Upgrading Marantz 7C capacitors

There is two ways in improving the bass, change the Elect-Cap , currently you are using RIFA (330U) and BHC, Try to change the RIFA 330U to BHC, You can also change all  0.22U (WIma to other brand) and also change 2.2U to other brand. Personal, I do not like WIMA on tube amp as they will sound "thin" You can try auricap but I do suggest to change 2.2U to at least 3U. Since I only got the photo, it is only a guess and you should post the circuit.

I know this schematics, I have done it for my friend but I have change the value as follows :
B+ is too low, M7 is running at +280V in order to sound good.
Add a 3.3K resistor per channel between B+ and R2
Change C3 to a larger value capacitor say 2u to 3U.
Try not to use WIMA, it sound terrible on tube amp.
There are a lot of Marantz 7 circuit but this one definitely is not a good one as B+ voltage is too run. +240V should just be the voltage for T1 before the load resistor.No wonder it sound bad without bass.

The value that i suggest to you is not marantz as the value use by Marantz is too small for modern capacitors. The schematic is based on Sid Smith 7.

For the B+, yes, there is nothing you can do unless there is significant changes. I do not like DIYZONE's kit as they always change a lot and lost the original spirit. At the moment, you can change the caps and this will improve the tone and the bass. However, "好低音難求", sometimes, it is just a little bit of bass and cost you an arm and a leg.

Since you are already using RMG (or RMA?), It will sound very good if you are using the right caps. You next upgrade will proper cost you more as the elec-caps are worth upgrading but it is really expensive as you can only upgrade to BHC or Blackgate.

Oh, BTW, Auricap needs about 50-100 hours run in before really give the best performance....

Upgrade tp Blackgate may not solve the problem. In my opinion, the power supply voltage is too low.

The last tube is a cathay follower ( 陰極輸出), The original design is that it should work at 280V, the two tubes in front, it is design to work at lower voltage (240V), so the 3.3K resistor is to reduce the operating voltage from 280V to 240V.

This one is reference as using 2 tubes, Fantasy is using 4 tubes but  each tubes are run in parallel . If you look at the circuit, they are essential the same but two tubes in parallel means more problem on matching the tube. So I think reference sound better. For circuit, you should search the forum as it was posted before.

Dear CAT,
Shit, I must quote you the wrong number, It should be C2 which will affect most, it should be 3U, The Sid Smith circuit has corresponding value as follows :

C3 & C11 0.33u  400V
C1 &  C7 0.33u  400V
C2 &  C8 2-3U 400V
C14 &  C15 3.3U 200V

Since you are trial without knowing the result,  I suggest that you go for Aruircap first.  I still have reservation on the power supply.
C14 & C15 is also important, i suggest that you should change it too.
Jensen is certainly good but it will be quite expensive as for a trial.
You need to change both as it is for left and right channel.

ALPs is already very good. Hope your friend like the upgrade.

Yep, you can only listen it after 50 hours of running.

東京光音 volume 好貴！600+不如用 Holco volume 啦，俾多 兩百元好聲好多。東京光音的聲偏薄。

Ladder volume is certainly better than other volume as the sound signal only pass through one resistor. However, the type of resistor had significant influrence in the sound, normally , the best sounding resistor is RMG, than Holco, than Dale . AB had too much noise and is not suitable for such application. If you find the step is too loud, actually, you can modified the value of the resistor in the first few steps so that it suit you needs.Other volume like ALPS using carbon film, the sound is ok but in terms of music definition, those ladder volume will definitely win. One of the reason why Matisse sound so good is its volume is made of a pair of Holco Ladder Volume. the others are BHC caps .

Actually, one resistor is on the signal path and one resistor to the ground. Change the value of the resistor to the ground (Rg) in the daigram will affect the loudiness of the sound. The below web will certainly help you

http://home.so-net.net.tw/chufamily/StepVR/Calculation/StepVR.htm

You can use the appropriate value on trial and error.

Basically, i hatre those Japanese Electic-cap, If you really want a firm base, you should consider to upgrade those elect caps to black gate C1 and C2. If you do not want to spent a lot of money, consider Jensen elect caps.  C9 is also important as it is for the -Ve, consider blackgate as this will not too expensive. The circuit is so small that i cannot really read. The feedback resistor (R11 or 13??? ) is also important, suggest to change to RMG 2W.

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.

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.

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.

[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.