Pioneer SA-7500 II

[robyrony]

Hello AK members,
This is my first thread, so if I'm doing something wrong please let me know.
I'm pretty new to this vintage stuff, but I already like it a lot.
A few months ago I bought my first vintage amplifier: Pioneer SA-7500 II. After I bought it I found that this isn't one of the best sounding amplifier from Pioneer, but I have to live with it for now.
The amplifier had one burned output (I knew that before I bought it), and since I wanted to recap it anyway I figured it wouldn't be a major problem- just have to buy the transistors as well
I've read a lot of threads on recaping old amplifiers and I felt confident I can do the job myself.
I'm not an expert on fixing stuff (I'm an accountant), but I learned how to mount a transistor and a diode.
I used Panasonic FC and Nichicon PW for the caps, and for the transistors On Semiconductor and Fairchild.
After the rebuild I tested the bias and now things turned out to be more difficult- it measured 2 mV.
So I cut the jumper and the idle current incresed to 3 mV.
The manual says it should be between 10-70 mV
The unit sonds OK, well almoust OK; the sound is there but something is missing. The bass is a little short, like not full enough.
Since there are no pots to adjust, I don't know what to do next.
If someone has this unit and encountered the same problem and would like to share the answer, I would be verry gratefull.
*Also, english is my second language, so please forgive me if I misspelled something.

 

[audiojones]

If you have it hooked up to speakers make sure that they are wired "in phase", in other words the red connector from the amp to the red or + terminal on the speakers and the black terminal on the amp to the black or - terminal on the speakers. If one of these gets hooked up backwards you will have weird sound with very little bass and a big "hole" in the frequency response.

 

[robyrony]

I've checked the speakers and everything is connected correctly.

 

[robyrony]

I found the problem.
Turned out that I have a crappy meter, who can't test bias diodes correctly.
So I put the original bias diodes back and everything is OK.
Bias voltage increased to 16 and 20 mV.
I'm happy now.
If someone still knows how to increase the bias voltage, I still want to know because I want to see how it sonds with higher bias voltage.

 

[Musicdove]

Yesterday I bought a Pioneer SA-7500 II amp. for 150 Euros. I don't know if this is a lot of money for this machine, but I took the risk. Today I started testing the amp by hooking up my regular cd player (Musical Fidelity Elektra E60) on the AUX input and my Sennheiser HD 600 on the headphone input and after having put a cd in the player (Tchaikovsky's First Piano Concerto). I must say that I was quite disappointed concerning the sound of the Pioneer amp. The sound was swampy, unpronounced and bumpy. Probably I am spoiled with my regular amplifier, which I use with great satisfaction, a Cambridge CXA 60.
What was I expecting? That the old Pioneer - it is from 1976 - is capable of producing the same well-shaped sound of the Cambridge? Was that really what I was expecting? After everything I read so far about the Pioneer, I think I did. Is it fair to expect from this ageing lady that she performs as if she is in her twenties? Probably, the amp just needs maintainance? It is not unthinkable that some of her major parts need to be replaced. There are some damn good vintage repairshop down here in Holland. But after one of them gave here a damn good whacking, what can I expect?
What is reasonable for the sound? Is the Pioneer less good than the Cambridge? I fear she is... Or is she not?

Someone any good suggestions? What will it sound like when I use the tape-input instead of aux for example?

 

[PTL-Pioneer]

Musicdove, while i have not heard a 7500 or a Cambridge CXA60, i came across an sx750 recently which sounded fine. But then i done a full recap and transistor change and it really was a big improvement, not earth shaking but certainly brought the point home that these units are old, require a bit of love and graft, and at the end the rewards are tangible!
Previously i had a Sony TAF550ES which to my ears is a cracking amp. I would rate the sx750 better after the work and it has 30w less to work with. Just my two cents, which might not be worth the 2 cents.
I also recently got a restored SX1010 from Zeb and it kills anything i have ever listened to, truly fabulous.
Do not write the unit off, ask the questions here, get some input from the gurus, they will provide the guidance you require.
Hope this helps somewhat.

Also please start a new thread for yourself and your unit, it is encouraged, and you should get more focus that way also. Thanks

 

[PTL-Pioneer]

If someone still knows how to increase the bias voltage, I still want to know because I want to see how it sonds with higher bias voltage.

I would not increase it more, get it to range that is prescribed by the service manual.
As far as i know (open to correction) adjusting the bias higher will not make it sound better at all, and if you go too far there could be heat issues or worse.
Stick to the service manual recommendations, unless told otherwise by someone else here

 

[Plugin]

Yesterday I bought a Pioneer SA-7500 II amp. for 150 Euros. I don't know if this is a lot of money for this machine, but I took the risk. Today I started testing the amp by hooking up my regular cd player (Musical Fidelity Elektra E60) on the AUX input and my Sennheiser HD 600 on the headphone input and after having put a cd in the player (Tchaikovsky's First Piano Concerto). I must say that I was quite disappointed concerning the sound of the Pioneer amp. The sound was swampy, unpronounced and bumpy. Probably I am spoiled with my regular amplifier, which I use with great satisfaction, a Cambridge CXA 60.
What was I expecting? That the old Pioneer - it is from 1976 - is capable of producing the same well-shaped sound of the Cambridge? Was that really what I was expecting? After everything I read so far about the Pioneer, I think I did. Is it fair to expect from this ageing lady that she performs as if she is in her twenties? Probably, the amp just needs maintainance? It is not unthinkable that some of her major parts need to be replaced. There are some damn good vintage repairshop down here in Holland. But after one of them gave here a damn good whacking, what can I expect?
What is reasonable for the sound? Is the Pioneer less good than the Cambridge? I fear she is... Or is she not?

Someone any good suggestions? What will it sound like when I use the tape-input instead of aux for example?

Musicdove,

Can you describe what you meant by swampy, unpronounced, and bumpy? I've been using a mint condition of the SA-7500 II for the past six years as a main system, and to me, it's VERY musical and punchy. I do admit that compared to certain modern amps, it may seem a little too smooth/warm in the lower midrange, but that's why I like it. May amps today favour analytical clarity - which is great to hear details - but will bore you after a few minutes, unless you're willing to pay for more expensive amps that have more refined high frequencies. The SA-7500 II is a an amp which will allow you to appreciate music while making it fun (yes, it is coloured) without weird artifacts jumping out at you. Plus, the phono stage is in line with the amp's sound.