Why it sounds different.. ?

[hebaton]

O.K., I have this, I think, very well built JTM45 clone. It was made buy Stephen at Trinity amps. The work looks impeccable, the parts look right...
But it sound very different from another good JTM45 clone I previously owned.

I already established the OT is probabley responsable for part of this because of a "different winding pattern" but I also noted some differences on the board and would like opinions on their importance. I have attached pics of the board with indications to the parts I am questionning. If someone could explain how they may or may not be involved...
I compared this build to a Metropoulos kit as described on Valvestorm. Included are pics of both layouts.

The way I would characterise the difference in tone between this and other JTM45's Ihave played and heard is that the "mids" seem to be sitting in a very different place making it difficult to find an agreable ( to me ) tonal balance

There is No double 16uf can inside the chassis on the Trinity, but an additional 16uf cap on the board... comments on the impact of that change would also be appreciated.

I identified two resistors that have different values forn the ones called for. ( see pictures )

1- is 125K instead of 100K

2- is 31K instead of 27K

I also note there is no bright cap on the bright channel volume pot.

Very very interested in comments here !

Thank you all

[martin manning]

the OT is probabley responsable for part of this because of a "different winding pattern"

The OT may be responsible most of the difference you are hearing.

I also noted some differences on the board and would like opinions on their importance. I have attached pics of the board with indications to the parts I am questionning. If someone could explain how they may or may not be involved...
1- is 125K instead of 100K

This is the load for the cathode follower V2b. I'm not sure what the intent is there, but you could assess the effect on sound by temporarily paralleling a 470k.

2- is 31K instead of 27K

This is the negative feedback resistor. 31k vs. 27k results in ~13% less FB voltage, which will make it a bit louder and break up a bit sooner. To see what this difference sounds like, temporarily parallel a 220k.

[hebaton]

the OT is probabley responsable for part of this because of a "different winding pattern"

The OT may be responsible most of the difference you are hearing.

I also noted some differences on the board and would like opinions on their importance. I have attached pics of the board with indications to the parts I am questionning. If someone could explain how they may or may not be involved...
1- is 125K instead of 100K

This is the load for the cathode follower V2b. I'm not sure what the intent is there, but you could assess the effect on sound by temporarily paralleling a 470k.

2- is 31K instead of 27K

This is the negative feedback resistor. 31k vs. 27k results in ~13% less FB voltage, which will make it a bit louder and break up a bit sooner. To see what this difference sounds like, temporarily parallel a 220k.

THank you !

I will assess both those changes !
What about the double 16uf can, absent and the additionnal single 16UF on the board. Does that ot leave this with 16uf less filtering somewhere ?

[bepone]

i allready gave my opinion about probably major OT difference and lamnations in previous thread (why we are opening new threads with the same question?)
but here i see that material composition is NOT the same, we have difference in almost all resistors , like carbon films against carbon comps, different coupling caps..
then v2b cathode resistor is drifted to 125k it is carbon comp soak humidity, increased value and need repacement.. changing working point.. probably pushing V2 over max cathode/heater voltage allowance (over 200V). also all resistors need to be measured for drifting.

so how this 2 amps can sound similar at least? there is no way.

i have metroamp JTM at home, exactly like from layout picture and it sounds great. mids are perfect, smooth and little bit gritty.

[bepone]

if i can guess.. bottom picture amp sounds too dark, and is not cutting in the mix.

[bepone]

rebuilt all with carbon films 2w and sound will be different, it is several h work.. nott to much to find out,

[martin manning]

What about the double 16uf can, absent and the additionnal single 16UF on the board. Does that ot leave this with 16uf less filtering somewhere ?

See if you can follow the B+ string from the rectifier to V1. Vintage JTM45 should look like this:
Rectifier -> 32u (OT CT) -> Choke -> 32u (screens) -> 10k ->16u (PI) -> 10k -> 16u (V1 & V2)
Does yours look like that?

[hebaton]

i allready gave my opinion about probably major OT difference and lamnations in previous thread (why we are opening new threads with the same question?)
but here i see that material composition is NOT the same, we have difference in almost all resistors , like carbon films against carbon comps, different coupling caps..
then v2b cathode resistor is drifted to 125k it is carbon comp soak humidity, increased value and need repacement.. changing working point.. probably pushing V2 over max cathode/heater voltage allowance (over 200V). also all resistors need to be measured for drifting.

so how this 2 amps can sound similar at least? there is no way.

i have metroamp JTM at home, exactly like from layout picture and it sounds great. mids are perfect, smooth and little bit gritty.

I measured pretty much all resistors and found onlyt those two that are giving significantly diferent readings...
BUt what coupling cap differences areyou refering to ?

[Roe]

What about the double 16uf can, absent and the additionnal single 16UF on the board. Does that ot leave this with 16uf less filtering somewhere ?

See if you can follow the B+ string from the rectifier to V1. Vintage JTM45 should look like this:
Rectifier -> 32u (OT CT) -> Choke -> 32u (screens) -> 10k ->16u (PI) -> 10k -> 16u (V1 & V2)
Does yours look like that?

originals had:
32uf OT
32uf or 20uf screens
16uf or 20uf phase inverter
16uf preamp (dual caps were introduced on the last jtm45 faceplate amps in 67, often 20+20uf or 32+32uf)
In 67-68 filtering gradually increased more generally.

[sluckey]

1- is 125K instead of 100K

The resistor on the board is marked brn-blk-yel which is 100K

2- is 31K instead of 27K

The resistor on the board is marked red-vio-orn which is 27K.

[martin manning]

The way I read it is the pictures show what is expected (per the manual), and the values given are what was found in the amp.

[hebaton]

1- is 125K instead of 100K

The resistor on the board is marked brn-blk-yel which is 100K

2- is 31K instead of 27K

The resistor on the board is marked red-vio-orn which is 27K.

But that'S not how they measure !

[martin manning]

Are you trying to measure them in-circuit?

[bepone]

I measured pretty much all resistors and found onlyt those two that are giving significantly diferent readings...
BUt what coupling cap differences areyou refering to ?

You have difference in 95% visual components without even looking the tranformers, chokes.. except all resistors are diferent composition, capacitors are different too.
You have sozo/mustard combo, Metro has all Mallory 150.

There is cumulative effect in each component. What is your question? Looks like you dont believe what you are seeing, like all compoenents sound the same, so hence your question..Also lead dress is kinda amater looking in Trinity amp.

Just look the amps and there is 95% difference, we can say that mox resistors are more or less the same but for sure is not the same brand..so...all together result is what it is.

[TUBEDUDE]

I have this, I think, very well built JTM45 clone. It was made buy Stephen at Trinity amps. The work looks impeccable, the parts look right...
But it sound very different from another good JTM45 clone I previously owned.

So your trying to find component level differences in this amp compared to a clone amp you no longer have to compare?
That will devolve into a guessing game. A better plan to remedy the difference might be to analyze what's missing and try component changes that will likely change the particular deficiencies in response you perceive. As others have mentioned, the O.T. is the place to start. Speaker type and age are a factor to consider also. Good luck.