and Players, am I right?

I still got a funny problem with my CD ... sigh ... The Left Channel is significantly louder than the Right channel. What could have gone wrong? I checked my soldering points, they are all okay. And the difference is pretty obvious ...

CAT

Most circuit is basically a switch , to reduce the power from the power supply to drive the speaker. In that sense, the power supply is important in all HiFi equipment. Pre-amp , power-amp, CD and DAC, the quality of power supply will determine basically it is a good or bad sound.

Dear Accphoto,

If I would like to learn circuit designs, should I therefore learn about how amplifiers are constructed? Should it be the simplest type to start off with?

CAT

Hi Cat,

have you try to swop the valves around in your cd player.....

kkwan

Dear KKWAN,

Yes, I have tried that before. Actually I have 3 sets of 396A tubes. I marked them and swapped them once in a while, using different combinations. Still the output on the Right Channel is still lower.

BTW, your remote works okay or not?

CAT

Yes CAT the remote works, but not all the time i don't know why, when i open the case of the cdp it works better or when its warmed up. anyway it better then not working.
           Cat what audio setup you got? like what power amp connect to you marantz 7c etc.....

Thanks

kkwan

[quote:212449ba8c="alfcat"]Dear Accphoto,

If I would like to learn circuit designs, should I therefore learn about how amplifiers are constructed? Should it be the simplest type to start off with?

CAT[/quote]

Got to learn some basics on electronics and then you should be able to learn more. I am not a engineer and all my knowledge are from self-study.

Dear KKwan,

That is really interesting. Maybe there is a poor soldering point or so in your CD's PCB. I tested it out a number of times, inter-changing it with my remote on TWO different CD 33. It worked all evening.

I don't have the Marantz 7C anymore. I sold it to my colleague and I changed the WIMA caps to Auricaps, changed the ladder type volume control to Alps for him as well.

Under Accphoto's advice, I changed the Matisse caps to Auricaps as well. After around 40 hours of running in, the Matisse sounds much much better than before. The base is more solid and the sound is "thicker" than before. Also, it is not that "fast" (Hi Fi sense). As I listen to female vocals relatively more, the ladies sound "sweeter".

I connect the modified CD 33 to the Matisse and then to the Antique Sound Lab AV25 Mono Blocks. I changed two capacitors and some resistors in the AV25 as well. More details and better base now I have.

The speakers are just Chinese clone ProAc 1SC. Low price (HK$ 2200) resting on a beautiful but not heavy pair of stands. My next modification will be the cross-over and alike of the speakers.

CAT

Dear Accphoto,

In the past, I should be called an "Arts" student as well. However, some of my classmates in my class were constructing amplifiers even at the age of 15. They eventually went overseas and became engineers.

I am doing self - study as well. Actually I also learned a lot of stuffs through this method; computers, cats raising, aquatic plantation, etc. Nice to see people going through the same route.

Sorry to bother you but I will have another question to ask you later this week. It is about an EL34 Mono Block amp I am doing for my colleague. I followed all the procedures carefully but when I turn the amp on, one capacitor (known as C12 -- 47uf/63V) explodes. This happends for BOTH mono block but I couldn't figure out why.

The schematics had already been scanned (this time should be able to read clearly, ha..ha). I will take some photos as well. Hopefully you can help to show me some hint or help me to solve the problem.

Thanks in advance.

CAT